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Pests, Diseases and Weeds
Level 3
Title: Monitor Pests, Diseases and Weeds on Crops
Applied Title: Monitor Pests, Diseases and Weeds on Citrus
Field: Agriculture and Nature Conservation
Sub-Field: Primary Agriculture
SETA (SGB): AgriSETA
Skills Area: Pests, Diseases and Weeds
Context: Citrus Production
US No: 116265 Level: 3 Credits: 2 Notional Hours: 20
Copyright ©
P.O. Box 461, Hillcrest, 3650
(031) 313-3364
Author: Cabeton Training and Development et al Based on the Production Guidelines of: Supported by:
Citrus Growers
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Learner Guide Skills Area: Pests, Disease and Weeds Level: 3 Unit Standard: 116265
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Table of Contents Directions .......................................................................................................................................... 4 Introduction ...................................................................................................................................... 5 1. Purpose ...................................................................................................................................... 5 2. Learning Assumed to Be in Place .............................................................................................. 5 3. Prescribed Material .................................................................................................................... 5 Revision of Level 2 ............................................................................................................................ 6 1. Common Pests in Citrus Production .......................................................................................... 6 2. Common Diseases in Citrus Production .................................................................................... 6 3. Common Weeds in Citrus Production ........................................................................................ 6 4. Scouting ..................................................................................................................................... 7 Chapter 1 ........................................................................................................................................... 9 1. Introduction ............................................................................................................................... 9 2. Good Agricultural Practice ......................................................................................................... 9 3. Damage Symptoms .................................................................................................................. 10 4. Scouting and Sampling Procedures ......................................................................................... 12
Fruit Fly Infestation Assessment ............................................................................................... 13 5. Correct vs. Incorrect Protocols during Pest Collection and Analysis ..................................... 14 6. Observation and Recording of Pests and Predators ............................................................... 14 6.1. Scouting categorisations ...................................................................................................... 15 6.2. The Difference between Pests and Predators ..................................................................... 16 7. Pest Monitoring and Scouting ................................................................................................. 16 7.1. Deciding when to scout ........................................................................................................ 16 7.2. Scouting Methods ................................................................................................................. 16 7.2.1. Data Tree Method ............................................................................................................. 17 7.2.2. Diagonal Method ............................................................................................................... 17 7.3. Inspection Points or Units on a Citrus Tree ......................................................................... 17 8. Reporting Methods .................................................................................................................. 18 9. Trapping Unknown Pests for Identification ............................................................................ 19 9.1. The Importance of Identifying Unknown Pests .................................................................. 20 9.2. Methods of Dealing with Unknown Pests ............................................................................ 20 10. Recordkeeping ...................................................................................................................... 20 Chapter 2 ......................................................................................................................................... 22 1. Introduction ............................................................................................................................. 22 2. Different Types of Traps: ......................................................................................................... 22 2.1. Pheromone Traps ................................................................................................................. 22 2.2. Sticky Traps .......................................................................................................................... 23 2.3. Pit-fall traps .......................................................................................................................... 23 2.4. Trapping with colour and light ............................................................................................. 23 3. Assessing Traps ........................................................................................................................ 24 4. Monitoring Techniques ............................................................................................................ 24 5. Monitoring of Diseases and Weeds ......................................................................................... 24 6. Recordkeeping ......................................................................................................................... 24 7. Pest Data .................................................................................................................................. 24 Chapter 3 ......................................................................................................................................... 26 1. Introduction - The impact of disease on Citrus production and profitability ........................ 26 2. Monitoring Disease symptoms in Citrus .................................................................................. 26 3. A list of known diseases and their symptoms ......................................................................... 27 4. The protocols surrounding disease prevention in Citrus ........................................................ 27 5. The protocols for dealing with the outbreak disease in Citrus ............................................... 28 Phytophthora foot rot can best be controlled by preventative practices, including use of resistant rootstock and planting in well-drained land. ......................................................................................................... 31 Budding seedlings high, avoiding wounds, and keeping soil off the lower trunk are among recommended control practices. Soil fumigation of seedbeds should be practiced in field nurseries. ................................. 31
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Chapter 4 ......................................................................................................................................... 39 1. Introduction to weeds and their impact on Agriculture in General and Citrus production specifically ....................................................................................................................................... 39 2. Monitoring plans for weed eradication in line with Good Agricultural Practice .................... 39 3. Advantages of monitoring plans related to weed control ...................................................... 40 4. Implementation and actions related to weed monitoring plans ............................................ 40 4.1. Survey and mapping ............................................................................................................. 40 4.2. Listing resources and select control methods ..................................................................... 40 4.3. Planning monitoring operations related to weed control ................................................... 40 4.4. Implementation of monitoring operations related to weed control .................................. 41 4.5. Record keeping related to the monitoring of weeds ........................................................... 41 5. Monitoring and reporting protocols related to unwanted plant growth (weeds that are not necessarily invasive species). ......................................................................................................... 41 6. Monitoring and reporting protocols for Invasive species ....................................................... 42 6.1. A list of frequently occurring invasive species for Citrus farms ......................................... 43 6.2. New or unknown plant species observed during weed monitoring actions ....................... 45 Bibliography .................................................................................................................................... 47
Learner Guide Skills Area: Pests, Disease and Weeds Level: 3 Unit Standard: 116265
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Directions This learning material has been developed to assist the learner wishing to complete this unit standard. The guide contains all necessary learning to ensure that the learner will attain the competencies required by the unit standard. The learner guide is accompanied by a Learner Assessment Guide. Please ensure that you have access to this guide as well. The learner guide was designed to be used by a learner during the presentation of a skills program based on the unit standard, and to be kept afterwards by the learner for reference purposes. The learner assessment guide was designed to be completed during and after the presentation of the skills program, and forms part of the assessment process. Although this learner guide contains all the information required for attaining competency in this unit standard, references to additional resources, both printed and electronic, are provided for further study by the learner. Information in boxes is indicated by tags that show:
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Introduction 1. Purpose
A learner achieving this standard will be able to recognize, monitor and apply basic control of insects, plant diseases and common weeds, in a specific agricultural enterprise. In addition they will be able to report their findings to management or advisors. Learners will gain an understanding of sustainable agricultural practices as applied in the animal-, plant and mixed farming sub fields. This unit standard focuses on the application of pest control practices in primary agriculture. They will be able to participate in, undertake and plan farming practices with knowledge of their environment. This unit standard will instil a culture of maintenance and care for both the environment as well as towards farming infrastructure and operations.
2. Learning Assumed to Be in Place It is assumed that the learner has successfully completed the unit standards listed below:
NQF Level Unit Standard Number Unit Standard Description
2 Literacy and Numeracy
3 116272 Demonstrate a basic understanding of the physiological functioning of the anatomical structures of a plant
2 116124 Control pests and diseases ad weeds on crops effectively and responsibly.
3. Prescribed Material
The following material is prescribed for this unit standard: Identification Manual for Citrus Pests and Their Natural Enemies published by Citrus Research International Contact Details: (013) 759-8000 or www.cri.co.za
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Revision of Level 2 1. Common Pests in Citrus Production
The main impact of pests and diseases on commercial citrus production is damage to trees that may
lead to lower yields and poorer quality fruit, damage to fruit that may render it non-exportable and the presence of phytosanitary pests and diseases that may lead to export rejections.
All insects are not pests.
Pests are those insects which reduce or damage the crop quality and quantity.
Beneficial insects assist in pest control through predatory or parasitic behaviour.
Insects damage plants by sucking, stinging or chewing the plant parts, laying eggs on or in plant parts, damaging the surface of fruit when moving over it, causing access points to other pests or diseases, or by acting as a vector for other diseases.
Numerous control measures exist for controlling pests, including chemical sprays, systemic chemicals, beneficial insects, and traps.
Chemical spays are not the only option for controlling pest populations.
2. Common Diseases in Citrus Production
Diseases in citrus are detected through the presence of their symptoms.
Diseases are caused by micro-organisms, such as bacteria, viruses and fungi.
Fungi grow on the plant parts and are more likely to occur in humid conditions.
Viral diseases destroy their host and prevention is the only means of control.
Bacterial diseases spread very rapidly and are very difficult to control.
The most common disease symptoms are wilting, discolouration, gum formation and dieback of plant parts.
Citrus diseases are classified as fruit and foliar diseases, soil-borne diseases, and graft-transmissible diseases.
3. Common Weeds in Citrus Production
Weeds are any plants that are not wanted in the area where the citrus crop is produced.
Invasive plants are plants that come from a different country or area and that have no natural
enemies in the specific area.
Invasive species pose a threat to ecosystems and can cause the decline of natural vegetation and beneficial organisms.
Invasive plants have been categorised by the Botanical Society of South Africa and the ARC into three categories.
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Category 1 plants have to be removed wherever they are found and category 3 plants are the least threatening.
Weeds and invasive plants can be controlled through manual or chemical actions or through the introduction of biocontrol agents.
Weed germination can be suppressed through the use of mulch or cover crops.
4. Scouting
Scouting means observing orchard and plant conditions in order to gain information about the visible signs and symptoms of pests and diseases.
Scouts must have excellent vision and a positive attitude to their job, and they must be well trained to understand the principles of scouting so that results are not biased.
A formal scouting strategy is required for each production unit, and should include all the necessary procedures including reporting and recordkeeping procedures.
Scouting procedures normally include selecting permanent data trees, unit inspections, pest traps, cursory examinations, and recordkeeping and reporting.
Old damage refers to damage that was caused before by pests and diseases that have probably already been eradicated and new damage refers to new injuries to plants that are caused by a new outbreak of a pest or disease, which should be identified and dealt with.
Certain symptoms occur at specific points in the production cycle or at a specific time of the year.
Recordkeeping of pest and disease populations, damage found and actions taken will assist in active pest and disease control.
Recordkeeping of climatic conditions and the developmental stages of the plant aid in predicting the occurrence of pests and diseases.
Threshold values indicate the pest density at which suppression measures should be implemented in order to prevent the pest population from reaching the economic injury level.
Pest Organisms In agriculture, pest organisms are organisms that cause damage to livestock, crops, humans, or land fertility, for instance tsetse fly, fruit fly and malaria mosquitoes. Citrus pests are organisms whose feeding and / or reproductive habits lead to a reduction in the quantity and quality of the citrus fruit produced.
Beneficial Organisms In agriculture, beneficial organisms are organisms that contribute positively by their habits, for example by feeding on pest organisms or by pollinating flowers to enable fruit development.
Vector A vector is an organism, such as an insect, that transmits disease-causing micro organisms from infected plants to other plants.
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Plant Disease A plant disease can be described as an impairment of the plant’s functions through organisms such as fungi, bacteria or viruses.
Weeds “Weeds” is the generic word for plants growing in a place where they are not wanted. Weeds become important in commercial farming when they damage crops or poison domestic animals.
Alien Plants Alien plants are plants that originate from other countries or areas. Alien plants were brought to this country or region for economic or ornamental reasons.
Invasive Plants Invasive plants are alien plants that have become harmful to the natural ecosystem. Not all alien plants are invasive – in South Africa only 2.5% of plants that are introduced become invasive. Invasive plants do not have natural enemies or other limitation on their growth. They tend to overrun ecosystems that they are introduced into. Invasive plants are a major threat to biodiversity and ecosystem stability.
Scouting Scouting means observing orchard and plant conditions in order to gain information about the visible signs and symptoms of pests and diseases. It involves looking at strategic positions in orchards and recording pest numbers, disease symptoms.
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Chapter 1 After completing this chapter, the learner will be able to: Monitor the common pests prevalent in the specific agricultural enterprise. Collect insects not familiar and that had been identified. 1. Introduction
Scouting, or monitoring pest populations, is part of an integrated pest management (IPM) system. According to the principles of IPM, one should scout for specific pests periodically and monitor the increase in population by gathering specific types of data and samples. It is recommended that the data that is gathered be analysed by an expert in pest and disease control. The expert should then try to find a responsible and suitable method of controlling pests and diseases. IPM principles require that all alternative pest control methods are considered, with chemical pesticide application as a last resort. In some cases, IPM prescribes treating only the portions of a farm or orchard where higher than threshold levels of pests have been found, rather than treating the whole farm resulting in using less chemical plant protection products.
Integrated Pest Management An approach to pest control that includes biological, mechanical and chemical control methods. The goal of IPM is to produce a healthy crop in an economically efficient and environmentally sound manner. The benefits of scouting and continuous monitoring of pests and diseases and the analysis of the data that is gathered are as follows: • Recognise damage done by pests and symptoms of diseases early enough to react against it.
• Enabling recordkeeping of the appearance of pests and diseases. If you analyse data over a period
of time, patterns and cycles appear. This means that you can be better prepared and can ensure that certain pest populations are controlled pre-emptively.
• Assisting in future planning for the management and control of pests and diseases.
• Monitoring the efficacy of control measures against pests and diseases. Pests often develop a resistance to one method of pest control. If the pest population is monitored before and after control actions, you will immediately note if such a resistance develops.
• Prevent the spread of pests and diseases to other orchards or the surrounding farms or environment.
2. Good Agricultural Practice
Good agricultural practices are basic environmental and operational conditions that are necessary for the production of safe, wholesome fruit. The term includes practices used in growing, harvesting, sorting, packing and storage operations, as well as pest, disease and weed control. Good Agricultural Practices
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(GAP) is prescribed by the legislation and all citrus growers are compelled to adhere to these prescriptions. The application of integrated pest management forms part of GAP. Overseas markets require accreditation to international GAP schemes such as GlobalGAP and EurepGAP before producers are allowed to export fruit to these countries. GAP principles in terms of pest scouting and monitoring require scouting for pests and diseases according to specific procedures at set intervals. The objective is to react against pests and diseases in time to prevent the spread of the pest or disease and to limit the amount of damage that it does to the crop.
3. Damage Symptoms The CRI Identification Manual for Citrus Pests and Their Natural Enemies is one of the most important tools that a scout needs. It provides pictures and descriptions of all the citrus pests and of disease symptoms, which allows a scout to identify the presence of the pest or disease in the orchard. It is important to distinguish between old damage and new damage caused by pests. The distinction between old and new damage was discussed in detail in the level 2 guide. Repeated scouting in the same orchard by the same scout, and detailed recordkeeping assist in identifying new damage. Identify the plant part on which the damage is most visible and use the tables below to determine what pest or disease caused it.
Plant Part Symptom or Damage Possible Causes
Fruit Abnormal shape • Budmite • Bollworm
Lesions or marks • Red Scale • Thrips • Bollworm • Brown leafhopper • Green leafhopper • Wind • Hail
Fallen fruit • False codling moth • Fruit fly • Budmite • Bollworm • Alternaria • Burst
Residue • Mealy Bug • Aphids • Australian bug
Visible insects • Mealy Bug • Aphids • Australian Bug
Prematurely coloured or discoloured • False coddling moth • Fruit fly • Leafhopper • Mites • Alternaria
Foliage Malformation • Budmite • Aphids • Thrips
Residue • Mealy bug
Learner Guide Skills Area: Pests, Disease and Weeds Level: 3 Unit Standard: 116265
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Plant Part Symptom or Damage Possible Causes
• Aphids • Australian bug
Feeding marks • Leafminer • Orange dog butterfly • Thrips • Grasshopper
Discolouration • Red scale • Mites • Leafhoppers
Visible insects • Leafhoppers • Mealybug • Australian bug • Soft brown scale • Mites
Blossoms Abnormal blossom shape • Budmite
Insects present on blossoms • Bollworm • Aphids
Residues on blossoms • Aphids Table 1.1: Pest Damaged Plant Parts and Possible Causes Table 1.2 indicates identifying features of specific insects.
Identifying Feature Options
Flying insect • False coddling moth • Fruit fly • White fly • Brown leafhopper • Green leafhopper • Orange dog butterfly
Sedentary insect (not moving)
Mealy bug Australian bug Red scale Aphids Soft brown scale
Beetle • Tip Wilter • Ladybird • Stink bug
Caterpillar • Orange dog • Bollworm
Very small insect • Thrips • Green leafhopper • Mites
Table 1.2: Identifying Features of Insects Table 1.3 indicates the months of the year in which specific insects occur most frequently. This information has been compiled form data analysis and recordkeeping and it can assist you further in identifying the pest insects found in the orchard.
Learner Guide Skills Area: Pests, Disease and Weeds Level: 3 Unit Standard: 116265
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January February March
Red scale on the fruit, Mealybug, Mites (Especially Rust Mite), Thrips, Ants, Psylla, Aphids
Mites, Red scale, Mealybug, Ants, Psylla, Aphids
False Codling Moth, Red scale, Mealybug, Fruit Fly, Ants, Psylla, Aphids
April May June
Ants, Psylla, Aphids Ants, Psylla, Aphids Ants, Psylla, Aphids
July August September
Ants, Psylla, Aphids Thrips on the leaves, Ants, Psylla, Aphids
Thrips (leaves and fruit), Bollworm, Red scale (twigs), Ants, Psylla, Aphids
October November December
Thrips (fruit), Red scale (fruit & twigs), Mealybug, Bollworm, Ants, Psylla, Aphids
Thrips (fruit), Red scale (fruit & twigs), Mealybug, Ants, Psylla, Aphids
Thrips (fruit), Red scale (fruit & twigs), Mealybug, Mites, Ants, Psylla, Aphids
Table 1.3 – Pest Occurance Months
4. Scouting and Sampling Procedures To manage pests successfully, the problem pest must be identified correctly. It would be pointless and expensive to apply the wrong type of pest control action. The most effective way to identify pests is simply to walk around and actively scout or look for pests in the orchard. Scouting is not just aimless wandering and looking around but must be a structured and regulated approach to monitoring the occurrence of pests. Citrus pest scouts are well trained individuals who search and scout with very specific goals in mind. In order to recognise the emergence of a pest population, two different facets must be concentrated on during scouting:
• You will actively look for a specific pest, or • You will actively look for damage to the fruit, leaf or blossom, or plant parts that would be
caused by a specific type of pest. The findings of a scout need to be well documented and reported as part of the larger pest monitoring program. It is thus important that scouts are trained carefully in both the recognition of specific pest populations, as well as the recording of the necessary data that will make the information valid and valuable. The following types of pests are considered phytosanitary pests. The occurance of these pests should be monitored, specifically:
• fruit fly • false codling moth • mealy bugs
The presence of phytosanitary pests in the orchard can lead to huge losses and have to be monitored and controlled on a regular basis. In terms of Good Agricultural Practice it is important to keep scouting records that will confirm counts of other pests such as red scale, thrips, leafhopper and leaf-miner as well as phytosanitary pests. Remember that not all pests occur in all geographical or production areas. It is vital to familiarise yourself with the prevalent pests that are a problem in the area where your farm is situated. The following records must be kept in good order and be available at all times for official inspection or on request:
• Trap counts.
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• Dates when lures are hung and changed. • Volumes of bait sprays. • Products used in the baits. • Active ingredient of chemical products used. • Records of minor pests must be kept. • Monitoring include the knowledge of economic threshold or action levels and the control options
chosen if above the economic threshold or action levels are reached.
The Department of Agriculture will inspect orchards earmarked for selected export markets to issue a phytosanitary certificate. The producer is responsible to keep records concerning the status of pests and any chemicals or other measures used to control pests. Below follows a detailed example of the guideline for the monitoring of Fruit Fly presence in the orchard. This kind of guideline is also sometimes called a protocol.
The following is an example used as a guideline in the Vaalharts area: Fruit Fly Infestation Assessment Monitoring
o Weekly monitoring of fruit fly from February. o Make a note of any activity noticed concerning both species Mediterranean - and Natal
Fruit Fly and both sexes, male and female. o Hang out of traps in week 5 of the production cycle. That is before colour break. o Change lures and dichlorfos blocks in traps in week 12,19, and 26 for the whole area and
week 34 for Valencia orchards.
Product To Use - Compulsory o The use of Questlure traps are recommended by government legislation. o One trap for every 6 ha of Citrus should be used. o Traps must be placed more than 50 meters apart. o Change traps every 7 weeks until the harvest has been completed. o M3 traps must be hanged out in week 5. o M3 control effective for 4 months. o M3 is a perishable product and can only be used in one season and not kept for the next
season.
Product to use – Recommended o In addition to the Questlure, Capilure attractants are recommended by government. o In Vaalharts only the use of Questlures are compulsory, thus avoiding a confusion of
traps, counts of male and female flies and time of spraying. Economic threshold
o One female fly per week per trap in Questlure is acceptable. o The economic threshold is reached if there is two flies or more per week in the trap. o As the Questlure catches mostly female flies, you do not have to identify the sex of the
flies. Control options
Cultural control Biological control Chemical control
o Orchard sanitation weekly o There is no virus or o Protein Bait : 250 ml
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o Bugweed (weeds with berries or fruit) should be removed within 100m of citrus orchards
o After harvesting, all remaining fruit must be stripped and be disposed of.
parasites at this stage to treat fruit fly infestations.
Buminal or 400ml Hymlure in 100 litres of water
o 300 – 800 ml per tree o Mantis or Ladybird
applicator. o The protein is
concentrated 15 times to 6ml per 100ml water as only 45 ml bait is applied per sprayed tree.
o Bait before it gets hot. o The toxicant concentration
must never be increased. This remains as 50 g of Dipterex or 175 ml Malathion EC or 300g Malathion WP per 100 litres of water
o The harvest interval is 28 days if Dipterex is used and 7 days for other chemicals.
o Spray orchards after harvesting once or twice for fruit fly
5. Correct vs. Incorrect Protocols during Pest Collection and Analysis Scouting is a vital part of a farm’s IPM program. Scouting involves systematically moving through orchards looking for pests, measuring populations, and then using this information to make pest control decisions. The information helps growers determine if a pest control treatment is needed, where it’s needed, and what options are available and practical. IPM principles refer to economic thresholds. Economic thresholds refers to the cost of the pest damage weighed against the cost of the pest treatment, this comparison is used in the decision-making process. This information can be helpful when deciding whether or not a pest situation warrants treatment. IPM can help a pest suppression program. Potential problems often are identified early and managed, thereby reducing the control costs and crop losses. Since pest populations vary, spraying without scouting first may result in unnecessary or insufficient pesticide applications. A grower can use pesticides more effectively by knowing what pest is in a field and treating it accordingly. When scouting for insects, it is important to get a random sample. However, the scout also needs to observe and note any high population areas in the orchard. The decision to spray is never one that can be taken lightly. Not only is the cost of any chemical application high but the effect that pesticides can have on the environment must also be considered. Spraying must be the last option available to a grower before it is used. In order to make an informed decision a grower needs as much information as possible concerning the presence of pests and diseases in the orchard. A grower must also know where these pests and diseases occur to ensure that non-infected areas are not treated and money thereby wasted. Pests control decisions must never be based on historical data. Spraying must only be done after the presence of pests and diseases have been physical confirmed by a thorough, structured, well implemented and recorded monitoring, scouting and trapping plan. 6. Observation and Recording of Pests and Predators
Learner Guide Skills Area: Pests, Disease and Weeds Level: 3 Unit Standard: 116265
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As discussed previously, the pest scout has to actively inspect orchards on an ongoing basis and keep record of the findings. Pests that are found must be collected and identified. Insect identification can be achieved through referring to the Identification Manual for Citrus Pests and their Natural Enemies published by Citrus Research International - CRI.
6.1. Scouting categorisations All pests are categorised according to very specific categories for scouting purposes. These pests are also each identified by a specific scouting symbol. This means that this is the symbol that the scout should write down or record on the scouting sheet when they encounter such a pest. Table 1.4 below is a list of all the pests and their scouting symbols that are important for Citrus, as is identified in the CRI manual.
Scale Lepidoptera Homoptera
• Mussel Scale MS • Bollworm BW • Australian Bug
AB
• Red Scale RS • Leafhoppers LR • Leafhoppers LH
• Circular Purple Scale
PS • Citrus butterflies
OD • Aphids AP
• Soft Scales SS • Citrus looper or measuring worm
MW • Citrus Psylla CP
• Waxy Scale WS • False codling moth
FCM • Mealybug MB
• Powdery Scale
AS
• Black Scale BS
Mites: Snails: Sundry pests:
• Grey mite GM • Brown snail BS • Ants A
• Budmite BM • Dune snail DS • Citrus Thrips T
• Lowveld citrus mite (Oriental mite)
LM • Tower snail TS • Fruit flies FF
• Flat mite PM
• Rust mite RM
• Red spider mite
RSM
• Silver mite SM
• Citrus red mite
RM
Table 1.4 – List of Pests and Scouting Symbols
It is important to know that all insects found in the orchards are not pests. The natural enemies of the main pests of citrus are listed in the Identification Manual for Citrus Pests and their Natural Enemies of the CRI.
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There is an increasing interest in attracting predators to the orchards or placing specially bred predatory organisms in the orchards. This practice can effectively control the outbreak of pests and diseases in an controlled manner and not cause any harm to the environment.
During pest and disease monitoring, it is also important to scout for the known predators. If the predator count is sufficiently high, chemical action might not be necessary.
6.2. The Difference between Pests and Predators
Pests affect the plant negatively while predatory insects or organisms feed on or do damage to these pests. The most important predatory organisms for citrus are listed below in table 1.5.
Host (The pest) Organism (Predator)
Mealybug Anagyrus (Parasitic wasp)
Red scale, circular purple scale, mussel scale Aphytis (Parasitic wasp)
Soft scales Coccophagus semicircularis
Red Scale Comperiella bifasciata (Predatory wasp)
Citrus Mealybug Coccidoxenoides (Small wasp)
Red scale, circular purple scale Chilocorus distigma (Ladybird)
Red scale Chilocorus nigritus (Ladybird)
Red scale, mealybug, psylla, aphids, mites Chrysoperla pudica (Green lacewing)
Mealybug Cryptolaemus montrouzieri (Ladybird)
Thrips, mite pests Euseius spp (Predatory Mite)
Mealybug, scale, aphids, occasionally mites Exochomus spp (Predacious ladybird)
Circular purple scale, Red scale Lindorus lopanthae (Predatory beetle)
Australian bug Rodolia spp (Vedalia beetle)
Pest mites Strethorus spp (Strethorus beetle)
Citrus thrips, lepidopteron eggs, mites, possibly scale crawlers
Orius thripoborus (Predatory bug)
Table 1.5 – Pests and Predators
7. Pest Monitoring and Scouting
7.1. Deciding when to scout Choosing the right time to scout is often determined by analysing past scouting and monitoring records. There is also a wealth of information available from scientific research bodies and plant improvement programs that will advise scouting times determined by past experience with a pest, crop growth stage, or using models that predict the timing of pest occurrence. Commonly the occurance of pests specific to the area where the farm is based and when those pests normally occurs will determine when scouting will be done.
7.2. Scouting Methods
Learner Guide Skills Area: Pests, Disease and Weeds Level: 3 Unit Standard: 116265
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There are two scouting methods commonly used in the Citrus Industry, the data tree method and the diagonal method.
7.2.1. Data Tree Method Specific, representative trees evenly distributed throughout the orchard are selected and marked. These trees are inspected on each occasion that scouting is conducted. The advantage of this method is that the trees to be inspected are easily identifiable within the orchard and that the same tree is visited each time. In this way a history of the pest status of the orchard and specific trees is built.
Figure 1 – Data tree method representation as seen from the top of an orchard.
7.2.2. Diagonal Method A diagonal line is selected and the scout moves through the orchard examining trees at various points, for example, tree number 1, row 1 then tree number 3, row 3 and then tree number 5, row 5, etc. The number of trees selected per orchard will depend on the size of the orchard. Citrus Research International (CRI) recommends 5 trees per hectare. The number of trees selected will vary from farm to farm depending on what resources are available and what is practical. The greater the number of trees inspected, the more accurate scouting data will be.
Figure 2 – The diagonal method representation as seen from the top of an orchard
7.3. Inspection Points or Units on a Citrus Tree An inspection point or unit is the branch, fruit, fruit cluster, leaf or leaf flush examined during the scouting procedure at a specific position on the tree. What you will examine at the inspection point will
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depend on the time of year and the pest that you are looking for. The recommended method is to select 10 inspection points per tree, 2 on each side of the tree and 2 points inside the tree. See a detailed example of the inspection points in Fig. 3 below.
Figure 3 – Suggested inspection points on citrus trees
8. Reporting Methods Effective pest control requires keeping careful records of pests observed during scouting of orchards, and actions taken to control pests including crop protection products used and other methods aplied. This data is normally recorded in an organised manner on a pre-designed scout sheet. Data from monitoring tools such as sticky traps and pest sighting logs is used in the decision making process, and also to evaluate the success of pest management strategies used. Below follows an example of a completed scout sheet that might be used on a Citrus Farm:
Name of Pest Scout: Joe K Orchard or Block Number : 7 East
Date: 7 March 2010 Time of Day: 07:35
Temperature: 28 °C Production Week Number: 6
General Weather Data Information: Overcast and humid, thunderstorms first thing in the morning
Mark the trees to be inspected in the Orchard with an X
Row or Inspection Unit Number
Tree
Num
ber
1 2 3 4 5 6 7
1
2
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3
4
Record the information observed on each tree:
Row Number
Tree Number
Pest Symbol / s for
observations
Number of this Pest
Observed
General Information or Notes
1 4 Nil 0 No pests observed
1 7 A Too many to count
A lot of Ants Visible to the Eye, but no Mealy Bug
1 7 FCM 2 Checked trap placed on 01.03
2 3 Nil 0 No pests observed
2 6 Nil 0 No pests observed
3 4 A Too many to count
A lot of Ants Visible to the Eye, but no Mealy Bug
4 2 FCM 1 Checked Trap placed 01.03
4 5 A Too many to count
A lot of Ants Visible to the Eye
4 5 MB 7
General Observations and Comments:
There is some damage to the bark and lower branches of trees in row 1 (Trees 1 and 2) caused by the wild pigs that broke through the boundary fence on 02.03.
Leaf damage noted on trees 2-5 in rows 2 and 3, looks like necrotic spots and unknown residue.
9. Trapping Unknown Pests for Identification Sometimes during the scouting exercises and through the monitoring process, one might come across new or unknown pests and insects. If a significant number of these pests are observed, or the damage that they cause is of significant concern, then it would be wise to trap some of the insects and have them professionally identified. Trapping insects means attracting the insect by some means and, having attracted it, preventing its escape. Different trapping mechanisms exist. They usually fall into one of the following categories:
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• Physical or pitfall traps where the insects are drawn to a food source and trapped or move over a surface and then get trapped when they fall into the trap. Physical traps can also be sticky to ensure that the insect clings to the sticky material when coming in contact with it.
• Light traps such as ultraviolet lights which draw the insects toward the light. This often also includes electrocuting the insects once they come in contact with the surface of the trap.
• Pheromone traps which mimics one sex of the insect (usually the females) and draws the males away from the females eliminating mating between the sexes to control pest populations.
Information about unknown pests If unknown pests or disease symptoms are observed, then the following organisations can be contacted to assist in identifying the pest and its potential economic impact on the crop. Control mechanisms and recommendations can also be recommended or prioritised by these organisations:
• Citrus Research International www.cri.co.za Tel. +27 13 759 8000 • Agricultural Research Council www.arc.agric.za Tel. +27 21 809 3457
9.1. The Importance of Identifying Unknown Pests
Unknown pests are most likely a sign that a new organism has found its way into the area. In some cases these new organisms might cause economic damage to the crop, and new methods of control might have to be developed. These organisms often come from other areas or other countries and might have no natural enemies to control its population size in that specific area. Especially in terms of vector insects (insects that spread disease) and phytosanitary pests, early detection can ensure early reaction and prevent the pest from spreading to the environment and other orchards or disallowing the crop to be exported. 9.2. Methods of Dealing with Unknown Pests
It is important to identify the insect which is unknown accurately and then decide what danger it holds to the citrus crop. All known information about this insect must be gathered, including its anatomy and feeding habits. If it is identified as a pest insect, it should be reported and dealt with immediately. It is recommended that any suspicious unknown insect be reported to such institutions as plant pathology laboratories and research programs. There is always a risk of pests entering an area or invading the country from a different country. Just because it isn’t currently listed in the identification manual, does not mean that it is safe to disregard the insect.
10. Recordkeeping
IPM requires keeping careful records of pests reported in orchards and surrounding fields or areas, and actions taken to control pests (including pesticides used). Data from monitoring tools such as traps and pest sighting scout sheets or logs, are used in the decision making process, and also to evaluate the success of pest management strategies used. If accurate records are not kept, then unnecessary or wrong pest control actions might be undertaken, which will cause unnecessary chemical residues to the crop and might potentially harm the viability of
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the crop as well as the surrounding environment and negatively affect the profitability of the farming enterprise.
Chapter 1
Scouting, or monitoring pest populations, is part of an integrated pest management (IPM) system. According to the principles of IPM, one should scout for specific pests periodically and monitor the increase in population by gathering specific types of data and samples.
Good agricultural practices are basic environmental and operational conditions that are necessary for the production of safe, wholesome fruit.
Repeated scouting in the same orchard by the same scout, and detailed recordkeeping assist in identifying new damage and determining the cause of the damage.
The most effective way to identify pests is simply to walk around and actively scout or look for pests in the orchard.
Scouting involves systematically moving through orchards looking for pests, measuring populations, and then using this information to make pest control decisions.
During pest and disease monitoring, it is important to scout for known predators. If the predator count is sufficiently high, chemical action might not be necessary.
Choosing the right time and to scout and the method of scouting is often determined by analysing past scouting and monitoring records.
If a significant number of these pests are observed, or the damage that they cause is of significant concern, then it would be wise to trap some of the insects and have them professionally identified.
Data from monitoring tools such as traps and pest sighting scout sheets or logs, are used in the decision making process, and also to evaluate the success of pest management strategies used.
Complete activity * and * in the Learner Workbook.
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Chapter 2 After completing this chapter, the learner will be able to: Demonstrate a basic knowledge of trapping, monitoring and recording the incidence of pests, diseases and weeds. 1. Introduction
It is not always possible to gain an accurate count of the insect pests in an orchard by observation only as insects might be more active at night or fly around. Trapping can assist the pest scout in gathering more accurate information. Different traps can be set to trap different pests or types of insects. When these traps are checked at set intervals, the numbers of insects found inside the trap are recorded. If recorded numbers exceed a specific count, the threshold value is exceeded and action needs to be taken against these insects. Different traps can also be combined on ‘trap stands’ to lure and trap different insects and to gain an overall impression of the insect pests present in an orchard.
Figure 1 – Insect Science ™ trap stand place in rows to trap multiple insect pests
2. Different Types of Traps:
2.1. Pheromone Traps
These traps mimics pheromones excreted by females of a specific insect to attract males. In this way it traps the males and disrupts mating, preventing an increase in the population. False Coddling Moth is often trapped and controlled in this manner.
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2.2. Sticky Traps
These are traps with either a sticky substance on a piece of card board or a sticky liquid inside a container. These are mostly used to trap flying insects, but insects walking over the surface will also be trapped. The insect cannot escape the sticky surface or liquid once they are attached to it.
2.3. Pit-fall traps
This is a trap for catching ground crawling insects, made out of a cuplike container buried in the ground into which insects fall. Insects often trapped in this manner are ants.
Figure 2 – Simple pitfall trap covered with screening and provided with hanging bait. 2.4. Trapping with colour and light Alternative methods of trapping include placing specific coloured sheets in orchards usually blue or yellow to which the insect are drawn. Although not commonly practiced in agriculture, light traps emitting UV light can also be used to lure insects and then electrocute them.
Figure 3 – Yellow Bug Sheets These yellow ‘Bug Sheets” from Insect Science ™ are placed in greenhouses, shade houses and open fields for the mass trapping of different agriculturally important pests. The yellow sheets are used for Leaf Minors, Whiteflies, Leafhoppers and Thrips.
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3. Assessing Traps
Traps are assessed by checking the insects that was trapped. IPM and GAP regulations determine when traps should be checked. The manufacturers of the different types of traps also have recommendations on the frequency when the different types of traps should be assessed for insect activity. Insect found in traps must be identified and recorded. In the case of insects such as fruit flies it is important to record the gender of the insects trapped as well as the presence of certain genders in the orchard have an effect on the decision to treat the orchard chemically or not.
4. Monitoring Techniques When not using traps the only other avenue of monitoring the presence of pests and insects in citrus orchard is scouting. Scouting procedures and processes is discussed in chapter 1. Although a well designed and implemented scouting plan can effectively monitor the occurance of certain pests in the orchard modern day farming practices requires the use of traps to ensure that the presence of all pests and predators in the orchard are identified and recorded.
5. Monitoring of Diseases and Weeds While scouting and assessing traps the scout are also responsible to monitor the orchard for occurrences of diseases and weeds. 5.1. Diseases Diseases are caused by fungi, viruses, bacteria and nematodes and are much more difficult to control than insect pests. By the time disease symptoms are visible, the disease causing organism has already been present for some time and has already multiplied and possibly even spread. For this reason, most diseases present in Citrus production are dealt with in a preventive rather than a reactive way. Diseases often destroy the plant or cause so much damage to the plant that it has to be replaced. When plants are replaced, it normally entails great economic expense and lost production time in terms of a crop to sell at profit. The process used to detect and identify diseases is discussed in chapter 3. 5.2. Weeds Weeds pose many hazards to successful crop production. Weeds compete with citrus trees for nutrients, light, water, space and harbour insects and rodents that attack citrus trees. There are three categories of weeds that should be monitored in citrus orchards, namely broadleaf, grasses, and sedges. The procedures of how weeds are identified, classified and control is discussed in chapter 4.
6. Recordkeeping Records are kept of all monitoring and scouting practices. The most common record in use on a farm where scouting practices and monitoring activities and findings are recorded is the scouting sheet of which an example is given in chapter 1. All records of scouting and trap monitoring procedures must be evaluated and the data recorded. The effectiveness of the IPM is measured against these records. GAP also requires that records are kept and be available for inspection by accreditation and auditing agencies.
7. Pest Data The data collected from scouting and trap monitoring records will determine how pests controlled. By collecting and evaluating data the effectiveness of control measures can be determined as well as the occurance of any new infestations.
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Data must be collected and evaluated on a regular basis. By evaluating data the effectiveness of scouting practices can also be determined and changes to the IPM can be implemented where necessary.
Chapter 2
Trapping can assist the pest scout in gathering more accurate information. Different traps can be set to trap different pests or types of insects
Traps are assessed by checking the insects that was trapped. IPM and GAP regulations determine when traps should be checked.
While scouting and assessing traps the scout are also responsible to monitor the orchard for occurrences of diseases and weeds.
Records are kept of all monitoring and scouting practices. The data collected from scouting and trap monitoring records will determine how pests
controlled. The data collected from scouting and trap monitoring records will determine how pests
controlled.
Complete activity * in the Learner Workbook.
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Chapter 3 After completing this chapter, the learner will be able to: Monitor the symptoms of disease associated with the agricultural enterprise. 1. Introduction
Diseases are caused by fungi, viruses, bacteria and nematodes and are much more difficult to control than insect pests. By the time disease symptoms are visible, the disease causing organism has already been present for some time and has already multiplied and possibly even spread. For this reason, most diseases present in Citrus production are dealt with in a preventive rather than a reactive way. Diseases often destroy the plant or cause so much damage to the plant that it has to be replaced. When plants are replaced, it normally entails great economic expense and loss of production as new trees require time to grow before they produce fruit. Diseased plants can also not be used for propagation purposes. It is thus important to ensure that the trees used during the establishment of an orchard are sourced from a reputable nursery and are certified as disease free. Diseased fruit either decreases the quality of the crop, resulting in inferior prices for the crop, or prevents the crop from being sold, or at the least, exported in the case of the occurance of phytosanitary diseases.
2. Monitoring Disease symptoms in Citrus
Good disease management requires an in depth knowledge of how different factors interact in the development of the disease; particularly, knowledge of environmental conditions that stress the plant, making it more susceptible to disease. In most cases if you apply this detailed knowledge it will help to prevent a disease problem. However, it is unwise to simply assume that all diseases will be pre-empted and avoided. Regular monitoring is needed to detect diseases as soon as they occur and before they become well established. It is important to report any abnormal appearance or activity of a citrus orchard immediately. Just because the causing organism cannot be seen or found doesn’t mean that such an organism isn’t present and causing disease. To monitor orchard for diseases, disease symptoms should be known and responded to. The monitoring procedures and protocols for diseases are very similar to that of pests. The only major difference is that one often has to take samples in the orchard and send it away to a laboratory for identification, rather than simply noticing and counting a number of insects. Remember that the appearance of some pests and insects may also be an indicator that disease is about to occur, or has already infected your orchard. In conjunction with the CRI, Diagnostic Centre (DC) in Nelspruit, specific analyses can be done to detect diseases. Here follows a list of techniques used to determine if diseases are present in the orchard:
• Citrus leaf bating technique is used to isolate Phytopthora. This attracts fungal zoospores by plant exudates to the leaf discs. This method can also be used to isolate Pythium. Different cultures are used to grow these organisms and thus determine the presence of either disease in the Diagnostic Centre.
• The DC has also altered the leaf disc baiting technique to test irrigation water for the presence of Phytophthora and Pythium.
• Fruit samples can be submitted to the DC to have them isolate above-ground fungi leaving lesions on the fruit.
• The DC can assist in nematode root counts. • A detailed description of making and placing a Spore Trap to analyse irrigation water is described
in the CRI Integrated Production Guidelines Volume III p. 164.
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• All samples submitted to the DC should be done as per their guidelines and must be accompanied by filled in analysis forms obtainable from the DC.
• The DC releases the results of any samples submitted within approximately 10 days.
The CRI, Diagnostic Centre contact details
Laura Huisman P O Box 28 NELSPRUIT 1200 Telephone No 013 7598000 Fax No 013 7440578 Or visit http://www.cri.co.za/disease/diag.htm
3. Diseases and Symptoms Table 3.1 defines a list of the most commonly occurring and economically damaging pests in citrus orchards.
List of Diseases
Fruit or Foliar Soil borne Graft transmittable
• Alternaria Navel-end rot • Nematode • Tristeza
• Botrytis • Citrus Root rot • Greening
• Phaeoramularia • Armillaria Root Rot
• Diplodia
• Phytophthora
• Brown rot
• Citrus black spot Table 3.1 – List of Diseases The specific symptoms of these diseases were discussed in detail in the level 2 guide. Please revise them in order to train yourself in the requirements of monitoring and identifying these diseases by revising this carefully. 4. Disease Prevention in Citrus To minimise the occurance of diseases, the following rules should be adhered to:
• Only purchase plant material from certified and approved nurseries that have declared the plants disease free.
• Prevent the movement of plant material between production areas, especially if a known disease is found in one area and not the other.
• Before a new orchard is established, remove all traces of former plant material from the soil before planting and have the soil analysed for the presence of disease causing organisms. Nematicides can often be used to treat the soil before the new trees are planted and to prevent new plants from contracting diseases.
• Never bring fruit and plant material into the country on your own without declaring and clearing it through import control. Diseases easily spread from one country to the next in this way.
• Be alert to abnormal growth and unusual occurrences in the orchards and consult experts to identify the source.
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• Adhere to a strict pest and weed control program. Remember that certain pests act as vectors in spreading certain diseases and by controlling the pest you will automatically control the spread of the disease. Weeds attract pests and can harbour diseases.
• Follow a pest and disease scouting program and record all findings. • Alert surrounding farms and authorities such as the CRI, PPECB and the DOA when phytosanitary
pests and diseases are found on the farm or in the area. • Prevent nutrient and water stress in plants. These stresses often assist the development of diseases. • Avoid the excessive spraying of the same agrochemical pest control product. Many pests and
diseases develop resistance to a chemical if it is used continuously. • Consider alternative crops for the farm other than just citrus also known as monoculture.
Monoculture increases the risk of the outbreak of diseases because many of the same plants are grouped together and offer an ideal habitat for diseases to break out. If monoculture is practiced, one can consider such practices as companion planting with specific edge crops or cover crops.
• In case of a suspected disease, contact your agricultural advisor or the CRI for assistance. You can also call in the help of the Diagnostic Centre in Nelspruit.
By following these simple guidelines the occurance of the most common pests in the citrus orchard can be negated, but even the best prevention programme can never totally ensure that diseases will not occur so effective scouting and monitoring is vital.
5. Dealing with the Outbreak of Disease in Citrus Table 3.2 list the most common diseases that occurs in the citrus orchard as well as the prevention and treatment strategies that should be employed once a disease outbreak is noticed.
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Disease Name Identification Symptoms (Damage Caused) Seasonal Activity Prevention/Control
Fruit & Foliar Diseases
Alternaria Navel-end rot
Premature colouring Fruit drop The rot is not always evident on the outside of the fruit. Eventually (frequently not until after harvest) a dark slightly sunken spot appears on the blossom end (as opposed to the stem end) of the fruit. This rotten spot may eventually cover one-fourth of the fruit. The tips of several segments show a dark rot, and the juice of the entire fruit has an unpleasant taste.
The fungus grows on dead citrus tissue during wet weather. It produces airborne spores which can land and grow on the blossom end of the fruit.
Keep the tree healthy and minimize stress by a proper maintenance, irrigation and fertilization. Remove and destroy infected fruit as soon as infection is identified. Intensify scouting procedures to identify further infection.
Botrytis
Botrytis rot occurs mainly on lemon fruit, but the fungus may also infect twigs and small branches of lemon trees. The fungus infects through injuries and forms grey, velvety mats of fruiting bodies on infected tissue, causing the surface of fruit to be bumpy. Infected twigs may die back several inches.
General preventive measures, such as avoiding mechanical injury, protecting against frost and brown rot, and pruning regularly, help reduce the incidence of Botrytis rot. Once it occurs all infected fruit, twigs and leaves must be removed and destroyed.
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Identification Symptoms (Damage Caused) Seasonal Activity Disease Name Prevention/Control
Phaeoramularia
Brown or greyish spots up to 1.27cm in diameter are formed both on leaves and fruit and are usually surrounded by yellow halos. The lesions are often flat or sunken, which differ from those of citrus canker. Premature defoliation and fruit drop can occur when infections are severe. The affected fruit produce poor quality juice, and thus are not suitable for processing or the fresh market.
The spread and infection processes of Pseudocercospora fungus are similar to other citrus fungal pathogens whose asexual spores (conidia) are primary sources for new infection. Infection is apparently favoured by wind-blown rains that occur when susceptible young leaves and fruit are present and temperatures are warm.
All infected fruit and branches must be removed and destroyed. The application of a short term fungicide can prevent the disease from spreading.
Diplodia
Fruit are contaminated with the fungus in the field, but the disease commonly occurs at the packing house or in transit. Decay occurs around the stem end and advances in streaks down the side of the fruit. There is no fungal growth on the surface of the fruit.
Decay is reduced by dipping the fruit in fungicide solutions before placement in de-greening rooms. Promptness in handling and shipping, as well as refrigeration during transit, will minimize losses.
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Disease Name Identification Symptoms (Damage Caused) Seasonal Activity Prevention/Control
Phytophthora
This disease can affect the root system, the trunk below and above ground, branches, leaves, blossoms and fruit. It is especially troublesome during prolonged rainy periods. Trees with the bud union beneath or close to the soil and trees in poorly-drained locations are highly susceptible.
Phytophthora foot rot can best be controlled by preventative practices, including use of resistant rootstock and planting in well-drained land.
Budding seedlings high, avoiding wounds and keeping soil off the lower trunk are among recommended control practices. Soil fumigation of seedbeds should be practiced in field nurseries.
Brown rot
Symptoms appear primarily on mature or nearly mature fruit. Initially, the firm, leathery lesions have a water-soaked appearance, but they soon turn soft and have a tan to olive brown colour and a pungent door. The infection progresses over the fruit, but not beyond the albedo, which is the white, spongy inner part of citrus fruit rind. Infected fruit eventually drop. Occasionally, twigs, leaves, and blossoms are infected, turning brown and dying.
Brown rot is caused by Phytophthora fungi when conditions are cool and wet. Brown rot develops mainly on fruit growing near the ground when Phytophthora spores from the soil are splashed onto the tree skirts during rain storms; infections develop under continued wet conditions. Fruit in the early stage of the disease may go unnoticed at harvest and infect other fruit during storage.
Brown rot management relies on prevention. Pruning tree skirts above the ground can significantly reduce brown rot.
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Identification Symptoms (Damage Caused) Seasonal Activity Disease Name Prevention/Control
Citrus black spot
The symptoms are necrotic lesions on fruit that make them unacceptable for fresh market. When disease is severe, black spot may cause extensive premature fruit drop that reduces yields of fruit for processing.
Infection of citrus black spot is favoured by warm wet conditions in the summer, presence of susceptible fruit, and presence of abundant inoculum. While conidia (asexual spores) may cause infection, the primary source of infection is ascospores (sexual spores) produced on dead leaves on the ground. Ascospores are forcibly ejected during rains or irrigation onto fruit and infection occurs mostly in late spring and summer. Fruit are susceptible for 4-5 months after petal fall. Although infection occurs when fruit are young, the fungus undergoes a long period of latency and symptoms may not appear until the fruit become mature.
Due to the long latency of the characteristics of the spores once infection is noted all fruit from the tree should be removed and destroyed to combat the disease from spreading. Neighbouring trees should be tested for the presence of the disease and all fruit be destroyed on trees found infected.
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Disease Name Identification Symptoms (Damage Caused) Seasonal Activity Prevention/Control
Soil Borne Diseases
Nematode
Plant parasitic nematodes are very small worms that cannot be seen with the naked eye. Several plant parasitic nematodes are known to attack the root system of citrus plants, especially the citrus nematode. The burrowing nematodecauses a disease known as spreading decline and is a serious pest of citrus.
Nematicides can often be used to treat the soil before the new trees are planted and to prevent new plants from contracting diseases.
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Identification Symptoms (Damage Caused) Seasonal Activity Disease Name Prevention/Control
Citrus root rot
Initially symptoms of dry rot consist of a dark area of decay in the bark which will eventually have a dry, cracked appearance. The wood below this lesion will be dry with a brownish-grey stain which could also turn slightly purple. The disease may progress in the wood for many years with the only symptoms being a slight wilting under dry conditions. This disease could however reach the "sudden death" stage, when leaves may suddenly wilt, turn yellow, and the tree dies rapidly. This phenomenon is often observed in conjunction with conditions that causes stress in the trees.
The most effective control measure against Fusarium root rot comprises elimination of conditions that cause stress in the trees. Maintaining soil conditions favourable for root development is of the utmost importance. Soil compaction, water logging and salinity are all interlinked factors causing stress in the tree, predisposing the root system and thereby aggravating root disease. Under suitable soil conditions, methods such as deep ploughing can successfully neutralise soil compaction, thereby improving soil structure and drainage which can drastically improve root health and reduce root rot.
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Disease Name Identification Symptoms (Damage Caused) Seasonal Activity Prevention/Control
Armillaria root rot
Armillaria root rot, also known as oak root fungus, can occasionally damage and kill citrus trees. Symptoms may not develop until after the disease is well established. The first symptoms of Armillaria root rot are poor growth or dieback of shoots, small yellowing leaves, and premature leaf drop.
Management of Armillaria root rot relies primarily on preventing infection of new trees. Once infection is apparent, it is very difficult to save a tree. Avoid planting in a site likely to be infested with Armillaria. If there are infected trees in your orchard, remove them completely, including the roots, and let the trees dry thoroughly before disposing of them. Also remove the neighbouring, apparently healthy trees; once symptoms appear on a tree, the disease has probably already spread to the roots of the surrounding trees.
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Disease Name Identification Symptoms (Damage Caused) Seasonal Activity Prevention/Control
Graft Transmissible Diseases
Tristeza
When trees are propagated on susceptible rootstocks and are infected with CTV decline strains, typical symptoms include: decline, wilting, dieback, "quick decline," leaf chlorosis and curling, heavy fruit set, honeycombing, bud union staining, scion overgrowth, thickened bark at bud union, starch depletion in roots, and loss of feeder roots.Tree decline results from the necrosis and death (blockage) of the conductive tissue (phloem) at the bud union, whereby sugars produced in the leaves by photosynthesis are effectively blocked from being transported to the roots. Without the transport of sugars and starches to the feeder roots, the roots use up stored starch and begin to decline, leading to the ultimate death of the tree.
Citrus tristeza virus is transmitted by aphids in a semi-persistent manner. The aphid can acquire the virus within minutes of feeding on an infected plant and transmit it to healthy plants within minutes after acquisition of the virus. Aphids lose the ability to transmit the virus within 24-48 hours after acquiring the virus from an infected plant.
Monitor and control the presence of vector pest such as aphids in the orchard. Once infection is noted the tree must be removed and destroyed after it has been allowed to dry thoroughly. Neighbouring trees must be monitored for the development of the disease.
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Disease Name Identification Symptoms (Damage Caused) Seasonal Activity Prevention/Control
Greening
CGD results in a chronic decline of citrus. The leaf veins often initially turn yellow.Later leaf symptoms may resemble zinc deficiency. The disease usually begins in one branch or sector of larger trees and gradually spreads throughout the tree. On branches or trees affected by greening, the leaves are small, point upright, and show chlorosis. Fruit from infected trees are small, misshapen, and have a sour or bitter flavour, whereas fruit from trees affected with severe citrus tristeza virus (CTV), blight, or stubborn are sweet. Seeds in symptomatic fruit are usually aborted, and the fruit remains green on one end. Premature fruit drop occurs
Citrus Psylla (Trioza) are vectors of the bacteria
Monitor and control the presence of vector pest such as citrus psylla in the orchard. Once infection is noted the tree must be removed and destroyed after it has been allowed to dry thoroughly. Neighbouring trees must be monitored for the development of the disease.
Table 3.2 – Citrus Diseases Symptoms and Treatments
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Chapter 3
Diseases often destroy the plant or cause so much damage to the plant that it has to be replaced. When plants are replaced, it normally entails great economic expense and loss of production as new trees require time to grow before they produce fruit.
Good disease management requires an in depth knowledge of how different factors interact in the development of the disease; particularly, knowledge of environmental conditions that stress the plant, making it more susceptible to disease.
By following simple guidelines the occurance of the most common pests in the citrus orchard can be negated, but even the best prevention programme can never totally ensure that diseases will not occur so effective scouting and monitoring is vital.
Complete activity * in the Learner Workbook.
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Chapter 4 After completing this chapter, the learner will be able to: Monitor and report the incidence of weeds in the agricultural enterprise. 1. Introduction to weeds and their impact on Agriculture in General and Citrus production
specifically
Weeds pose many hazards to successful crop production. Weeds compete with citrus trees for nutrients, light, water, space and harbour insects and rodents that attack citrus trees. It is important to monitor the growth and occurrence of weeds in the Citrus orchard because:
o Weeds can increase fire hazards o Weeds may increase cold damage from radiation freezes, o Weeds increase the incidence of Phytophthora foot rot, o Weeds may impede harvesting of citrus crops, o Weeds may intercept soil-applied chemicals, thereby reducing their effectiveness. o Weeds also affect water distribution patterns from irrigation systems emitters, disease control,
and environmental conditions within the grove.
There are three categories of weeds that should be monitored in Citrus orchards, namely broadleaf, grasses, and sedges. These can in turn be classified as annuals and perennials. This means that monitoring plans and procedures might have to be applied in annual cycles for certain types of weeds.
Broadleaf (dicotyledons) have broad leaves with net-like veins, display branching growth habit and generally reproduce by seeds. Grasses (monocotyledons) have narrow, strap-shaped leaves and rounded stems, are generally perennial, and reproduce by seeds and/or rhizomes or underground stems. Sedges are similar to grasses but have triangular stems. Sedges may reproduce by seeds, rhizomes or tubers.
2. Monitoring Weed Presence
It is important to consider Good Agricultural Practices when planning the monitoring principles related to weeds. The different methods of weed eradication were discussed in detail in the level 2 guide pertaining to the control of pests, diseases and weeds. Any control programme for alien vegetation must include the following 3 phases: • Initial control: drastic reduction of existing population. • Follow-up control: control of seedlings, root suckers and secondary growth. • Maintenance control: sustain low alien plant numbers with annual control programs.
Once a decision has been reached and a commitment made to control alien plants, planning is required to make the best use of the limited available resources.
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3. Advantages of Monitoring Weed Control Plans As with any agricultural action plan the effectiveness of the plan can only be determined by recordkeeping and the constant monitoring of the process. There are several advantages that the efficient monitoring of the weed control plan can have for the citrus grower. It can: • Provide systematic allocation of the limited available resources. • Aid in times of crisis management for e.g. after floods or fire. • Promote continuity between successive land managers. • Allow progress to be measured and maintained. • Correct implementation of the management plan and monitoring progress, results in the following:
o Decrease in the extent and/or densification of the infestations. o Decreased annual control costs. o Increased value of the property.
4. Implementing the Weed Control Plan
4.1. Survey and Mapping To implement an effective weed control plan the farm or production area must firstly be divided into alien plant infestations control areas. Use natural or man-made boundaries, e.g. rivers, roads and fences to define area and number these control areas for record purposes. Secondly a detailed alien plant survey must be conducted in each control area. The following information must be recorded during the survey:
• All the alien plant species present and their growth habits (trees, seedlings, coppice). • Estimate the percentage cover, e.g. 75-100% is very dense, 50-75% is dense, 25-50%
is medium density, 5-25% is sparse, and 0-5% describes a scattered infestation. • The terrain, e.g. access roads or steep slopes that will slow down the control operations. • Sites of future wood lots for local community needs.
Thirdly control areas must be prioritised into high, medium or low priority for control and rehabilitation, according to importance criteria such as the threat to biodiversity, water yield or carrying capacity. Lastly a map showing the numbered high, medium and low priority control areas and the surveyed alien plant infestations must be drawn up. The best practice is to drawn up the map by using a aerial photos or existing 1:10 000 maps.
4.2. Listing Resources and Selecting Control Methods
To determine what control measures will be used to control weed infestations list the required resources for each high priority control area such as labour, herbicides, and equipment that will be needed to control the infestation. Next evaluate the resources requirements and select the appropriate control methods, using registered herbicides. Calculate the control costs for different methods of control for the high priority control areas and decide on the most cost effective and reliable method. When making this decision remember that cheaper control methods might save money in the short run but can mean greater capital outlay is necessary in subsequent seasons to control the same infestation again. Lastly a strategy, or a collection of appropriate control methods, must be drawn up for alien plant infestations in each control area.
4.3. Planning Monitoring Operations Related to Weed Control
When planning seasonal monitoring and weed control operation a plan of operations for the current year’s work in high priority control areas must be drawn up. The plan must be flexible and allow adjustment as progress is made. The plan should include a budget for the resources such as labour, herbicides and equipment that will be required during the first year. Do not plan to control too large an area; budget 75% for follow-up control work and rehabilitation of previously cleared areas, 20% for initial control of a new
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area, and 5% for an emergency ‘fire/flood fund’ to cope with catastrophic occurrences, such as mass seed regeneration of wattle after fire, or loss of planted grass seed during heavy rains. Next, allocate labour, herbicide, equipment and transport resources to the high priority control areas. Draw up timetables for control operations that include contingency or “catch-up’ times for use when operations have fallen behind due to climatic condition or labour disputes, etc.
4.4. Implementation of Monitoring Operations related to Weed Control
Weed monitoring works on a similar principle to pest and disease monitoring and requires the scout to frequently walk through orchards and record the weeds found as well as the stage at which the weeds are found. To implement the control plan effectively train the labour team in the correct alien plant control and grass planting methods at the beginning of the implementation phase. The labour team can then be used to scout and monitor the presence of weeds in all the control areas. To ensure the effectiveness of the control plan regular and close supervision of control operations must be maintained.
4.5. Recordkeeping
Recordkeeping are required to determine the effectiveness of the weed control and monitoring plan. To ensure that records are sufficient keep simple records of daily operations, for e.g. record the labour days, herbicide volumes and equipment that were required for each operation. This establishes standards or norms for the control work. Also keep records that monitor progress with the control work. Collect and evaluate data and feed this information back into the budget to update and amend the plan of operations for year two, for instance the plan for follow-up operations to control re-growth.
5. Reporting Protocols related to Unwanted Plant Growth
For successful non-invasive weed monitoring, a good knowledge of the plants that are considered unwanted growth and their growth cycles for the geographical area where the orchard is situated is essential. Most citrus farms have their own response plans against weeds that work in conjunction with their monitoring plans for invasive species. These often include frequent removal of or chemical actions against weeds before the weeds become too large or go to seed. These weed control methods can include manual eradication techniques, such as:
• Manual or mechanical action for example the pulling up of weeds up or chopping them down. • Chemical sprays against specific weeds or on targeted groups of weeds. • Planting cover crops. • Placing mulches in the rows to suppress weeds.
Monitoring and scouting activities on the farm will identify and report the occurance of weeds or unwanted plant growth. Once the presence of weeds has been reported by the scouting teams weeds must be identified and control measures decided upon. Table 4.1 gives a simple breakdown of the three most commonly occurring weed types on a citrus farm.
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Broadleaf Weeds Grasses Sedges
Leaves with net-like veins, display branching growth habit and generally reproduce by seeds
Have narrow, strap-shaped leaves and rounded stems, are generally perennial, and reproduce by seeds and/or rhizomes or underground stems
Similar to grasses but have triangular stems. Sedges may reproduce by seeds, rhizomes or tubers
Example: Dandelion Example: Kweek Example: Nut grass Table 4.1 – Common Weeds 6. Monitoring and Reporting Protocols for Invasive Species
Monitoring for invasive species includes surveys of the immediate environment around the farm and looking out for invasive species. The fight against invasive alien plants is spearheaded by the Working for Water programme, launched in 1995 and administered through the Department of Water Affairs and Forestry. This programme works in partnership with local communities, to whom it provides jobs, and also with Government departments including the Departments of Environmental Affairs and Tourism, Agriculture, and Trade and Industry, provincial departments of agriculture, conservation and environment, research foundations and private companies. The WFW initiative currently runs over 300 projects in all nine of South Africa’s provinces. Scientists and field workers use a range of methods to control invasive alien plants. These include:
• Mechanical methods such as felling, removing or burning invading alien plants. • Chemical methods such as using environmentally safe herbicides. • Biological control such as using species-specific insects and diseases from the alien plant’s
country of origin. To date 76 bio-control agents have been released in South Africa against 40 weed species.
• Integrated control such as combinations of the above three approaches. Often an integrated approach is required in order to prevent enormous impacts.
Landowners are under a legal obligation to control invading alien plants occurring on their properties. This obligation exists as a result of the various laws. The relevant laws identified at this stage are the following:
• The common law relating to neighbours and nuisance. • Section 151(1) of the National Water Act 36 of 1998. • Section 28 of the National Environmental Management Act, 107 of 1998. • Section 31A of the Environment Conservation Act, 73 of 1989. • Municipal by-laws and the National Veld and Forest Fire Act 101 of 1989. • Regulations in terms of the Conservation of Agricultural Resources Act, 43 of 1983.
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Working for Water contact details and information about the legal obligations of landowners in terms of invaders Website: http://www.dwaf.gov.za/wfw/ Postal Address: Private Bag X4390 Cape Town 8000 South Africa Tel: (021) 441 2700 Fax: (021) 441 2781 E-mail: [email protected]
6.1. Frequently occurring Invasive Species
If the monitoring process identifies invasive plant growth a grower need to be able to classify the plant and determine what steps, if any, needs to be taken. The present legislation forms part of the Conservation of Agricultural Resources Act, 1983 (Act No 43 of 1983) (CARA). Regulations 15 and 16 under this Act, which concern problem plants, were amended during March 2001. CARA is currently (2003) in the process of being revised.
Whereas CARA previously classified problem plants into two groups - declared weeds and plant invaders - the amended regulations make provision for four groups: declared weeds (Category 1 plants), plant invaders (Category 2 and Category 3 plants) and indicators of bush encroachment. The first three groups consist of undesirable alien plants and are covered by Regulation 15. Bush encroachers, which are indigenous plants that require sound management practices to prevent them from becoming problematic, are covered separately by Regulation 16.
6.1.1. Category 1 plants, or declared weeds
These are prohibited plants that will no longer be tolerated, neither in rural nor urban areas, except with the written permission of the executive officer or in an approved bio-control reserve. These plants may no longer be planted or propagated, and all trade in their seeds, cuttings or other propagative material is prohibited. They may not be transported or be allowed to disperse. Table 4.2 is a list of current category 1 plants.
Declared weeds − Category 1
Common name Botanical name
Triffid weed, Chromolaena Chromolaena odorata
Lantana Lantana camara
Pereskia, Barbados gooseberry Pereskia aculeate
Bugweed Solanum mauritianum
American bramble Rubus cuneifolius
Red sesbania Sesbania punicea
Mauritius thorn Caesalpinia decapetala
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Inkberry Cestrum laevigatum
Balloon vine Cardiospermum grandifl orum
Field bindweed Convolvulus arvensis
Morning glory (perennial) Ipomoea indica
Madeira vine Anreda cordifolia
Water hyacinth Eichhornia crassipes
Brazilian pepper tree Schinus terebinthifolius
Yellow-flowered Mexican poppy Argemone Mexicana
Montanoa tree daisy (spreading in area) Montanoa hibiscifolia
Camphor Cinnamomum camphora
Indian laurel Litsea glutinosa Table 4.2 – Category 1 plants
6.1.2. Plant invaders of Category 2 These are plants with the proven potential of becoming invasive, but which nevertheless have certain beneficial properties that warrant their continued presence in certain circumstances. CARA makes provision for Category 2 plants to be retained in special areas demarcated for that purpose, but those occurring outside demarcated areas have to be controlled. The exception is that Category 2 plants may also be retained or cultivated in biological control reserves, where the plants will serve as host plants for the breeding of biological control agents. The growing of Category 2 plants in a demarcated area qualifies as a water use, and is subject to the requirements of section 21 of the National Water Act, 1998 (Act No. 36 of 1998).
Declared invader − Category 2
Common name Botanical name
Guava and hybrids Psidium guajava
Johnson grass Sorghum halepense
Leucaena Leucaena leucocephala
Castor oil bush Ricinus communis
Black wattle Acacia mearnsii
Silver wattle Acacia dealbata
Bluegum Eucalyptus grandis
Pine trees Pinus patula/elliottii There are some additional species that are currently recommended for listing as Category 2 invaders:
Declared invader − Category 2
Common name Botanical name
Couch grass, kweek Cynodon dactylon
Perennial ryegrass Lolium perenne
Kikuyu Pennisetum clandestinum
Napier grass Pennisetum purpureum Table 4.3 – Category 2 Plants
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6.1.3. Plant invaders of Category 3 These plants are undesirable because they have the proven potential of becoming invasive, but most of them are nevertheless popular ornamentals or shade trees that will take a long time to replace. A few of them were placed into this category instead of into category 1 because they do not cause problems in all situations. In terms of Regulation 15 of CARA, Category 3 plants will not be allowed to occur anywhere except in biological control reserves, unless they were already in existence when these regulations went into effect. The conditions on which these already existing plants may be retained are that they do not grow within 30 m from the 1:50 year flood line of watercourses or wetlands, that all reasonable steps are taken to keep the plant from spreading, and that the Executive Officer has the power to impose additional conditions or even prohibit the growing of Category 3 plants in any area where he has reason to believe that these plants will pose a threat to the agricultural resources.
Declared invader − category 3
Common name Botanical name
Syringa Melia azedarach
Peanut butter cassia Senna didymobotrya
Morning glory (annual) Ipomoea purpurea
Jacaranda Jacaranda mimosifolia
Orange cotoneaster Cotoneaster franchetii
Loquat Eriobotria japonica
Australian silky oak Grevillea robusta
Common mulberry Morus alba Table 4.4 – Category 3 Plants
6.2. New or unknown plant species observed during weed monitoring actions If any “unknown” or new plant species appear suddenly during monitoring operations, these weeds should initially be treated as “unwanted plant growth” and not necessarily as invasive species. It is also important to try and identify certain types of “new” plant species, as they might be an indication of soil degradation and might be emerging as “pioneer species”. Pioneer species of plants can only exist in very poor soil conditions, and they are nature’s way of trying to repair the nitrogen balance in the soil. If pioneer species are emerging in your orchards, it would be wise to report this immediately and contact as soil specialist for assistance.
Chapter 4
There are three categories of weeds that should be monitored in Citrus orchards, namely broadleaf, grasses, and sedges.
It is important to consider Good Agricultural Practices when planning the monitoring principles related to weeds.
As with any agricultural action plan the effectiveness of the plan can only be determined by recordkeeping and the constant monitoring of the process.
To implement an effective weed control plan the farm or production area must firstly be divided into alien plant infestations control areas.
When planning seasonal monitoring and weed control operation a plan of operations for the current year’s work in high priority control areas must be drawn up. The plan must be flexible
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and allow adjustment as progress is made. Weed monitoring works on a similar principle to pest and disease monitoring and requires the
scout to frequently walk through orchards and record the weeds found as well as the stage at which the weeds are found.
Recordkeeping are required to determine the effectiveness of the weed control and monitoring plan.
For successful non-invasive weed monitoring, a good knowledge of the plants that are considered unwanted growth and their growth cycles for the geographical area where the orchard is situated is essential.
Landowners are under a legal obligation to control invading alien plants occurring on their properties. This obligation exists as a result of the various laws.
Complete activity * and * in the Learner Workbook.
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Bibliography Literature: 1. Integrated Production Guidelines for Export Citrus Volume III, Citrus Research International,
Research and Extension Services 2. CRI Identification Manual for Citrus Pests and their Natural Enemies; T.G. Grout, J.H.
Hofmeyer, S.D. Moore, A.B. Ware, 2005 3. CGA Learner Guide 116125; Apply crop protection and animal health products effectively and
responsibly 4. A Guide to the use of Herbicides. Grobelaar H, Vermeulen JB and van Zyl K (2000). Seventeenth
edition. National Department of Agriculture, Pretoria. 5. Plant Protection Research Institute Handbook No.12. Henderson L (2001), Agricultural Research
Council, Pretoria. World Wide Web: 1. www.cri.co.za 2. http://ipmcitrus.co.za/general/damage_symptoms.htm 3. http://www.insectscience.co.za 4. http://www.ars.usda.gov/Main/site_main.htm?docid=10141&page=1&pf=1&cg_id=0 5. http://en.wikipedia.org/wiki/Good_Agricultural_Practices 6. http://aggie-horticulture.tamu.edu/citrus/l2328.htm 7. http://edis.ifas.ufl.edu/CH144 8. http://www.dwaf.gov.za/wfw/Control/ 9. www.cga.co.za 10. http://edis.ifas.ufl.edu/CH144 11. www.academic.sun.ac.za/agric/pathology/research 12. http://aggie-horticulture.tamu.edu/citrus/l2313.htm 13. http://ipm.ifas.ufl.edu/agricultural/fruit/citrus/ASP-hoy.htm 14. http://www.agric.nsw.gov.au/reader/gr-varieties/h217.htm 15. http://edis.ifas.ufl.edu/TOPIC_Citrus_Pests_Diseases 16. http://www.arc.agric.za/home.asp?PID=1&ToolID=63&ItemID=2358 17. http://www.agriseta.co.za/downloads/LearningMaterial/116124_LG.pdf 18. http://edis.ifas.ufl.edu 19. http://www.mainepotatoipm.com/ipmfactsheets/scouting.pdf 20. http://citrusent.uckac.edu/PPS%20for%20Citrus%202007.pdf 21. http://www.nda.agric.za/docs/Subtropical.pdf 22. http://agriculture.kzntl.gov.za/portal/Portals/0/production%20guidelines 23. http://www.arc.agric.za/home.asp?pid=1031 24. http://www.ipm.ucdavis.edu/PMG/selectnewpest.citrus.html 25. http://www.up.ac.za/academic/fabi/citrus/rootrot.html 26. http://www.sugar.org.za/sasri/ISHEETS/Weeds SME’s: 1. B. Harington – B.Sc Agric (Viti & Oen); University of Stellenbosch 2. C. Harington – B.Tech Hotel Management; Technicon Witwatersrand and OBET