Common diseases of cucurbit vegetables, mango,

Common Diseases of Cucurbit Vegetables,

Mango, Corn and Onion

Agricultural Extension 217 – Advanced Crop Protection

Mr. Pedro Ramos Professor

Ronel D. Cana Student, MSA

Introduction

Crop Production

involves in depth plant

sciences

and up-to-date technologies

aim

production of food and other

related products and commodities

Introduction

Crop Protection

application of different technologies for the purpose of increasing yield and minimizing, if

not totally eradicating yield loss

engages both the recognition and control of plant pests and

diseases

Introduction

Tropical Agricultural

Crops

among the crops that are most susceptible to plant diseases

these susceptible crops include cucurbit vegetables, mango, corn and onion

Diseases of Cucurbit VegetablesAlternaria leaf spot

Cause: Fungus – Alternaria cucumerina and Alternaria alternata

Symptoms: Small spots develop on the upper surface of leaves which could develop into larger coalescing lesions. These lesions might have concentric rings.

Control: Use of disease-free seeds; Use of recommended fungicides.

Diseases of Cucurbit VegetablesAlternaria leaf spot

Diseases of Cucurbit VegetablesDowny Mildew

Cause: Fungus – Pseudoperenospora cubensis

Symptoms: Leaves have a mottled appearance. Leaf spots turn a pale yellow color, enlarge and dry out. Can be confused with the bacterial disease angular leaf spot.

Control: Use tolerant varieties where available; Use a fungicide program that allows for the rotation of protective and systemic fungicides which reduce the chance of fungicide resistance developing.

Diseases of Cucurbit VegetablesDowny Mildew

Diseases of Cucurbit VegetablesPowdery mildew

Cause: Fungus – Podosphaera xanthi

Symptoms: White powdery spots develop on leaves. Symptoms usually develop first on the underside of leaves before covering both sides. Leaves gradually turn yellow to a papery brown and eventually die.


Control: Use tolerant varieties where available; Monitor crops closely; Use a fungicide program involving the rotation of protective and systemic fungicides that reduce the chance of fungicide resistance developing; Petroleum spray oils, milk and bicarbonates might offer some control.

Diseases of Cucurbit VegetablesAnthracnose

Cause: Fungi – Colletotrichum orbiculare

Symptoms: Brown to black spots develop on leaves; long dark spots develop on stems and round sunken spots develop on fruit. Fruit symptoms might develop in transit.


Control: Use tolerant varieties where available; Monitor crops closely to identify the disease early in its cycle; Use recommended fungicides; Don’t replant in sites that have previously had the disease, or use a long rotation.

Diseases of Cucurbit VegetablesScab

Cause: Fungus – Cladosporium cucumerinum

Symptoms: Can affect leaves, petioles, stems and fruits. Water-soaked spots occur on leaves and runners. These spots eventually turn grey to white. Lesions on fruit are often confused with anthracnose. These spots are 3–4 mm in diameter and might ooze a gummy substance. The spots could then be invaded by secondary rotting bacteria which cause the spots to smell.


Control: Use resistant cultivars; Use disease-free seed; Apply appropriate fungicides particularly if cool, wet weather is expected; Rotate cucurbits with other crops, with two or more years between cucurbits; Avoid low-lying, shaded areas prone to moisture and dews.

Diseases of Cucurbit VegetablesDamping-off of seedlings and fungal root rots

Cause: Fungi including Pythium, Rhizoctonia and Fusarium

Symptoms: The first symptoms are water-soaked lesions occurring at soil level. This leads to wilting and seedling death. Often, plants that have survived damping-off might show symptoms of root rot. Roots can have a watery grey appearance, particularly the finer feeder roots.


Control: Usually sporadic outbreaks and can be difficult to control; Fungicide seed treatments provide some control of damping-off; Plant to allow vigorous growth, and do not overwater; Ensure residue from previous crops is well-decomposed.

Diseases of Cucurbit VegetablesBacterial leaf spot

Cause: Bacterium – Xanthomonas campestris pv. Cucurbitae

Symptoms: Spots first appear leaves as small water-soaked or greasy areas on the underside of leaves, and as indefinite yellow areas on the upper side of leaves. In about five days the spots become round to angular with thin, brown, translucent centres and a wide, yellow halo.


The spots enlarge up to about 7 mm diameter. Occasionally young stems and petioles are attacked. Young fruit may also be affected. Fruit may produce a light brown ooze from small, water-soaked areas, which can extend into the seed cavity, causing seed infection.


Control: Use disease-free seed; Do not work in the crop when it is wet; Practise rotation and destroy plant debris by burning, if possible, or ploughing in; Use recommended chemical treatments, but often it is too late after fruit symptoms are noticed.

Diseases of Cucurbit VegetablesMosaic

Cause: Watermelon mosaic virus, papaya ringspot virus and tomato mosaic virus.

Symptoms: Light and dark green mottling of the leaves. Distortion of leaves and stunting of the plant might occur. Squash fruit might show sunken concentric circles or a raised marbled pattern.


Control: Use tolerant varieties; If only a few plants are affected they should be removed and destroyed; Insect control (Aphids) is an option if monitoring is practised and appropriate insecticide applications are made; Plant residue should be incorporated as soon as possible after harvest.

Common Diseases of MangoAnthracnose

Cause: Glomerella cingulata, Colletotrichum gloeosporiodies, Gloeosporium mangiferae.

Symptom: The disease appears on young leaves, stem, inflorescence and fruits. Leaves show oval or irregular grayish, brown spots which may coalesce to cover larger area of the leaves.

Consequently, the development of the affected leaves is hampered and they dry and shed off. On young stem, grey brown spots develop. These enlarge and cause girdling and drying of affected area. Often, black necrotic I areas develop on the twigs from the tip downwards causing a dieback.


Control a. The fungus survives on dead and dried twigs,

therefore, they should be pruned/cut and burnt as soon as possible.

b. The disease can be controlled by spraying Bordeaux I mixture (3:3:50) Blitox or Phytolan (0.3%), Bavistin or Benlate (0.1 %), thrice a year..

c. Affected full grown fruits should be dipped in hot water (51OC) for 15 minutes before storage.


Common Diseases of MangoPowdery mildew

Cause: Odium mangiferae

Symptom: A white superficial powdery mass of fungus growth covers the leaves, the stalks of the panicles, the flowers and tender fruits. The powdery mass consists mainly of fungal spores. The mildew affects the flowers before fertilization and the fruits in their earliest stages.

The affected flowers and fruits drop prematurely, reducing the crop considerably or preventing the fruit set. Rain and mist accompanied by cool nights during the flowering period, favors the development of the disease. Shedding of infected leaves may also occur.


Controla. The most effective method of control is by

dusting finely powdered sulfur on the flowering branches. More than one round of dusting will be necessary. The first round should be given before flower opening. This will be followed by two or more rounds at fortnightly interval.

b. It can also be controlled by the application of Kemthane (0.1%) or Bavistin (0.1%) or Benlate «0.1%). The spray should be given before the flowering, as a preventive measure.


Common Diseases of MangoBacterial canker

Cause: Pseudomonas mangiferae

Symptom: The earliest symptom is the formation of small dark green water soaked spots which finally assume the shape of a raised black spot. These areas on the fruits develop longitudinal cracks and gum starts oozing out from the splits.

Seriously affected fruits drop down and the yield is reduced since affected fruits are unattractive and unmarketable.


Controla. Bordeaux mixture (4:4:50) may be applied at

fortnightly interval from the first appearance of the disease on the leaves.

b. Recently, two sprays of Streptocycline (200 ppm) have been found to be helpful in reducing the incidence of this disease.

c. Field sanitation and seedling certification as preventive measures and seedling branches and fruits are reported to minimize the infestation of this disease.


Reading Excercise Muna!

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OK, back to our lesson:

Common Diseases of CornSeed Rot, Seedling Blight, Root Rot

Cause: Pythium, Fusarium, Gibberella, Trichoderma and Penicillium

Symptoms: The color of the roots most often provides a good indication of which organism(s) are present:• greyish-white indicates Diplodia• tan to pink indicates Fusarium or Gibberella• reddish to brown indicates Rhizoctonia•blue-green indicates Penicillium or Trichoderma


Symptom: Seed, seedling and roots infected by Pythium are most often soft (wet) and dark coloured, as opposed to roots infected with Fusarium, Gibberella, Diplodia and Rhizoctonia, which are firm or leathery.

Common Diseases of CornAnthracnose Leaf Blight

Cause: Colletotrichum graminicola

Symptoms: Anthracnose may affect both leaves and stalks. The main symptoms are leaf spotting, top dieback and stalk rot. Leaf spots are oval, up to 15 mm (6 in.) long, with a tan centre and reddish-brown border. Individual lesions may join, forming streaking along the margin or midrib.


Symptom: A general yellowing of the tissue surrounding the infected areas often develops. With the aid of a hand lens, small black spots can be seen in the centre of the lesions. The disease is first observed on the lower leaves and later on the upper leaves. Top dieback can occur late in the season as diseased leaves wilt and gradually die.

Controla. Planting resistant varietiesb. Practicing crop rotationc. Using of effective fungicides


Common Diseases of CornCommon Smut and Head Smut

Cause: Ustilago zeae and Sporisorium holci-sorghi

Symptoms: Greyish smut galls up to 10 cm (4 in.) in diameter develop on the stalks, ears and tassels, while smaller galls often appear on the leaves. The galls initially have a white membrane cover that eventually breaks and releases dark-brown or black powdery spores.


Symptom: On the leaves, galls develop into a hard, dry growth. Smut galls can replace kernels. Unlike common smut, head smut occurs only on the ears and tassels.

Controla. Minimizing mechanical and chemical injury to

the plant;b. Practicing a balanced-fertility programc. Using of effective fungicides


Common Diseases of CornAnthracnose Stalk Rot

Cause: Colletotrichum graminicola

Symptoms: Large, dark brown-to-black shiny areas or streaks on the outer stalk rind. These shiny or discoloured areas are often found at the base of the stalk. Cutting the stalk lengthwise will reveal a discolored and rotted pith. Premature death occurs above the ear, with the plant tissue below the ear remaining green.


Examination of the stalk in these dead areas will show the same shiny black areas that are found at the stalk base. Plants with top dieback symptoms correspond to areas of the field that had late-season stresses.

Controla. planting hybrids that have good resistance or

tolerance to leaf diseases and stalk rotsb. managing insects such as corn borerc. good weed controld. appropriate plant populationse. a balanced N and K fertility programf. crop rotation


Common Diseases of CornFusarium Ear Rot

Cause: Fusarium verticilloides

Symptoms: Unlike gibberella ear rot, kernels infected with fusarium ear rot will be scattered around the cob among healthy-looking kernels or on kernels that have been damaged (by corn borer or bird feeding). Silks are susceptible to infection during the first 5 days after initiation.


Fusarium infection produces a white-to-pink or salmon-coloured mould. A "white streaking" or "star-bursting" can be seen on the infected kernel surface.

Controla. Harvest as early as possible.b. If bird damage is evident, harvest outside

damaged rows separately. Keep and handle the grain from these rows separately.

c. Adjust harvest equipment to minimize damage to corn.

d. Cool the grain after drying.e. Clean bins before storing new grain.


Common Diseases of Onion Purple Blotch

Cause: Alternaria porri

Symptoms: Small white sunken spots develop on the leaves. These enlarge and under moist conditions, turn purple. These are also prominent on the inflorescence stalks. Infection can cause a semi-watery rot on necks of bulbs that turn yellow-red in color. Infected bulb tissues become papery.

ControlCultural control methods include long rotations with unrelated crops and good drainage. Lowering the density of transplanted crops will reduce infection, as will the application of high rates of calcium superphosphate and potassium fertilizer. Nitrogen fertilizer at low and high rates will increase the prevalence of disease. Routine (weekly interval) field sprays with dithiocarbamate fungicides, particularly mancozeb and chlorothalonil.


Common Diseases of OnionAnthracnose

Cause: Colletotrichum gloeosporioides

Symptoms: The leaves become twisted due to infection.

ControlControl measures are similar to purple blotch.

Common Diseases of OnionAnthracnose

Common Diseases of OnionDowny Mildew

Cause: Peronospora destructor

Symptoms: Appearing as white specks, usually confined to the oldest leaves of young plants. A white mold develops rapidly in cool damp weather and progresses down the sheath, and plants eventually fall over and dry up.


ControlYoung plants can be treated with mancozeb at weekly intervals until bulbing begins.

Common Diseases of OnionBasal Rots

Cause: Fusarium spp.

Symptoms: Outwardly, the bulb may appear normal. It eventually becomes soft, however, and will develop a watery rot under moist conditions or a dry shriveled bulb in a dry environment.


ControlApplication of fungicides, good field drainage and removal of excess moisture in the storage area.

That’s it...

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Common diseases of cucurbit vegetables, mango,

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