BIOLOGICAL COMPETITORS

Significance of Pests

Modern agriculture is largely a

Monoculture

• Efficent but . . .• May encourage pest buildups

Chemical vs. Biological Control

Developed countries depend on chemicals . . .

Ideally, long-term control is based on biological methods

Numerous techniques

Chemical Pest Control History

Late 19th century Bordeaux mixture on vineyards Iron sulfate

Early 20th century Application equipment

1904 power sprayer (Germany) Aerial application in 1921 (U.S.)

New Chemistry

War-time chemicals Three chemical classes around WWII

Organophosphorus insecticides Dithiocarbamate fungicides Phenoxy herbicides

DDT (1939) Dichloro-diphenyl-trichloroethane Insecticide controlled fleas, lice, mosquitos Odorless, grayish-white powder Banned in U.S. in 1972-73 (environment)

Biological Techniques

Resistant plant types bred/engineered

Natural enemies Sterile male release Attactants including pheromones Juvenile hormones Insects feeding on weeds (not crops) Antagonistic fungi/bacteria

Integrated Pest Management

IPM (Integrated Pest Management) implies that no single control

procedure will control a pest successfully...

IPM seeks to: Integrate a variety of physical,

biological, and chemical methods to control pests

Integrated Pest Management

In IPM: natural controls are emphasized artificial controls are used only as

required potentially harmful species

continue to exist at tolerable levels

WEEDS

A weed is any plant growing out of place!

Weeds compete with crops for:• Space• Water• Mineral nutrients• Sunlight

WEEDS (cont)

Annuals vs. Perennials Control methods vary Annuals – focus on preventing seeding Perennials – seed and underground parts Means of control:

Pulling Hoeing Mechanical (tillage, mowing, etc.) Chemical Mulching Fire

MODERN WEED CONTROL

Early 1940’sMechanical control alone expensive!Four basic methods of control developed:

1) Preventative measures (prevent seed)2) Crop competition (good shades bad)3) Biological control (natural enemies)4) Chemical control

1930’s – study of auxins1940’s – synthetic auxin 2,4-D (herbicide)

Chemical Weed Control

Chemicals classified as:• Selective• Nonselective

Selective kills certain kinds of weedse.g. broad-leaved vs. grasses

Nonselective kills all vegetation it is applied to

Chemical Weed Control (cont)

Herbicides also classified by:

• Timing of application related to growth cycle of weeds or crops

• Preplant• Preemergence• Postemergence

• Method of application• Broadcast• Banding• Spot treatment

Types of Weeds

Annuals Complete life cycle in one year; seeds

Biennials Seeds germinate 1st spring, grow

vegetative 1st summer, winter chill, flower 2nd spring, seeds 2nd summer

Perennials Can live indefinitely; seeds and

vegetative (root, rhizome, stolon, tuber)

Plant Diseases and Insects

Annual losses in crops, ornamentals, and turf hundreds of billions $$

Methods of control fall into four groups• Biological control• Cultural practices• Government quarantine/eradication

programs• Application of pesticides

Plant Diseases

Disease (dis - ease) Plant condition which is abnormal as a

result of an infectious pathogen Three (3) major groups:

Bacteria Fungi VirusesAlso: mycoplasmas, parasitics

(including nematodes)

Plant Diseases (cont)

Infectious diseases require: Susceptible host Causal agent Favorable environment for pathogen

Appearance requires primary inoculum (portion of pathogen)

Symptoms may appear when inoculum : penetrates and becomes established in the host sets up a life cycle including the host

Plant Diseases (cont)

Disease symptoms: Abnormal tissue coloration Wilting Tissue death Defoliation Abnormal increase in tissue size Dwarfing Replacement of host plant tissue by

tissue of the infectious organism

Pathogens of Infectious Diseases

Bacteria Fungi Viruses Mycoplasmas Parasitic plants Nematodes

Pathogens of Infectious Diseases

Bacteria Both beneficial and pathogenic Bacterial diseases difficult to control Resistant plant species, cultivars, seeds Spread by rain, wind-blown dust, birds,

insects, poor cultural techniques Moisture aids entry into plants through

stomata, scars, wounds Chemical control limited effectiveness

Pathogens of Infectious Diseases

Fungi Both beneficial and pathogenic Obtain nutrients from other sources Some live on dead O.M. – others live on

living tissues; facultative on either Beneficials decompose dead matter Mycorrhiza – symbiosis with plant roots Other beneficials: penicillium, bread,

cheese, and alcohol production

Pathogens of Infectious Diseases

Most plant diseases caused by fungi Famines, blights, epidemics, starvation Mycelium consist of thread-like hyphae Hyphae absorb food from host Fungi reproduce by spores Fungal diseases usually easier to control than

bacterial or viral diseases Control by:

resistant varieties, proper sanitation, crop rotation and other cultural practices, fungicides, and antagonistic fungi

Pathogens of Infectious Diseases

Viruses Extremely small (electron microscope) Outer protein shell, inner nucleic acid Depend on living cell in order to grow Depend on transmitting vector carrier to move

from plant to plant Named for the disease they cause Control by resistant varieties Chemicals only control insect vectors Heat therapy renders some viruses inactive Propagate virus-free plants from shoot tips

Pathogens of Infectious Diseases

Mycoplasmas Similar to animal mycoplasmas Intermediate size between virus and bacteria Cells have three-layered membrane Have own energy and enzyme system Occur in phloem, disrupt food transport Named after plant first infected Transported by vectors Control by eliminating vectors Certain antibiotics are effective (tetracycline)

Pathogens of Infectious Diseases

Parasitic Plants Three groups:

Epiphytes Little harm; physical support Spanish moss, epiphytic orchid

Hemiparasites Do harm; water and mineral nutrients Can photosynthesize carbohydrates Witchweed, Mistletoe

True parasites Lack chlorophyll; depend entirely on host Dwarf mistletoe, Dodder, Broomrape

Pathogens of Infectious Diseases

Nematodes A.K.A. threadworms, roundworms, and

eelworms Attack roots, stems, foliage, inflorescence plant parasitics approx. 1 mm long damage by piercing/puncturing/injecting

secretions classified by visible effects caused to

plants...

Pathogens of Infectious Diseases

Nematodes (cont) root knot cyst lesion stubby-root also spread certain viruses/diseases Various methods to reduce crop losses

from nematodes: Resistant species/cultivars, Nematode-

free stock/soil, fumigate soil, Nematicides

Insects and Mites

Compete with humans for food Also spread disease Not all are bad; predators, beneficials

Praying mantis, ladybird beetle, green lacewing, predatory Aphytus wasp

Honeybee, silkworm Some are eaten Some for research

Control essential – world food supply

Insects and Mites

Control methods Biological Cultural Physical/mechanical chemical

Insects and Mites

Classification of Insects Order Metamorphosis Chewing/sucking additional damage by:

egg laying spread of disease

Insects and Mites

Action of pesticides control Stomach poison

Systemic action kills chewing/sucking Contact action Fumigation Suffocation Dessication Repellant action Attractant action Hormone action