Crop Pests and Control

Chapter 13

Factors that can limit crop yield: 1. Insect Pests 2. Disease

3. Weeds

4. Non-insect invertebrate or vertebrate pests

Problems That Have Occurred Due To The Use of Pesticides:

Integrated Pest Management (IPM): Makes use of many pest control methods

in order to preserve the environment and prevent pest resistance.

Goals of IPM

Basic Principles of IPM: Exclusion –

Suppression –

Eradication –

Plant resistance –

Steps of IPM: Identify pests Take preventative measures Crop scouts Use economic thresholds

IPM Involves The Use Of: 1. Natural controls

Biological control – Cultural control Mechanical control - Sanitation Chemical control

Successful IPM makes use of the following practices

Beneficial Insects: Insects that benefit crops by pollinating or

feeding on crop pests.

Keys to successful IPM Programs: Scouting Fields –

weeds should be scouted within 2 weeks of crop emergence

avoid boarder rows scout at least once a week. Samples should be representative of field

Economic Thresholds (ET)-

Damage Thresholds –

Used on pathogens – bacteria, fungi etc. Economic Injury Level (EIL) –

Insect Pests Crop Losses: Crop losses due to insects and mites range

from 5-15% annually = $4 billion in losses. Annual losses for:

Corn 12% Sorghum 9% Wheat 6% Soybean 3%

Damage Caused by Insects: 1. Defoliation – 2. Necrotic spots – 3. Boring or tunneling- 4. Lower quality – leave frass (excrement

and exoskeletons) 5. Higher harvest losses 6. More susceptible to virus’ – from open

wounds from sucking insects. 7. Increase erosion due to less dry matter

Insect Orders: Coleoptera - Diptera – Hymenoptera – Orthoptera – Lepidoptera – Acarina –

Insect Life Cycles: Metamorphosis – change in form from

egg to adult insect. 2 Types of Metamorphosis: Gradual - egg nymph adult Complete - egg larva pupa adult

Ametamorphic – without metamorphosis Hatches as a miniature adult

Two Major Types of Mouthparts: Chewing - jaws used to tear and grind

food i.e. Grasshoppers, crickets, honeybees

Sucking Mouthparts: used to obtain liquid foods.

Damage Caused By Chewing Insects:

Defoliators –

Borers –

Leaf miners -

Root Feeders -

Orders With Chewing Mouthparts: Orthoptera – Odanata – Neuroptera – Coleoptera – Hymenoptera –

Damage Caused by Sucking Insects: Distorted Plant growth:

Stippling Effect on Leaves:

Burning on leaves:

Pest Control Program: Made up of 3 basic principles:

1. 2. 3.

Methods of Insect Control: Genetic – using resistant or tolerant varieties Cultural - crop rotation, tillage methods,

resistant or tolerant varieties Mechanical – screens, traps, light and sound Biological – parasites, predators, diseases, male

sterility, temperature, moisture, pheromone traps

Chemicals – kill, repel, attract, sterilize Integrated control – using both artificial or

natural bio-control and chemicals.

Genetic Control: Non-preference control

Plant is not palatable to the pest – taste, smell, color, or texture is altered

Antibiosis Crop plant has harmful effect on the growth or

reproduction of the pest Tolerance

Plant doesn’t suffer economic damage even though it is infested

Chemical Control: About 75% of all pesticides are applied to

agricultural lands. Should only be used as last resort Classified by mode of action:

Contact – used for sucking insects Stomach – used for chewing insects Systemic – absorbed by plant and then

ingested during feeding.

3 Broad Classes of Insecticides: 1. Chlorinated hydrocarbons – DDT,

chlordane, lindnae Do not degrade easily Build up in fat tissues of animals and are passed

along the food chain Has led to a ban or restriction of most chemicals in

this category.

2. Organic phosphates – Ethyl and Methyl parathion and malathion Can be extremely toxic to mammals

3. Carbamate – Lower effect on mammals

Crop Losses From Diseases: 10-20% of production annually Diseases reduce yields:

Wheat & Soybean 14% annually Corn 11% Sorghum 9% Cotton 15% Potato 20-25% annually

Definitions: Symptoms - outward appearance of a plant that

are identifiable with a particular disease. Pathogen – causal organism, infectious agent Host – the plant infected with the pathogen Parasite – feeds off the host organism it invades.

Obligate – can survive only on the living tissue of the host Non-obligate - can survive on dead organic matter or

inorganic materials as saprophytes

Disease affects yield by: 1. Increasing respiration rate 2. Rob plant of: water, nutrients,

photosynthate. 3. Block translocation of nutrients 4. Replace the grain – ergot, smut 5. Increase plant respiration rate 6. Block photosynthesis 7. Affect crop quality too.

Classification of Diseases: 1. Infectious – caused by a living organism

that invades the host disrupting normal growth

2. Noninfectious – crop injury that involves no pathogen

Weather Nutrient deficiency Chemical injury

Pathogens Causing Disease: 1. Fungi-

Live in plant tissue, soil, weeds etc. Parasitic or saprophytic

2. Bacteria Parasitic or saprophytic Enter plants through openings or wounds Symptoms are: galls, blights, leaf spots, rots

3. Virus – Submicroscopic pathogenic particles Can not grow and multiply without a host Parasites Cause stunting and death; dwarf mosaic virus or dwarf potato virus

4. Nematode Microscopic worms that attach to roots, stems, leaves and flowers of

plants Live in soil or water

Fungi: about 100,000 fungal species have been

identified, about 8,000 of them are parasitic to plants. Have been responsible for a number of crop disasters that have lead to famines.

Classified mainly by what they feed on:

Obligate saprophytes – feed on dead plant and animal tissue

Obligate parasites – live only on living plants

Facultative saprophytes – can live on dead or living tissue

Facultative parasites – normally saprophytic but occasionallyparasitic.

How they work: Spread by – spores. Spores spread by: wind, water, insects, and other

agents. Enter plants through wounds, natural openings,

or by direct penetration of the epidermis. Upon germination spores produce hyphae that

grow and branch to produce other structures called mycelia or fungal bodies.

They attack – flowers, seeds, leaves, stems, and roots

Symptoms of Fungal Diseases: a. Necrosis – leaf spots, blight, die back,

canker, anthracnose, damping off, scab. b. Symptoms involving growth – galls leaf

curl hypertrophy or hyperplasia. Other symptoms – wilt, rust and mildew.

Control of Fungi:1. Chemicals – fungicides2. Treat seed3. Resistant cultivars4. Prevention – clean equipment

Bacteria and Mycoplasmas

1. Bacteria are classified by: *Form (or shape) spherical (cocci), rod-shaped

(bacilli), spiral (spirilli), and filament (filamentous)

*Reaction to Gram’s stain – either Gram+ (stain violet) or Gram – (stain pink-red)

2. Mycoplasmas are wall-less microbes that occur in phloem tissue.

-Have DNA and RNA but cannot reproduce themselves.

-Carried by vectors – such as grasshoppers, and aphids

-Treatment – spray insects

Bacteria and Mycoplasmas Occur where it is moist and warm Spread by: wind, splashing from

irrigation or rain, infected seed Enter host through – stomata or

wounds Symptoms – soft rot, bacterial cankers,

wilts, overgrowth, scabs and rots.

Control of Bacterial Diseases: *High temperature *Prevention *Bactericide *Resistant varieties * There are many beneficial

bacteria that are not pathogenic (Bradyrhizobium (fixes Nitrogen for legumes), Agrobacterium (used in biotechnology) etc.

Viruses – Need a host tissue to stay alive (obligate

parasite). Not true animals – cannot digest or respire. Consist of a core nucleic acid that may be RNA

or DNA encased in a protein or lipoprotein coat (capsid).

How viruses work Enter plants through a mechanical wound

or a vector (carrier). Viruses get into the phloem of the plant and move towards the apical meristem.

What are the vectors ? -Sucking and chewing insects (aphids and

thrips)- Seed transmitted virus might be in the

ovule of infected plant- Nematodes - Mites- Fungi

Symptoms of Viral Diseases:

Mosaics (light-green, yellow or white patches mingled with normal green)

Stunted growth Some are asymptomatic (show no

symptoms)

Classified mainly according to host, because they are host specific

Tobacco mosaic virus (TMV) Maize dwarf mosaic virus

(MDMV)

Control of plant viruses Prevention Resistance cultivars Heat therapy – high heat

for 2 to 4 weeks (100+ temps).

Requirements for Disease to Occur: 1. Pathogen –

Level of infestation

2. Host- Must be susceptible to invasion, establishment and

development

3. Favorable environment

Interact make the Disease Complex Severity of disease is decided by the level

of interaction of all three.

Epidemic Or Endemic? Epicemic Disease:

One that occurs frequently over a wide crop area but only periodically.

1971 Race T of Southern Corn Leaf Blight causing 14% yield loss.

Endemic Disease: Usually present in a crop area from year to

year causing moderate to severe damage. Corn stalk and root rots are examples

Stages of Disease Development: Page 177 – Disease Cycle: Stage:

1. Inoculation – pathogen enters host Insects, Wounds

2. Incubation – Pathogen becomes established in a plant Begins upon inoculation, ends when the plant reacts

to the disease 3. Infection -

Disease symptoms appear, producer notices Economic crop losses occur in this stage

Economic Impact Depends on: Monocyclic: disease goes through one life

cycle

Polycyclic: disease goes through several life cycles.

Disease Control: 1. Genetic

Avoidance Resistance Tolerance

2. Cultural Change in field operations that will alter life cycle of the

disease Crop rotation Planting time

3. Chemical- Seed treatment

Noninfectious Disease:1. Weather Damage:

FrostDroughtSun scaldHail damage

2. Soil Problems:Low or high pHNutrient deficiencyAccumulation of salts.

3. Chemical Damage:Over application of pesticidesCarry over from previous crop