Organic Pest Management(building healthy soil without succumbing

to weeds, insects & diseases)

Michael Bomford, PhD

Kentucky State University

Organic Agriculture Working Group

What are

agricultural pests?

• Compete with humans

for food / fiber

• Well-adapted to

agricultural

environments

• Represent all kingdoms

– Bacteria

– Protozoa

– Fungi

– Plants

– Animals

Pests:

• Defined and created by people

• Product of habitat

– Food

– Breeding opportunities

– Overwintering locations

– Destruction of competition• predators

• parasites

• diseases

WorldWatch, 2000

Healthy Plants, Fewer Pests

• Key claim of organic agriculture

• Relates herbivore damage back to soil

quality (Steiner, Howard)

• Pests seen as “weeding out the weak”

• High sugar content indicator of plant

health and pest tolerance

• Wishful thinking?

– Often attacked, research lacking

Reduced moisture; higher brix

Machado, R. & do Rosario G. Oliveira, M. (2005), 'Tomato root distribution, yield and fruit quality

under different subsurface drip irrigation regimes and depths', Irrigation Science 24, 15-24.

Grapes: Higher brix, lower yield

http://lenewa.netsync.net/public/bates/BatesMR.htm

1994

1995

Leafhopper nymphs/leaf

Leaf brix

No relationship between leaf brix

and leafhopper density (4 CA vineyards over 2 years)

Mayse et al. 1994. Leaf sap brix and leafhoppers in vineyards.

Organic Farming Research Foundation Project Report. http://ofrf.org/funded/reports/mayse_94-36.pdf

Diversity

• More diverse

habitats have

lower herbivore

populations

– Resource concentration hypothesis

• Easier for pests to find uniform habitat

• Easier for pests to stay in uniform habitat

– Natural enemies hypothesis

• Predators / parasitoids more common in diverse habitat

– Trap crop hypothesis

• Alternate hosts draw pest away from main crop

Crop Diversity

• In space

– intercropping

– companion planting

– mixtures

– small fields / plots

• In time

– rotation

– timing

Diversity

More diverse habitats have less

disease damage

– Yunnan province, China: mixed

varieties of rice reduce rice

blast levels and allow farmers to

stop fungicide use (Nature,

2000)

– Disease epidemics dampened

• Pathogen population must be

more complex to attack

complex crop mixture.

Increased competition

between pathogen

genotypes.

Suppressive Soils

• Soil microfauna effect

• Destroy soil-borne pathogens

– (e.g. take-all of wheat after years without

rotation)

• Destroy weed seeds

– (e.g. soils from European weed place of origin

30-40% more weed suppressive than PNW soils)

• Destroy soil-dwelling arthropods

– (e.g. entomopathogenic nematodes)

Mechanisms of

disease suppression

• Parasitism: one organism consumes another– Several Trichodermaspecies can eradicate Rhizoctonia solani (one of the fungi responsible for damping off)

• Induced systemic resistance– More plant defense compounds produced when cucumbers grown in compost-treated soils

Hoitink et al. 2000.

Ohio State University

Bulletin 177-01

Organic cultivation goals

• Keep manure and crop residues in surface biologically

active zone

– anaerobic decomposition below

• Avoid bare soil

– wind and water erosion

– nutrient leaching

– reduced biological diversity

– loss of organic matter

• Avoid excessive cultivation

– too deep, too often

Tillage

Between

Rows

• Large scale

– rolling cultivators

– finger weeders

– torsion weeders

• Small scale

– wheel hoes

– stirrup hoes

Not all tillage is equal

Crop rotation avoids pests

• Helpful for specialist pests -- not a cure-all

• Break cycles

• Insects – especially those that overwinter in vicinity of host

• Weeds – crops promote weeds with similar life cycles

• Pathogens – especially those that overwinter in soil

Stagger Nutrient Needs

• Alternate heavy N users with N fixers

– Corn and brassicas are heavy N users

– Peas, beans, clover, and alfalfa have

symbiotic relationship with rhizobia (N-fixing

soil bacteria). Inoculate with care – some

rhizobia have been genetically modified.

• Protect water quality (grasses and

legumes take up excess nutrients)

Use N-fixers

Average Yield Response of Barley to N Fertilizer When

Grown on Barley, Fababean, Field Pea and Lentil Residues

in Northeastern Saskatchewan (Wright 1990)

Crop

Selection

• Common choices:

– fava beans, vetch, wheat,

rye, clovers, mustard

Crop Selection

• Nitrogen fixers:

– fava beans, vetch, clovers other peas

& beans

– treat with legume inoculants to

improve fixation (caution: some

genetically modified)

Crop Selection

• Extensive root systems:

– wheat, rye

– benefits soil structure

– high C content prevents N leaching

Rye roots: “The world’s greatest shovel”

Green Manuring

• Winter cover crop turned into soil

-or-

• Fallow ground planted to cover crop,

which is turned into soil

Sheet Composting

• Plant material grown elsewhere spread

on soil, covered with earth

Long lasting benefits

• Adds organic matter

– reduces compaction

– improves tilth

• “first resort” for poor soils

Drawbacks

• Not a quick fix; poor soils

require many years

• steals space from main crops

• Reduces erosion

• Chokes out

weeds on non-

crop soil

Green Manure Sheet Compost

Roots loosen soil

and add extra

OM

No roots in

treated area

Local cycling Need to move

material

Takes space from

treated area

Can use less

valuable areas to

grow soil

ammendment

Incorporation

• Not too early

– Wait until soil has

drained

– working soil too early

destroys structure

• Not too late

– ~ 2 weeks before

planting

– high C:N ratio plants

initially tie up soil N

Organically Approved

Pesticides

• Biorational

• Inorganic

• Botanical

• Microbial

• Oils

• Soaps

Botanicals

• Chemicals derived from plants

– Rotenone

• rat poison, very toxic to fish, linked to Parkinson’s

• allowed under NOP; temporary ban in Europe

– Pyrethrum

• neurotoxin, quick

knock-down

• chemistry inspired

synthetic pyrethroids

– Neem

• inhibits moulting

• biorational

Microbials

• Bacteria

– e.g. Bacillus thuringiensis

• Fungi

– e.g. Coniothyrium minitans

• Nematodes

– e.g. Steinernema

Inorganics

• Copper

– toxicity problems with heavy, prolonged use

• Sulfur

– 59% of agricultural fungicide use, by weight

– high ecological impact (Cornell)

• Lime

• Bordeaux mixture (copper sulfate + lime)

Oils & Soaps

• Oils

– Petroleum / vegetable based

– kill through suffocation

– most widely used insecticide, by weight

• Soaps

– kill through desiccation (penetrate protective waxy

covering)

– mainly kill soft-bodied insect

• No resistance observed to these modes of

action

Historical Look at SBDM

• Until 1930’s, animal/green manures, composts, and crop rotation were principle methods of soil-borne disease control.

• Since then, methods have been largely replaced by synthetic pesticides along with synthetic fertilizers.

• Non-specific pesticides decrease natural fertility; strong fertilizers feed pathogens and compromise plant defense mechanisms. Use of one increases need of the other.

• This “pesticide treadmill” and its associated problems are leading us to develop alternative, sustainable production systems.

Soil-Borne Disease Overview

• Pathogens are present

in soil

• Outbreaks of disease

occur when: susceptible

hosts meet disease-

causing pathogens in a

favorable environment.

KSU Study

• Sclerotinia sclerotium

-cool season high tunnel systems (Au Naturel Farm)

• Phytopthora capsici

-warm season field

vegetable systems

(Bray’s Orchard)

Field Studies at Au Naturel Farm

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Surviving sclerotiaper bag ±S.E.

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Average Germ

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Average Average SclerotiaSclerotia Survival at Different Survival at Different

Soil Depths and TreatmentsSoil Depths and Treatments

Biofumigation Biofumigation

+ SolarizationControl Solarization

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Average Average ScerotiaScerotia Survival After 2, 4, Survival After 2, 4,

and 6 Weeks of Treatmentsand 6 Weeks of TreatmentsGerm

inating Slcerotia(of 160)

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Average Average SclerotiaSclerotia Survival at Edge Survival at Edge

and Middle of Treatment Plotsand Middle of Treatment Plots

Average Germ

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Average Germ

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Sclerotia(of 40)

(of 40)

••Edge Edge

••MiddleMiddle