building healthy soil without succumbing to weeds, … · organic pest management (building healthy...
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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
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.
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
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
• 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
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)
0
10
20
30
40
50
Control Solarization Contans WG Solarization +
Contans WG
Intact summer
Intact winter
Germination
0
10
20
30
40
50
Control Solarization Contans WG Solarization +
Contans WGTreatment
Surviving sclerotiaper bag ±S.E.
2 cm depth
5 cm depth
12:00:00 AM
5:00:00 AM
10:00:00 AM
3:00:00 PM
8:00:00 PM
Control - 0
Control - 5
Control - 10
Control - 15
Solarized - 0
Solarized - 5
Solarized - 10
Solarized - 15
25
30
35
40
45
50
55
60
Temp.
(°C)
Temp.
(°F)
77
86
95
104
113
122
131
140
Average Germ
inating Slcerotia(of 40)
Average Average SclerotiaSclerotia Survival at Different Survival at Different
Soil Depths and TreatmentsSoil Depths and Treatments
Biofumigation Biofumigation
+ SolarizationControl Solarization
0
5
10
15
0
5
10
15
20
25
30
35
40
Average Average ScerotiaScerotia Survival After 2, 4, Survival After 2, 4,
and 6 Weeks of Treatmentsand 6 Weeks of TreatmentsGerm
inating Slcerotia(of 160)
Biofumigation Biofumigation
+ SolarizationControl Solarization
2 week
4 week
6 week
0
5
10
15
20
25
30
35
40
BiofumigationBiofumigation +
SolarizationControl
Solarization
0
5
10
15
20
25
30
35
40
Average Average SclerotiaSclerotia Survival at Edge Survival at Edge
and Middle of Treatment Plotsand Middle of Treatment Plots
Average Germ
inating
Average Germ
inating Sclerotia
Sclerotia(of 40)
(of 40)
••Edge Edge
••MiddleMiddle