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Organic Pest Management
Debbie RoosNorth Carolina Cooperative Extension
www.growingsmallfarms.org
Outline
Insect Management
Disease Management
Weed Management
What the NOP Says about Pest Management
When cultural, mechanical, and biological strategies are insufficient to prevent or control crop pests, a biological or botanical substance or a substance included on the National List of synthetic substances allowed for use in organic crop production (www.ams.usda.gov/nop/NationalList/FinalRule.html) may be applied to prevent, suppress, or control pests, weeds, or diseases
The conditions for using the substance must be documented in the organic system plan
Organic farming is all about building
healthy soil and using optimal
cultural practices to prevent insect,
disease, and weed problems
The emphasis is on biodiversity and a systems approach
Organic Pest Management Approach
· pests are indicators of how far a production system has strayed from the natural ecosystems it should imitate
· pests are attracted to a plant that is weak or inferior
· in a well-balanced system, massive pest outbreaks are rare due to the presence of natural predators, parasites, and disease agents
Organic Pest Management Approach
prophylactic, holistic approach vs. remedial approach
not just treating symptoms
pest problem usually indicates sub-optimal growing conditions and imbalance
emphasis on biodiversity and optimal cultural practices
Soil Fertility
Rotations
Field Planting Decisions
Labor
Weed Control, Irrigation, Trellising
Harvest & Postharvest
Pest Management
Peregrine Farm
Organic Pest Management: Example
Conventional approach: spray insecticide to control caterpillars, which often results in a secondary outbreak of aphids or spider mites because beneficial insects such as lady beetles and other predators are also killed
Organic approach: enhance habitat for beneficial insects to increase population, reduce stress on crop plant, use adapted varieties, and use non-chemical methods to control pests (Bt, hand-picking, row covers, alternating planting dates, traps, etc.)
NOP Hierarchical Approach to Pest Management
Level 1: Systems-based Cultural Practices
Level 2: Mechanical and Physical Practices
Level 3: Materials (Pesticides)
Cultural Controls
Physical Controls
Biological Controls
Organic Pesticides
Insects
Cultural ControlsThe goals of cultural practices: 1. reduce initial pest levels
by making the crop environment unfavorable for pest development
2. produce favorable conditions for natural enemies
3. increase the plant host's ability to withstand pest damage
In organic systems, cultural practices that prevent pest problems are the first line of defense for farmers
Cultural Controls
Resistant cultivarsCrop rotationCompanion plantingTiming of plantingSanitationSoil Management
MulchesCompostingTillageFlamingVacuumingTrap crops
Resistant Cultivars
Some varieties may be less attractive to pest species or tolerate more damage than others
Plant size, shape, coloration, leaf hair, cuticle thickness, and natural chemicals (attractants and repellents) can all affect pest susceptibility
Resistant Cultivars
Morphological characteristics include those plant structures that interfere with insect movement, feeding, or reproduction associated with that plant
Examples include color, thickness of the cell walls and plant tissue, surface wax, spines and trichomes
waxy cabbage leaf
edamame
bean leaf beetle
stink bug
Resistant Cultivars
Physiological defenses include plant-produced compounds that deter certain pests – e.g., pyrethrum, is derived from the blooms of an African chrysanthemum
Some plants have specific color-related resistance
Most insects are attracted to leaves in the yellow-green color range. Healthy, dark green leaves are less attractive than yellowing plants under stress
pyrethrum pesticide
Crop Rotation
Insects overwinter in soil and debris, reinfest new crop if susceptible and build up populations
3 questions to consider when deciding whether crop rotation will help manage a pest:
How long can the pest persist in the field without any hostHow capable is it of invading from other areasHow well does it survive on other hosts when the crop is not present
Design your rotation plan to present a non-host to pest insects
Crop rotation is effective for pests such as nematodes, CPBs, corn rootworm, squash vine borer
Also, design your rotation to include lots of cover crops which will help build soil food web which helps control pests
Sample Farm Rotation Plan
Companion Planting
Attractant crops - small-flowered - carrot family, daisy family, mint family - catnip, caraway, dill, fennel, hyssop, lemon balm, parsley, rosemary, thyme, yarrow, etc.
Repellent crops - catnip and tansy repel aphids, Artemesia repels flea beetles???
Lots of recommendations out there with little scientific evidence; need more study before recommending; some companion plants increase pest populations
Timing of Planting
Keep notes to record pest and disease outbreak patterns - the first date you see a problem and the coinciding phenological events
Adjust planting schedule accordingly to avoid peak pressure
Experiment with different planting dates - e.g., to avoid corn earworm or flea beetle or squash bug
Plant crops susceptible to nematodes early or late while soil temperatures are cooler
Timing of Planting:Pickleworm Problem
winter squash is planted before June 1 to reduce pickleworm
damage
pickleworm larva
adult moth
Method of Planting
The method of planting – direct-seeded vs. transplants – can also affect a crop’s ability to resist pests
Direct-seeded crops require the right conditions to emerge quickly and grow fast
The use of transplants when possible can speed crop development
Plants struggling to survive or under stress will be more attractive to insect pests and more affected by damage
Sanitation
The goal is to prevent the introduction of pests from off the farm, prevent the movement of pests within the farm, and to remove overwintering or breeding sites for pests on the farm
Start with healthy plants & inspect plants brought in from off-farm
Remove and destroy infested plants as soon as possible
Sanitation
When working in an infested area clean equipment and clothes before going to another area of the farm
Remove crop debris and culls promptly to reduce overwintering sites for pests
Exclude pests with barriers, screens, etc.
Eliminate alternate hosts, but be careful about timing
Soil Management
Healthy soils high in OM and with a biologically diverse food web support plant health and nutrition better than soils low in OM and species diversity
Healthy plants are generally less susceptible to pest damage
Approximately 75% of insect pests spend part of their life cycle in the soil. Healthy soils contain many natural enemies of insect pests, including insect predators, pathogenic fungi, and insect-parasitic nematodes
TillageDisrupts life cycle of pests and beneficials
Can expose pests to predators, the elements
Till before planting to control weeds that harbor armyworms, cutworms, plant bugs, aphids
Till in the fall to destroy overwintering sites for flea beetles, corn borers, squash bugs, etc.
Balance with need to maintain groundcover and not burn organic matter
Soil Management
A soil’s physical condition – its level of compaction, water-holding capacity, and drainage – all affect soil and plant health
The chemical aspects of soils – pH, salt content, availability of nutrients, etc. – can affect crop health and pest susceptibility
Strategies for Improving Soil Health
Increase soil organic matter
Keep soils covered with cover crops and/or crop residue to reduce erosion and protect from extremes of moisture and temperature
Plan tillage operations carefully
Example of Soil Management
Affecting Pests
crimson clover cover
crop next to beds
wilted broccoli plant
seedcorn maggots feeding
on root ball
Nutrient Management
Both the type and amount of fertilizer can have a significant impact on a crop’s susceptibility to pests.
Increasing soluble nitrogen levels in plants can decrease resistance and increase pest numbers and crop damage.
Research has shown that organic systems that rely on more slow-release nutrient sources tend to be less susceptible to insect pests.
One example from California found that organically fertilized broccoli developed lower populations of
flea beetles and cabbage aphids than conventionally fertilized
broccoli.
Mulches
Plastic mulches that speed early season crop growth can enhance plant’s ability to withstand insect feeding
Reflective mulches can reduce thrips and aphid populations in crops
Straw mulch can reduce problems with Colorado potato beetle
CompostingHelps control pests above- and below-ground
Improves structure, moisture-holding capacity, nutrient content, beneficial organisms
Flaming
Technique aimed at overwintering Colorado potato beetle
Propane burners used to quickly pass a flame over young potato plants when beetles are on top
Does little harm to the crop when the plants are less than 4-5” tall
Vacuuming
Sizes range from tractor-mounted to handheld
Some pests too adept at hiding for it to be effective
Used successfully for CPBs, Harlequin bugs, flea beetles
Research has shown that vacuuming has little negative effect on beneficial populations
Trap Crops
A trap crop is a crop that is planted to lure insect pests away from the cash crop.
Successful use of trap crops can be challenging. Trap crops are not effective against pests that are weak fliers (e.g., aphids) or are wind-dispersed (e.g., spider mites).
In organic systems with fewer insecticidal options, pests in trap crops are often killed through crop destruction. But the timing of crop destruction is critical.
Trap Crop in Organic Broccoli in NC
Harlequin bugs
striped flea beetles
mustard trap crop
Farmscaping to Attract Beneficials
ambush bug on Monarda punctata
Physical Controls
Physical Controls
Manual controlsPhysical barriersBaits, traps, and lures
Manual Controls
Hand-pickingMowingPruningShakingWater sprays
Physical Barriers
Bagging fruitCopper stripsCrawling pest barriersCutworm collarsFloating row coversMulchesTrenchesTrunk bands
Baits, Traps, and Lures
Bait trapsJapanese beetle trapsPheromone trapsSlug and snail trapsSticky boardsTrap cropsWater traps
Biological Controls
Biological Controls
Beneficial animals and insectsBeneficial microorganisms - Bt, milky spore, Beauveria bassiana (fungus), Nosema (protozoan)
Biological Control in Action
Augmentationincrease population through purchase & release
Conservation increase existing populations through habitat conservation & other means
Beneficial Organisms
Predators: larva or adult hunts, attacks, and consumes prey; examples include lady beetles, lacewings, praying mantids, syrphid flies, assassin bugs, minute pirate bugs, spiders, and predatory mites
Each one eats many insects in its lifetime
Not picky eaters
Predators: Examples
Wheel Bug
wheel bug nymph
nymph feeds on Colorado potato beetle larva
wheel bug molting
Lady Beetles
seven-spotted lady beetle
aphid dinner
pink-spotted lady beetle
convergent lady beetle
larva and eggs larvae hatching
larva feasting on aphid
Predatory Flies
robber fly
syrphid fly
syrphid fly larva
long-legged flysyrphid fly
pupa
Other Predators
eggbig-eyed bug
lacewing larva
tiger beetle
predatory stink bug
minute pirate bug
spider
Beneficial Organisms
Parasitoids: immatures develop on or inside a host, killing it as they mature; they emerge as adults and continue the cycle; examples include parasitic flies and wasps
Each one eats only one insect in its lifetime
Usually very picky eaters
Parasitoids: Examples
Braconid Wasp on Hornworm
Trichogramma wasp on tomato hornworm egg
parasitized egg
More Parasitic Wasps
Scelionid wasp parasitizing stink bug egg cluster
Aphidius just emerged from aphid mummy
Tachinid Fly
Tachinid fly egg laid on spined soldier bug!
Beneficial Organisms
Pathogens: colonize and kill host; examples include nematodes, bacteria, viruses, fungi and protozoa
Weed Feeders: weeds can be attacked by arthropods, vertebrates, and pathogens (fungi, viruses, bacteria, and nematodes)
Insect Pathogens
fungus on loopers
fungus on fly
nematodes on larva
fungus on soldier beetle
Organic Pesticides:Rescue Treatments
Organic Pesticides for Insect Management
Botanical pesticides
Microbial pesticides
Inorganic pesticides
Botanical Pesticides
Plant-derived materials such as neem, pyrethrum, rotenone, ryannia, and sabadilla
Characteristics of botanical insecticides:break down rapidly in the environmentsome are more toxic (mammalian) than synthetic pesticidesbroad spectrum must be used carefullymany are not approved for organic production; only neem and pyrethrum, and they are regulated and to be used only as a last resort after other strategies have failed
Toxicity of Botanical PesticidesInsecticide LD50
Parathion 18-50Sevin, Nicotine 246-283
Ryania 1,200Aspirin 1,200
Rotenone 1,500Pyrethrin 1,500Malathion 2,800Table Salt 3,320Sabadilla 5,000
Neem, pyrethroids >5,000
Botanical Pesticides
Pyrethrum - extracted from a flower in the chrysanthemum family; a contact poison with quick “knock down”; little residual effect; OMRI-approved products include Pyganic®broad-spectrum insecticide that is highly toxic to honey bees and other beneficials
Insects controlled: aphids, beetles, caterpillars, thrips, true bugs
Neem (azadirachtin) - extracted from the fruit of a tree grown from India to Africa; acts mainly as an insect growth regulator, repellant, stomach poison and some fungicidal properties have been reported; it is relatively non-toxic; OMRI-approved products include AZA-Direct®, Neemix®Neem products have little to no negative effect on adult beneficials
Insects: CPB, Mexican bean beetle, squash bugs, aphids, and more
Neem
Frequent applications are more effective than single sprays because neem does not persist well on plant surfaces
Use against immature insects
Begin applications before pest levels are high
Works best under warm temperature conditions
Neem’s systemic properties suggest that applying it to transplants just before planting to the field could be an effective and inexpensive way to control certain pests
Microbial Pesticides
Microbials tend to not be as toxic as botanicals and are more selective and softer on beneficials
Bacillus thuringiensis (Bt)
parasitic fungi - e.g., Beauveria bassiana
parasitic nematodes – e.g., Heterorhabditis
Spinosad
Microbial Pesticides
Limitations of microbialsSlow host deathHigh dosages requiredNeed favorable environmentUV light and temperature affect persistance
Bacillus thuringiensis (Bt)
Bacillus thuringiensis (Bt) – contains a toxin made by a soil bacterium; choose appropriate formulation for the pest
Because Bt must be eaten by the insect to be effective, it is very important to apply the spray to the parts of the plant where and when the insect is feeding;thorough coverage is required
Young larvae more susceptible
Sprayed formulations sensitive to UV light; best applied late in the day
Several OMRI-approved formulations
Parasitic Fungie.g., Beauveria bassiana
The spores of the fungus germinate once they come into contact with the insect pest, then the fungus must penetrate the cuticle and infect the body cavity to kill the pest
Effective on many insects including aphids, thrips, whiteflies, and grasshoppers
Work best when applied at onset of infestation; takes a week or more after application to see evidence of control
OMRI-approved formulations include Mycotrol®, Naturalis L®
Fungal spores are readily killed by solar radiation and infect
best in cool to moderate
temperatures
Parasitic NematodesNaturally occur in soil
Semi-aquatic; live and move in soil water
Sensitive to UV radiation and desiccation
Heterorhabditis (Hb) for control of deep-dwelling lethargic pests like Japanese and June beetles
Steinernema (Sc) nematodes for control of shallow-dwelling active pests such as fungus gnat larvae, shore flies, etc.
Parasitic NematodesApplication - spray or irrigation; drip, fertigation; aerial, watering can; application should be followed by irrigation; don’t apply during hottest part of day but soils should be >60º
Soil physical properties affect efficacy
Works well in labs; poor understanding of why failures occur in field
Important to follow instructions
SpinosadSpinosad gets its name from the microbe that produces it, a soil-dwelling bacterium called Saccharopolyspora spinosa. Controls beetle larvae, caterpillars, thrips, etc. Most effective when ingested rather than as a contact insecticide
Fast-acting, better than Bt on caterpillars; supposedly not as soft on beneficials so use in targeted areas
Entrust® - Formulation approved for organic production in many vegetables
Inorganic Pesticides
Diatomaceous earthKaolinInsecticidal soapHorticultural oil
Diatomaceous Earth
Diatomaceous earth (silicon dioxide) - finely milled fossilized remains of diatoms; product can scratch insect exoskeleton or puncture gut lining (if ingested); can be used as a desiccant; can be put on wet foliage to get it to stick
Insects: aphids, mites, caterpillars
Particle Film Barrier
Kaolin - clay material ground to a uniform size; when sprayed forms a particle barrier on plant surfaces that is effective for both insects and some diseases; must be sprayed ahead of time on a 7-14 day schedule; washes off easily & must be reapplied after rain; agitation is required to keep it suspended
A proven product, just need to sort out what it works on
Residue can pose a problem for some vegetables and is not useful on flowers because it can’t be washed off
OMRI-approved product: Surround®
Insecticidal Soap
Soaps smother soft-bodied pests and disrupts their cuticle layer. In order to be effective, it is necessary to thoroughly coat the pest.
Soap products are most effective when they dry slowly, so spraying in the evening or at night is best
Can help control aphids, some caterpillars, scale crawlers, leafhopper nymphs, mealybugs, thrips, whiteflies
OMRI-approved formulations include M-Pede®, Safer®
Most (Un)Wanted Insect Pests
(and how to control them!)
Flea Beetles
Row covers
Sanitation to control weedy hosts
Trap crops
Crop rotation
Timing of planting
Organic pesticides: insecticidal soap, Spinosad, neem, pyrethrum, particle film barrier?
Hb nematodes
striped flea beetle
eggplant flea beetle
Harlequin Bugs
Sanitation
Trap crops
Vacuuming
Pesticides: Insecticidal soap, pyrethrum
Colorado Potato Beetle
Crop rotationControl Solanaceous weedsEarly maturing resistant varietiesStraw mulchFlaming, vacuumingTrenchesRow coversSpinosad, neemParasitic Hb nematodes?
Caterpillars
Spinosad, Bt, neem provide control
Good idea to rotate pesticides with different modes of action to avoid resistance
Corn earworm: oil + Bt mixture applied to silks
Squash Bug
Hand-pickTrap cropsDelay plantingPrune vines to remove egg-laying sites?Trap boardsRow coversSanitationNeem, Surround®, insecticidal soap
Squash Vine Borer
Crop rotation can help delay problems, although adults are strong fliers and can find fieldsUse pheromone lures to monitor arrival of adults and start of egg-laying; remove eggs laid at base of stems and leaves in April and MayUse row covers early in season and remove at floweringExtract borers from infested vinesPost-harvest tillage will prevent late borers from completing life cycleSome farmers have tried injecting either Bt or parasitic nematodes into the stem with a syringe; effectiveness not documented
Mexican Bean Beetle
Row coversNeemPyrethrinRelease parasitic wasp Pediobius foveolatusVacuuming??
Fire Ants
Boiling water – need ~3 gallons per mound; reported 60% success rate; works best after a rainfall when fresh mounds are present
Mound drench – ideal if few mounds are present because doesn’t affect native ants (which help keep fire ant populations in check)
Baits – apply to individual mounds instead of broadcasting Biological control – nematodes, Beauveria baits, Phorid flies, protection of native ant species!
OMRI-listed Fire Ant Products
Mound drenches:Entrust®Monterey Garden Insect SpraySafer Brand Fire Ant Killer®
Baits:Greenlight Fire Ant Control with Conserve® Come and Get It!
Research has not shown boric acid or diatomaceous earth to be very effective
For More Information on Organic Fire Ant Management…
http://www.ces.ncsu.edu/chatham/ag/SustAg/fireants.html
For More Info on Pest Management…Photos and Fact Sheets
of NC Insects Pests and Beneficials:
http://chatham.ces.ncsu.edu/ growingsmallfarms/insects.html
Diseases
Address the Three Conditions Required for Pathogens
Susceptible host plant – avoid with resistant and tolerant cultivars, crop rotation
Presence of inoculum – reduce through sanitation
Environmental conditions – limit with cultural practices
Site Selection Considerations
Soil type and associated drainage patterns
Field layout and exposure
Soil compaction
Plan for Diversity over Time
Rotation - soil inhabitant or soil invader
Crop-free periods - obligate parasites
Sowing dates and harvest time can be adjusted
Plan for Diversity over Space
Most small farms are already diverse!
Use variety mixtures
Employ intercropping
Plan for Genetic Diversity
Host plants
Soil microbial communities
Use of cover crops, no-till
broccoli with rye/vetch cover crop
Exclusion and Evasion
Use of plant quarantines
Don’t import diseases on seeds or in soil
Control weeds and alternative hosts
Evade problems by growing seed plants in areas of low or no disease pressure for that particular plant
Variety Selection
Disease resistance vs. disease tolerance
Select cultivars that have disease resistance/tolerance characteristics that are appropriate for your climate
Local/regional heirloom varieties have often evolved with particular disease-resistant characteristics
Keep good records of a cultivar’s performance and the disease pressure for each season
Resistant Varieties
Host resistance is the easiest, cheapest, safest, and most effective means of managing diseases!
Especially important for soil-borne diseases such as fusarium wilt, verticillium wilt, bacterial wilt, nematodes, Phytophthora crown and root rot of peppers
Sanitation to Reduce Inoculum
Start with clean seedHot water treatmentDisease-tested certified seed Western-grown
Transplant Production
Buy from a reputable producer
Use clean, sterile containers and growing structures
Use soilless mix
Provide good air movement, temperature control and optimal germinating conditions
Keep seedling flats up off the ground avoiding contact with soil-borne pathogens
General Strategies
Rogue isolated infected plants from the field during the growing season
Increase air movement by staking, pruning, and using wide-row spacing
Use drip irrigation to minimize leaf wetness period
Use mulch to prevent soil splashing onto foliage and fruit
Avoid working in the field when foliage is wet to reduce the spread of inoculum
General Strategies
Use tunnels or greenhouses to reduce moisture on foliage and soil splashing
Vegetable Grafting
It started in Japan and Korea in the 1920s to control soil-borne diseases in the greenhouse – watermelon grafted onto gourd
Today almost 95% of the watermelons, oriental melons, cucumbers, tomato and eggplant crops are grafted before being transplanted to the field or greenhouse in Japan
Grafting can give the best of both worlds: it allows the grower to combine the good genetic disease-resistance of hybrid rootstock without hindering fruit quality
Benefits of Vegetable Grafting
Disease resistance
Improved stress toleranceSalt-tolerantExtreme moistureSeason extension
Improved yields – vigorous rootstock varieties can improve water & nutrient uptake
North Carolina State University Grafting Research
Dr. Frank Louws and grad students Cary Rivard and Suzanne O’Connell are grafting heirloom tomato varieties onto hybrid disease-resistant rootstock
Tomato Grafting
stem is cut before grafting
scion graveyard
grafting clip healing tent
graft union
General Strategies
Use raised beds to improve drainage
Cultivate carefully to promote healthy root growth
Use floating row covers and reflective mulches to reduce insect vector activity
Harvest gently to minimize cuts and bruises on the produce
Cool produce rapidly after harvest to slow microbial activity; store at cool temperatures
General Strategies
Optimize NPK fertility to reduce stress
Rotate crops and incorporate crop residues to reduce inoculum buildup
Plow, disk or roto-till immediately after harvest to speed up the decomposition of plant tissue
Wash equipment frequently to reduce the spread of inoculum
Organic Pesticides for Disease Management
Organic Pesticides for Disease Management
Copper & SulfurPlant ExtractsBiofungicides MicroorganismsParticle Film BarrierPeroxides & BicarbonatesCompost Tea
Some of North Carolina’s Most Wanted Vegetable Diseases
(and how to control them!)
Use crop rotations of at least 3 years to non-hosts
Use early maturing varieties (avoidance)
Early Blight
Provide optimum growing conditions and fertility (low N and early senescence aggravates EB)
Use drip irrigation to keep the period of leaf wetness to a minimum
Allow for good air circulation
High tunnels?
Early Blight
Stake or cage plants to keep fruit and foliage away from soil Disinfect stakes or cages with an approved product each season before using
Treat seed at 122°F for 25 minutes
Apply mulch to help prevent splashing of spores from soil up to lower leaves
Early Blight: Pesticides
Serenade® - Bacillis subtilis
Trichoderma products (e.g., PlantShield®) applied as a drench at planting
Copper?
Southern stem blight on pepper; note white mycelium and sclerotia at soil line
Remove and destroy infected fruit
Prevent excessive moisture
Stake plants to prevent the fruit from touching the ground
Deep disking will bury host plant debris and sclerotia
Soil solarization
Crop rotation – grass crops reduce inoculum
Southern Stem Blight
Southern Stem Blight
Biorationals: Trichoderma® products
Gliocladium products: SoilGard® sprayed against base of young plants provides some protection
Bacterial Wilt
Resistant varieties
Water management
Avoid problem areas
Grafting!
Local Crop Problems
on GSF Website www.growingsmallfarms.org
Weeds
Weed Management
What is a weed?any plant growing where it is not wantedusually causing economic or aesthetic loss
a plant whose virtues have not yet been discovered
Ralph Waldo Emerson
Organic Weed Management: Philosophy
control weeds to prevent seed rain and to prevent establishment of noxious or poisonous species
understand and appreciate the potential benefits of weeds:
beneficial insect habitattrap cropnutrient cyclingreduce erosion and improve soil structurealternative crop?
Cultural Control Strategies
Sanitation
Clean machinery so you don’t introduce root parts from an infested section to a clean section
Be sure that all manure used in your fertility system has been hot composted to 140º F to kill weed seeds and pathogens
Use certified seed to decrease likelihood of planting weeds
Reducing the Weed Seed Bank
The longevity of weed seed, together with the large numbers of seeds produced by individual plants, can lead to the long-term build-up of enormous seed banks in the soil
Anything you can do to remove weeds prior to seed production will help reduce weed pressure in subsequent seasons
one barnyardgrass plant can produce 1,000,000 seeds!
Optimizing Planting Date
Later planting date means warmer soils so crops germinate quicker; allows for pre-germination of weeds
Increasing Crop Competitiveness
Examples of competitive vegetables: potatoes, beans, squash, cucumbers, pumpkins, sweet corn, and sweetpotatoes
Examples of non-competitive vegetables: garlic, onions, carrots, asparagus
Increasing Crop Competitiveness
Transplanted crops vs. direct-seeded crops
Seeding rate and plant spacing can affect competitiveness
Try and choose varieties that germinate and develop rapidly
Water and Nutrient Management
Nitrogen plays a role in breaking weed seed dormancy, and the source of N can affect weed germination and growth
Use of drip irrigation and banding or side dressing of fertilizer may help to deprive weeds of resources
Mulching
Use clean mulch to avoid importing weed seeds
Benefits of organic mulches: suppress weeds, conserve water, moderate soil temperature, keep crops clean, prevent soil crusting, and increase penetration of rain or irrigation water
Inorganic mulches: black plastic, clear plastic, IRT plastic, landscape fabric
Cover crop residue
Mulching
Crop Rotation
To effectively break the life cycles of various weeds, crop rotations should include cold and warm weather crops, legumes and grasses
Crop Rotation
Rotate weed suppression activity and crops where weeds can be mechanically controlled
Rotate difficult to cultivate crops after crops where effective control can be achieved
Rotating perennial crops or winter covers may disrupt the life cycle of weeds present
Stale Seed Bed
Takes advantage of the weed seeds’ light requirement for germination
Method: prepare seed bed two weeks ahead of planting date for crop; encourage weed seed germination then eradicate weed seedlings by flaming or shallow cultivation
Useful especially when planting direct-seeded and noncompetitive crops like carrots, parsnips, lettuce
Cover Crops
Living cover crop vs. dead cover crop mulch
Can reduce germination of weeds by preventing adequate light penetration
Can reduce soil moisture and temperature which may affect weed germination
rye cover crop with beans
rye cover crop residue with beans
Cover Crops
Allelopathic Cover Crops
Rye residue contains generous amounts of allelopathic chemicals; when left on the soil surface, these chemicals leach out and prevent germination of small-seeded broadleaf weeds for about 30-60 days
Other allelopathic crops include sorghum-sudangrass, sunflower, rapeseed
Smother Crops
Starve weeds of water, light, and fertility
Warm season examples: buckwheat, Japanese millet, sorghum-sudangrass, sunflowers
Cool season examples: rye, oats, field pea, ryegrass
Intercropping
The practice of creating multiple crop layers that may include planting a cover crop along with a cash crop
Benefits include weed suppression, reduction of soil erosion, and reduction of wind injury to the cash crop; care must be taken to avoid competition with the cash crop
French beans intercropped with
cilantro
No-till Production
The production of high residue cover is crucial to successful weed control in no-till system
Benefits of high residue include moisture conservation, weed suppression, erosion control, increased soil organic matter, food and habitat for soil organisms; if a legume is used as a cover crop the benefits include biologically fixed N
Follow-up methods of weed control are hand-pulling, high-residue cultivators, weeder geese, hand-hoeing
Soil Solarization
Covering soil with clear plastic for 5-6 weeks during the hottest, sunniest months has been shown to kill weed seeds, pathogens and nematodesSoil temperatures should be 140º F at 2 inches and 103º F at 18 inches of soil depthSolarizing soil after the addition of composted manure may be effective in reducing annual dicots Weed seeds sensitive to solarization include winter annual grasses, black nightshade, cocklebur, chickweed, redroot pigweed and velvetleaf
Mechanical Control Strategies
Mechanical Control
StrategiesHand-weedingHoeingMowingFlamingHot WaterTillage
Evolving Strategies
Biological Control Strategies
Biological control involves the use of a living agent – insect, fungus, bacteria, animal, plant - to control another living agent (weed, insect pest, disease)
So far biological control of weeds has been achieved in only 30% of the cases reported
Two successful examples: Weevils to eat the seeds of musk thistle Rust disease to control yellow nutsedge
Biological Control Strategies
Cover Crops
Bio-herbicides
Herbivores
Bio-herbicides
Limited effectiveness of organically acceptable herbicides
Examples of bio-herbicides include corn gluten, acetic acid, citric acid, herbicidal soap
Note: Certified organic growers should consult their certifying agency before applying any bio-herbicide
Herbivores
Grazing herbivores is an excellent way to control weeds
Grazing prevents the invasion of aggressive species
Grazing ruminants can improve the health of land base by increasing plant diversity
Herbivores
Chicken tractors Pigerators Weeder geese
Grower Resource List on the Growing Small Farms Websitehttp://chatham.ces.ncsu.edu/growingsmallfarms/resourcelist.html
Books and publicationsOrganic seedsFertilizers and soil amendmentsEquipment & supplies for season extension, pest management, cut flowers, etc.Transplants, plants, & bulbsLivestock & pastured poultryBeekeeping