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