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Natural Controls for Vegetable Pests

Aphids
Aphids

Vegetable garden insect pests are susceptible to many controls. Limit the damage of insects by identifying pests quickly and recognizing the damage they inflict. Regular visits to the garden will help you spot pests before they become established. Then choose the most effective control given the infestation. The quickest controls for light infestations are listed below under “Prevention and controls.” The “natural insecticides” listed here are the last line of defense; natural insecticides can harm beneficial insects if not used carefully. Encourage beneficial insects–listed under “biological controls.”

Here are 26 common vegetable insect pests A to Z:

Aphid

• Description. Tiny soft-bodied, pear-shaped insects may be pale green, brown, yellow, pink, blue, or black. Usually wingless but some females may be winged. Adults less than 1/10-inch long.

• Susceptible plants. Nearly all vegetables, fruits, and many other plants.

• Damage. Sucks sap from leaves, fruit, stems causing foliage to curl, pucker, and yellow; loss of plant vigor; some transmits diseases such as mosaic; excrement supports black, sooty mold; attract ants.

• Emergence time. Eggs over-winter hatch in early spring, throughout growing season.

• Prevention and controls. Spray away with strong water; soapy water spray; aluminum foil place on ground under young plants reflects the sky and confuses insets; as a lure, use yellow containers of soapy water, commercial yellow stick traps, or a board painted yellows an coated with sticky solution such as Tanglefoot; cover plant with Spun polyester blanket or other row cover.

• Biological controls. Ladybugs; spiders; syrphid flies; lacewings.

• Natural insecticides. Insecticidal soap; nicotine. Pyrethrum; sabadilla; use with care, insecticides also kill beneficial insects. Light horticultural oil spray.

• Plant companions. Plant aster and parsley family plants also alyssum or clover to attract aphid-easting beneficial insects. Onions and garlic may repel aphids. Trap crops: early cabbage, marigolds, and nasturtiums.

Asparagus Beetle

• Description. Blue-black with four white spots and red margins; oblong to ¼ inch long.

• Susceptible plants. Asparagus

• Damage. Chews leaves and spear tips.

• Emergence time. Over-winter in garden, emerge in spring.

• Prevention and controls. Remove plants and debris after harvest; shake beetles from foliage into soapy water; use row covers as barrier early in season; use rock phosphate or bone meal dust on plants.

• Biological controls. Ladybugs, predatory flies.

• Natural insecticides. Pyrethrum, rotenone dust for serious problems; use with care, insecticides also kill beneficial insects.

• Plant companions. Beetles dislike tomatoes, nasturtiums, and calendula.

Cabbage Looper

• Description. Light green caterpillar with yellow stripes running down back; loops as it walks. Adult is brownish night-flying moth with sliver spot in mid-forewing.

• Susceptible plants. Brussels sprouts, cabbage, cauliflower, Chinese cabbage, collards plants, greens, beans, peas, potatoes, tomatoes.

• Damage. Small to large holes eaten in leaves. Eats seedlings.

• Emergence time. Spring.

• Prevention and controls. Dust looper-worms with flour or salt; cover plants with spun polyester blanket or other row cover to prevent moths from laying eggs; plant resistant varieties, time planting to avoid insect growth cycle.

• Biological controls. Trichogramma wasps, lacewing, lady bug; Bacillus thuringiensis spray every 2 weeks.

• Natural insecticides. Rotenone; pyrethrum-diatomaceous earth blend; sabadilla; use with care, insecticides also kill beneficial insects.

• Plant companions. Celery as a trap crop. Intercrop with marigolds. Repelled by garlic, hot peppers, hyssop, onions, rosemary, sage, tansy, thyme.

Cabbage Maggot

• Description. Small, gray-white, legless worm to ⅓-inch long, blunt end. Adult looks like a housefly.

• Susceptible plants. Brussels sprouts, cabbage, cauliflower, Chinese cabbage, collards, parsnips, radishes, turnips.

• Damage. Brown tunnels into stems just below soil, seedlings wilt and die.

• Emergence time. Early spring to fall, several generations.

• Prevention and controls. Apply lime or wood ashes around base of plants; time planting to avoid insect growth cycle.

• Biological controls. Beneficial nematodes, chalcid wasps, trichogramma wasps.

• Natural insecticides. Lime-water mix drench: 2 pounds of lime per 5-gallons of water.

• Plant companions. Radishes and turnips as trap crops. Mint, rosemary, sage, tomatoes repel cabbage maggot.

Carrot Rust Fly

• Description. Black fly to 1/5-inch long with yellow head and legs. Maggots are yellow to white about ⅓ inch long.

• Susceptible plants. Carrots, celery, parsley, parsnips.

• Damage. Maggots tunnel into roots causing stunting of plants; soft rot.

• Emergence time. Spring, over-winter as maggots.

• Prevention and controls. Sprinkle wood ashes around crown of plant; cultivate in winter to expose maggots; rotate crops; time planting to avoid insect growth cycle, carrots come to harvest in fall..

• Biological controls. Parasitic nematodes.

• Natural insecticides. Use with care, insecticides also kill beneficial insects.

• Plant companions. Onions and leeks repel fly, Also pennyroyal, rosemary, salsify, sage, wormwood.

Colorado Potato Beetle

• Description. Yellow convex beetle to ⅓-inch long with black stripes and orange head covering. Grubs are red with black spots and a black head.

• Susceptible plants. Potatoes, tomatoes, eggplants, peppers.

• Damage. Skeletonized leaves, growth tips chewed.

• Emergence time. Spring.

• Prevention and controls. Hand pick beetles and larvae; remove orange egg masses from undersides of leaves; spray with mixture of basil leaves and water; place 1-inch thick layer of clean hay or straw mulch around plants to keep beetles from climbing to the stems; cover plants with spun polyester blanket or other row cover; plant resistant varieties; time planting to avoid insect growth cycle.

• Biological controls. Ladybugs, Bacillus thuringiensis

• Natural insecticides. Rotenone; sabadilla; use with care, insecticides also kill beneficial insects.

• Plant companions. Interplant with catnip, coriander, tansy; intercrop with basil.

Corn Earworm

• Description. Spiny caterpillar, white, green, or red to 1½-inches long. Adult is brown moth.

• Susceptible plants. Corn

• Damage. Feed buds and leaves and later on silks and kernels at tip of ear.

• Emergence time. Late spring.

• Prevention and controls. Hand pick from husk after silks brown. When silks tassels brown, apply 10-20 drops of mineral oil with eye dropper to tassels or spray mineral oil on tassels. Remove debris from garden in fall and cultivate thoroughly.

• Biological controls. Trichogramma wasps, Bacillus thuringiensis, beneficial nematodes.

• Natural insecticides. Spray young plants with horticultural oil mixed with Bacillus thuringiensis every 2 weeks. Rotenone; use with care, insecticides also kill beneficial insects.

• Plant companions. Plant smartweed as trap crop.

Cutworm

• Description. Dull gray to brown caterpillar, plump to 2-inches long, curls when disturbed.

• Susceptible plants. Beans, broccoli, Brussels sprouts, cabbage, cauliflower, Chinese cabbage, collards, corn, eggplants, kohlrabi, lettuce, radishes, rutabagas, peppers, potatoes, tomatoes, turnips,

• Damage. Chew through plant stems just below soil line; eat roots, leaves, buds, and fruits.

• Emergence time. Early spring; repeat generations through growing season.

• Prevention and controls. Place 3-inch collar of newspaper or plastic around stem when transplanting into garden; clear garden of weeds, grass and plant debris in fall to discourage egg-laying; sprinkle wood ashes around base of plants.

• Biological controls. Braconid wasps; tachinid flies; beneficial nematodes, Bacillus thuringiensis.

• Natural insecticides. Diatomaceous earth.

• Plant companions. None.

European Corn Borer

• Description. Gray to pink-flesh colored caterpillar with dark head and small brown spots on each segment to 1-inch long. Adult moth has zigzag pattern on wings.

• Susceptible plants. Corn, chard, peppers, potatoes, tomatoes.

• Damage. Young larvae chew on leaves and tassels; older larvae bore into stalks.

• Emergence time. Caterpillars in spring, moths in early summer.

• Prevention and controls. Remove old stalks and plant debris in fall or early spring before adults emerge; keep grass and weeds down; time planting to avoid insect growth cycle; hand pick caterpillars.

• Biological controls. Ladybugs; braconid wasps; tachinid flies; Bacillus thuringiensis.

• Natural insecticides. Ryania; rotenone; sabadilla. Use with care, insecticides also kill beneficial insects.

• Plant companions. Grow sunflowers as a trap crop.

Flea Beetle

• Description. Shiny black, brown, or bronze beetles with large hind legs to ⅛-inch long. Jump like fleas when disturbed.

• Susceptible plants. Beans, beets, broccoli, Brussels sprouts, cabbage, cauliflower, chard, collards, corn, eggplants, kohlrabi, muskmelons, peppers, potatoes, radishes, spinach, tomatoes, turnips, watermelons.

• Damage. Chews tiny holes in leaves; causes wilting and slows plant growth.

• Emergence time. Over-winter in garden; emerge in spring.

• Prevention and controls. Cultivate often to disturbs eggs; remove old plants and debris from garden after harvest; plant susceptible plants near shade-giving crops, beetles do not like shade; sprinkle wood ashes on plants; use garlic or hot pepper spray; cover with spun polyester blanket or other row cover; plant resistant varieties; time planting to avoid insect growth cycle.

• Biological controls. Beneficial nematodes.

• Natural insecticides. Diatomaceous earth; rotenone; pyrethrum; sabadilla; use with care, insecticides also kill beneficial insects.

• Plant companions. Use bok choy, Chinese cabbage, and radishes as trap crops. Interplant crops with collards and tomatoes.

Harlequin Bug

• Description. Shiny black and red shield-shaped bug to ¼-inch long; large triangles on back.

• Susceptible plants. Brussels sprouts, cabbage, cauliflower, Chinese cabbage, collards, collards, kohlrabi, mustard, radish, turnip.

• Damage. Sucks sap from plants resulting in blotchy leaves, wilting, and death.

• Emergence time. Over-winter in debris; emerge in spring.

• Prevention and controls. Hand pick; remove weeds and debris from garden; plant resistant varieties.

• Biological controls. Sparrows and mockingbirds.

• Natural insecticides. Liquid rotenone-pyrethrum, sabadilla; use with care, insecticides also kill beneficial insects.

• Plant companions. Grow turnips and mustard greens as trap crop.

Hornworm, Tomato Hornworm

 

• Description. Green caterpillar 3- to 5-inches long with white stripes; horn projects from rear. Adult is large, mottled gray or broth moth with orange spots on each side of body.

• Susceptible plants. Tomatoes, peppers, eggplant, potatoes, dill.

• Damage. Chew holes in leaves and sometimes fruit.

• Emergence time. Over-winters in soil; moths emerge in late spring to early summer.

• Prevention and controls. Hand pick; sprinkle dried hot peppers on plant; diatomaceous earth around base of plants; time planting to avoid insect growth cycle.

• Biological controls. Bacillus thuringiensis, trichogramma wasps; braconid wasps.

• Natural insecticides. Pyrethrum; rotenone; use with care, insecticides also kill beneficial insects.

• Plant companions. Grow dill and four-o’clocks as trap crop.

Japanese Beetle

• Description. Adult metallic, blue-green beetle with bronze wing covers to ½-inch long. Grayish-brown grub with brown head.

• Susceptible plants. Asparagus, beans, okra, peaches, raspberries, rhubarb, leaves of corn.

• Damage. Grubs feed mostly on grass roots; adults feed on leaves and flowers of susceptible plants.

• Emergence time. Adult beetles emerge in early summer after over-wintering underground.

• Prevention and controls. Hand pick; remove all plant debris from garden; grubs are discouraged by high soil pH; place commercial pheromone traps around garden; time planting to avoid insect growth cycle.

• Biological controls. Bacillus popilliae (milky spore) infects grubs, requires wide application; beneficial nematodes.

• Natural insecticides. Sabadilla, liquid rotenone or pyrethrum controls adult beetles; use with care, insecticides also kill beneficial insects.

• Plant companions. Larkspur foliage is toxic to beetles; geraniums repel beetles; smartweed repels insects. Grow light-colored geraniums and zinnias as trap crops.

Leafhopper

• Description. Green, brown, or yellow bugs to ⅓-inch long with wedge-shaped wings; bugs move sideways.

• Susceptible plants. Potatoes, beans, carrots, celery, chard, eggplant, rhubarb, beets, lettuce, spinach, squash, roses.

• Damage. Suck juices from leaves and stems causing stunted, crinkled, mottled, curled leaves; some transmit viruses.

• Emergence time. Spring.

• Prevention and controls. Insect prefers open areas so shelter susceptible plants; cover with spun polyester blanket or other row cover for about 4 weeks after plants sprout; plant resistant varieties.

• Biological controls. Green lacewing, braconid wasps, trichogramma wasps.

• Natural insecticides. Diatomaceous earth; insecticidal soap; summer horticultural spray oil; liquid rotenone or pyrethrum; use with care, insecticides also kill beneficial insects.

• Plant companions. Grow corn as a trap crop.

Leaf Miner

• Description. Tiny black flies about 1/10-inch long with yellow stripes. Larvae are pale green maggots.

• Susceptible plants. Beans, beets, cabbage, chard, lettuce, peppers, tomatoes.

• Emergence time. Adults emerge in spring.

• Damage. Larvae tunnel inside leaves, stunt growth.

• Prevention and controls. Destroy infected leaves; cultivate garden to disturb life cycle in fall; cover plants with spun polyester blanket or other row cover; time planting to avoid insect growth cycle.

• Biological controls. Chickadees, finches, robins.

• Natural insecticides. Light horticultural oil spray.

• Plant companions. Grow radishes as a trap crop.

Mexican Bean Beetle

• Description. Round yellow- to copper-colored beetle with 16 black dots in three rows down the back, similar to a lady bug.

• Susceptible plants. Beans, squash.

• Damage. Skeletonize leaves, plants dry out and die; also feed on bean pods and stems.

• Emergence time. Adults emerge in spring.

• Prevention and controls. Destroy eggs; hand pick beetles; keep garden free of plant debris to limit egg-laying habitat; time planting to avoid insect growth cycle: earlier plants are less susceptible; plant resistant varieties.

• Biological controls. Ladybugs; Pediobius wasps kill larvae.

• Natural insecticides. Liquid rotenone or pyrethrum; use with care, insecticides also kill beneficial insects. Rotenone dust; sabadilla; summer horticultural spray oil.

• Plant companions. Plant nasturtiums, marigolds, savory, or garlic nearby. Grow lima beans as a trap crop.

Onion Maggot

• Description. Maggots are brown, legless, hump-backed and hairy to ⅓-inch long.

• Susceptible plants. Onion, radishes.

• Damage. Tunnel into lower stem of onion near bulb, damaging neck.

• Emergence time. Adult flies emerge in late spring to lay eggs at base of plants.

• Prevention and controls. Remove and destroy infested plants; avoid planting crop too closely or full crop in one place. Use wood ashes and diatomaceous earth as a barrier.

• Biological controls. Beneficial nematodes, predatory flies, spider, ichneumonid wasps.

• Natural insecticides. None.

• Plant companions. Intercrop with plants that are not susceptible to onion maggot.

Slug

• Description. Mollusk; brown, gray, white, purple, or yellow snails without shells to 2-inches long.

• Susceptible plants. Almost all vegetables.

• Damage. Eat large, ragged holes in leaves, stems, and fruit.

• Emergence time. Early spring; prefer cool temperatures.

• Prevention and controls. Hand pick and destroy; sprinkle slugs with salt; place protective borders of sand, lime, or ashes around plants; mulch with wood shavings or oak leaves; trap with saucers of stale beer set out at soil level; place boards or newspapers as traps; border with copper bands; protect plants in plastic tunnels.

• Biological controls. Garden birds, woodpeckers, robins; snakes, toads, turtles; black rove beetles, centipedes, ground beetles, soldier beetles eat slugs and slug eggs.

• Natural insecticides. Diatomaceous earth.

• Plant companions. Low-growing shade plants will shelter slugs; hand pick from beneath shelter.

Spider Mite

• Description. Tiny spider-like arachnids: red, black, or brown.

• Susceptible plants. All vegetables and fruit crops.

• Damage. Suck plant juices causing stippled leaves that yellow, dry, and drop.

• Emergence time. Hot, dry weather; many generations in a year.

• Prevention and controls. Spray cold water or solution of water, wheat flower, buttermilk on leaves; soapy water sprays; light horticultural oil sprays.

• Biological controls. Ladybugs; lacewings, predatory mites.

• Natural insecticides. Liquid rotenone or pyrethrum; use with care, insecticides also kill beneficial insects; insecticidal soap; horticultural oil spray.

• Plant companions. None.

Squash Bug

• Description. Flat-backed, shield-shaped black or brownish bug to 5/8-inch long with triangle on its back.

• Susceptible plants. Vine crops: cucumbers, muskmelons, pumpkins, squash, watermelons.

• Damage. Sucks plant juices and injects toxin resulting in wilt and death.

• Emergence time. Adults emerge when squash vines begin to grow.

• Prevention and controls. Hand pick; keep garden free of debris and hiding places; use trellis to raise off of ground away from bugs; dust with wood ashes and lime; cover with spun polyester blanket or other row cover; plant resistant varieties; time planting to avoid insect growth cycle.

• Biological controls. Tachinid flies

• Natural insecticides. Sabadilla; rotenone dust; liquid rotenone or pyrethrum; use with care, insecticides also kill beneficial insects.

• Plant companions. Plant trap crops: marigolds, radishes, tansy, or nasturtiums nearby.

Squash Vine Borer

• Description. Fat, white caterpillar with brown head. Adult is moth with red, black, and copper rings to 1½-inch long.

• Susceptible plants. Vine crops: cucumbers, muskmelons, pumpkins, squash, watermelons.

• Damage. Bores into stems, stems or plant wilts.

• Emergence time. Late spring.

• Prevention and controls. Wrap strips of nylon stocking around stems to keep adults from laying eggs; mound soil up to blossoms and keep covered; cover with spun polyester blanket or other row cover; plant resistant varieties; time planting to avoid insect growth cycle.

• Biological controls. Trichogramma wasps.

• Natural insecticides. Rotenone; sabadilla; use with care, insecticides also kill beneficial insects. Also diatomaceous earth.

• Plant companions. Plant early summer squash around late winter varieties as trap crop. Destroy infested early summer squash and replant for late crop.

Spotted and Striped Cucumber Beetle

• Description. Yellow beetle with black head and three wide black stripes or spots on the wing covers; beetle to ¼-inch long. Larvae: slender, white grubs.

• Susceptible plants. Cucumbers and other vine plants; beans, corn, peas, and flowers of many plants.

• Damage. Larvae feed on roots and stems; adults feed on leaves and shots; can transmit wilt and mosaic virus.

• Emergence time. Adults emerge in late spring.

• Prevention and controls. Hand pick; mulch around plants; cover plants with spun polyester blanket or other row covers; plant resistant varieties; dust with wood ashes or rock phosphate; grow plants on trellises; time planting to avoid insect growth cycle.

• Biological controls. Braconid wasps, tachinid flies, beneficial nematodes.

• Natural insecticides. Liquid rotenone or pyrethrum; sabadilla; use with care, insecticides also kill beneficial insects.

• Plant companions. Interplant with catnip, tansy, or radishes.

Tarnished Plant Bug

• Description. Oval, brown and mottled yellow and black bug to ¼-inch long; very mobile.

• Susceptible plants. Beans, celery, chard, lettuce, strawberries, peaches, pears.

• Damage. Suck juices from stems, buds, and fruits leaving black spots and pitting; injects toxin that deforms flowers, blackens terminal shoots, dwarfs and pits fruit; can carry fireblight.

• Emergence time. Spring.

• Prevention and controls. Keep garden frees of plant debris; white sticky traps.

• Biological controls. None.

• Natural insecticides. Sabadilla dust; liquid rotenone or pyrethrum; use with care, insecticides also kill beneficial insects.

• Plant companions. None.

Thrips

Thrip damage

• Description. Very tiny to minute insects, yellow, brown, or black with narrow, fringed wings; leave dark fecal pellets behind.

• Susceptible plants. Onions, beans, cucumbers, corn, melons, squash, tomatoes, many flowers.

• Damage. Scrape plant tissue, scars leaves, stems, fruits; transmit viruses.

• Emergence time. Five to 15 generations per year; slow reproduction in winter.

• Prevention and controls. Keep garden free of weeds and debris; place aluminum foil mulch around plants; diatomaceous earth; soapy water sprays; yellow stick traps.

• Biological controls. Green lacewings, lady bugs, predatory mites.

• Natural insecticides. Liquid rotenone or pyrethrum; insecticidal soap; use with care, insecticides also kill beneficial insects; tobacco and sulfur dusts.

• Plant companions. None.

Weevils

• Description. Many types of small beetles; usually brown or black and tear-shaped with hard-shelled bodies and long snots. Larvae are small whitish grubs.

• Susceptible plants. Most vegetables, also apples, blueberries, cherries, peaches, pears, plums, raspberries, strawberries.

• Damage. Puncture holes in leaves, stems, and fruits, sometimes defoliating plants. Larvae eat into roots, fruit, and stems.

• Emergence time. Over-winter in soil; adults emerge in late spring.

• Prevention and controls. Hill up soil around stems of sweet potato vines; rotate crops; remove plant debris; time planting to avoid insect growth cycle.

• Biological controls. Beneficial nematodes, spiders..

• Natural insecticides. Diatomaceous earth. Pyrethrum, rotenone: use with care, insecticides also kill beneficial insects.

• Plant companions. None.

Wireworm

 

• Description. Larvae of click beetles: ⅓- to 1½-inches long; dark brown to yellowish jointed, cylindrical, hard-shelled, legless worm often confused with a millipede.

• Susceptible plants. Potatoes, beets, beans, lettuce, carrots, cabbage, corn, onions, muskmelons, turnips.

• Damage. Chews roots, seeds and tubers; plants wilt and die.

• Emergence time. Beetles lay eggs in soil in spring; worms emerge and take 2 to 6 years to reach adulthood.

• Prevention and controls. Cultivate to expose worms and discourage egg laying; plant green manure crop such as clover. Potato trap: bury halved potatoes cut side down in soil to trap worms then discard potatoes after two days.

• Biological controls. Beneficial nematodes.

• Natural insecticides. Tobacco dust or tobacco tea.

• Plant companions. Alfalfa and clover crops repel wireworms.

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2 Comments

  1. We have been infested by potato bugs. Too many to try & pick off. Some plants have been stripped. Would you recommend pulling these plants up? We have sprayed all the plants with an ‘every bug’ killer. If this kills the beetles, should we still try and take off as many of them as possible? First year we were hit. Could this be the hot dry season to date in WI? Thanks for advise!

    • Check out the article on Colorado potato beetles posted here. Handpicking the adults and larvae and rubbing out the yellowish egg clusters on the undersides of leaves is the quickest and most effective way of getting ahead of an infestation. It takes time, but you will want to rid these pests from your garden–otherwise they will keep reproducing and will overwinter in the soil and be back next year. If your plants are destroyed, pull them up and bag them and put them in the trash. Weather could contribute to a bad infestation, but the growth of the bug population and future generations is the bigger concern. So spend the time getting rid of them now. Next year plant later (the pests will not find potato plants when they emerge in spring) or rotate potato family crops out of your garden for a year or two.

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