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13 Headache-inducing Garden Pests and How to Control Them

You might have seen these pest insects lurking around the garden. Find out how to identify them and keep them off your precious edibles.

By Jessica Walliser


Aphid

Aphid
(many species)
Photo courtesy Whitney Cranshaw/Colorado State University

Physical Description: Tiny, pear-shaped soft-bodied insects up to 1/8 inch long. Aphids can be green, yellow, brown, red, gray or black. Some species have winged forms; others do not. At the hind end of an aphid are two small, tube-like structures called cornicles.

What Attracts Them: soft, green growth caused by excessive fertilization with nitrogen

Crops Affected: Because there are numerous species of aphids, there are many potential host plants. Highly susceptible plants include nasturtiums, roses, milkweed, mums, tomatoes, lettuce, peppers, carrot crowns, geraniums and members of the brassica family, among many others.

Damage: Aphids feed by using their piercing-sucking mouthparts to penetrate plant tissue and remove sap. They feed in groups on new plant growth or on leaf undersides and cause stem tips, new leaves and buds to become curled and distorted.

North American Geographical Range: all

Seasons of Prevalence: spring, summer and fall in northern areas; year-round in the South

Control Techniques: Physically removing aphids with a sharp stream of water from the hose knocks them off plants to where they are easily found by predators, such as spiders, big-eyed bugs and other beneficial insects. Interplant susceptible crops with sweet alyssum and flowering herbs: Their flowers are attractive to a species of parasitic wasp that preys upon aphids. Product controls include horticultural oil, insecticidal soap and neem oil.

Asparagus Beetle

Asparagus Beetle
(Crioceris asparagi)
Photo courtesy David Cappaert/Michigan State University

Physical Description: Adult beetles are 1/4 inch long and black with creamy yellow spots and a red section behind the head. Their wing borders are also red. Larvae are 1/16-inch, dark-green grubs with a black head. The black, elongated eggs are often found attached on-end to asparagus spears.

What Attracts Them: emerging asparagus spears

Crops Affected: asparagus

Damage: Damage is caused by both adult and larval feeding. Growing spears can become ragged, might have dark splotches and might start to bend due to scarring. Brown sections will appear on mature ferns, and with severe infestations, entire stems may turn brown and die. Both beetles and larvae can be easily spotted on plants.

North American Geographical Range: all

Seasons of Prevalence: spring and summer

Control Techniques: Handpick beetles, cover emerging spears with floating row cover until ready to harvest. Wipe eggs from spears as soon as they appear. Product controls include citrus oil, spinosad, and neem oil.

Colorado Potato Beetle

Colorado Potato Beetle
(Leptinotarsa decemlineata)
Photo courtesy Scott Bauer/USDA Agriculture Research Services

Physical Description: Adult beetles are 1/3 inch long with a rounded, hard shell. Wing covers are black-and-tan striped with several irregular black spots on the head. Full-grown larvae are 1/2 inch long, fat and reddish-pink with rows of black dots on their sides.

What Attracts Them: host plants

Crops Affected: all members of the nightshade family, including potatoes, tomatoes, eggplants, peppers and tobacco

Damage: Both larvae and adults skeletonize foliage quickly. They also leave behind pellets of black excrement.

North American Geographical Range: all areas of the U.S. except the Pacific Northwest and the extreme South; also present in southern Canada

Seasons of Prevalence: spring and summer, through autumn

Control Techniques: Cover potato plants with floating row cover, which can remain in place until harvest. Handpick adults and larvae. Rotate crops. Product controls include Bacillus thuringiensis (Bt) var. san diego, Bt var. tenebrionsis, spinosad and neem oil.

Corn Earworm

Corn Earworm
(Helicoverpa zea)
Photo courtesy Clemson University 

Physical Description: Adults are dark-brown or olive-green moths with a 1½-inch wingspan. Fully grown larvae are 1½ inches long and have a cream, yellow or black stripe down the length of their body, which can be pink, green or yellow.

What Attracts Them: host plants

Crops Affected: corn (They also feed on tomatoes, where they’re called tomato fruitworms, and cotton, where they’re known as bollworms.)

Damage: Early season damage is the result of the young larvae feeding on the leaves, shoots and tassels of the corn plant. The most significant damage is a result of larval feeding on the corn ears themselves.

North American Geographical Range: all

Seasons of Prevalence: Adults appear in June, and females lay individual eggs singly.

Control Techniques: As soon as the silk develops, place a clothespin at the top of the ear where the silk emerges. This prevents earworms from crawling into the ear. Trichogramma wasps are parasitoids that target corn earworm eggs. These tiny non-stinging wasps can be purchased for release into the corn patch. Apply five drops of corn oil spiked with a commercial formulation of the biological insecticide Bt to the tip of each developing ear when the silk begins to brown. Research from the Iowa State University Extension and Outreach suggests using 3 teaspoons of Bt per quart of oil. An applicator called the Zea-Later, developed at the University of Massachusetts, makes this chore considerably easier.

Cucumber Beetle

Cucumber Beetle
(striped: Acalymma vittata; spotted: Diabrotica undecimpunctata howardi)
Photo courtesy Russ Ottens/University of Georgia

Physical Description: Both common species, striped and spotted, measure 1/4 inch long. Adult striped beetles are bright yellow with three broad black stripes. Spotted beetles are greenish-yellow with 11 (eastern species) or 12 (western species) black spots on the wing covers. Larvae live underground while feeding on plant roots. The larvae of some species are known as corn rootworms.

What Attracts Them: cucurbitacins present in host plants

Crops Affected: all members of the curcurbit family, including cucumbers, melonspumpkins and squash; also occasionally affects beans, corn, sweet potatoestomatoes and soft fruits

Damage: Feeding damage occurs as ragged holes in plant leaves and flowers. The beetles also feed on germinating seeds. Cucumber beetles transmit deadly bacterial wilt and cucumber mosaic virus.

North American Geographical Range: all

Seasons of Prevalence: summer

Control Techniques: Cover susceptible plants with floating row cover and remove when plants flower. Place yellow sticky cards, which can be purchased at your local garden store, above plant tops. These are rigid plastic cards coated with a nondrying glue that you can attach to wooden or metal stakes and place in the soil around plant. Mulch newly planted seedlings with a loose material, such as straw or hay, as soon as they’re planted; this creates a barrier to females needing to access the soil to lay eggs. Product controls include neem oil, spinosad and pyrethrins.

Flea Beetle

Flea Beetle
(many species)
Photo courtesy Eric Coombs/Oregon Department of Agriculture

Physical Description: These members of the beetle family are extremely small (about 1/10 inch long) and hop like a flea. They can be shiny black, though some species are iridescent or striped. They are quick and are often seen hopping off damaged plants.

What Attracts Them: host vegetable plants

Crops Affected: Choice hosts include members of the brassica family, corn, eggplant, peppers, potatoes, radishes, tomatoes and turnips.

Damage: The distinctive damage of flea beetles appears as small, ragged holes that make the plant look as if it's been riddled with tiny buckshot. The larvae live underground and can do minor damage to plant roots and potatoes.

North American Geographical Range: all

Seasons of Prevalence: spring, summer and fall

Control Techniques: Beneficial nematodes of the species Heterorhabditis bacteriophora can be applied to the soil surface before new transplants are set out. This microscopic creature targets the larvae of flea beetles. Cover susceptible plants with floating row cover and remove when plants flower. Product controls include citrus oil, garlic oil, kaolin clay-based sprays, neem and spinosad.

Four-lined Plant Bug

Four-lined Plant Bug
(Poecilocapsus lineatus)
Photo courtesy Johnny N. Dell

Physical Description: These fast-moving insects measure 1/4 inch long. Greenish-yellow wing covers have four black lines. Nymphs occur in early spring and are bright red and black.

What Attracts Them: lush new growth; plants with high essential-oil content

Crops Affected: herbs, such as basil, lavender, mint and sage; ornamentals, such as azalea, mums, Shasta daisy and viburnums

Damage: Distinctive damage appears as small, sunken round pockmarks caused by the insect's piercing-sucking mouthpart. The pockmarks eventually turn brown, and the damaged tissue might fall out, leaving small holes in the leaves. Damage is purely aesthetic and can easily be pruned out.

North American Geographical Range: everywhere east of the Rockies and into southern Canada

Seasons of Prevalence: Four-lined plant bugs feed for only four weeks in late spring.

Control Techniques: Prune affected plant material in midsummer after feeding damage ceases. Cover susceptible plants with floating row cover until midsummer when the bugs are no longer present.

Imported Cabbageworm

Imported Cabbageworm
(Pieris rapae)
Photo courtesy Jack Kelly Clark/University of California Statewide IPM Program 

Physical Description: Caterpillars are light green with a faint yellow stripe down the side. They measure about 1 inch long. Adult butterflies have a 1- to 2-inch wingspan and are white to yellowish-white with up to four black spots on the wings.

What Attracts Them: host plants

Crops Affected: all members of the brassica family, including broccoli, cabbage, cauliflower, kale, kohlrabi, radishes and turnips

Damage: ragged holes in leaves; cabbageworm might also attack flower clusters of broccoli and cauliflower, leaving round holes scattered throughout. Small cabbageworms are difficult to spot so carefully examine leaf undersides and midribs. Their dark excrement is also an indicator of their presence.

North American Geographical Range: all

Seasons of Prevalence: spring, summer and fall

Control Techniques: Cover susceptible plants with floating row cover until harvest. Place plenty of birdhouses in and around the vegetable garden—many insectivorous birds find cabbageworms a treat. Handpick worms and crush the yellow, bullet-shaped eggs. Remove infected plants from garden. Product controls include Bt, spinosad, botanical oils and citrus oils.

Japanese Beetle

Japanese Beetle
(Popillia japonica)
Photo courtesy David Cappaert/Michigan State University

Physical Description: Adult beetles are metallic-green with copper wing covers. They are 1/2 inch long and 1/4 inch wide. They may stick up their two back legs when threatened, and they drop off plants when disturbed. The larvae are plump, C-shaped, grayish-white grubs with light-brown heads.

What Attracts Them: host plants; Japanese beetles also produce a congregating pheromone when feeding, which lures other Japanese beetles to the same site to feed and breed.

Crops Affected: Grubs feed on the roots of turfgrass and many ornamentals. Adults feed on more than 300 different landscape plants, including cherry and plum trees, grapes, raspberries, blueberries, roses, rhubarb, and zinnias.

Damage: Grub damage occurs as irregular brown patches of turf that peel back in a carpet-like fashion. Adults cause skeletonization of leaves and damage to flower buds. Adults feed heaviest on warm days.

North American Geographical Range: heaviest east of the Mississippi River and north into parts of Canada, but also scattered throughout most of the U.S., with the exception of the extreme Southeast

Seasons of Prevalence: Adult beetles emerge from in-ground pupation in late June and feed for 30 to 45 days before laying eggs in areas of turfgrass. Grubs are most active in fall and spring.

Control Techniques: Beneficial nematodes (Heterorhabditis species or Steinernema carporcapsae) are effective against the grubs when applied to turfgrass each spring. Withhold water from the lawn in late summer when females are laying eggs. The eggs need moisture to survive, so allowing your lawn to go dormant in summer's heat reduces next year's population. Knock adult beetles into a jar of soapy water. Early-season handpicking works best to limit the release of the congregating pheremone. It’s been shown that Japanese beetle traps attract more beetles than they actually trap so avoid using them. Product controls against adults include neem oil and spinosad.

Mexican Bean Beetle

Mexican Bean Beetle
(Epilachna varivestis)
Photo courtesy Clemson University

Physical Description: Adult beetles look like a ladybug on steroids. Their wing covers are copper colored with 16 black spots. Mexican bean beetle larvae are 1/3 inch long, light yellow and covered in bristly spines.

What Attracts Them: host plants

Crops Affected: Choice hosts include all beans, including black-eyed peas, cow peas, green beans, pole beans, snap beans, lima beans and soybeans. Occasionally, they’ll also feed on cabbagekale and mustard greens.

Damage: Damage occurs as skeletonization of the leaves with only the veins remaining intact. Both adults and larvae attack plants. Larvae are often found on the undersides of leaves. They’ll also eat the flowers, developing beans and stems.

North American Geographical Range: almost every state east of the Rockies, down to Mexico and up into southeastern Canada

Seasons of Prevalence: Damage is most severe in July and August.

Control Techniques: A tiny, non-stinging beneficial predatory wasp (Pediobius foveolatus) from India is regularly released in several eastern states to control Mexican bean beetle numbers. The wasp does not survive winters in the U.S., so there are no worries about its release here and the control it provides is extraordinary. You can purchase the larval wasps for release in your own garden from various insectaries, such as the Rincon-Vitova Insectary, when Mexican bean beetle larvae are present. Handpicking adults and larvae is also affective. Product controls include Bt var. san diego, Bt var. tenebrionis, citrus oil and spinosad.

Slug

Slug/Snail
(several species)
Photo courtesy Gary Bernon/USDA APHIS

Physical Description: These land mollusks are brown, gray and black, depending on the species. Snails have shells; slugs do not. Both excrete a slimy coating to protect themselves and to make traveling easier. They leave a telltale slime trail behind. Slugs and snails feed mostly at night but also on overcast or rainy days.

What Attracts Them: host plants; wet conditions

Crops Affected: Slugs and snails love young seedlings as well as a variety of perennials, annuals and vegetables: lettuce, ripening strawberries, tomatoes, artichokes and many others.

Damage: Irregular holes in leaves, along the margin or in the center. If you don't see the culprit, look for the slime trails or visit the garden at night.

North American Geographical Range: all

Seasons of Prevalence: Most active in the wet, cool weather of spring and fall, they go dormant during periods of hot, cold and dry weather.

Control Techniques: Ducks, moles, shrews, garter snakes, salamanders, frogs, toads and turtles consuming enjoy slugs and snails. Water plants only in the morning to discourage nighttime feeding on wet foliage. Copper strips placed around susceptible plants deliver a mild shock to slugs (the slime reacts to contact with copper). Sprinkle iron phosphate-based baits around plants. Do not use baits containing metaldehyde or methiocarb, as these are toxic to pets and other wildlife.

Squash Bug

Squash Bug
(Anasa tristis)
Photo courtesy Whitney Cranshaw/Colorado State University

Physical Description: Adults are 5/8 inch long, dark brown or grayish in color, and have flat backs. Young nymphs are wingless and gray with spindly legs and dark markings. Nymphs often feed in groups, and all stages of squash bugs emit an unpleasant odor when crushed. Eggs are bronze-colored ovals laid in groups on leaf undersides.

What Attracts Them: Host plants

Crops Affected: all curcurbit crops, including cucumbers, melons, pumpkinssquash and zucchini

Damage: Feeding is performed with piercing-sucking mouthparts that remove plant juices and leave behind small specks on leaves that soon turn yellow and then die completely. Vines wilt and turn crispy and then black. Substantial populations of squash bugs can often be found gathered on stems, fruits and the ground around infested plants.

North American Geographical Range: all

Seasons of Prevalence: summer

Control Techniques: Plant resistant varieties whenever possible. Trellis plants to keep them off the ground. Cover young plants with floating row cover until they develop flowers. Handpick adults and nymphs and crush eggs. Neem oil and pyrethrins are effective when used early in the bug's lifecycle (when they are still nymphs).

Spider Mites

Spider Mite
(several species)
Photo courtesy Eric Coombs/Oregon Department of Agriculture

Physical Description: These tiny arachnids are relatives of spiders and ticks and have eight legs, though you'll need a microscope to count them. They are a mere 1/20 inch long and live in large groups. Collectively, they spin fine webbing for shelter, and the webbing is often noted before the mites are. To confirm a spider-mite infestation, shake the plant over a piece of white paper and look for tiny moving specks.

What Attracts Them: They are most attracted to the tender growth of an overfertilized plant, though any host plant will do. Mites can be carried from plant to plant on the wind.

Crops Affected: The most common species of spider mite, the twospotted spider mite, feeds on more than 180 different plant species, including azalea, dwarf Alberta spruce, grapes, melons, phlox and strawberries.

Damage: Mottled, yellow foliage with the leaf undersides and stems covered in fine webbing.

North American Geographical Range: all

Seasons of Prevalence: spring, summer and fall; most prevalent during hot, dry weather when plants are stressed

Control Techniques: Encourage the presence of beneficial predatory insects, such big-eyed bugs, damsel bugs, ladybugs, predatory mites and minute pirate bugs, by adding lots of flowering herbs and other tiny flowers to the garden. Some chemical pesticides actually stimulate mite reproduction, but because these products also kill the beneficial insects that keep mite numbers in check, refrain from spraying whenever possible. If absolutely necessary, effective product controls include horticultural oil and insecticidal soap.

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13 Headache-inducing Garden Pests and How to Control Them

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Reader Comments
One of the best on subject. No fluff writing. To the point. Informative. Only suggestion would be to have more pics of various stages of pests - eggs, larva, adult. (Probably limited by space!) Still great job. Thanks. Posted on Facebook.
James, Peru, NY
Posted: 7/13/2013 4:37:03 AM
why is there never any help on grasshoppers? they eat my whole place almost every year! I can't use pesticides as I have animals and none of them work anyway on these devils!
Linda, Laurel, MT
Posted: 7/12/2013 6:15:48 PM
I had a spider mite infestation indoor that wiped out all three of my angel's trumpet! They were growing beautifully but wasn't able to survive the onslaught of the pest. The pest was so much the were dripping from the plant like a drool. I tried a lot of the recommended cure but I wasn't able to keep up.
Dante, Hyde Park, MA
Posted: 12/22/2012 12:40:03 PM
Excellent. Wish I would have seen sooner!
Kimberly, Midlothian, TX
Posted: 9/13/2012 8:53:12 AM
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