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Insects: Identification and Control

Insects – Identification and Control

The average home vegetable garden may contain more than a dozen different types of vegetable crops, and each of these crops may be attacked by several different species of insects. Being able to manage and control these insect pests is one of the keys to successful vegetable gardening.

Insect pests can damage vegetables in several different ways. Pests like tomato fruitworms, cowpea curculios, stink bugs, and pickleworms cause direct damage by feeding on the fruit. Pests like tobacco hornworms, which feed primarily on the leaves, or aphids, which suck sap from the plant, cause indirect damage. Even though the fruit is not damaged directly, the plant’s ability to produce fruit can be reduced if it loses enough leaf area or sap. Pests like thrips and bean leaf beetles also can cause damage by transmitting plant diseases. In addition to the direct damage they cause, pests like corn earworms and cowpea curculios also contaminate food.

Even though there are many different species of insect and mite pests that can occur in home vegetable gardens, they do not usually all occur at one time, so you probably will not have to “spend the summer spraying bugs” in order to have a successful garden. There are many methods besides insecticide sprays that can manage insect populations and keep them from reaching levels where insecticide sprays are necessary. Many of these methods are passive, requiring relatively little effort from the gardener, and many are things that you will do anyway if you want to grow a vigorous, productive crop.

Sometimes insect pest populations will reach damaging levels and you will need to treat with insecticides. Apply these treatments only to the crop (or crops) being attacked. Rarely will you need to apply a broadcast treatment of insecticide to every crop in the garden. In fact, doing so can be counter-productive, causing pest problems that you otherwise would not have had. This is because unneeded insecticide treatments can destroy beneficial insects, allowing the pests that they were keeping in check to increase in numbers.

However, there are situations when repeated insecticide treatments may be needed to adequately protect certain crops. This is especially true when you are trying to produce a crop when pest populations are especially high (because of the time of year or planting location).

For example, yellow squash are very likely to experience heavy infestations of squash bugs and squash vine borers when grown in midsummer to fall. When grown in the same location year after year, southern peas are likely to experience heavy infestations of cowpea curculios if you do not apply timely insecticide treatments. Fall tomatoes normally experience heavy infestations of stink bugs and tomato fruitworms. There are many other examples, and experienced gardeners quickly learn which pests are especially troublesome in their area and when to expect these pests.

Common Garden Insect Pests

Insects damage plants by eating the foliage, boring in stems or roots, sucking plant juices, and attacking the fruit. The type of damage caused by a particular insect depends on the type of mouthparts the insect has. Pest insects can be classified as having one of two different types of mouthparts: sucking or chewing.

The following two sections briefly discuss some of the more common insect pests in these two groups. For more detailed information on insect management and control, see Extension Publication 2347 Insect Pests of the Home Vegetable Garden.

Sucking Insects

Insects that have sucking mouthparts inject saliva into plants and remove plant juices. The results of feeding may be on individual leaves and stems, or the whole plant may be affected, especially seedling plants. Sucking insects can deform fruit like peas and beans before the pod hardens. The following paragraphs describe examples of garden pests with sucking mouthparts.

Aphids or plant lice are soft-bodied insects that may be green, pink, black, or yellow. They remove the sap from leaves or stems, causing curled leaves and yellowish plants on many garden crops. They also can inject poisonous saliva or disease-causing organisms during feeding. Very large numbers of these insects can occur on cabbage, tomatoes, mustard, and peas. These insects secrete a sticky substance known as “honeydew,” which supports the growth of black sooty mold fungi. Although sooty mold fungi do not invade the plant, heavy buildup of sooty mold is unsightly and can interfere with photosynthesis.

Harlequin cabbage bugs overwinter as adults in old cabbage stalks, bunches of grass, or other areas that give protection. They are black with brilliant red or yellow markings. They suck sap from cabbage, collards, mustard, and turnips, and cause the plants to wilt and die.

Stink bugs can be either brown or green. They give off an unpleasant odor when handled or crushed. Stink bugs are large, shield-shaped insects that may or may not have any distinguishing marks. They suck the sap from seeds in developing bean and pea pods, scarring the developing seed. In some cases, the punctured seed will not develop normally. The outside of the pod will be marked with a small, pimple-like structure at the puncture site.

Thrips are very small insects rarely more than one-sixteenth of an inch long. The insect is straw-colored with a pair of fringed wings. It damages plant leaves or flower buds by puncturing plant cells with its single, ice pick-like mouthpart and feeding on the escaping sap. The feeding causes the leaves to curl and have a silvery appearance. The shoots of infested onions take on the same silvery appearance. To check for thrips, place a handkerchief between the rows and slap the plants toward the handkerchief, or pull one or two plants and shake them over an empty box. If the insects are present, you will see them on the white background.

Whiteflies are small white insects commonly found on the underside of leaves. When infested plants are disturbed, the insects flutter about. Both adults and immatures are damaging. They feed by piercing the tissue and removing plant sap. Whiteflies can occur in great numbers on plants like eggplant and tomatoes. Early detection and complete plant coverage are important to control this pest.

Chewing Insects

Insects with chewing mouthparts cut holes in leaves and fruit, and bore into stems and fruit. The following paragraphs describe examples of garden pests with chewing mouthparts.

Ants are attracted to the garden for many reasons. Some feed on honeydew produced by aphids, some feed on decaying fruit, and some search for other insects. In many cases, ants are considered only a minor nuisance pest, but fire ants can inflict a painful sting. Control ants by controlling aphids, keeping fruit harvested, and using labeled fire ant baits around the perimeter of the garden (not in the garden).

Bean leaf beetles overwinter as adults in or near garden sites. They are ready to feed on young beans and southern peas as they emerge from the ground. Adult coloration and markings can vary, but they are typically reddish to yellowish with a black band around the edge of the first pair of wings. Sometimes, but not always, they may have three or four black spots on the back. However, there are numerous exceptions to this color pattern, and some specimens are red, solid tan, and even pink. You may overlook the beetles because they feed on the underside of the leaves. If disturbed, they will drop to the ground and hide. Adults eat small holes in the leaves. When treating for bean leaf beetles, be sure to apply insecticide to both the upper and lower leaf surfaces.

Blister beetles are gray, black, or striped slender beetles about three-fourths of an inch long. The adults eat the foliage of most garden crops, especially tomatoes.

Cabbageworms or cabbage loopers are pale green measuring worms with light stripes down their backs. Imported cabbageworms are velvety green. They make ragged holes on the undersides of leaves and bore into the heads of cabbage, collards, and related plants.

Corn earworms are green, pinkish, or brown with light stripes along their sides and on their backs. These worms reach a length of nearly 2 inches before they are ready to pupate. They attack corn at two different growth stages. In corn that has not tasseled, the worms will feed in the whorl, damaging new leaves as they form. Later, the adult moths are attracted to the new silks for egg laying. After hatching, the young larvae will burrow into the ear and feed on kernels near the tip of the ear. Many gardeners do not bother with trying to control this pest in corn, preferring instead to simply discard the damaged portion of infested ears. However, this insect will also attack tomatoes, and heavy infestations can cause severe injury to this crop.

For control of earworms in corn during the whorl stage, direct sprays into the whorl when you first note damage. To prevent damage to the ears, apply insecticide when silks first appear. Make spray applications 3 to 4 days apart until the silks are dry. Treat the ear area of the stalk thoroughly. To provide as much protection as possible for bees, make applications in early morning or late afternoon, and do not treat the tassel.

Cowpea curculio adults are secretive insects that are rarely seen. They are small and dark gray. The larva, a white legless grub, is the most damaging stage. It feeds on developing seeds within the pods of beans and peas and destroys their usefulness. To control cowpea curculios, apply a foliar spray when small pea pods first appear, and make a total of three applications at 5-day intervals.

Cutworm adults are dull-colored moths that are most active during the night. The worms are dull gray, brown, or black and may be striped or spotted. Cutworms feed at night and remain hidden during the day. They damage stands by cutting young plants at the soil line. Control cutworms by using aluminum foil or wax paper collars to protect young transplants. You can also use sprays containing permethrin to control cutworms and/or prevent injury.

Fall armyworm adults are dull-colored, night-flying moths. They usually do not appear in our area until the first part of June. Larvae will vary in color from light tan or green to nearly black, with yellowish lines down their sides. The larvae feed primarily on corn but will sometimes feed on peas, tomatoes, and beans. They infest the whorls of corn and can be found 1 to 2 inches deep in the whorl. It is difficult to get insecticides to the target; direct sprays into the whorls.

Flea beetles are small with enlarged hind legs. They jump vigorously when disturbed. These beetles eat tiny round or irregular holes out of leaves. The leaves often look as if they had been peppered with very fine soot. The beetles attack cabbage, eggplant, peppers, potatoes, spinach, sweet potatoes, tomatoes, turnips, and related crops.

Mexican bean beetles are short, yellow to coppery-brown beetles with a curved shape. When the insects are at rest, 16 black spots are visible on their backs. Good coverage of upper and lower leaf surfaces will help control this insect.

The pickleworm and melonworm are similar in appearance but vary in their feeding habits. The pickleworm often enters the fruit from the ground side, causing the inside of the fruit to sour after air enters. It also tunnels in the vines. The melonworm rarely enters the vine. It feeds on the foliage more than the pickleworm. When mature, both worms are about three-fourths of an inch long and range from whitish to green. Damaging populations are more likely to develop on late-planted crops. Start control procedures when young caterpillars are in and around blooms.

Seed maggots are small, white to dirty-white fly larvae. Seed attacked by this insect usually fail to germinate, or plants are weak and stunted. Infestations are usually most severe during wet, cool springs and on ground that is high in organic matter. If these conditions are present, delay planting until conditions are right for good germination and growth.

Serpentine leaf miner adults are tiny flies. Their maggots feed on the tissue between the upper and lower surfaces of leaves, causing slender, white, winding trails through the interiors of the leaves. They can severely damage beans, cucumbers, peas, squash, tomatoes, and other vegetables.

Squash vine borer adults are distinctly colored, wasp-like moths. The front wings are covered with metallic, olive-brown scales; the hind wings are transparent. The abdomen is ringed with red, black, and copper. Eggs are placed on leaves and stalks. Small larvae will bore into the plant from these locations, causing the runner to wilt eventually. As with all borers, this insect is difficult to control once it enters the plant because insecticides cannot reach the feeding site. Infestations are more common on pumpkins and late-planted squash, and weekly insecticide treatments are often required to protect these crops. Apply in late afternoon to protect bees.

Cucumber beetles, striped or spotted, damage several garden vegetables. Some of these are cucumbers, muskmelons, squash, and to a lesser extent, beans and peas. The spotted cucumber beetle (SCB) is more of a problem on these latter vegetables than is the striped. They feed on leaves, tender stems, and in some cases, the root system. The larvae of the SCB damage seedling corn and are known as the southern corn rootworm. Use foliar sprays of carbaryl or other recommended insecticides to control adults.

Tobacco hornworm adults are large moths that feed on the nectar of various plants. They do not damage any portion of the plant, but the larvae can eat large amounts of foliage quickly, and larvae will occasionally feed on fruit. This worm is green with diagonal white lines located along the sides and a prominent horn at the tail. These insects are found on tomatoes, eggplant, peppers, and related plants.

Slugs are not insects. However, they can be annoying. These pests leave a trail of thick, sticky material over plant parts that will appear as a silver trail when dry. They feed on young foliage and low-lying fruit like strawberries. Slugs rest in moist, shaded areas during the day and become active at night. To control slugs, use methaldehyde on iron phosphate baits according to label directions. Be sure not to contaminate edible parts of plants. Trapping can be effective. Place wet burlap bags in your garden late in the afternoon. The next morning, look under the bags for slugs and destroy any you find.

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