Vegetable Garden Insects is part 15 of The Alabama Vegetable Gardener series.
Vegetables grown in the southern United States are vulnerable to attack by a variety of insect pests. Our warm temperatures and long growing seasons are not only ideal for vegetable crops but also for insects—beneficial and pest. Insects have highly developed senses for locating host plants, so some form of insect control is often necessary to protect vegetable plants from severe feeding damage. The best approach is a combination of differing control tactics: (1) cultural controls, (2) mechanical or physical controls, and (3) chemical controls (biorational or conventional). Insects are less able to adapt to and overcome this multitiered management style. This multiple strategy approach is called integrated pest management—IPM. Prevention rather than delay of controls until peak insect activity is the best approach with any combination.
Control tactics, used singly or in combination, termed as cultural methods include planting under optimal and timely conditions, reducing water stress, timely harvesting, using trap crops, rotating crops, early planting, optimal seedbed preparation, removing crop residues, planting resistant varieties, etc. Implementing cultural practices can prevent or minimize insect migration and establishment in the garden, thus requiring fewer (or possibly no) insecticide applications. Crop rotation helps prevent some insects, particularly those that live in the soil (wireworms and white grubs). This practice also helps prevent some disease problems (Fusarium wilt fungi and many others). Annually moving the garden may not be possible due to space restrictions, but you can change the location of individual vegetable crops within the garden each year. Early planting of crops prevents damage by many of the late-season insects (late-season crops are the hardest hit due to higher insect populations feeding together). Optimal seedbed preparation promotes vigorous, new plant growth allowing plants to better tolerate minor insect damage. This is especially important in the spring garden. Wait for a good weather forecast before planting seed or transplants. Removal of plant debris, or sanitation, at the end of the seasonreduces insects’ overwintering sites. Many pests mature during the winter in the stems and roots of host plants left in the garden. Trap cropping is an emerging technology in several southern states. Research in Alabama shows promise in reducing leaffooted bugs on tomato and yellow-margined leaf beetle on cabbage. The basic approach is to plant perimeter trap crops and treat them instead of the vegetable with approved insecticides. Trap crops can extend the harvesting period, reduce pesticide use, and grow better quality produce. Trap crops like Peredovik Sunflower and silage sorghum (NK300) not only deter leaffooted bugs and stink bugs but also increase biodiversity providing habitat for natural enemies such as syrphid flies and lady beetles. Resistant varieties are not completely immune to damage but are less attractive to the insect pest and may be able to tolerate more damage than a nonresistant, susceptible variety. Check seed catalogs and transplant labels for information on resistant varieties that grow well in your area.
Mechanical controls are those that physically remove the pest or prevent pests from interacting with the crop. In small gardens, handpicking insect pests can be an effective and practical control. This requires daily attention and will not be effective for most flying insects and night feeders. Exclusion devices, such as netting and row covers (fabric or plastic materials), are useful mechanical controls that prevent, reduce, or delay pest invasion with a physical barrier. Net houses of 50-mesh fabric can offer complete blockage of tomato hornworm and fruitworm moths.
Chemical controls are pesticides and include any substance that causes harm to a pest (mammal, insect, bacteria, fungi, or other). Pesticides are chemicals (plantbased, biorational, or synthesized in a lab) that deter or kill the organism damaging a crop or desired plant. Use pesticides when cultural and mechanical tactics fail to fully manage the pest problem. This minimizes your exposure to chemicals and protects the beneficial organisms associated with your garden environment.
Many biorational insecticides have low environmental persistence and are slow acting. They can be used as soon as the pest is detected but may also necessitate additional applications as new pest populations appear. Always read the pesticide label (biorational or synthetic pesticide) for instructions and other information before using it. The label tells you everything you need to know from the harvest waiting period (time needed between the last spray and harvesting), handling and application instructions, beneficials that might be harmed by it, and the acceptable crops that the chemical can safely treat.
Correct use of pesticides means applying only when necessary and using the label-directed procedures to apply the recommended amount at the right time. Excessive use of insecticides does not result in better insect control, can harm beneficial insects (vulnerable to many synthetic and natural insecticides), and actually causes outbreaks of secondary pests and pesticide resistance in a pest population.
Choosing the best insecticide for the situation solely depends on correct identification of the insect pest and of the plant you intend to treat. Gardeners can subscribe to the Alabama IPM Communicator newsletter to stay informed of pest outbreaks, insect identification, scouting strategies, and management tactics. Sign up for the IPM Communicator newsletter here.
Note: Insecticides must be applied when pest numbers are low and their size is small. Applying insecticides in an outbreak (high population) is not cost effective for the garden or for managing the pest.
Bt (Bacillus thuringiensis). This beneficial bacterial species kills the larval stage of moths and butterflies. It offers the best control on most caterpillars if used on new, young larvae. Do not use in or near a butterfly garden. Do not apply Bt on top of leaves when weather is excessively hot and dry as the bacteria are damaged in these conditions. Be sure to direct sprays to the underside of leaves, on stems, and on all shady corners of a plant where caterpillars may hide.
Horticultural Soaps and Oils. Oil and soap sprays control a variety of insects by physically disrupting their body functions. They are effective on a wide variety of small pests, such as aphids, scale, mites, and whiteflies. Oils can be used both on dormant or actively growing plants. Do not apply soaps and oils during peak summer to avoid leaf burn. Repeated treatments may be necessary to suppress heavy pest populations.
Sevin (carbaryl). Carbaryl is available as dust (5 to 10 percent) and spray. It is also available in granular formulation for early season soil pest control. It controls a wide variety of insects including mites, thrips, flea beetles, stink bugs, earworms, fruitworms, cucumber beetles, and many others. Avoid applications when pollinators are actively foraging.
Pyrethrins. They control a wide range of insects including caterpillars, beetles, and true bugs. They act on contact causing “quick knockdown.” Formulations with piperonyl butoxide and rotenone improve control. Do not mix with insecticidal soaps.
Synthetic pyrethroids (such as Cyfluthrin, Permethrin, and Bifenthrin). These control a wide variety of insect pests with rapid knockdown. Read the label for cautions concerning pollinators and aquatic life.
Imidacloprid. This is the first systemic insecticide approved for use on home garden vegetable crops. The product is taken up by the roots and then translocated to other plant parts. It provides excellent control of early season insect pests such as aphids and flea beetles. Do not use the product in the late season.
Spinosad. This fast-acting insecticide is derived from a bacterium, Saccharopolyspora spinosa. The organic-approved formulation called Entrust is available for small farmers. Spinosad has excellent activity against caterpillars, Colorado potato beetle, thrips flea beetles, and many other small insects. Read the label; it is highly toxic to pollinators.
Aphids, also known as plant lice, are small (inch or less), soft-bodied insects with two projections on the rear end that look like tail pipes. Aphids may be yellow, green, pink, brown, or black. Adults and their young suck plant juices and cause distortion and stunting of tender plant growth. Small plants may be severely weakened or killed. Because of their feeding method, aphids c a r r y several plant virus diseases that may be more destructive than the aphids themselves. Aphid damage to vegetables begins early in the spring and can continue throughout the growing season. Find colonies of aphids near growing points and under leaves. They feed on a variety of vegetables including cole crops, cucurbits, beans, peas, potatoes, and tomatoes. Observe small plants closely in the spring. In some cases, small aphid populations can be washed off plants with a strong stream of water spray. Insecticidal soaps and oils are also effective with multiple spray treatments. Early season application of transplants with imidacloprid (soil drench) can also provide plant protection for up to 3 weeks.
Corn earworms are alson known as tomato fruitworms and feed on a wide variety of vegetables including beans, peas, sweet corn, okra, tomatoes, cabbage, eggplant, and peppers. Minor leaf feeding may be seen, but most damage is done to the corn ear. Earworms feed in the whorls of young sweet corn resulting in large ragged holes. They later feed on the silks and kernels from the tip of the ears downward. Larval feeding on the silks may interfere with pollination.
Fully grown corn earworm larvae are up to 1 3/4 inches long and vary in color from light green to pink to brown to nearly black. The body is marked with alternating light and dark stripes running lengthwise. The head is yellow and the legs are dark or nearly black. The skin of the larva is coarse with short black hairs. Larvae mature into tan-colored, night-flying moths. Damage from this insect becomes more severe as the season progresses. Thus, early planting and use of early maturing varieties prevents some damage. Varieties with tighter husk leaves may also minimize pest entry. Corn earworms seem to prefer “supersweet” varieties. Use recommended insecticides as soon as larvae are found. Corn earworms feed primarily on the ear tips, often leaving most of the ear undamaged. Insecticides may not be needed if the tips are discarded before eating. However, spraying every 2 to 3 days beginning at silking achieves totally clean ears.
Mexican Bean Beetles
Adult and larval stages feed on the leaves of snapbeans, pole beans, lima beans, and, to a lesser extent, cowpeas. The adults are copper colored with 16 black spots on their backs. Larvae are yellow and covered with spines. Eggs and pupae (the inactive stage before the adult stage) are also commonly seen on the foliage along with the feeding stages. Distinctive orange-yellow eggs are laid in clusters of 40 to 60 on the undersides of leaves. Pupae are yellow, smooth, and resemble the head of a cobra. There are usually three to four generations of Mexican bean beetles per year in Alabama. Hot, dry summers as well as extremely cold winters tend to reduce populations. Feeding begins on the lower surfaces of leaves, but high populations can be seen feeding on all above-ground portions of the plant. They leave leaf veins undamaged, giving the leaf a skeletonized appearance. Mexican bean beetles are easily killed with most garden insecticides, but if left unchecked, they can completely defoliate bean plants. Sprays should be directed to the undersides of leaves.
Spotted Cucumber Beetles
The larvae feed on the roots of corn as well as cucurbits (cucumbers, melons, squash, and pumpkins). The adults are yellowish-green with 12 black spots on their backs. Larvae are small, white, and soft-bodied. The beetles eat holes in the leaves and flowers. Young plants may be killed. Larval feeding on roots results in wilted, unproductive plants. Cucumber beetles also transmit bacterial wilt, a very destructive disease of cucurbits. This insect survives the winter as an adult in crop residue and weeds. Therefore, cleaning up weeds and garden debris in the fall will reduce the next year’s population. Cucumber beetles can be controlled by spraying a recommended insecticide when beetles are seen.
Squash Vine Borers
The larvae damage squash plants by boring into the vines and crown. Infested plants may wilt and die. Sawdust-like insect excrement coming from holes in the vines is evidence of active larvae inside the stem. Adults are clear-winged moths that lay their eggs on vines early in the season (moths may look like red wasps hovering at the base of vine). Pheromone-based sticky traps are excellent tools for removing the early season moths or for scouting. Once hatched larvae enter a plant, insecticides cannot control them. Chemical control depends on the young larva being exposed to an insecticide during its short period after egg hatching and before entering the plant. Other control measures that may prevent problems are early planting and destruction of old crop residues. Squash vine borer populations are higher later in the summer so early planting can avoid much of the damage. Mechanical deworming of vine is another way of removing the caterpillars. Squash vine borers survive the winter in dead squash vines so destroying these overwintering sites is critical to reducing next year’s population.
Colorado Potato Beetles
As adult and larval forms, Colorado potato beetles are very serious pests of Irish potatoes. They can also damage tomatoes, eggplants, and peppers. The adult beetle is about 3/8 inch long, yellow with 10 black stripes, and hard shelled. Larvae are humpbacked, soft bodied, and brick red with rows of black spots along each side. Groups of a dozen or more orange, barrel-shaped eggs are often visible on the undersides of leaves. Each female lays approximately 500 eggs. In Alabama, there are two or three generations per year. Both adult and larvae are voracious foliage feeders. Untreated infestations can result in complete defoliation. Handpicking will help protect plants if done often. Otherwise, apply Sevin or Thiodan when an infestation is first detected. Repeat applications may be necessary as eggs hatch. Spinosad is effective against the larvae.
These feed on all forms of cruciferous plants but prefer cabbage and cauliflower. They frequently damage turnips, kale, collards, radishes, and mustard. When cabbage plants are small, cabbageworms feed primarily on the undersides of the developing leaves. When the heads develop, cabbageworms feed on the outer leaves and bore into the centers. Larvae also cause damage by contaminating the heads with their greenish-brown excrement.
The adult form, a familiar insect to all growers of crucifers, is a white butterfly with a wingspan of about 2 inches. These butterflies are commonly seen around gardens. When fully grown, the larva is about 1 inch long and velvety green with a faint yellow stripe along the middle of the back and a row of yellow spots along each side. The larva crawls slowly over the plant and does not show any of the looping action characteristic of the cabbage looper, another important pest of cabbage. The pupae, the immobile stage prior to the adult butterfly, are also commonly found on cabbage plants.
Pupae are about 4/5 inch, sharply angled, and green with black spots. There are usually four to six generations of imported cabbageworms per year in Alabama. Naturally occurring parasites and insect diseases play an important role in controlling imported cabbageworms. However, insecticides are often necessary to prevent excessive damage. Bt’s are very effective in controlling this and other worm pests of cole crops. They are nontoxic to humans and have no preharvest waiting periods. Other effective insecticides are available.
Predominately a pest of cowpeas, it may occasionally damage snap beans and lima beans. Adult female weevils lay eggs in young pods; damage is done by the larvae feeding within the developing seeds. Damaged pods have black wartlike marks where the eggs were laid and have poorly developed peas.
Eggs hatch 3 days after being laid and the young larvae eat their way into the developing peas. After about a week of feeding, the larvae drop out of the pod to the soil to pupate; new adults emerge about 1 month after egg laying. Two generations per year occur in Alabama. Late-planted peas (late July) will sometimes escape damage.
Crop rotation and sanitation techniques are helpful, but insecticides are usually necessary to prevent excessive damage. Start spraying when the first pods are 1/2 inch long. Repeat three or four more applications every 3 to 5 days. Endosulfan is effective against curculio and is less harmful to beneficial insects than some other insecticides.
These pests are tiny (barely visible) and damage many vegetable crops by sucking juices from the undersides of leaves. Mites are a close relative of insects. When populations are high, mites can cover plants with fine webs resembling spider webs. Spider mite problems are more prevalent during hot, dry weather. Damage is first evident as small white or pale yellow spots on the leaves. Severe infestations may result in the loss of leaves.
Spider mites are readily moved within gardens by the activities of humans. Therefore, avoid moving infested plants to uninfested areas.
Spider mites are very difficult to control in a home garden. Light infestations can be controlled by washing off plants with a strong stream of water. Insecticidal soaps often work as well or better than other insecticides and have no preharvest waiting periods. Soaps will need regular reapplications.
Bifenthrin, insecticidal oils, and sulfur powder may provide mite control at low pest pressure. Results are inadequate for high populations during hot, dry weather. Do not mow lawns near the vegetable garden during drought (prolonged dry weather) to avoid spider mite transfer to leaves. Overuse of some miticides can actually lead to increased spider mite infestations due to death of more sensitive predatory mite species. Spot treatment of plants and timely removal of infested plants may reduce spread of spider mites to healthy plants.
About an inch long as adults and green or brown in color, these pests earn their names by giving off a foul odor when handled. The young resemble the adults in shape but are somewhat more rounded. Young stink bugs are often seen clustered around the group of eggs from which they hatched. Stink bug eggs are barrel shaped, laid in clusters, and usually on leaf undersides. Adults and young suck plant juices. Leaffooted bug adults are larger than other stink bugs and have leaflike expansions on the hind legs. Both of these have strong host preferences and migrate long distances searching their preferred host plants. In recent years, the leaffooted bug has become the dominant sucking-pest insect on high-value vegetables, especially in the late season when multiple generations are feeding. Be aware of the predatory stink bugs similar in appearance to plant-feeding pests; careful observation and correct identification protect these and avoid misapplication of insecticides.
Characteristic damage varies with the type of vegetable. On lima beans, little evidence of feeding damage may be visible on the exterior of the pods, but inside, damaged beans are shriveled and spotted with slick brown stains. Stink bug feeding on young okra pods and corn ears causes these vegetables to be distorted or become crescent shaped. Damaged tomato fruits show whitish yellow spots and pithy tissue inside.
Perimeter trap crops of forage sorghum and sunflower (planted 2 weeks before the squash) can delay leaffooted bug and stink bug feeding on vegetables and allow longer harvest time. Avoid leaving tomato fruits to rot on the vine and keep the garden weed free. If needed, apply a recommended insecticide after confirming the pest species.
Find links to all the sections of the Alabama Vegetable Gardener below.
- Part 1—Planning for the Home Garden
- Part 2—A Well-Drained Soil
- Part 3—Acid Soils Create Gardening Problems
- Part 4—Excessive Phosphorus in Garden Soils
- Part 5—Wood Ash for Lime and Potash
- Part 6—Garden Fertilizer
- Part 7—Fertilizing the Organic Garden
- Part 8—Weed Control in the Home Garden
- Part 9—Growing Tomatoes
- Part 10—Bitter Cucumbers
- Part 11—Home-Grown Seed
- Part 12—Vegetable Information
- Part 13—Control Diseases for Top-Quality Tomatoes
- Part 14—Nematodes Could Be the Reason Garden is Unproductive
- Part 15-Vegetable Garden Insects
- Part 16-Garden Problem Guide
- Part 17-Harvesting Your Own Groceries