University of Illinois Extension

Insect Control

Bugs Worm Their Way Into Gardens

Many kinds of insects can be found in your garden. Some insects are destructive. Others are beneficial, such as lady beetles, because they feed on destructive insects. Aphis lions feed on aphids. Parasitic wasps feed on caterpillars and other insects.

Insects that attack vegetable plants are divided into three groups - sucking, chewing and boring.

Sucking insects feed on plant juices, sucking them out and causing the leaves to turn a yellow or bronze color. Leaves and plant shoots also may wilt and curl.

Chewing insects eat holes in leaves, flowers or fruits.

Boring insects get inside plants. These pests bore into stems or mine shallow tunnels into leaves, fruits and roots.

When trying to tell if a plant is suffering from insect or disease problems, there are two symptoms to remember. Insects may eat plant material, leaving holes on the leaves and also leaving waste material near the feeding area. This waste material may be in the form of a sugary syrup, granules, sawdust-like material or moist, dark excreta. These symptoms do not occur with plant diseases. Insect-infested plants also may be stunted.

Destructive Insects

Insect Description
Crops Attacked
Symptoms or Damage
Aphids or plant lice
Tiny (less than 1/8 inch long), soft-bodied, usually wingless insects. Color ranges from pale green to black. Slow-moving. Often not noticed until there are many upon a plant.
Bean, broccoli, cabbage, cucumber, Irish potato, muskmelon, squash, sweet corn, tomato, watermelon. Curled leaves; "honeydew"(clear, sticky substance on leaves and fruit given off by aphids, turns black from mold growth); many tiny, soft-bodied insects.
Blister beetles
1/2-5/8 inch long. Soft-winged black, gray, or striped beetles. Fast-moving. Usually appear in groups.
Bean, Irish potato, tomato Blister beetles damage foliage by chewing and by secreting a toxin that causes wilting and leaf-burn. If unchecked, beetles can strip foliage from plants in a short time.
Cucumber beetles
1/4 inch long. Black and yellow spotted or striped beetles. Feed on foliage, flowers, stems, or fruit. Fly from one plant to another.
Cucumber, muskmelon, squash (summer and winter), pumpkin, watermelon. Holes in foliage; chewed flowers; scarred stems and fruit surfaces. Beetles may carry bacterial wilt disease that causes plants to wilt and die.
Cutworms
Up to 1-1/2 inches long. Black, gray, or mottled caterpillars. Usually a single cutworm found curled up beneath soil surface at base of damaged plant.
Broccoli, Brussels sprout, cabbage, cauliflower, eggplant, kohlrabi, pepper, sweet corn, tomato. Cut-off or wilted plants. Cutworms chew through plant stems at or just beneath soil surface. They may also feed on ripening tomato fruits, leaving small, round holes.
Flea beetles
Shiny, usually black beetles, often not observed because of their small size (1/16 inch) and ability to jump quickly from plants when disturbed.
Cabbage, Chinese cabbage, eggplant, radish, spinach, sweet corn, turnip. Flea beetles scratch holes or leave white streaks in green foliage in late spring. Intense feeding results in wilting and dying of leaves and decreased yield.
Grasshoppers
Vary widely in size, up to 1-1/2 inches long. Color ranges from green to brown. Hop or fly. Young present in early summer, develop into large-winged adults by late summer.
Most vegetables. Holes chewed in foliage.
Leafhoppers
Up to 3/8 inch long. Green color. Wedge-shaped. May migrate from one area of garden to another. Hop away in large numbers when foliage is disturbed.
Bean, carrot, cucumber, Irish potato muskmelon. Curled or crinkled foliage; "hopper burn"(caused by leafhoppers' feeding, indicated by brown edges on leaves). Leafhoppers may have migrated from damaged plants.
Maggots, root
Tiny (up to 1/8 inch long), white, legless worms. Found in tunnels in underground parts of vegetables. Usually confined to northern one-third of Illinois.
Cabbage, onion, radish, rutabaga, turnip. Wilting or stunting of plants. Numerous brown or gray tunnels throughout underground parts of vegetables.
Slugs
(snails without shells)
Range in size up to 2 inches long. Shiny, slimy, soft, legless animal. Seldom seen in daylight.
Most vegetables. Paths of slugs marked by shiny mucous trails. Some feeding on foliage and scarring of fruit.

Squash Bug Problems in the Beginning

The following practices are recommended for preventing or controlling insect damage. Keep the garden free of weeds and mow the surrounding area. Remove and compost plants that have finished producing. Do not leave them planted in the garden. Plant varieties that grow well in your area and follow proper fertilizing and watering recommendations. Some insects such as aphids and spider mites may be washed off the plants with a garden hose. The tomato hornworms or insect egg masses may be hand-picked from the plant to prevent further damage. Crop rotation will help hold down the population of chewing insects. When buying an insecticide, read the label to see if it is recommended for the insect and plant you are treating. Follow the directions. When using chemical control for sucking insects, spray the underneath of the leaves as well as upper surfaces. Insecticides are most effective if used before large numbers of insects take over the plants.