Cooperative Extension Service/The University of Georgia College of Agricultural and Environmental Sciences
PDF

	Control Insects on Greenhouse Tomatoes Entomology Fact Sheet

 

David B. Adams, Extension Entomologist

Insect control in the tomato greenhouse can be especially difficult. Insect pest populations often soar because conditions in the greenhouse are usually near optimum for insect development and reproduction. Insects and related pests are protected from natural control factors such as temperature extremes, wind, rain and natural enemies that often keep populations low enough to prevent economically important damage on field grown tomatoes.

The insecticide arsenal for greenhouse insect control is limited because only a very few insecticides have been registered by the Environmental Protection Agency for this purpose. In addition, the relatively closed environment increases the hazard of insecticide poisoning for humans and other warm-blooded animals as well as the likelihood of plant injury.

The grower should be able to recognize the pests described in this publication so he or she can apply the appropriate control measure recommended in the chart as soon as it is needed.

Aphids are small, soft-bodied, pear-shaped insects that cluster on the underside of leaves and on stems. They puncture the plant tissue with needle-like snouts to

Aphid

suck sap. They cause leaves to curl and crinkle downward, and they secrete a sticky substance called honeydew on which a black fungus called sooty mold grows to cover the leaf. Although heavy aphid populations can severely damage or even kill plants, aphids are probably even more important as carriers of virus diseases to tomato plants.

Whiteflies are probably the most frequently occurring pest of greenhouse tomatoes. The adults are tiny, white, moth-like insects about ¹/₁₆ inch long that swarm about infested foliage when disturbed. The young suck sap from the underside of the leaves and, like aphids, secrete honeydew, which supports the growth of sooty mold. The young are difficult to see because they are motionless, flattened and nearly transparent. These insects are very difficult to control and it may be necessary to increase the frequency of insecticide applications to every four days with heavy populations.

Whitefly	Cabbage Looper

Cabbage loopers are pale green caterpillars with white or pale yellow stripes that run the length of the body. The caterpillar forms a loop with the middle part of its body by bringing the rear legs up to the front legs as it moves along. Cabbage loopers mainly chew holes in the leaves and usually do not bother the fruits.

Tomato fruitworms eat holes in the fruits. Newly hatched caterpillars are pale in color with a black head. Soon the body becomes yellow, green, pink, brown

Tomato Fruitworm

or nearly black. The head is usually yellowish. Tomato fruit-worms usually have dark stripes that run the length of the body. Tomato fruitworm damage is more likely to occur in the fall after moths from heavily infested outdoor crops fly into the greenhouse and lay eggs.

Other caterpillars that may become problems in the tomato greenhouse are hornworm, beet armyworms and yellow-striped armyworms. These pests usually chew holes in the leaves.

Tomato pinworm are small caterpillars that mine the leaves, fold leaves together with silken webs, and bore pin-sized holes into the fruits. Severely damaged plants may fail to set fruit or bear fruit that is stunted or deformed. Tomato pinworm are yellowish, gray or green, purple-spotted, brown-headed caterpillars that are only about ¹/₄ inch long.

Thrips are slender insects about ¹/₂₅ inch long that feed by rasping the leaf surface and lapping up the exuding juices. Adults have four slender wings that are bordered with a row of long hairs. Those that are most common on tomato leaves are yellowish-brown and have green nymphs, or young. Heavily infested leaves appear silverish on the upper surface and somewhat shiny on the lower surface.

Thrips	Spider Mite

Spider mites cause leaves to become stippled with tiny white or yellow specks as they such sap from the lower surface. Severely infested leaves may be covered with silken webs. Spider mites are only about ¹/₅₀ inch long or smaller and cannot be seen easily without the aid of a microscope. These eight-legged pests are not insects but are closely related to spiders. Those most commonly found on tomato leaves are green or yellow and marked by a dark blotch on each side.

Leafminers are whitish or pale yellow maggots about ¹/₈ inch long that cause slender, winding, whitish tunnels as they feed between the two surfaces of the leaf. Heavy infestations can cause leaf drop and reduce yields.

Slugs and snails are grayish or brownish, soft-bodied, legless animals usually ¹/₂ to 2 inches long. They are mollusks and not insects. These pests feed mostly at night by chewing on the leaves and fruits; they are especially troublesome on fruits that are allowed to rest on the mulch or soil surface. Both slugs and snails leave characteristic white, slimy, shiny trails wherever they travel. During the day, they hide under flats, pots and similar objects in the greenhouse.

Snail	Slug

Control

It is unlikely that you can control insect pests on greenhouse tomatoes without using insecticides. You can, however, take supplemental measures to decrease insect damage, lower insect control costs and increase profits.

See that transplants, soil, tools and other articles you bring into the greenhouse are free of insect pests. Practice good housekeeping by keeping the greenhouse and the area surrounding it free of debris and articles such as unused flats and pots under which slugs, snails and other pests can hide. Keep the area surrounding the greenhouse bare of vegetation or closely mowed. Keep doors, screens and ventilator screens in good repair. After harvest, remove all plant debris from the greenhouse and destroy it.

Closely examine your plants at least once a week so the proper insecticide can be applied just as soon as it is needed. The chart on page 3 contains insecticide recommendations for the insect pests usually found on greenhouse tomatoes.

For more information, see the Georgia Pest Control Handbook and contact your county extension agent.

Attention: Pesticide Precautions

• Observe all directions, restrictions and precautions on pesticide labels. It is dangerous, wasteful and illegal to do otherwise.
• Store all pesticides in original containers with labels intact and behind locked doors. "Keep pesticides out of the reach of children."
• Use pesticides at correct label dosage and intervals to avoid illegal residues or injury to plants and animals.
• Apply pesticides carefully to avoid drift or contamination of non-target areas.
• Surplus pesticides and containers should be disposed of in accordance with label directions, so contamination of water and other hazards will not result.
• Follow directions on the pesticide label regarding restrictions as required by State and Federal Laws and Regulations.
• Avoid any action that may threaten an Endangered Species or its habitat. Your county extension agent can inform you of Endangered Species in your area, help you identify them and, through the Fish and Wildlife Service Field Office, identify actions that may threaten Endangered Species or their habitat.

Trade names are used only for information. The Cooperative Extension Service, the University of Georgia College of Agricultural & Environmental Sciences, does not guarantee or warrant published standards on any product mentioned; neither does the use of a trade or brand name imply approval of any product to the exclusion of others that may also be suitable.

The original material for this publication was developed by Dr. A. Leon Stacey, former Extension Entomologist.

Leaflet 194/June, 2001

The University of Georgia and Ft. Valley State University, the U.S. Department of Agriculture and counties of the state cooperating. The Cooperative Extension Service, the University of Georgia College of Agricultural and Environmental Sciences offers educational programs, assistance and materials to all people without regard to race, color, national origin, age, sex or disability.

An Equal Opportunity Employer/Affirmative Action Organization Committed to a Diverse Work Force

Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, The University of Georgia College of Agricultural and Environmental Sciences and the U.S. Department of Agriculture cooperating.

Gale A. Buchanan, Dean and Director