E-194 2-08 Managing in Vegetable Gardens John A. Jackman* For a fresh, satisfying and tasty way to termine whether they are beneficial or help lower your grocery bill and provide pests. Learn to recognize the common personal satisfaction, nothing is better insects in the area, especially common than vegetable gardening. pests, and the signs of pest damage. But growing vegetables is not always Inspect the garden for pests at least once easy, especially when it comes to con- a week. trolling insects and other pests. Whether they arrive by walking or fly- ing, insect pests can take up permanent Understanding insects residence in the garden. Flying insects About 30,000 species of insects are are highly mobile and can migrate in found in Texas; fewer than 100 routinely large numbers. In addition, pests such cause problems in vegetable gardens. as aphids and mites can have a complete Most garden insects are either incidental life cycle in about a week under good or beneficial when they help with pol- conditions, so their populations can lination, recycle organic matter or keep increase rapidly. When many pests seem pests under control. A garden with many to appear overnight, they have either insects may be quite healthy and pro- flown in or are reproducing rapidly. ductive. As insects grow, they change size, However, insect pests can reduce the shape and color in a process called meta- vegetable crop’s quantity and/or qual- morphosis. In some insect species, both ity or transmit diseases from one plant the immature and adult stages damage to another. When that happens, control plants. Because their forms change, measures may be necessary. insects can be difficult to identify; the When dealing with insects in the damage they cause to plants also can garden, first identify the species to de- change with their forms. Size matters too—small caterpillars may barely scrape • Professor and Extension Entomologist, the surface of a leaf, while larger cater- The Texas A&M System pillars may eat great chunks. Damage to plants depends on the insect’s Host plant resistance mouthparts. Insects with sucking mouthparts Through a natural process called host plant feed by piercing leaves or fruit, leaving pock resistance (HPR), vegetable varieties can contin- marks or mottled leaves. Insects with chewing ue to produce in spite of the presence of insects mouthparts chew holes in plant tissues. Recog- and other pests. These plants show tolerance, nizing how an insect feeds can help a gardener nonpreference or antibiosis. Tolerance is the select the proper insecticides; choose stomach plant’s ability to grow and produce even with poisons for chewing insects or contact poisons pest damage. Nonpreference is exhibited when a for sucking insects. plant has structures, such as plant hairs, repel- lent odors or colors that cause insects to choose Plan ahead other plants. Some plants produce chemicals When planning a vegetable garden, consider that kill or slow development of a pest—this is possible pests and how to manage them before called antibiosis. they cause problems. Implement the manage- Extensive trials are needed to understand the ment plan in plenty of time to deal with pest host plant resistance of vegetables. Most vari- problems. ety selection emphasizes appearance, taste and production volume without regard to pests. The Integrated pest management host plant resistance status of many varieties has Integrated pest management, often called not yet been tested. IPM, uses a combination of pest control tech- Recently researchers have altered the genetic niques that balance economic production and material of some vegetables including tomatoes, environmental stewardship. IPM is the overrid- potatoes and corn—these are called transgenic ing strategy for most of production agriculture plants. Dramatic results can be achieved when today and is being adopted in urban environ- genes for insect resistance are incorporated in ments as well. the new varieties. Most of the insect-resistant Monitoring crops for the presence and ab- transgenic vegetable varieties incorporate genes sence of pests is an important part of IPM. In of the bacterium, Bacillus thuringiensis, making situations where a pest is present and could them resistant to some caterpillar pests. This cause significant damage, management is justi- resistance inhibits the growth of caterpillars fied. feeding on these plants. Resistant transgenic veg- Although many practices can be implemented etable varieties are expected to become increas- as part of an IPM program, the use of insecti- ingly available to homeowners. cides is a control option. When non-chemical control practices are used, the IPM approach is Biological control much like organic gardening. Biological control uses one organism to The following sections list many control prac- control another. Three successful approaches to tices available for home vegetable gardeners. biological control are importation, conservation and augmentation. Cultural control Importation requires bringing a parasite or Gardening practices that reduce pest num- predator from a foreign country to control an in- bers or impact are called cultural control. These troduced exotic pest species. Because it is highly practices include variety selection, crop rotation, regulated by state and federal agencies, importa- cultivation, weed management, water manage- tion is not available to home vegetable garden- ment and fertilizer use. For some pests, the best ers, although they do benefit from successful choice is to interrupt their life cycle by leaving importation research programs. the land fallow and weed-free for a period or by Conservation encourages natural enemies rotating crops. Plant debris can harbor pests; already in the area. Conservation methods in- always remove it from a garden area. Weeds can clude: attract insect pests and also must be controlled. • Planting nectar-producing flowers that pro- vide food for parasites. 2 • Avoiding unnecessary pesticide applica- Chemical control tions. Pesticides in any form are regulated for safety • Selecting pesticides that are toxic to a pest by the Environmental Protection Agency (EPA); but relatively nontoxic to beneficial insects. the sale and use of these products is regulated Augmentation is the release of additional by the Texas Department of Agriculture. These predators and parasites, such as lady beetles, agencies do not consider effectiveness in the praying mantids and parasitic wasps, into the registration process. Labeled insecticides may natural populations. However, the benefit of ad- or may not be effective in killing pests that are ditional releases may be marginal because many mentioned on the product label. The number of these predators and parasites already exist in of products available for use in home vegetable the environment. gardens and the rapid turnover in the market Biological control is not an instant solution makes the effectiveness of products difficult to to pest problems. A sound biological control determine. Their effectiveness can change as program must be supported by careful study, pests become more tolerant or as environmental starting with proper identification in order to factors interact with a chemical. Furthermore, a match pests and beneficial organisms. Increased pesticide may fail if it is not applied according to monitoring is necessary. Many biological control the label directions. agents are specific to certain pest species. Usu- The user is always responsible for the proper ally, biological controls are not available for a use of any pesticide. Using a product in a man- specific pest. ner or situation not defined on a pesticide label is illegal. Mechanical control Product labels list restrictions that must be Mechanical control—including barriers, cov- considered, including limits on product rate, ers, high pressure water sprays and hand-picking number of applications per season, specific pests—uses physical means to reduce insect crops the product may be applied to, method of numbers or damage. application and number of days required from Barriers, which prevent the movement of last application to harvest. pests onto plants, include cardboard or plastic Some generic insecticides have several trade cylinders around the base of transplants or cloth names; special restrictions may be noted on a or plastic screening to protect a newly planted specific label. Read the label for additional re- garden. Screening may increase the temperature strictions and follow directions carefully. of a planting bed, often an additional benefit. The EPA approves pesticides for use on a Screening is most useful for susceptible young particular crop after evaluating safety data only, plants and seedlings and may provide some pro- in most cases. If a crop is not listed on a product tection from frost as well. label, the pesticide can not be considered safe for High pressure water spraying, one of the few use on that crop. The EPA considers greenhouses options available when vegetables are near har- to be separate from crop lands; therefore prod- vest, is most effective against small, soft-bodied ucts must specifically state for greenhouse use pests such as aphids. High pressure water sprays on the product label. These products may not may help remove webbing, dissolve droppings be safe to use on some crops because of other and reduce the number of pests in a short time. factors such as phytotoxicity. Table 1 lists a sum- However, water sprays may not kill all of the mary of the chemicals registered for use in home pests and may distribute pests to other hosts. gardens. This list was prepared from product Hand-picking and destroying some pests may labels; not all products have been examined by be feasible in small gardens, and can be success- the Texas AgriLife Extension Service. ful for tomato hornworms and even squash bugs Product labels also list suggested target pests. if persistently done. Obviously, hand picking is Table 2 lists product labels reviewed for this more feasible for larger insects than for small guide, and includes most of the common active insects.