Managing Insect and Mite Pests in Vegetable Gardens Managing Insect and Mite Pests in Vegetable Gardens
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E-194 11-03 Managing Insect and Mite Pests in Vegetable Gardens Managing Insect and Mite Pests in Vegetable Gardens John A. Jackman Professor and Extension Entomologist The Texas A&M University System Vegetable gardening can be an entertaining pas- eration time, about a week under good condi- time and a source of fresh, homegrown produce. tions, and their numbers can increase rapidly. Producing your own vegetables adds to the When pests seem to appear in large numbers enjoyment of consuming them and may also be almost overnight, they have either flown in or cheaper than purchasing produce. are reproducing rapidly. However, growing your own vegetables can be As insects grow, they change size and shape. challenging. One of the challenges is successful- This process is called metamorphosis. Some ly dealing with pests, especially insects. This insects damage plants in both the immature and publication discusses some of the management adult stages. Because insects change form, they alternatives that vegetable gardeners can use to may be difficult to identify and their damage deal with insects and other pests and provides may change with them. Small caterpillars may information on insecticides that are registered barely scrape the surface of a leaf, while larger for use in home gardens. caterpillars may eat great chunks of leaves. An insect’s mouthparts often determine the type Understanding Insects of damage expected from a pest. Insects with Although there are about 30,000 species of sucking mouthparts feed by piercing leaves or insects in Texas, fewer than a hundred are rou- fruit. Damage appears as pock marks or mottled tine pests in vegetable gardens. Actually, most leaves. Insects with chewing mouthparts chew insects in gardens are either incidental or bene- holes in plant tissue. Recognizing how an insect ficial organisms that contribute to pollination, feeds also helps a gardener select the proper the balance of nature or recycling of organic insecticides — stomach poisons for chewing matter. A garden with an abundant supply of insects or contact poisons for sucking insects. insects may actually be quite healthy and pro- ductive. However, some pest species can reduce Plan Ahead the quantity and/or quality of the vegetables When planning a vegetable garden, anticipate produced or transmit plant diseases from one the pests that may occur later. Consider the plant to another. Consider control measures management practices for specific pests before when insects threaten a garden. they become a problem. Implement the manage- Identify the insects in your garden to determine ment plan in plenty of time to deal with the whether they are beneficial or pest species. pest problems. Use past experience as a guide to Learn to recognize the common insects in your anticipating pests for the upcoming season. area, especially the common pests, and the signs of pest damage, and inspect your garden at least Integrated Pest Management once per week to detect pests. Integrated pest management — IPM — is a phi- Insect pests can enter vegetable gardens by losophy of managing pests by using a combina- walking or flying. Flight especially allows many tion of control techniques. IPM balances the insects great mobility, and their movement in goals of economic production and environmen- large numbers is possible. Moreover, certain tal stewardship when implementing control pests such as aphids and mites have a short gen- practices. IPM is the overriding strategy for 3 most of production agriculture today, and it is many modern varieties is not well known rapidly being adopted in urban environments as because of the need to test new varieties as they well. become available in the marketplace. Monitoring or scouting crops for the presence Recently, researchers have altered the genetic and abundance of pests is an important part of material of some field crops and vegetables such IPM. IPM programs typically reserve the use of as tomatoes, potatoes and corn. These are called insecticides for situations where a pest is known transgenic plants. Dramatic results can be achiev- to be present and the numbers are high enough ed when genes for resistance to insects are incor- to justify the cost of control practices. porated in the new varieties. Most of the insect- resistant transgenic vegetable varieties incorporate Although many other insect control practices genes of the bacteria, Bacillus thuringiensis, mak- can be implemented as part of an IPM program, ing them resistant to caterpillar pests. This resist- the use of insecticides is generally included as a ance is an antibiosis effect that inhibits the control option. When alternate control practices growth of caterpillars on these plants. Resistant are substituted for insecticides, the IPM transgenic vegetable varieties are expected to approach is much like organic gardening. become increasingly available to homeowners. Many of the control practices available for home vegetable gardeners are categorized in the fol- Biological Control lowing sections. Biological control is the use of one organism to control another. Three approaches to biological Cultural Control control have been successfully implemented: im- Cultural control consists of physical garden portation, conservation and augmentation. Impor- management practices that reduce pest impact. tation requires bringing a parasite or predator This may include crop rotation, cultivation, from a foreign country into our country to con- weed management, water management and trol a pest species. Importation is highly regulat- proper fertilizer use. For some pests, it is effec- ed and is generally beyond the scope of home tive to interrupt the life cycle of the pests by vegetable gardeners, although we all benefit from leaving acreage fallow for a period or by rotat- importation programs performed by research ing crops. Always remove plant debris from a groups. garden area because it can harbor pests. Control The conservation approach to biological control weeds because they can attract insects that may is encouraging natural enemies that are already feed on vegetables. Some pests of landscape present in an area. Conservation methods are plants may also move into vegetable gardens. useful in home gardens. They include planting Host Plant Resistance nectar-producing flowers that provide food for parasites and avoiding unnecessary pesticide Vegetable varieties differ in susceptibility to applications. Conservation also includes selecting insect pests, a response called host plant resist- pesticides that are toxic to a pest but relatively ance (HPR). Resistance can be expressed as tol- non-toxic to beneficial insects. erance, non-preference or antibiosis. Tolerance is the ability of a plant to grow and produce Augmentation is the release of additional preda- even with insect damage. Non- preference is tors and parasites, such as ladybird beetles, prey- exhibited when an insect chooses to feed on or ing mantids and parasitic wasps, into the natural lay eggs on alternate varieties or host plants. populations of biological control organisms. How- Antibiosis is the ability of a plant to kill or slow ever, many of these organisms occur naturally in development of a pest, usually with chemicals the environment, and any additional benefit from that occur naturally in the plant. such releases may be marginal. There are many commercial sources of biological control agents. Extensive trials are needed to understand the HPR of vegetables. Most variety selection Biological control should not be considered an emphasizes other factors, such as appearance, instant solution to pest problems. Generally, a taste and production volume. HPR status of sound biological control program needs to be 4 supported by careful study. Proper identification Labeled insecticides may or may not be effec- of pests, careful selection of beneficial organisms tive in killing pests that are mentioned on a and increased monitoring are all necessary for product label. The number of products available success. Biological control solutions cannot be for use in home vegetable gardens and the rapid implemented for all pest situations because bio- turnover in the market makes it difficult to logical control agents are not available for every know the efficacy of products available to gar- pest. deners. The response of pests can also change as they become tolerant or as environmental fac- Mechanical Control tors interact with a chemical. Furthermore, pes- Mechanical control is the use of physical means ticides may fail because a user did not read the to reduce the number of insects or their dam- label and/or calibrate the application equipment age. Mechanical methods include the use of bar- and, consequently, applied the wrong amount of riers, covers, high pressure water sprays and product. hand picking of pests. The USER is always the person responsible for Barriers come in many shapes and sizes to pre- the proper use of any pesticide. It is illegal to vent the movement of pests onto plants. use a product in a manner or situation that is Cardboard or plastic cylinders around the base not defined on a pesticide label. of transplants are an example of a type of barri- Product labels may carry a number of restric- er that discourages cutworms and other soil tions that must be considered by the user. inhabiting pests from attacking transplants. Labels include limits on product rate, number of Cloth or plastic screening can prevent the inva- applications per season, specific crops, method sion of pests into a newly planted garden. of applications, days from last application to Screening may raise the temperature of a plant- harvest and other items. There are numerous ing bed, often an additional benefit. Screening is trade names for generic insecticides, and special most useful for young plants and seedlings that restrictions may be noted on a specific label. Be are most susceptible to pest attack. sure to read the label for additional restrictions High pressure water sprays are another mechan- and follow the directions carefully. ical control method. These are most effective The EPA approves pesticides for use on a partic- against small, soft-bodied pests such as aphids.