Introduction

Vegetable gardening can be an entertaining pastime and a source of fresh produce that is difficult to surpass. Producing your own vegetables adds to the enjoyment of consuming them and may be lucrative compared to purchasing produce. However, producing your own vegetables is sometimes challenging. One of the challenges is successfully dealing with pests, especially insects. This publication provides information and discusses some of the management alternatives that vegetable gardeners should consider when dealing with insects and other pests.

Understanding insects

There are about 30,000 species of insects in Texas. Fortunately, less than a hundred are routine pests in vegetable gardens. Actually, most insects in gardens are either incidental or beneficial organisms contributing to pollination, the balance of nature, or recycling of organic matter. Contrary to some opinions, a garden with an abundant supply of insects may actually be quite healthy and productive. However, pest species can reduce the quantity or quality of the vegetables we produce or may transmit plant diseases. Control measures should be considered when insects are a threat to the garden.

Identification of insects in your garden is important to determine if they are beneficial or pest species. Learn to recognize the common insects in your area, especially the pests. Recognizing damage from pests is also useful to help identify the pest.

Insect pests can migrate into vegetable gardens by walking or flying. Flight especially allows many insects to have great mobility and their movement in large numbers is possible. Moreover, certain pests like aphids and mites have a short generation time of about a week under good conditions and their numbers can increase rapidly. One of these two methods of increase are usually underway when pests seem to appear in large numbers almost overnight.

As insects grow they change size and shape and this process is called metamorphosis. Some insects damage plants in both the immature and adult stages. Because insects change they may be difficult to identify and their damage may change with them. Small caterpillars may barely scrape the surface of a leaf while the same caterpillar may eat great chunks of leaves when they are larger.

Mouthparts are often a key to understanding the type of damage expected from a pest. Insects with sucking mouthparts feed by piercing leaves or fruit. Damage appears as pock marks or mottled leaves. Insects with chewing mouthparts can be expected to chew holes in plant tissue. Recognizing feeding type also helps select the proper insecticides, like stomach poisons for chewing insects.

Plan ahead

Anticipate the pests that may occur when planning a vegetable garden. Consider all management practices that will help deal with the pests before they become a problem whenever possible. Implement the management plan in plenty of time to deal with the pest problems. Use past experience as a guide to anticipate pests in the upcoming season.

Integrated Pest Management

Integrated pest management, IPM, is a philosophy of managing pests with the use of multiple control techniques used together to produce a crop or manage an environment. IPM balances the goals of economic production and environmental stewardship when implementing control practices. IPM is the overriding strategy for most of production agriculture today and is rapidly being adopted in the urban environment as well.

Monitoring or scouting crops for the presence and abundance of pests is an important part in the decision process of IPM. Most IPM programs reserve the use of insecticides for situations when the pest is known to be present and the numbers are high enough to justify the cost of return on the investment in control practices.

Many specific insect control practices can be implemented as part of an IPM program but generally the use of insecticides is included as a control option. When alternate control practices are substituted for insecticides, the IPM approach is much like organic gardening. Selection of a particular control practice is determined by the manager. Many of the control practices available for home vegetable gardeners are categorized in the following sections.

Cultural control

Cultural control consists of a variety of management practices that impact pest numbers including such things as crop rotation, cultivation, weed management, water management, and good fertilizer use. Many of these practices impact pest numbers even though the impact may not be considered. Opportunities to interrupt the life cycle of pests with fallow periods and crop rotation should be implemented for several pests. Always destroy plant debris that can harbor pests. Keep weeds under control because they attract insects that may feed on vegetables.

Host plant resistance

Vegetable varieties differ in susceptibility to insect pests and this response is called host plant resistance (HPR). Resistance can be expressed as tolerance, non-preference, or antibiosis. Tolerance is the ability of the plant to continue to develop and produce even with insect damage. Non-preference is exhibited when an insect chooses to feed on or lay eggs on alternate varieties or host plants. Antibiosis is the ability of a plant to kill or slow development of a pest usually with chemicals that occur naturally in the plant.

Extensive variety trials are needed to understand the HPR of vegetables. Most variety selection is done emphasizing other factors like appearance, taste, and production volume. HPR status of many of our modern varieties is simply not know well.

Recently, transgenic plants have been developed for field crops and some vegetables including tomatoes, potatoes, and corn. Transgenic plants have their genetic material altered and dramatic results can be achieved when genes for resistance to insects are incorporated. Most of the resistant transgenic vegetable varieties incorporate genes of the bacteria, Bacillus thuringiensis, and are resistance to caterpillar pests. Resistant transgenic vegetable varieties are expected to become increasingly available to homeowners.

Biological control

Biological control is the use of one organism to control another. Three approaches to biological control have been successfully implemented: importation, conservation, and augmentation. Importation requires foreign exploration for a parasite or predator that can be introduced into our country to control a pest species. Importation is highly regulated and is generally beyond the scope of home vegetable gardeners although they do benefit from successful importation programs that have been completed by various research groups.

The conservation approach to biological control is the perpetuation or encouragement of natural enemies that are already present in the area. Conservation methods have good potential for impact in home gardens. They include the providing nectar-producing flowers that provide food for parasites and the avoidance of unnecessary pesticide applications.

Augmentation is the release of additional predators and parasites to contribute to the natural populations of biological control organisms. Releases of ladybird beetles, preying mantids, parasitic wasps, and various other organisms can contribute to biological control. However, many of these organisms occur naturally in the environment and the additional benefit contributed by releases may be marginal. There are many sources of biological control agents available through commercial channels.

Biological control should not be considered an instant solution to pest problems. Generally, a sound biological control program needs to be supported by careful study and increased knowledge. Proper identification of pests, careful selection of beneficial organism, and increased monitoring are all necessary for success. Biological control solutions can not be implemented for all pest situations because biological control agents are not available for every pest.

Mechanical control

Mechanical control is the use of physical means to reduce the number of insects or their damage. Several mechanical methods are available including the use of barriers, covers, high pressure water sprays, and hand picking of pests. Barriers come in many shapes and sizes and prevent the movement of pests onto the plants.

Cardboard or plastic cylinders around the base of transplants are an example of a barrier which discourages cutworms and other soil inhabiting pests from attacking transplants.

Cloth or plastic screening can serve as a cover to prevent the invasion of pests into a newly planted garden. Screening may increase the temperature of a planting bed so additional benefits of temperature management may be achieved. Screening is most useful for young plants and seedlings when they are most susceptible to pest attack.

High pressure water sprays are also a mechanical control method. These are most effective against small soft-bodied pests like aphids. High pressure water sprays may help remove webbing, dissolve droppings, and reduce the number of pests in a short time. It is one of the few options available when vegetables are near harvest.

Hand picking and destruction of some pests may be feasible especially in small gardens. Hand picking can be successful for tomato hornworms and even squash bugs if persistently done. Obviously, hand picking is more feasible for larger insects than for small insects.

Chemical control

Pesticides come in many forms and provide a wide array of tools for pest management. Pesticides are regulated for safety by the Environmental Protection Agency, and the sale and use of these products is regulated by the Texas Department of Agriculture. These agencies do not consider efficacy, or "how well it works", in the registration process but concentrate on safety issues instead. The number of products available for use in home vegetable gardens and the rapid turnover in the market makes it difficult to know the efficacy of products available to gardeners. The response of pests can also change as they are selected or as environmental factors interact with a chemical treatment.

The USER is always the person responsible for the proper use of any pesticide. It is illegal to use a product in a manner or situation that is not defined on a pesticide label. Therefore, the user needs to read the product label thoroughly and follow directions specifically. Table 2 is a list of the product labels that were reviewed to develop the information in this guide. It is not an exhaustive list but includes most of the common active ingredients available for use in home gardens. Use this list as a guide when purchasing products for use in home vegetable gardens.

There are numerous trade names for some generic insecticides and special restrictions may be present on the labels. Read the label carefully. Space limits the number of labels included herein.

Insecticide registration by EPA is approved for use on a particular crop and registration on a crop should be a primary consideration for safe pesticide use. Table 1 summarizes the chemicals registered by vegetable. There are many products with more than one active ingredient and only a few of them were reviewed and included here. The list of products with multiple active ingredients is potentially quite large.

Product labels may carry a number of restrictions that must be considered by the user. There are limits on the product rate, the number of applications per season, specific crops, the method of application, and the days from last application to harvest are some of these limits. Be sure to read the label for additional restrictions and follow the directions carefully.

Product labels also have a suggested list of target pests on the label. A summary of the chemicals available for use in home gardens is included as Table 1. This list was prepared from product labels and not all products have been examined by the Texas Agricultural Extension Service. Your results may vary depending on the environmental conditions, method of application, and other factors.

Pesticides vary widely in their hazard to humans and the environment. The key words on the label, e.g., CAUTION, WARNING, and DANGER, are an indication of the product toxicity. Use this information on your product label as a guideline on product use and potential hazard.

Insecticide products can be categorized by their compound class. Insecticide classes provide a key to understanding the mode of action of the product and thus the pests that are most likely controlled by the product. When insect control is unsatisfactory it is wise to change to a product from another compound class (See table 3).

Less Toxic Approaches

Many gardeners prefer to use less toxic approaches to insect management rather than standard insecticides. Individual philosophy varies about these approaches and opinions differ on what should be considered as management options. Less toxic approaches range from selecting "soft" insecticides to natural control with no action. There are increasingly more products available for the use by organic gardeners than ever before. These products generally carry the CAUTION signal wording on the label and may be sold along side more traditional pesticide products that also carry the CAUTION word on the label. Some of the products that could be considered less toxic are included in this guide if they are registered and sold as pesticides.

Less toxic chemicals are becoming available under different legal registrations. Chemicals listed in the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) EPA Title 40, Chapter 1, Subchapter E, Part 152.25 which are considered "minimum risk pesticides" and are exempt from FIFRA registrations. This list includes: cedar oil, citric acid, citronella, cloves, garlic, lemongrass oil, mint, peppermint, rosemary, thyme, white pepper, and several other products. For a complete list of these products see FIFRA. These products may be sold as repellents, e.g., Garlic Barrier, Hot Pepper Spray.

PUTTING IT ALL INTO PRACTICE

Here are a few tips and practices that should be considered for any garden.

PLANT A GARDEN OF MANAGEABLE SIZE

Garden size directly affects control methods that work for individual plants or small gardens. Hand removal of pests and swabbing pests with alcohol may not be feasible in larger gardens. The larger the garden the more need there may be for insecticides.

LEAVE THE GARDEN FALLOW BEFORE PLANTING

Insect pests such as white grubs, wireworms and cutworms over-winter in the soil and feed on abandoned plants or weeds. Remove these food sources during the off season to reduce pest numbers before spring planting.

GOOD SANITATION

Remove dead leaf piles, boards, railroad ties and other objects where pests such as cutworms, slugs, snails, pillbugs, sowbugs and other pests congregate. Mulches are often used to maintain moisture and provide shelter for spiders and predatory insects. However, mulch also provides shelter for pests.

SELECT PEST-FREE TRANSPLANTS

Inspect plants at the store to be sure they have no pests. Most common insect and mite pests can be found on the under surfaces of leaves. Purchase only healthy pest-free transplants.

SELECT PEST-RESISTANT VEGETABLE VARIETIES

Some vegetable varieties are unattractive or resistant to certain pests. Planting resistant varieties adapted to your area can dramatically reduce the need for insecticides. For example, the sweet corn variety 'Seneca Sentry' is resistant to corn earworms and is adapted to central Texas. In this variety, the leaves that wrap around the corn ear tip are much tighter around the silk than in more susceptible varieties. Unfortunately, the pest resistance status of only a few vegetable varieties is known.

PRACTICE GOOD HORTICULTURAL METHODS

Properly prepare the soil before planting. Thorough tilling of the soil will kill many soil insects and provide good growing conditions for seedlings and transplants. Healthy plants will be less susceptible to severe pest damage. The composition of the soil and spring growing conditions (weather) also affect pest populations. Soils with high organic matter are more likely to support white grubs, root maggots, pillbugs, and sowbugs, even though these soils may promote better plant growth.

Keep a weed-free garden. Weeds supply food for insect pests. They also compete with vegetable plants for soil nutrients and water, and can decrease vegetable yield considerably. Keep weeds out of the garden and keep grass mowed short around the garden to discourage insects such as grasshoppers and armyworms from moving in.

Fertilize properly. Plants need adequate nutrients to grow well. Without them, plants may be slow growing, stunted and more susceptible to pest damage. However, using too much fertilizer can produce lush green plants that attract insects such as aphids.

Water properly. Either too much or too little water can be unhealthy for plant growth. Drought-stressed plants are more likely to attract spider mites.

INSPECT PLANTS FOR PESTS AND PROPERLY IDENTIFY THEM

Learn to identify the various insects and other creatures encountered in the garden. Many of them are actually beneficial. County Extension Agents can be helpful in identifying plant pest problems. Avoid treating undiagnosed problems. Pests attack garden plants from seed to maturity. Inspecting plants weekly or more often helps you detect pest infestations early, monitor natural enemies and evaluate the effects of control tactics. Check the undersides of leaves for aphids, whiteflies and spider mites, as well as egg clusters of armyworms, Colorado potato beetles and squash bugs. To detect low populations of spider mites and thrips, beat plants on a piece of off-white paper. The pests can be seen and identified on the paper. Although yellow sticky cards are occasionally promoted as insect control devices, they are best used to monitor pest activity. These cards attract to the winged adult stages of aphids, leaf miners, thrips, whiteflies and a wide variety of flies. Cards should be inspected and replaced regularly so that pests can be detected early and their numbers monitored. Sex attractant chemicals called pheromones are also available commercially to monitor many insect pests especially moths.

CONSIDER ALL PEST SUPPRESSION METHODS

When a pest outbreak occurs, consider how it might have been prevented and the best method of reducing pest numbers to a tolerable level.

Reflective mulches. Highly reflective mulches such as foil paper slow infestation by some pests such as aphids.

Barriers. Young plants or transplants are vulnerable to attack by cutworms, sowbugs or pillbugs. They can be protected by placing a barrier around the base of each plant. Barriers can be made of cardboard, plastic or metal containers with the bottoms cut out.

Barrier screens over the garden. Fine mesh screens or fabrics can provide a barrier through which even tiny insects such as thrips can not cross. Several products are used to cover and protect crops. This method works best in early spring or fall when frost is a possibility. When barriers are properly maintained, insects can be excluded. However, plants should still be monitored regularly, which requires removing the barrier.

Cages and trellises. Plants growing on the ground are susceptible to soil pests. Vine plants such as cucumbers and even tomatoes are easier to manage when grown in trellises or cages. It is easier to monitor pests and spray plants thoroughly when they are held up off of the ground.

High pressure water sprays. Small pests such as aphids, spider mites and others can be dislodged from plants with high pressure water sprays directed to the undersides of leaves. Commercial spray devices are now available (Water Wand and Jet-All Water Wand), but these devices also can be homemade. Care must be taken not to harm the plant or to distribute pests around the garden. Repeated treatments may be necessary to keep pest numbers low.

CONSERVE NATURAL ENEMIES AND PROTECT BEES

The first line of defense against insect pests is their natural enemies. Spiders, praying mantids, lady beetles, ground beetles, green lacewings, ambush bugs, assassin bugs, minute pirate bugs and even some wasp species prey upon insects. However, the most effective natural enemies are the tiny parasitic wasps and flies, together with bacteria, fungi and viruses that are rarely observed with the naked eye. Whether naturally occurring or released into the garden, these organisms should be preserved and encouraged to thrive. Do not use pesticides except as a last resort; allow natural enemies an opportunity to suppress the pest infestation. Should a pesticide be required, wherever possible select the least toxic, most target-specific pesticides that decompose quickly in the environment.

Natural enemies can be released in the garden to control pests. Lady beetles and green lacewing larvae eat aphids and whiteflies; predaceous mites eat two spotted spider mites; and certain wasps parasitize certain insect pests (Trichogramma species develop inside caterpillar eggs; and Encarsia species develop inside immature whiteflies). Companies that sell these natural enemies do not guarantee the results, particularly in outdoor sites. Factors such as the number of pests present, the environment, timing of releases, prior pesticide use and the presence of ants can affect such releases. Parasitic nematodes (Biosafe 100 and other products containing Steinernema carpocapsae) are available to control a wide variety of vegetable garden soil pests.

Bees are necessary for pollinating vegetables such as cucumbers, pumpkins, squash and melons and should be protected. Don't apply pesticides while bees are active during the day. Instead, treat plants early in the morning or late in the afternoon. Avoid using products or formulations highly toxic to bees. If a bee hive is located nearby, cover it during pesticide application or arrange to have the hive protected from pesticide drift.

PROPERLY APPLY PESTICIDES ONLY WHEN JUSTIFIED

If a pest population becomes too damaging and other control measures have failed, a pesticide may be required. Pesticides are regulated by law and must be applied strictly according to label directions. Pesticides can be toxic, and must be used carefully to reduce risk of negative side effects.

To control leaf-feeding insects effectively, the pesticide must thoroughly cover the undersides of leaves. This is difficult to do with dust-formulated products. When using liquids (emulsifiable concentrates, wettable powders), mix the directed amount with water and spray immediately. Alkaline water will decompose the active ingredients of some products if the solution is allowed to stand. Agitate the mixture while treating. If spray droplets bead up and roll off the treated foliage, a spreader-sticker may be necessary. After treatment, clean the sprayer thoroughly, store pesticides properly and wash protective clothing separately from other laundry.

The user is always responsible for the effects of pesticide residues, as well as problems that could arise from drift or movement of the pesticide to neighboring areas. ALWAYS READ AND CAREFULLY FOLLOW THE INSTRUCTIONS ON THE CONTAINER LABEL. Proper disposal of left over pesticides and "empty" or used containers is an essential step in safe pesticide use.

POLICY STATEMENT FOR MAKING CHEMICAL CONTROL SUGGESTIONS

The Texas Agricultural Extension Service bases its suggestions for pesticide use on:

Product registration status;

Avoidance of residues in excess of allowable tolerances;

Avoidance of toxicity to desirable vegetation and animals, and to humans; and

Avoidance of adverse side effects upon beneficial predators and parasites, honeybees, fish and other wildlife, plants, animals and humans.

Suggested pesticides must be registered and labeled for use by both the Environmental Protection Agency and the Texas Department of Agriculture. The status of pesticide label clearances is subject to change and may have changed since this publication was printed. County Extension agents and appropriate specialists are advised of changes as they occur.

Table 1. Registered Pesticides for Use on Home Garden Vegetables, and Common Insect Pests.

Only some of the more common pests and vegetables are listed herein.

NA means that no specific pre-harvest interval information was found on the label.

P means that the application is a pre-plant soil application. Such applications are generally for pests in the soil.

S means that the application is allowed on the soil only and not on the vegetable plants directly. This is usually only for baits.

Product labels found in trade channels were the primary source of information in this table. This includes many, but not all, of the products available to the home vegetable grower. A list of the products reviewed during preparation of the guide are included in table 2. Only a few products with a mixture of two or more active ingredients where reviewed for this guide. Multiple active ingredients complicates the summary so these were not included in the listing in this table.

The column with pesticides registered on the commodity is a list of the common name of the chemicals that have that particular vegetable listed on the label. Pesticides registered by pest is similarly the pesticides that have that pest on the label. The user should be aware that the pesticide may not specifically state the combination of commodity and pest on a particular label. The user is responsible for reading the label and following directions on the label.

Pests sometimes have several common names. Additional common names for the same pest are given in parenthesis. Some labels have a general common name for a pest group. This group is listed under the pest name and specific examples are listed behind the colon. In a few cases the adult and immature form have different common names and control measures. The control measures for each stage are indicated in the table or both names are listed separately with different control measures. An example is cucumber beetles with immatures called rootworms. This example actually includes several species that can be damaging in Texas with adults that feed on flowers and foliage and larvae that feed on roots.

Additional pests

Ants - Several ant species can be found in vegetable garden with fire ants and Texas leafcutting ants being the most severe pests. Ants should be controlled outside the garden if possible. Bait formulations or individual mound treatments are preferred. Inside the garden use a mound drench of boiling water if this is feasible.

Snails and slugs - Products containing metaldahyde are the primary control measures for snails and slugs. These products are typically granular baits or pastes.

Grasshoppers and Crickets - Grasshoppers and crickets may move into gardens rapidly, especially when winged. When these pests are abundant, protecting foliage with an insecticide may not be very successful. Insecticides like carbaryl are generally preferred. Bait formulations with carbaryl and metaldahyde are available for this situation. Treating the premises outside of the garden may help. Use barriers to protect the most valuable plants.

Sowbugs, pillbugs, millipedes, centipedes, mole crickets, cutworms, and earwigs are considered soil insects. These pests are typically controlled with pre-plant treatments of insecticides incorporated into the soil. Typical treatments are granular formulations of diazinon or chlorpyrifos which are watered into the soil.