Managing Insect and Mite Pests In Vegetable Gardens

Gardening should be fun! It should also be a continuous learning experience and allow for endless experimentation. Unfortunately, in Texas there are many insects and related pests that also will enjoy your garden. Their damage can interfere with growing acceptable produce. There are several approaches to dealing with insect pests. Natural control merely allows nature to run its course; whatever vegetables survive are harvested. Organic gardening stresses plant health through the use of natural fertilizers; controlling pests with cultural, mechanical and biological methods; and using only pesticides of natural origin (botanical insecticides, microbial insecticides and insecticidal soaps and oils).

The Texas A&M University System advocates the philosophy of Integrated Pest Management or IPM. This philosophy is similar to organic gardening except that it does not rule out the judicious use of synthetic insecticides. IPM is a way of keeping pest populations below intolerable levels by using a combination of suppression tactics that are: 1) least disruptive to the environment; 2) socially acceptable; 3) most effective; and 4) least expensive, particularly in production agriculture. With the IPM approach, farmers and gardeners keep an eye on pest populations and the beneficial insects that are their natural enemies with routine monitoring or scouting. This helps them decide when control measures are needed.

Here are several good management practices for the home garden:

Plant a Garden of Manageable Size

Garden size directly affects pest management. Control methods that work for individual plants or small gardens (such as removing insects by hand or swabbing them with alcohol) may not be feasible in larger plantings. The larger the garden the more need there may be for insecticides.

Leave the Garden Fallow Before Planting

Soil-inhabiting insect pests such as white grubs, wire worms and cutworms over-winter in the garden, where they feed on abandoned plants or weeds. Removing these food sources during the off season can greatly reduce pest numbers before spring planting. Good sanitation is important, too. This includes removing dead leaf piles, boards, railroad ties and other objects where pests such as cutworms, slugs, snails, pillbugs and sowbugs congregate.

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 undersurfaces 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 insecticide. For example, the sweet corn variety 'Seneca Sentry' is relatively resistant to corn earworms and is adapted to central Texas. In this variety, the leaves that wrap around the corn ear are much tighter around the silk than in more susceptible varieties.

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 maggot species, 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 rob vegetable plants of 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. Both too much and 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 undersurfaces 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 offwhite 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 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.

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. This method works best in early spring or fall when frost is a possibility. When barrie rs 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, difficult to monitor for pests and almost impossible to spray thoroughly with water or other solutions. Viney plants such as tomatoes are easier to manag e when grown in trellises or cages.

• 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 undersurfaces of leaves. Commercial spray devices are available (Water Wand&# 153; 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, preying mantis, 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 twospotted spider mites; and certain wasps parisitize certain insect pests (Trichogramma species develop inside of caterpillar eggs, and Encarsia species develop inside of 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, the 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 and 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 the 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 follow carefully the instructions on the container label. Proper disposal of leftover pesticides and "empty" or used containers is an essential step in safe pesticide use.

Table 1 includes the generic names of pesticide ingredients registered by the -EPA to control specific pests. Table 2 indicates the crops for which pesticides are registered. By combining the information in both tables, the reader will be able to select an insecticide for each specific crop/pest combination.

Different formulations of products containing the same active ingredients may be registered for different crops and pests. This listing summarizes the registrations of many products. The USER of any pesticide is responsible for properly applying the product according to label information about the specific crop(s) and pest(s) for which the product is labeled. According to the Federal Insecticide, Fungicide and Rodenticide Act, the USER can legally apply a pesticide to attempt to control any pest provided that the usage site (crop) is listed on the product label. However, neither the product manufacturers nor The Texas A&M University System will assume any liability for problems associated with the use of a product not in strict accordance with instructions on the label.

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 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. Vegetable Garden Pests, Damage, Vegetables Attacked and Suppression Alternatives.

Table 2. Crop Registration Status for Insecticide Ingredients.

Table 3. Generic Insecticide Names and Examples of Product Trade Names.

The information given herein is for educational purposes only. Reference to commercial products or trade names is made with the understanding that no discrimination is intended and no endorsement by the Cooperative Extension Service is implied.

Educational programs conducted by the Texas Agricultural Extension Service are open to all people without regard to race, color, sex, disability, religion, age or national origin.

Issued in furtherance of Cooperative Extension Work in Agriculture and Home Economics, Acts of Congress of May 8, 1914, as amended, and June 30, 1914, in cooperation with the United States Department of Agriculture. Zerle L. Carpenter, Director, Texas Agricultural Extension Service, The Texas A&M University System.

20M-10-93, Revision

ENT

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Last modified: July 22, 1997 by Edgar Cross