Making Your Garden Vegetables Less Susceptible to Insect Damage is part one of three in the Garden Bugs series.
How can I keep “bad bugs” out of my garden?
How can I attract “good bugs” to my garden?
How can I control slugs and other soil insect pests?
What insect pests are common to Alabama?
How can I control insect pests without insecticides?
The best way to manage insect pests in the home vegetable garden is to use a combination of strategies, including cultural, mechanical, and biological controls. Organic gardeners rely totally on nonchemical methods. Most home gardeners can
tolerate some insect damage on their vegetables; consequently, they are able to use many nonchemical control strategies that can reduce, but not always eliminate, insect damage. Home gardeners not opposed to using chemicals may use chemical controls when nonchemical methods do not provide sufficient levels of control.
Modern pest management relies on “planning before planting” rather than responding to a pest problem after it has occurred. For example, you can prevent many insect pest problems by using what you know about the pest to make the vegetable planting less suitable for pest development. This could mean planting early to avoid high pest numbers that occur late in the season.
Correct identification of insect pests infesting the vegetable garden is critical so you can develop a management plan. Equally important is recognition of beneficial insects. Your county Extension agent can help you identify pests and develop management strategies for specific pest and crop situations.
In home vegetable gardens, insecticides should be used only as a last resort to prevent serious insect damage. Insecticides kill beneficial insects as well as harmful insects. You may not even notice that these “good” insects are present, but if they are destroyed, pest insect populations can increase to very high numbers.
You can reduce or eliminate the need for insecticides in your garden by using a variety of techniques. The best approach to successfully control garden pests is to use a combination of techniques.
Healthy soil will produce plants better able to resist insects and disease. Before planting your garden, turn over the soil and add organic matter such as manure or compost to supply essential nutrients. Organic nutrients are released slowly, in contrast to synthetic fertilizers which provide “quick-fix” nutrients.
It’s a good idea to have your garden soil tested to determine if soil nutrients and pH are suitable for growing vigorous plants. Soil testing can be done for a nominal fee; contact your county Extension agent for more information.
Some plants contain or give off compounds that repel insects. Companion planting is the practice of strategically placing insect-repelling plants next to crops that will benefit from their repellent effects. For example, planting garlic among vegetables helps to deter Japanese beetles, aphids, vegetable weevils, and spider mites; basil planted near tomatoes repels tomato hornworms; and marigolds interplanted with squash or cucumber repel cucumber beetles and nematodes. Check the organic gardening section in your library or bookstore for books on companion plants.
Planting different kinds of vegetables in a different section of your garden each year will help reduce pest infestation. Some insect pests overwinter in the garden soil and emerge in the spring and begin searching for food. If the plant they prefer to eat is located several yards away, the insect must move to the source. Many will die along the way or fall prey to birds and other insects.
Also, many vegetables may absorb a particular nutrient from the soil. By rotating your vegetable crops each year, the soil in a particular section of the garden will have the opportunity to rest and regenerate. In general, avoid planting crops in the same plant family in the same location in consecutive years. For example, potato, eggplant, and tomato are all in the Solanaceae family, so these crops should be rotated with vegetables in another plant family, such as the squash or cucurbit family, the bean or legume family, etc.
A common practice among home gardeners is to plant a single crop in a straight row. This encourages pests because it makes it easy for them to travel from one host plant to another. If different plants are intermingled and not planted in straight rows, an insect is forced to search for a new host plant thus exposing it to predators. Diversified planting also works well with companion planting.
If given a choice, some insects will opt to feed on one plant type over another. For example, pickleworms prefer squash to cucumber, and some tomato worms prefer dill over tomatoes. With a little knowledge of host preferences, you can take advantage of this by placing certain plants where they can lure harmful insects away from the plants you wish to protect. Once the “trap plants” have become infested, the target insect can be picked off and dropped in soapy water or the entire plant can
be disposed of.
Barriers and Traps
Barriers and traps can be employed to capture or impede movement of pests. A collar made of thick paper or cardboard which is placed around the stem of a plant and pressed into the soil an inch or so deep will prevent cutworms and other burrowing insects from getting into the soil around your plants. A board or thick piece of paper painted yellow and coated with a sticky substance, such as Tanglefoot, will attract and intercept aphids, whiteflies, and other small flying insects.
Mulching is the spreading of organic matter in the garden and around plants. It is an effective method to control weeds and also serves as a refuge for predatory insects like ground beetles. Mulch also helps the soil to retain moisture and stay cool, which promotes plant vigor and tolerance to insect attack.
Add mulch to the garden when plants are 4 to 6 inches high. Grass clippings, leaves, hay, sawdust, wood chips, and compost make excellent mulches. One drawback of using mulch may be increased numbers of slugs that may feed on young and succulent plants.
Fertile soil is the foundation of a healthy garden. One of the most effective ways to enhance soil fertility is to add compost. Compost is made by mixing organic matter and allowing it to decay through a natural process. The end product is a dark, rich substance called humus which can be added directly to the soil.
The first step in composting is to build a holding bin or composter. Construct the bin from chicken wire, scrap wood, or cinder blocks. The dimensions should be at least 3 × 3 × 3 feet but can vary depending on your needs. Place the bin in a convenient location. Add leaves, grass clippings, and household vegetable food waste. Do not add animal residues as they may attract rats and raccoons. Turn the pile to aerate the material. If you turn the pile every month, humus will be ready in about 6 months.
Not all insects are “bad bugs.” Your garden and surroundings contain many insects that are actually beneficial because they feed on harmful insects. Therefore, as a gardener, you should be able to identify garden insects and determine whether they are harmful or beneficial. Many organic gardening books provide pictures of the most common beneficial and pest insects and information on how to encourage populations of beneficial insects. Another good reference book with pictures of beneficial insects is Natural Enemies of Vegetable Insect Pests by Michael Hoffman and Anne Frodsham. This book may be ordered by phone (607-255-2080) from Cornell University Resource Center. Your county Extension agent can also assist you with insect identification.
A good way to attract beneficial insects into the garden is to incorporate plants inside or adjacent to the garden that will supply alternative sources of food, such as pollen and nectar, and shelter for beneficial insects. Remember that application of synthetic insecticides can destroy the natural balance by eliminating beneficial insects. Table 1 presents a partial listing of methods to attract some of the more common beneficial insects.
Table 1. Attracting Beneficial Insects
|Name of Beneficial Insect||Prey||Methods to Attract|
|Ladybugs||Adults and larvae eat aphids, scales, mites, and eggs of some pest insects.||Grow pollen and nectar plants like dill, goldenrod, yarrow, cosmos, sweet alyssum. Spray non-crop plants with sugar water. Provide water in a pan filled with gravel during dry periods.|
|Hover flies||Larvae feed on aphids and small caterpillars.||Grow pollen and nectar plants in the Umbelliferae family. Allow some broccoli to flower. Plant tall plants like sunflower so flies can hover.|
|Robber flies||Adults capture flying insects. Larvae live in soil and feed on soil pests like grubs.||Plant flowering plants as a nectar source.|
|Ground beetles||Feed on snails, slugs, cutworms and other caterpillars, and on potato beetle eggs and larvae.||Grow pollen-providing plants. Grow dense cover crops to provide shelter. Incorporate grass or stone walkways between garden beds.|
|Big-eyed bugs, flower bugs||Adults eat aphids, small caterpillars, mites, turf pests, thrips, and other small insects.||Grow pollen and nectar plants like sweet alyssum, alfalfa, goldenrod, and cosmos.|
|Assassin bugs||Both nymphs and adults use their needle-like stylets to suck fluids from and kill aphids and other small insects and their eggs. Larger wheel bugs attack large caterpillars.||Grow perennials to provide permanent shelter plantings.|
|Lacewings (green and brown)||Larvae eat aphids, scales, thrips, mites, and eggs of some pest insects.||Plant dill, sunflowers, caraway , cosmos, sweet alyssum, and golden rod flowers. Spray sugar water on non-crop plants to attract adults.|
|Tachinid flies||Larvae are parasites of squash bugs, cutworms, Japanese beetles, and many caterpillars.||Grow plants in the Umbelliferae family and other small-flowered plants like sweet alyssum and spearmint.|
|Wasp parasites (non-stinging to humans)||Adults eject eggs inside caterpillar prey; wasp larvae develop, eventually killing the hots. Some species parasitize insect pest eggs.||Grow pollen and nectar plants in the Umbelliferae family, also mints and herbs. White clover and other legume cover crops planted adjacent to garden beds also attract parasites. Provide shelter with tall plants like sunflowers. Let some broccoli and radishes flower.|
Trade names are used only to give specific information. The Alabama Cooperative Extension System does not endorse or guarantee any product and does not recommend one product instead of another that might be similar.
Garden Bugs Series
- Making Your Garden Vegetables Less Susceptible to Insect Damage
- Managing Soil Pests in the Garden
- Managing Above-Ground Pests in the Garden