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Insect Pest Management in the Home Vegetable GardenGeoff ZehnderIPM Coordinator Contents:
In home vegetable gardens, insecticides should be used only as a last resort to prevent serious insect damage. Although there are other reasons (i.e., expense, health hazards) to refrain from using insecticides unless absolutely necessary, from a pest management point of view the main reason is because insecticides kill beneficial insects. You may not even notice that these Agood insects are present, but if they are destroyed, pest insect populations can increase to very high numbers. There are many ways to reduce or eliminate the need for insecticides in your garden. The best approach to successfully control garden pests is to use a combination of techniques. Healthy Soil Healthy soil will result in plants better able to resist insects and disease. Before planting, turn over the soil in the garden 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 Aquick-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 local county agent for more information. Companion Planting 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 will repel cucumber beetles and nematodes. Check the organic gardening section in your library or bookstore for books on companion plants. Crop Rotation 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 predominately 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, it is best not to plant 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 (i.e, the squash or cucurbit family, the bean or legume family, etc). Diversified Planting 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. By intermingling different types of plants and by not planting in straight rows, an insect is forced to search for a new host plant thus exposing it to predators. This approach also works well with companion planting. Trap Plants 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. Mulch 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. Mulch should be added to the garden when plants are four to six 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 in the garden that may feed on young and succulent plants. Compost 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 is to build a holding bin or composter. Chicken wire, scrap wood, or cinder blocks can be used to construct a bin. The dimensions should be at least 3' x 3' x 3' but can vary depending on your needs. The bin should be placed in a convenient location. Leaves, grass clippings, and household vegetable food waste are some of the most common materials that can be added to a compost heap. Do not add animal residues as they may attract rats and racoons. The pile should be turned to aerate the material; if turned every month, humus will be ready in about six months. Beneficial Insects As mentioned above, not all insects are bad bugs. Your garden and surroundings contain many insects that are actually beneficial because they feed on harmful insects. Therefore, a gardener 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. 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 (i.e., pollen and nectar) and shelter for beneficial insects. Remember that application of synthetic insecticides can destroy the natural balance by eliminating beneficial insects. The following is a partial listing of methods to attract some of the more common beneficial insects: Methods to Attract Beneficial Insects to the Garden
General Recommendations for Management of Soil Pests in the Garden General Recommendations Many soil insect pest populations reach high numbers in grass or turf, and home gardens are often established in areas previously covered with grass. To reduce soil insect problems, thoroughly till or spade the area well in advance of planting (30 days or more) and again just before planting. This will bring soil pests up near the surface where their chances of mortality are increased. In most cases, tilling the soil or sod in fall and early spring will sufficiently control soil insects without the need for a soil insecticide. If tilling is not an option, a broadcast soil insecticide applied properly two weeks before planting will help to control some soil insects like cutworms, wireworms and white grubs. Slugs Slugs like to feed on young seedlings and succulent parts of plants. They leave a trail of mucus on the surfaces on which they crawl. Moist, humid environments favor slug development, and slugs usually overwinter in sheltered locations outdoors. Eggs are deposited in moist areas and maturity requires a year or more. Pesticide baits (i.e., metaldehyde) are minimally to moderately effective against slugs, and are best applied late in the afternoon. Baiting in the fall after the first fall rains will target slugs before they can lay eggs. The following are suggestions for minimizing slug damage to gardens:
Cutworms Cutworms are active only at night and remain buried below the soil surface near food plants during the day. They emerge to feed at night and often cut seedlings or small stems causing the plants to fall over. Because grass and many weeds are preferred hosts, remove grass and weeds in the garden, and plow the soil well in advance of planting. Damage can also be prevented by placing a paper or plastic sleeve over the plant and pressing the bottom into the soil. Paper cups with the bottoms removed or 4" high sections of 2 gallon paper milk cartons are ideal. Place sections or sleeves around newly set transplants or newly emerged seedlings so that 1" inch is below ground and 3" is above ground. Tuna cans with the bottoms removed may also work for this purpose. Wireworms Wireworms are the slender, yellowish-brown, hard-bodied larvae of click beetles. They can survive deep in the soil for up to 5 years, and can move up to attack seed or young plants. Several wireworm species prefer plants in the grass family, and are usually not a problem unless the garden is planted into land that previously contained grasses or crops in the grass family. Turning over the soil in the fall, and again in the spring well in advance of planting will help to reduce wireworm populations. White Grubs These are Japanese and May beetle larvae that are dirty white in color with the tip of their abdomen more of a blue-black; they roll into a C-shape when disturbed . Mature grubs may reach 2" in length. They live in the soil and sometimes feed on plant roots and tubers. About the only time they are troublesome is when parts of the lawn or sod are turned under in the spring for garden use. When gardens must be planted in these areas, prepare the garden well in advance of planting. As sod is turned over, raked and prepared for planting, hand collecting of grubs is the best control. Mole Crickets Mole crickets have brown, velvety bodies with broad front legs for digging in the soil. They have large eyes and are about 1" long when mature. As mole crickets tunnel through the soil, they can disrupt the root system of vegetables. They may also feed on plant root and underground stem tissue. There are no effective soil insecticides registered for use in vegetables. Avoid planting the garden in previously grassy areas. If mole cricket tunnels are observed around plants, tamp the soil back down to restore support to the root system. Management of Pests Feeding Above-ground This section provides some non-chemical methods for management. Aphids
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Questions or comments: Dr. Geoffrey Zehnder Last revised: |
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