Managing Insect Pests in Vegetable Gardens

Most insects found in gardens are not pests. Many are beneficial, preying on pests or performing other useful tasks.

One of the most important strategies for dealing with insects is to learn about insect life cycles, behaviors, habitats, and diets, and to recognize which are pests and which are actually lending you a helping hand.

A combination of the following mechanical and cultural strategies usually works well to reduce damage caused by insect pests without harming beneficial insects:

Grow vigorous, healthy plants.
Evidence suggests that stressed plants are more likely to be attacked by insects and suffer from more serious damage. Too much or too little water or fertilizer can weaken plants. Pay close attention to your soil, adding lots of organic matter to build good structure, tilth, and water-holding capacity. Make sure your soil pH is within the range that your plants need. Add lime or sulfur if it needs to be adjusted. Thin plants to recommended spacings and keep weeds in check to reduce competition between plants.

Rotate crops.
Planting the same crop in the same place year after year can cause pest populations to grow, especially populations of soil-dwelling insects such as grubs, wireworms, and maggots. If planting a garden where grass grew the previous year, do not grow crops susceptible to grubs or wireworms.

Choose varieties carefully.
Choose varieties recommended for your area and look for varieties that are resistant to pests you may encounter. For example, butternut squash is resistant to squash vine borer.

Practice good sanitation.
Many pests overwinter on weeds or plant debris in or near the garden. Remove weeds and organic mulches, which can provide homes for insects, slugs, and snails.

Check transplants.
Avoid bringing insect-infested plants into your garden. Carefully inspect transplants before you buy them.

Time your plantings.
Sometimes an earlier or later planting will be less susceptible to a specific insect pest.

Handpick pests.
Drop them into soapy water to kill them.

Use barriers.
To prevent cutworm damage, plant transplants inside collars made from cardboard, roofing paper, or disposable cups with their bottoms removed. The collars should be about 4 inches tall and buried 2 inches into the soil. Squares of carpeting or tarpaper placed securely around young cabbage family plants can prevent cabbage maggot flies from laying eggs at the base of the plants.

Use row covers.
Floating row covers allow air, light, and water through to plants, but not pests. Place covers over young crops until they are large enough to fend off pests themselves, or until the pest is no longer around. (Anchor them securely with soil, wood, special anchoring pins, or other means so that pests can't sneak in.) Remove covers about 4 to 6 weeks into the season before temperatures under the covers get too hot for crops. Crops such as cucumbers, eggplants, melons, and squash need pollinating insects to set fruit, so remove row covers before plants begin to flower. Commercial covers are made from spun polyester or other synthetics and are reusable. You can also use cheesecloth.

Mulch with aluminum foil.
This may repel aphids, thrips, and other insects. This is expensive, however, and practical only on a very small scale.

Use yellow sticky traps.
This is a good way to monitor insect populations. They are seldom enough to provide control, but they do help keep whitefly populations low as long as the sticky material is replaced when insects cover the board surface.

Take advantage of natural enemies.
Learn to recognize and conserve insects that prey on or parasitize pests. Small wasps, for example, parasitize aphids, leaving bloated gold to bronze "mummies." Immature lady beetles and lacewings, which look like tiny alligators, also frequent gardens. Other "beneficials" include spiders, predatory mites, predatory bugs, predatory flies, and ground beetles.

Introducing predators, parasites, or diseases that kill pests is becoming more practical as we learn more about managing pests. Remember, however, that beneficial insects will move elsewhere if there aren't enough pests to feed on. Also keep in mind that most pesticides don't discriminate between beneficial insects and pests.

If all else fails, consider pesticides.
If these mechanical and cultural strategies don't work, pesticides may also be used as part of the pest management program. Be sure to use only the amount you need and to treat only the crops that need treating. Spot treatments are effective and may be practical for home gardeners.

Note: Even if a pesticide is botanical in origin, it may be toxic. Some botanical insecticides are more toxic than some of the commonly available synthetic insecticides.

Microbial biopesticides such as Bacillus thuringiensis (Bt), a toxin produced by bacteria that kills caterpillars, are an alternative to some chemical pesticides. Insecticidal soaps and horticultural oils are other biopesticides that may be useful for certain pests, especially aphids. Diatomaceous earth, a desiccant, is sometimes used to control insects, slugs, and snails. Once it gets wet and compacted, however, it loses its effectiveness.

Before using any pesticide, check the label. Both the crop you want to treat and the pest you are treating for must be listed on the label. If they aren't, do not use the pesticide. Follow all label directions carefully!

No matter which methods you choose, keep records of what you did and whether it was successful. Such a record should be a great help in the future when you are faced with similar pest management decisions.

Covering young crops with a fabric row cover early in the season can prevent insect damage.

Collars made from cardboard or plastic cups (with the bottom removed) can prevent cutworms from killing young transplants.

Ladybird beetle larvae feed on aphids and other plant pests.

Green lacewings are another beneficial insect you should welcome into your garden.