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article number 178
article date 10-30-2012
copyright 2012 by Author else SaltOfAmerica
A 1972 USDA Primer on Garden and Farm Insects … How Many Still Exist Today?
author not stated

AS A GARDENER, you will compete with insects and mites, diseases, nematodes, and weeds for use of the plants you grow. The complex and competitive garden environment must be considered and efficiently managed to successfully grow productive food plants or plants of esthetic and ornamental value.

Entomologists say that more than 750,000 insect species have been identified. About 10,000 of these are known noxious pests. They cause losses estimated at more than $4 billion annually. In addition, 50,000 species of fungi cause 1,500 plant diseases; over 1,800 weed species annually cause serious economic losses; and about 15,000 species of nematodes attack crop plants with about 1,500 of them causing serious damage.

Two-spotted Spider mites.

Don’t be discouraged, though. As a home gardener, you will never be plagued with all of these pests. However, to understand the problems of pest control, it is important that you recognize and appreciate the competitive nature of the garden environment.

Insects and mite pests damage plants in different ways. There are insects that feed on leaves. There are insects that suck plant juices. These latter produce damaged and dead plant tissues. They also serve as disease vectors (carriers). There are insects that bore; they attack the woody parts of plants. Finally, there are insects that live in the soil and feed on roots and other plant parts.

Insects and mites only become garden pests when they do sufficient damage to result in loss. The insect population at the damage state reaches high enough levels to kill the plant or prevent its development. Many factors affect the ability of pests to develop large populations. The reproductive potential of most insects is tremendous.

Harmful garden insects eat parts of your plants.

Adult insects may lay several hundred eggs, increasing populations as much as five-fold or more in a generation. And a generation may be only 2 to 3 weeks. The numbers of insects present fluctuate greatly for many reasons. They are affected by seasonal and weather conditions, food supply, and natural enemies.

Many small plant eating aphids plus a big bug.

Assuming that an insect or mite species is adapted to an area, the most important factor regulating populations and preventing them from developing to damaging proportions is the presence of natural enemies (parasites, predators, and pathogens).

Less than 2 percent of the known insects are pests. Many others (parasites and predators) are vital factors regulating pest insect populations. These insects are among the best friends of the gardener. In addition, more than 1,100 viruses, bacteria, fungi, rickettsia, and nematodes attack insects in their environment.

These natural enemies of pest insects regulate the fluctuations of pest populations and keep them within bounds. In other words, they stabilize the pest population. Scientists call this the species equilibrium position.

Good garden insects eat other bugs, not your plants.

When a species is stabilized at equilibrium where the numbers present are causing economic damage to the plant life in the garden, they are called pests; conversely if the equilibrium is established where the numbers present do not cause economic damage, they are of little concern and there is no need to further reduce their numbers.

Many of the insects that the home gardener sees are beneficial and destroy insects and mites injurious to the food crops or ornamental plants.

The praying mantis is a good insect … eats other bugs.

In home vegetable and ornamental gardens, very few pests will cause appreciable plant damage if parasites and predators are protected. The commonly observed aphid lion, assassin bug, lady beetle, praying mantis, and a variety of wasps are only a few of the beneficial insects which are continually working in the garden environment feeding on aphids, scale insects, mites, and a number of other pest species.

Spider mites, cabbage caterpillars, Colorado potato beetles, and aphids are common pests that attack vegetables in the home garden. If you find any of these, treat them promptly to reduce populations. Some pests of ornamental plants are spider mites, aphids, beetles, lacebugs, thrips, and scale insects.

Cabbage looper ... a very bad insect.

Chemicals remain the number one weapon for immediate control of pest insects in the home garden. They probably will remain essential for the foreseeable future. However, chemicals used unwisely not only kill the target pest; they kill beneficial insects, too. Recognition of the pest-beneficial insect relationship is necessary if you are to take advantage of the best control features of both chemical and biological control.

Before selecting and applying any chemical, be sure you can accurately identify the insect. And don’t apply chemicals unless they are absolutely necessary to prevent damage to your plants.

The time when chemicals are applied is important. You will want to eliminate the pest without killing the pest’s natural enemies. You will have better control if your application of chemicals is based on a sound knowledge of the life cycle, seasonal occurrences, habits, and development of the pest, the natural enemies of the pest, and the host plant.

You obtain maximum control with different pests in different ways. Sometimes it’s best to apply a chemical when a pest species first appears; sometimes it’s best to wait until certain numbers appear; sometimes it’s best to wait for a particular stage of development of the pest.

Often, these situations occur when natural enemies are least susceptible to the effects of the chemical. For example, aphids, scales, and mites generally first appear and become active in early spring. If you apply chemicals for scale control before the plants begin to grow and it’s early in the season for mite and aphid control, your application may have minimum effect on natural enemies.

Generally speaking, you shouldn’t treat for pests when the pest’s natural enemies are active.

Spraying a broad-leaved plant with lukewarm water is one way to remove aphids, mealy-bugs, thrips and spider mites.

Other ways to kill the pest without harming the pest’s natural enemies include making sure you mix the chemicals according to the manufacturer’s instructions, being careful to use the proper dose, and putting the chemicals on the right part of the plant.

For example, some chemicals have been developed which are taken up by plant roots or through the leaves. These chemicals only kill insects which feed on the plant; natural enemies of the culprit insect are spared. Hopefully, more of these chemicals will be developed in the future.

You should be especially careful to protect bees and other insect pollinators. They are essential for producing many garden crops. You can minimize the effects of chemicals on them by following a few simple rules:

• Use the lowest effective dose of the least hazardous chemical.
• Apply the chemical only when necessary.
• Use granular formulations when possible (generally, they are less hazardous).
• Apply the chemical in the evening when bees are not active.

There are a number of other ways to control or help control injurious insects. Many species of insects and mites overwinter on plant parts and debris left in the garden from the previous year. These species emerge early in the spring to develop populations on weeds and newly planted garden material. You should clean up all plant beds in the fall. This will prevent or reduce overwintering insect and mite populations and minimize their effect. During the growing season, weeds provide another host material for many insects. Try to keep your plant beds free of weeds.

One of the best ways to combat insects in the garden is to use plants that are resistant to attack. Plants are resistant for several reasons. They may not be attractive to the insect as food, shelter, or for egg-laying; they may adversely affect the biology of the insect; they may be able to survive despite the insects’ attack, sustaining a number of insects that would stunt or kill the more susceptible plant types. Resistant plant types are present in nature and scientists are placing greater emphasis on identifying them and incorporating their resistance into desirable horticultural types for use of the gardener.

Japanese beetle.
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