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Larry Sagers
Spider mites feed on plants instead of other mites and insects. Gardeners usually don't notice them until weather gets hot and dry.

When it comes to pests in your garden, having none is better than having some, and having some is better than having many.

Preventing pests — rather than controlling them after they attack your plants — is the best of all.

A common question many gardeners ask is, "Where do all these pests come from?"

While the answer varies, in most cases pests are always there. There are some 50,000 kinds of insects in Utah and more than 1 million kinds in the world.

They are the most numerous creatures in existence and would overrun the world if it were not for one simple rule — that is that most insects stay alive because they eat other insects. Their predatory nature helps keeps them in check.

Getting back to prevention leads us to the concept of Integrated Pest Management, or IPM. The purpose of IPM is to manage pests to keep them from building up to damaging numbers as opposed to constantly spraying to try to totally eliminate the pest.

Embracing IPM is a way to minimize pesticide use and still have a successful crop. It requires you as the gardener to learn about the life cycle of the pest and to learn about when that pest is vulnerable to control.

Several plant pests attack both ornamental and fruit plants, and now is the time to prevent them from becoming a serious problem.

Utah is home to more than 600 kinds of aphids, all of which suck plant juices and keep them from growing well. Some aphids feed on the bark, but most feed on the newly emerging leaves. When aphids start feeding on the underside of newly emerging leaves, the top of the leaves continue to grow.

Eventually, the distorted leaf curls backward and protects the aphid inside. Once the leaves are curled, conventional insecticides are no longer effective because the insects are not where the spray will come in contact with them. Aphids attack many woody plants, and some, such as the woolly apple aphid, look more like bits of cotton or dryer lint than insects.

Scale is another pest you should control. You might not recognize this pest because it looks more like a part of the plant than an insect. This pest attaches itself to the plant and secretes a waxy coating over its body. This armor protects the pest from predators and most sprays.

Spider mites are not insect spiders — spiders that have gone bad. They feed on plants instead of other mites and insects. They attack almost any garden plant, but we usually don't notice them until the weather gets hot, dry and dusty.

The reason preventive sprays are emphasized is that in late winter and early spring the predators that control pests are still dormant. Normally, insect predators don't become active until after their prey has built up large populations. Intervening now allows you to knock out the potential pests before their numbers build.

Dormant oil sprays — which prevent aphids, scale and spider mites — are one of the oldest and most useful sprays for preventing serious outbreaks.

Insects breathe through tiny openings in their hard exoskeletons. Oils control insects because they coat the pests, plug these holes and prevent them from breathing. Oils kill by contact. They never kill insects that crawl on branches previously sprayed with oil, nor is there residual toxicity to pests, so timing is essential.

Another important feature of the oil sprays is that they kill both the eggs and the adult insects. Most pesticides have no effect on eggs. Some creatures hide inside plant buds, so let the buds crack open before spraying them.

Stone fruits are sprayed when flower color begins to appear on the end of the bud. Apples are sprayed when the green tips are clearly visible on the leaf buds. Apply the spray to your ornamental plants as they open their buds but before they bloom.

Most lawn and garden pesticide manufacturers package oil sprays. Brand names include Volck, Superior, Supreme and Scalecide. Mix the oil with the water according to the label directions.

Apply this preventive treatment as needed to keep plants pest free. This treatment is the only effective way to prevent the leaves from curling on fruit trees as well as flowering plum, cherry and snowball, or viburnum and other highly susceptible plants.

Larry A. Sagers is the horticulture specialist, Utah State University Extension at Thanksgiving Point.