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Fall is the Time for Insect and Disease Prevention for Next Year

By Laura Pottorff, Colorado State University Cooperative Extension agent, horticulture, plant pathology

If you are tired of gardening and are anxious for the seasons to change -- hold it! First you need to do some fall "yardkeeping" to prevent the potential for insect and disease problems next year.

Fall clean-up

Dead plant material can harbor many insects and disease-causing organisms, such as fungi, during the winter months. That's why it's a good idea to remove vegetable and annual flowering plants as soon as they are through producing and blooming. Perennial plants also will benefit by the removal of dead limbs or branches.

Clean-up will help prevent next year's leaf spot diseases, such as early blight of tomato, powdery mildews and rust diseases. Insects such as squash bugs, plant bugs, asparagus beetles, flea beetles, slugs and aphid eggs also can be controlled by removing plant debris.

Aspen trees with rust disease, for example, will display leaves that turn black. The leaves will show small orange or yellow spots on their undersides. When all these leaves drop to the ground, rake as many as possible and throw them away. By doing this, you'll greatly decrease the amount of disease that occurs the next year. Raking up leaves alone, however, may not give 100 percent control, but is a vital part in the management process of this disease.

Do not compost diseased or insect infested plant material. Temperatures in the compost pile often are not hot enough to kill these organisms.

Turning over or tilling the soil

Turning over or mixing layers of soil in vegetable and flower gardens is beneficial for many reasons. Not only will this incorporate plant debris that wasn't removed during the clean-up process, but tilling also helps enrich the soil by speeding up the decay of organic matter. Most important, it disturbs or injures overwintering pests or exposes them to freezing and natural enemies.

Working the soil will help reduce populations of fungi that cause root rot diseases as well as cutworms, white grubs and grasshopper eggs.

Examination of woody perennial plants

Examine all ornamental and fruit-bearing tree, shrubs, and vines. Plants that were damaged by last October's freeze will be prime targets for insect and disease infestation. Prune out any dead branches that were killed by last October's low temperatures. Dead or damaged stems and branches often attract insects and diseases. Also prune out branches killed by insects such as scale or canker diseases. Cankers are sunken areas on the stem, usually of a different color than surrounding bark.

Note heavy aphid, scale or spider mite infestations. If perennials were injured by these insects this past growing season, consider an application of dormant spray oil this winter or early next spring before new foliage appears.

You can prevent most insect and disease problems by a combination of good management practices. When pest problems do appear it is essential to obtain an accurate diagnosis from a qualified specialist before starting any kind of pesticide treatment. Your local Colorado State University Cooperative Extension office offers this service along with non-biased research-based information, free or for a minimal charge. For more information, call your local cooperative extension office.

Photo: Judy Sedbrook

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Date last revised: 01/05/2010