Joe Julian, Colorado State University Cooperative Extension Agent, horticulture and entomology
For many of us, the answer to garden pests still rests in chemical sprays or powders.
Before resorting to any treatment, it's important to find the cause of the problem. Insects or diseases are not always the culprits. If the problem is caused by environmental factors or human mismanagement -- as often is the case -- spraying will do nothing more than add another chemical to an environment already overloaded with pesticides.
What can the homeowner do to help reduce the use of pesticides? Most important is to identify plant problems and take recommended measures to correct them. Be aware that the wisest measures may call only for judicious use of pesticides or for no pesticides at all.
What are pesticides? What role do urbanites play in their overall use? Pesticides are compounds that have been made to interrupt and destroy living systems. They include insecticides, fungicides, herbicides, rodenticides and miticides.
About 20 percent of all pesticide use is by urban industry and government. Homeowners use an additional eight percent. This means that consumers in congested urban areas such as Denver are applying more than one-fourth of the pesticides in use. We tend to spray first and think later.
Sometimes we make serious mistakes. We may spray a systemic insecticide (one that is transported throughout the plant) on edible fruits and vegetables. We sometimes spray for weeds during the hottest part of the day when herbicide drift or volatilization can damage other garden plants, including our neighbor's. We use pesticides that can kill helpful as well as harmful insects.
We also overuse on the theory that if a little is good, more must be better. This leads to disruption of the biological balance by causing pesticide runoff into water, killing fish and contributing to pollution. Applying too much also encourages genetic resistance by insect pests.
How can we reduce the use of pesticides?
One way is to ask your local Cooperative Extension horticulturist to identify pest problems. By looking at a plant sample and determining appropriate procedures, pesticide use almost certainly will be reduced.
Suggestions may include monitoring plants for insects or diseases to catch the culprits in action, identifying beneficial insects to avoid their destruction or, if spraying for aphids, ensuring coverage on the underside of leaves where aphids hide.
A variety of environmentally sensible products are available. Two-to-four tablespoons of dish soap mixed with a gallon of water creates a safe, effective insecticide against small, soft-bodied insects and mites on vegetables--and the soap does not harm beneficial insects. A repeat application may be necessary every four to seven days.
Homeowners often use carbaryl (Sevin), but it is ineffective against most sucking insects and is toxic to honeybees and beneficial insects. Carbaryl also causes blossoms to shed on apples, hence should not be used when apples are in bloom. Soaps are an effective substitute for carbaryl in most cases.
Bacillus thuringiensis (Bt) products, sold under a variety of trade names, also provide safe control in the vegetable garden against cabbage worms, hornworms and other pests that evolve from caterpillars into moths or butterflies.
Some products are "natural" or "botanical," but this does not mean they are completely safe in the environment. Rotenone, for example, is a botanical insecticide used to control chewing insects, but it also is toxic to fish. Pyrethrum is a botanical insecticide derived from chrysanthemums, but it can produce allergic reactions in some people. It remains on plant foliage only briefly, however, so it can be used almost to harvest time.
The wise use of pesticides depends on public awareness of long-term health and environmental hazards. Contact your Cooperative Extension office for help in identifying plant and disease problem which, in turn, gives homeowners some control over protecting their environment.
Photo: Judy Sedbrook
© CSU/Denver County Extension Master Gardener 2010
888 E. Iliff Avenue, Denver, CO 80210
Date last revised: 01/05/2010