Although most home gardeners dislike using pesticides, they are sometimes compelled to do so as a last resort in order to control insects and diseases that otherwise would damage or destroy valuable trees, shrubs and flowers.

Most gardeners know that pesticides can harm humans, pets and plants--occasionally even wildlife--if they are not applied properly. It is important, then, to handle pesticides selectively, carefully and, above all, intelligently.

By law, the label of every bottle, can or package containing a pesticide must list specific directions for its use. When those directions are followed faithfully, there should be no problem.

The key to effective use of pesticides is proper identification of the pest suspected of causing the damage. Unnecessary and wasteful pesticide applications can thus be avoided. Although it may seem practical to load plants with preventive sprays, this is neither economically nor environmentally sound.

For accurate identification of pests, consult a reference book or talk to nursery people or professional pest control operators, who are licensed and registered for home-garden pest control. A number of governmental agencies--including your local county agricultural commissioner's office--can also provide assistance with identifying pests.

A second key is the choice of the material to be applied. Again, books and experts should be consulted. Sometimes, depending on the amount of damage, an expert might suggest that, rather than involving yourself in the hassle of chemicals, you live with the problem and use no pesticides at all.

Keep all pesticides in their original containers and store them only in a locked enclosure. Above all, do not store them with or near foodstuffs or pet foods. Discuss disposal of unwanted pesticides with a representative of your local agricultural commissioner's office or health office. Depositing such leftover materials in a trash container is a dangerous and illegal practice.

Q: Why do so many of the leaves on my shrubs have brown tips? --V.J., La Jolla

A: Scorching, or tip burn, of leaves can be a sign of the accumulation of high-soluble salts, caused by too much fertilizer or an excess of salts in the water supply. You should water only when the first inch or so of the soil has begun to dry out. An occasional heavy watering to leach salts out of the soil may be necessary.

Q: We live in an area that is regarded as fire-prone. Some time ago, we were told that we should surround our home with the type of shrubs and trees that tend to sprout again after drought or fire. Is that so? --H.L., West Los Angeles

A: Ground covers such as ivy, coyote bush and vinca will sprout again after having been burned over or after having suffered from lack of water. Oleander, myroporum and Canary Island pine also will sprout again, as will native plants such as ceanothus and California laurel.

Q: I don't want to kill friendly bees by spraying my flowering plants with insecticides, but I don't want to lose the plants to pests either. What should I do? --G.B., Westwood

A: Check the label on the sprays that you use and follow the directions to the letter. Spray applications made between dawn and 7 a.m. are considerably less dangerous to bees than applications later in the day.

Q: I keep a clean garden but it still has disease problems. Is there a general-purpose fungicide that will cure mildew, blight and rust?--D.S., Montebello

A: Diseases are a problem in even the cleanest of gardens--wherever humidity, temperature and light favor their development. The fungicide Bayleton is a systemic material that provides both preventive and curative control of the diseases you mention.

Questions will be answered only when a self-addressed stamped envelope is enclosed. Write to the Garden Doctor, Home magazine, Los Angeles Times, Times Mirror Square, Los Angeles 90053. Please allow at least six weeks for a reply. Plant specimens sent for determination of trouble should be wrapped and enclosed in an envelope. Boxes not accepted.

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