Temperature becomes important in the application of insecticides only when it is extreme. Most materials are effective at ordinary temperatures. Nicotine sulfate is an exception, as it kills insects much better at temperatures above 75 F., partly because of increased fumigating action. There is danger of injury to fruit or foliage if some materials are used in hot weather, although their effectiveness is not lessened. There is also danger of injury from oil sprays if followed by extremely cold weather.

Rains may wash off insecticides that are soluble in water, and their effectiveness is lost. Most of our modern insecticides are not especially soluble in water. Most of them are available in a form that adheres well to fruit and foliage. Their effectiveness is not reduced so much by ordinary rainfall as is sometimes supposed if the application has become thoroughly dry before it rains. Hard, driving rains, however, will remove much of the insecticide from exposed surfaces. This may be the reason why it is necessary, for example, to spray more often with DDT to control the codling moth in the Midwest, where rainstorms occur in summer, than in the drier parts of the Northwest, where such storms are infrequent. Dusts are removed more extensively than sprays by rains.

Trees or other plants may be sprayed when they are damp, but it is best not to spray them if they are dripping wet. The presence of dew or other moisture on plants is sometimes a help when dusting; it causes the dust to adhere better than if the surface is dry. A light spray of water has been used experimentally with a dust to increase its adherence.

The condition of the plant itself may often influence the effectiveness of an insecticide. Some plants or fruits grow faster than others, and fast-growing plants, such as potatoes, requite more frequent applications than those that are growing slowly. Some grow more rapidly at one season than at another. The surface area of apples, for instance, may double within 2 weeks early in the season, although later on it may not double in less than 3 months. The surface, if it is to be kept covered with an insecticide, must be sprayed or dusted more often in the early part of the season than later.

Any very smooth or waxy leaf or fruit surface is not easily coated with insecticides. Cabbage leaves are especially difficult to cover thoroughly with liquids. Dusts often adhere better to such surfaces. Rough or hairy surfaces are more easily covered with either dusts or liquids. The shape and density of the foliage is a factor, too. Very heavy foliage interferes seriously at times with getting an insecticide to the pests.

A PERSON who is not familiar with insects and insecticides will do well to consult his county agricultural agent about the pest that is bothering him and the best insecticide for it.

The home gardener also can get a great deal of practical information from the label of the insecticide he buys. Such directions usually suggest mixing certain amounts of the concentrated insecticide material in a given amount of water. That may require mixing the insecticide on a weight or volume basis. Scales that weigh small amounts in ounces or a few pounds are useful. For measuring a given volume of dust or liquid, users should have on hand measuring equipment for teaspoonfuls, tablespoonfuls, and cupfuls, pints, and quarts. For safety and convenience, it is recommended that such measuring equipment be provided and used only for mixing insecticide materials.

Mixing large quantities of spray is usually just a matter of using one or more packages, the net weight being given on the label. For small amounts of spray there is no rule-of-thumb that may be followed because materials differ greatly in specific gravity. Some packages have a dilution table on the label. If there is none, perhaps the easiest way is to have the insecticide dealer determine the weight of a tablespoonful, cupful, or pint and record those details on the label for future reference. Tables of equivalents for various quantities of spray will be found in the appendix to this volume.

The old saying, "If a little is good, more is better" does not hold true in the use of insecticides. The use of excessive amounts is wasteful, expensive, and often injurious to the plants, animals, or soil.

Sometimes one can combine various insecticides, insecticides and fungicides, or insecticides and fertilizers and save time and money in so doing. Again, though, it is well to read the labels of the preparations or consult official publications or competent authorities before making those mixtures at home. Many compounds are not compatible, and harmful combinations may be formed when they are mixed.

The same equipment can be used for applying insecticides, fungicides, and herbicides, but one should be aware of the danger of using spray equipment for insecticides and fungicides that has been used to apply weed killers. Ordinary rinsing of the sprayer is not enough to remove the weed killer completely. The sprayer, hose, and nozzle should be washed carefully with a suspension of activated charcoal, 1-3 ounces per gallon of water, or the sprayer should be filled with a solution of household ammonia, 2 tablespoonfuls per quart of water, and allowed to soak for 24 hours. If that cannot be done, a separate sprayer should be used for herbicides.

In summary, some points to be followed in using insecticides:

If the insect is not known to you, find out what it is from the county agricultural agent, extension entomologist, or similar authority.

Recommendations for the proper insecticide to be used on a given pest may be obtained from those authorities, from State or Federal publications, from entomologists representing insecticide manufacturers, or from pest-control operators.

Prepare and use the insecticide in accordance with recommendations. Read the label. Follow precautions and other directions carefully.

Do a thorough, careful, but not wasteful job of application. The proper insecticide, proper application, and proper timing are of equal importance.

Store insecticides in a safe place.

Clean up and care for dusting and spraying equipment as you would with any good piece of machinery.

E. J. NEWCOMER is an entomologist in the Bureau of Entomology and Plant Quarantine. He has been associated with research on the control of the insect pests of deciduous fruit trees since his graduation from Stanford University in 1911, most of the time in the State of Washington.

W. E. WESTLAKE, a chemist in the Bureau of Entomology and Plant Quarantine, works chiefly on problems concerning insecticides for fruit insect control in the State of Washington. He has degrees from Montana State College and the University of Minnesota.

B. J. LANDIS is an entomologist in the Bureau of Entomology and Plant Quarantine. Since 1941 he has been in charge of the Union Gap, Wash., field laboratory of the division of truck crop and garden insect investigations, and has carried on investigations of potato insects.

Tarnished plant bug.