Why Insecticides Don't Sometimes Fail to Work

By The Old House Web

Why Insecticides Don't Sometimes Fail to Work

Correct timing and thorough application of sprays

You can use the best, most effective insecticide in the world, but if you don't apply it to a plant thoroughly and at the proper time, you can expect poor results. To give its best performance, an insecticide must be applied when pests are present and vulnerable, and at the proper rate in sufficient gallonage to permit thorough coverage of the upper and lower surfaces of the leaves and branches. For best results, it must be repeated as often as needed.

Correct timing of sprays is important. For example, the eastern tent caterpillar, a pest of wild cherry and apple trees, begins its feeding about the time the buds are breaking on these trees and the leaves are starting to unfold. This is very early in the spring. By early summer, the caterpillars have completed their development and disappeared from the tree. If you wait until early summer to spray, the treatment would be of little value because the damage to the trees would have already occurred.

Another point to remember is that an insect is much easier to control when it is young. The older the insect, the harder it is to kill. An example is scale insects, which are a problem on many ornamental plants. The most effective time to control scale is immediately after the larvae have emerged, while they're in the crawler stage. During this stage, which may last only about a week, the tiny scale is unprotected and easily killed by even the less toxic insecticides. Once the larva secretes a protective covering over itself, it is very difficult to kill, even with toxic insecticides.

Wrong insecticide used

No insecticide will control every insect. If you use the wrong one, even though you apply it properly, the results will be disappointing. If you want the best results, you need to use the proper insecticide for your particular pest. The insecticides and miticides in the plant list are those that have proven most effective against the pests named.

Weather effects

Most insecticides do not perform efficiently at temperatures below 50 degrees F and will not give satisfactory results if used at or below this temperature. Rain will wash an insecticide off a plant so that it is ineffective against insects. Wind will alter the coverage by a spray, preventing the spray from reaching the target and often carrying the spray into areas you did not intend to spray. For the most part, it is best to apply an insecticide when the temperature is above 50 degrees F but below 95 degrees F, and when no rain is expected for at least 12 hours.

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