One of the safest on the market are those containing Bacillus thuringensis , a bacterial derivative that is effective specifically against caterpillars. The toxins produced by the bacteria is ingested by the larvae and destroys the digestive tract of the caterpillar. The product, commonly called B.t. is marketed under the tradenames of Dipel, Thuricide, Bactur, or Bioworm. It is safe to use on fruit and nut trees and on other caterpillars like cabbage loopers that attack vegetables. Also, be fore-warned that diazanon is no longer labeled for use on pecan trees.
Complete coverage is needed for good control.
A high pressure sprayer may be necessary for to reach the tops of trees or to penetrate dense webs. Breaking up the webs with long poles prior to spraying may increase contact of the insecticides with the larvae and increase effectiveness. It may be necessary to use a commercial tree spraying service for large trees or heavy infestations. Insecticide labels change frequently. Make sure you read and follow the label directions on the container for use and precautions.