68 PROTECTION OF PLANTS, 1917-18 



of poison should be used if the caterpillars are more than a few days old, and 15 

 pounds after they are one-third grown. ^ 



The first application should be made, if possible, just before the eggs hatch, 

 or at least as soon as the caterpillars appear; the sooner they are killed the less 

 the injury will be, and also the caterpillars are much less readily killed by poisons 

 after they become one-third grown, or even after a few days' feeding. Their 

 first meal should carry the poison. 



After the caterpillars have been killed by the use of poison, the trees may 

 again become infested by the older wandering caterpillars from nearby foliage- 

 While these may actually cause little injury to the foliage, they will spin their 

 cocoons on the trunks and branches and infest the trees for the following season. 

 For this reason it is necessary to band the trunks before the caterpillars begin to 

 migrate. 



Banding the Trees. 



It has already been pointed out that after the egg-masses or the caterpillars 

 have been destroyed the trunks of the trees should be banded so as to prevent 

 reinfestation by wandering caterpillars. If there is any danger of infestation 

 from hatching eggs on the ground or on objects near the trees the bands should 

 be applied before the eggs hatch, and at the latest they should be in place before 

 the migration time of the caterpillars. The date of hatching varies so widely 

 with the weather conditions of the season that no definite date can be recommend- 

 ed, but the bands should usually be in place by the middle of June, and in some 

 seasons before that time. 



Tree Tanglefoot. — Several devices for preventing the caterpillars climbing 

 the trees, such as bands of cotton, burlap, metal and various sticky substances, 

 have gradually given place to the sticky mixture known as "Tree Tanglefoot," 

 which may be obtained in bulk from any dealer in insecticides. A fair substitute 

 may be made by boiling together equal parts of castor oil and resin. 



The tanglefoot is applied with a wooden paddle so as to form a complete 

 ring about the trunk, 4 inches wide, from 5 to 8 feet from the ground. Before 

 the mixture is applied the surface of the trunk on which the application is to be 

 made should be scraped unless the bark is already sufficiently smooth. The 

 tanglefoot gradually hardens on the surface, and it is therefore advisable to break 

 its surface by scraping it over with a coarse comb at intervals of ten days or two 

 weeks. Instead of applying the tanglefoot to the bark it may be spread upon a 

 strip of canvas or burlap fastened around the trunk. 



^ The powdered form of lead arsenate is used at one-half these strengths. 



