Inside their nests, these tiny caterpillars are well camouflaged and protected from the effects of most pesticides. Remove the nests by hand if they are few in number or spray your juniper with a pesticide containing Bacillus thuringiensis, commonly known as Bt. Bt works best on young, actively feeding caterpillars, and will not be very effective if the nests are much larger than a quarter inch in length and the caterpillars are nearly full grown. Fortunately, the juniper webworm completes its life cycle long before junipers finish their spring growth spurt. Even heavily damaged junipers can quickly cover early spring damage with new growth.
Gypsy moths are on the increase in many parts of the country.
Apply a sticky barrier around the trunks of trees to intercept them before they eat the leaves. Hatchling caterpillars that originate from eggs on other trees and vegetation in the area will get stuck in the barrier and die. Apply wide masking tape around the tree and then apply sticky barrier material, available at garden centers and hardware stores, on the surface of the tape. You can trap the caterpillars that originate from eggs laid on the tree by tying a swath of burlap above the sticky barrier. Caterpillars seek the shelter of the burlap during the daylight hours.