Juniper webworm spins webs across the foliage of juniper and feeds upon it, turning the foliage brown. Generally, damage is more severe in northern Illinois than in the rest of the state although the pest can be found farther south. Severe damage causes all the foliage to turn brown, and loss of the plant can result.
Moths emerge to lay eggs at or near shoot axils in June in central Illinois and early July in northern Illinois. The young larvae feed within the needles as leafminers, with each larva mining several needles. Later in the season, they emerge from the needles to feed on the surface of needles, spinning silk around their feeding areas. Typically, about three caterpillars are present in each mass of silk webbing. The caterpillars are slender, with dark brown stripes and a tan to medium brown body. They are about 1/2 inch long when fully grown. They overwinter in these silk masses, emerging to feed again in the spring. Most of the webbing and heavy feeding occurs in the spring before they pupate.
Control the caterpillars at this time with sprays of acephate (Orthene), Bacillus thuringiensis kurstaki (Dipel, Thuricide), carbaryl (Sevin), or spinosad (Conserve). Use heavy pressure to force the insecticide into the interior foliage of the plant where many of the caterpillars are located and to penetrate the protective silk webbing.