Tiny "Bags" Hang on Branches
Bagworms - Small spindle-shaped bags hanging like Christmas ornaments from Juniper branches are bagworm cases. Each case is woven of silk and bits of needles, and houses a caterpillar. Dark brown with white or yellow heads, these bagworms carry their bags with them as they feed. They can kill a tree if left uncontrolled. A fully developed bag is about two inches long and protects up to 1000 eggs over the winter, which hatch out the following spring. During the winter, hand-pick the bags from the shrubs and burn them.
Leaves And Twigs Webbed Together
Webworms - Juniper webworms are 1/2 inch long and brown, with longitudinal reddish brown stripes. The adult females, moths with 3/5-inch wingspans, appear in June and lay eggs that hatch in 2 weeks. The pests overwinter in the immature larval stage. Webworms spin webbed nests which enclose Juniper leaves and eventually kill them. Hand-pick as many of these nests as possible and destroy them.
Foliage Curls; Turns Yellow
Aphids - Check Juniper stems and needles for small groups of soft-bodied, pear-shaped, reddish-brown insects a little bigger than the head of a pin. These are aphids, which suck sap from leaves and stems of Junipers, causing the needles to yellow. These insects also secrete a sticky "honeydew" on the foliage that coats it. It encourages sooty mold fungus, which then coats the leaves in black.
Small Bumps On Leaves and Twigs
Juniper Scale - Scale insects form groups of small bumps or blister-like outgrowths on stems and leaves. These are waxy shells that protect the insect feeding beneath. Early in the season they are white, then they dull to gray, then black, and are about 1/10 to 2/5 inch in diameter. Scale insects usually appear on Juniper twigs, where they join branches, or close to growing tips. They cause needles to turn yellow, and secrete honeydew, which covers leaves and encourages sooty mold.
Galls on Leaves; Branch Tips Die Back
Rust - A disfiguring disease caused by the cedar apple rust fungus sometimes covers Juniper branches with bright orange galls. These swellings, an inch or more in diameter, appear on Junipers that are near infected apple or crabapple trees (the disease needs both Junipers and apple trees to complete its life cycle). Leaves are infected during the summer, and by the following June they develop green swellings. By fall, the swellings have turned into a chocolate-brown circular gall. The next spring the galls form many long, yellow to orange "horns", especially during warm, rainy weather.
Spores released from these horns infect apple leaves, which fall prematurely. Infected Juniper branch tips die, but the shrubs are usually not seriously affected. Prune out galls in early April before the horns develop.