In many parts of Illinois, it is time to treat for pine needle scale, Chionaspis pinifoliae. Generally, egg hatch occurs when Vanhoutte spirea is in bloom. The young crawlers, which move around on the plant, are susceptible to insecticide applications. Mugo, Austrian, Scots, and red pines are most susceptible to attack by pine needle scale.
Mature pine needle scales are small (about 2 to 3 millimeters long), elongated, white scales on the needles of evergreens. The eggs overwinter underneath the mated adult female scale cover. Females lay up to 100 eggs. The eggs hatch into crawlers from late April to June. The crawlers move around on the plant foliage before finding a place to settle and feed. They extract plant juices from the mesophyll layer of needles, which causes the needles to turn yellow, then brown. Whole branches may be killed; heavy scale infestations can kill entire trees. The young crawlers may be blown onto other plants by wind. There are two generations per year in Illinois.
Pine needle scale management involves maintaining plant health and using insecticides. Properly implementing cultural practices--including irrigation, fertility, and mulching--minimizes stress and allows plants to tolerate low to moderate populations without suffering injury. Insecticides recommended include acephate (Orthene), insecticidal soap, and summer oil. These materials are applied when Vanhoutte spirea is in bloom. Second generation crawlers can be treated as hills-of-snow hydrangea blooms turn from white to green. Repeat spray applications 7 to 10 days later because the second-generation eggs hatch over a longer period. Be careful when applying summer oil, as it may discolor foliage.