In many parts of Illinois, now is the time to treat for pine needle scale, Chionaspis pinifoliae while Vanhoutte spirea, Spiraea x vanhouttei, is in bloom. It is during this time that the eggs have hatched into young crawlers that are moving about on plants, and these young crawlers are most susceptible to insecticide applications. Mugo, Austrian, Scots, and red pines are most susceptible to attack from pine needle scale.
Mature pine needle scales are 2 to 3 millimeters long, elongated, white scales on the needles of evergreens. Pine needle scale overwinters as eggs underneath the mated female scale cover. Females are capable of laying up to 100 eggs during their lifespan. Eggs hatch into crawlers from late April through June. Crawlers move around on the needles before finding a place to settle and feed. They withdraw plant fluids from the mesophyll layer of needles, causing the needles to turn yellow, then brown. Whole branches may be killed. Also, heavy infestations of pine needle scale can kill entire trees, particularly those pine trees that are stressed. Young crawlers may be blown onto other plants by wind--starting another infestation. There are typically two generations per year in Illinois.
As with many insect and mite pests of ornamental trees and shrubs, management of pine needle scale revolves around sustaining plant health and using insecticides accordingly. Properly implementing cultural practices--including irrigation, fertility, and mulching--minimizes stress and allows plants to tolerate low to moderate populations of pine needle scale without suffering injury. Insecticides recommended for controlling pine needle scale include acephate (Orthene), insecticidal soap, and horticultural (=summer) oil. All three insecticides are applied when Vanhoutte spirea is in bloom. Second-generation crawlers may be treated when hills-of-snow hydrangea, Hydrangea arborescens, blooms turn from white to green. Repeat spray applications 7 to 10 days later may be needed because second-generation eggs hatch over an extended period.