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Spruce Bud Scale

June 26, 2002

In southern and central Illinois, the eggs of spruce bud scale, Physokermes piceae, are hatching; crawlers are out and about, looking for a place to feed. In a couple of weeks, they will hatch in northern Illinois. This scale attacks a wide range of spruce species, including Alberta and Norway.

Mature females are rounded, gall-like, reddish brown, and 1/4-inch in diameter. They are generally found in clusters of three to eight, located at the base of new growth or branchlets. Because they closely resemble spruce buds, they are difficult to detect. Lower branches are more likely to be infested with higher populations. With high populations, entire branches may be killed. Stressed or weakened trees generally have higher scale numbers, compared to healthy trees.

Spruce bud scale overwinters on the underside of spruce needles as young crawlers. In late spring, the crawlers move around, and females migrate to twigs and finish their development. Eventually, the female dies with eggs retained within her body cavity. In June, the eggs hatch, and crawlers move around on twigs or branches and eventually settle down to feed. Spruce bud scale is a soft scale, producing copious amounts of honeydew, which serves as a medium for black sooty mold fungi. Also, the large quantities of honeydew attract bees. There is one generation per year in Illinois.

Treat for spruce bud scale in mid-June and July or when Hills-of-Snow hydrangea blooms are turning from white to green. Pest-control materials recommended include acephate (Orthene), diazinon, insecticidal soap, and summer oil. Apply when crawlers are active; however, be careful when using summer oil, as this may discolor foliage.

Author: Raymond A. Cloyd


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