Issue 12, August 11, 2014

Spruce Bud Scale

We have been seeing more spruce bud scale problems this year in Illinois. It is well-named, as the scale is located at the base of twigs and is similar in appearance to swollen buds. Mature scales are reddish-brown and rounded, about one-eighth inch in diameter. They commonly are coated with a whitish bloom.

Needles on attacked spruces are light green to yellow which eventually drop from the tree. Twigs, branches, and even entire trees can be killed. Lower branches and twigs are much more likely to be attacked than the upper part of the tree. The scale is more common on stressed, unthrifty trees than healthy trees. The drought of 2012 may have caused the current increase in the state.

Spruce bud scale is a soft scale, so it produces large amounts of honeydew. Black sooty mold grows on the honeydew. A good way to scout spruces with off-color needles for spruce bud scale is to look for blackened twigs and needles from sooty mold. Then check twig crotches for scale.

Crawlers are produced in mid-summer when Hydrangea arborescens 'Grandiflora' blossoms begin to turn from white to green. There is one generation per year. Effective crawler sprays include insecticidal soap, summer spray oil, bifenthrin (Onyx), cyfluthrin (Tempo), and acephate (Orthene). Because this scale does not mature until spring, treatment at this time of year may provide some control and save trees that are too heavily infested to survive until crawler hatch next year. Dormant oil sprays during the winter may also provide some control. Spray oils are likely to discolor foliage. (Phil Nixon)

Phil Nixon

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