Spruce bud scale attack several types of spruce

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.

Spruce bud scale (Physokermes piceae) is usually found mainly on Norway spruce, but it will attack other spruces. This past week, I found a pretty heavy population in a field of Colorado blue spruce and Norway spruce. We noticed this population because the trees were coated with “glistening” honeydew. Spruce bud scale may often go unnoticed since their size and color can cause them to be mistaken for buds. They are round, reddish-brown in color and are often clustered in-groups of three to eight at the base of new shoots. Lower branches are more often attacked than higher branches. Severe infestations can produce lots of honeydew that will allow sooty mold to grow.

On trees that are already weak or stressed, severe infestations may cause lower branches to die. There is only one generation per growing season. Young females overwinter on the underside of the needles. In the spring, females move onto the twigs to complete their development. Usually, we see eggs hatch and tiny crawlers move around the twigs and branches in June or early July (700 to 1,150 GDD base 5). With insect activity being ahead of schedule, growers should be checking your fields now. As with other scale insects, wait to apply treatments until you find the crawlers are active.

spruce bud
Photo 1. Spruce bud scale.

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