Spruce gall midge
Editor’s note: This article is from the archives of the MSU Crop Advisory Team
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The spruce gall midge, Mayetiola piceae, is an unusual pest that we have found on Black Hills spruce in the northern Lower Peninsula and the Upper Peninsula. The midge, a tiny fly-like organism, overwinters in numerous swellings that encircle the terminal shoots. Many of the swellings have a slight nipple or protrusion (see photo 1) at the end where the pupa has pushed up against (and occasionally through) the outer shell; ready to emerge when they complete their development.
The adults which are emerging now in the Lake City area will mate and lay eggs on the newly developing bud. The bright orange, but tiny, larvae (see photo 2) hatch within a couple of weeks and bore into the shoots to feed on plant juices. In response to the feeding, plant tissue swells up around the larvae to form the galls. The larvae continue to feed through out the season.
The damage can kill individual shoots (see photo 3). Repeated attacks can cause brooming, a proliferation of shoots at the ends of the twig and disfigured growth. (See photo 4)
Fortunately, a tiny parasitic wasp is a common natural enemy and chemical control is not normally needed. Inspect your trees in the early spring for signs of the galls. If found, prune those shoots out to remove the insects before they can emerge. Prune the shoots back to a side bud or lateral shoot. Be sure to burn or otherwise destroy the shoots you prune out. If damage is really severe, you miss the time to prune, and damage is so bad that you feel you must use a chemical product, treat the newly developing shoots in the next few weeks prior to egg hatch. Make sure to get good coverage.