Spruce gall midge adults are emerging

The spruce gall midge is an unusual pest found on Black Hills, white and Norway spruce.

The spruce gall midge, Mayetiola piceae, is an unusual pest that we have found on Black Hills, white and Norway spruce in the northern Lower Peninsula and Upper Peninsula. The midge, a tiny, fly-like insect, overwinters in numerous swellings that encircle the terminal shoots. Many of the swellings have a slight, pimply looking protrusion at the end where the pupa has pushed up against, and occasionally through, the outer shell; ready to emerge when they complete their development (Photo 1).

Gall on last year’s growth.
Photo 1. Gall on last year’s growth.

The adults who are emerging now in the Lake City area will mate and lay eggs on the newly developing bud (Photo 2). The bright orange, but tiny, larvae 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 throughout the season. The damage can kill individual shoots. Repeated attacks can cause brooming, a proliferation of shoots at the ends of the twig and disfigured growth (Photo 3).

Midge laying eggs in bud scales.
Photo 2. Midge laying eggs in bud scales.

Damage shoots Spruce gall midge.
Photo 3. Damage shoots Spruce gall midge.

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 in the next few weeks when the eggs begin to hatch. Make sure to get good coverage as we often begin to see this problem develop in the spray shadows where you are not getting coverage.

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