Over-wintering Douglas-fir midges are emerging
Douglas-fir needle midge infestations can cause severe needle loss and trees to be unsalable at harvest. Timing your pesticide application at emergence is critical for control.
Douglas-fir needle midge over-winter as larvae in the soil under trees that were infested in 2011. The adults are a small fly, about the size of a mosquito, and emerge in the spring (around 200 to 225 GDD50). We have begun to find emerging adults on yellow sticky traps in the Cadillac area (Photo 1).
Photo 1. Douglas-fir needle midge
adult. Photo credit: USDA Forest Service Archive, USDA
These adult midges will mate and females lay orange eggs in the soft needles of the expanding buds and elongating needles. Eggs hatch within a few days and the midge larvae immediately bore into the growing needles, causing elongating needles to form a gall around the larvae. The larvae hollow out the needles as they feed. Damaged needles may drop or remain on the tree. One or more white maggots can be found inside affected needles during the summer (Photo 2).
Photo 2. Douglas-fir needle midge
maggot in needle. Photo credit: Howard Russell,
MSU Diagnostic Services
At the site of the gall, the needle is frequently bent. The damaged area is initially pale-yellow (Photo 3), but as the season progresses, will darken and eventually turn brown. These needles may drop or remain on the tree. The damaged needles that remain on the tree can look similar to Rhabdocline needlecast or Cooley spruce gall adelgid. Even moderate needle loss can reduce the value of Christmas trees and heavily damaged trees may be unsalable.
Photo 3. Damage to needle from
Douglas-fir needle midge.
Photo credit: Jill O’Donnell, MSUE
Insecticides can be used to control Douglas-fir needle midge, but timing the application is critical. Time your insecticide application within a week of emergence of the adults. However, weather can impact emergence and heavy rain and cool weather can slow down the rate emergence.