Larch Sawfly Identification and Management
By: Glen Holt, Forester - Biologist

A sawfly – a non-stinging wasp. Shoots curl as they grow during attack. Larvae occur in groups or clumps.
Complete defoliation is rare but trees may appear very thin crowned.

Most trees are very tolerant of defoliation and gererally recover during the summer, however severe defoliation over several years can weaken trees causing them to be less able to survive harsh winters.

Larvae feed on the needles for 3-4 weeks, generally in late June – early July.

Larch Sawfly is native to Europe but introduced to North America in the late 1800’s. I was spotted in British Columbia in the 1930’s.

Epidemics seldom last more than 2-years.

Management There are no insecticides registered or silvicultural methods developed for control of this insect on a forest landscape or stand setting in our Regions. The reduction of larch basal area in stands may make them less susceptible to outbreaks.

Natural control. –Factors contributing to larch sawfly mortality include parasites, predators, disease organisms, weather, flooding, and competition. Two introduced ichneuman wasps Olesicampe benefactor Hinz and the Bavarian strain of Mesoleius tenthredinis Morley have proven to be very effective in suppressing outbreak populations.

Larch sawfly populations can be reduced by raking up and burning cocoons and debris from beneath larch trees in the spring. Larvae on small trees can be picked off and destroyed when they are first noticed. Spraying with water starting at the top and working down the tree can be effective in knocking larvae off of trees. Young larvae are easily controlled with insecticides such as: carbaryl; diazinon; dimethoate; malathion and permethrin. Due to prolonged adult emergence the trees must be sprayed several times throughout the summer to achieve control.

Please let me know that you received this text and picture. Regards, Glen.