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|Mountain Ash Sawfly Larvae||Mountain Ash Sawfly Larva with Ruler|
|Sawfly Feeding Injury on Cherry||Adult Female Sawfly
(Photo courtesy Cliff Sadof, Entomology Department)
If you are noticing defoliation of ash, cherry, or other fruit trees, you may want to take a closer look. Mountain ash sawflies (Pristiphora geniculata) feed in groups and eat entire leaves, leaving only the midrib, and can defoliate an entire tree. Trees usually survive defoliation, but repeated heavy defoliations will reduce tree vitality and could cause death.
Adult sawflies emerge in May from cocoons located in the soil beneath trees defoliated the previous season. Females lay eggs in slits along the edges of leaves, often producing a blistered appearance. Eggs hatch in about a week. There are two generations per year -- June through early August and a smaller generation late August through September. Young sawfly larvae are greenish with black head and six prolegs on the thorax. The body is marked with black dots. When disturbed, larvae will often raise their body in a signature defense mechanism. Adults are almost one centimeter long, black, and wasp-like in appearance.
Infested branches can be pruned out and destroyed. Larvae can be treated with horticultural oil sprays and residual insecticides. Bt (Bacillus thuringiensis) is not effective against sawfly larvae.
For more information:
Plant and Pest Digital Library and Digitally Assisted Diagnosis, Purdue University, West Lafayette, Indiana.