Trunk sprays of Dursban or permethrin are recommended for control of this insect. Trees along roadsides or in parking lots tend to be most commonly attacked. Also, there are greater problem in areas of the state, such as the Arkansas Valley where ash is more marginally adapted. Sawfly Brownheaded ash sawfly is a fairly new arrival to Colorado and has been on the move over the past decade. Original infestations appeared in the Arkansas Valley but have spread steadily northward and now can probably be found along the entire Front Range.
Damage is done by the larvae, which chew leaves in spring.
The larvae resemble a green caterpillar, usually with a pale stripe along the back. During outbreaks they can essentially defoliate ash by late May, adding a considerable stress to this most popular street tree. Numbers have been fairly low for the past three years, but this is due largely to late spring frosts, which killed the first flush of growth after eggs had been laid. However, more moderate weather this spring could allow ash sawfly to rebound quickly. First evidence of this insect are swarms of the adults around the new growth.