The brownheaded ash sawfly is a fairly new insect to Colorado. The green, worm-like larvae chew the leaves of ash trees in spring.
Weather is the most important natural control.
Late spring frosts and strong winds may kill large numbers of them. If necessary, brownheaded ash sawflies are easily controlled by almost any Garden insecticide, including soaps. Many can also be dislodged by a strong jet of water from a hose. In recent years the brownheaded ash sawfly, Tomostethus multicinctus , has become a common insect pest along the Front Range. It appeared in the Arkansas Valley area by the early 1980s.