The most common borer encountered in the Grand Valley is the ash or lilac borer. This borer is a serious pest of ash trees planted throughout Western Colorado. Ash borer larvae feed under the bark and into the wood of infested trees, weakening and often killing them. Trees infested with borers that are not treated will often die.
The adult ash borer is better known as a clearwing moth since the greater part of its wings have no scales and are transparent. The clearwing moth is from three-quarters of inch to an inch and one-half long and closely mimics a wasp in their appearance and flight.
The moths emerge during the spring, mate and lay eggs, before the larvae bore into the trunks of ash trees. The larvae work their way beneath the bark of infested trees causing severe damage. Ugly scars, accompanied by enlarged or swollen areas are associated with repeated infestations. The adult ash borer emerges as early as the third week of April in the Grand Junction, Colorado area. Insecticide sprays should be applied approximately 10 to 14 days after the adults emerge for effective control.