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Lilac/Ash Borer

A common wood borer found on ash trees throughout Colorado, the lilac/ash borer is native to North America.  Aside from ash trees, damage less commonly occurs to lilac and privet.  Damage most commonly occurs in trees that have been recently transplanted or are grown in less than ideal conditions including those experiencing drought like conditions.  Lilac/Ash borer damage is caused by the larvae feeding into the wood on the tree.  Females lay eggs along the lower portion of the tree trunk and upon hatching the larvae being to bore into the tree.  Damage ranges from distortion, irregular growth and excessive branching to weakened lower branches and trunks that may result in breakage or death of the tree.  Well established trees receiving adequate amounts of water are typically insignificantly damaged.  Larvae are creamy white grubs with a small dark colored head.  The presence of abdominal prolegs separates lilac/ash borer larvae from other wood borer type beetle larvae that are found on ash trees.  Exterior evidence of a lilac/ash borer infestation includes irregularly shaped round holes on the exterior of the bark where the adults will emerge from typically from mid-April through mid-May. Adults are look-alikes to paper wasps in size, coloration and markings.  Lilac/ash borer control is available in the form of sprays applied to the trunk and lower portions of the at risk trees in order to kill larvae before they enter the trunk.  Pheromone trap monitors are available for placement in order to determine when adult lilac/ash borers have begun their flight for the year in order to time treatment with the time when eggs will be present and hatching along the bark.