The Lilac Ash Borer
With the great number of lilac and ash trees in the Valley, the lilac-ash borer is a pest to be on the look out for. This wasp like insect lays eggs in cracks and wounds in the bark, which hatch then bore into the trunk. The larvae feed in the cambium then burrow deeper to over winter. The larvae return to the cambium in the spring to continue feeding then emerge as adults to mate and lay eggs in early summer. Both the feeding and burrowing weaken the tree and may lead to death or breaking.
Why here and now?
As the insect’s name implies, this species likes both lilacs and ash trees, which have been planted extensively throughout the Valley. While the lilac-ash borer does not require both species to complete its life cycle, it thrives when both are present. Furthermore, insects are attracted to stressed trees planted in marginal sites. Many ash trees are planted in medians and streetscapes, also known as marginal sites, offering limited opportunity for root expansion. Furthermore, because of the need to mow these narrow strips of grass, mowers and trimmers have wounded most of the ash trees. These wounds weaken the trees and create points of entry for pests and pathogens.
What can be done?
While there is ongoing debate about the success of controlling lilac-ash borers already in a tree, there is little debate on the efficacy of preventative spraying. Preventative spraying will protect trees that have not been impacted and prevent additional hits to those that have been impacted. Furthermore, increasing a tree’s vitality through feeding, pruning, proper watering, and mulching will help a tree survive in marginal sites. Utilizing an integrated pest management program that focuses on increasing trees’ health while reducing their exposure to pests is vital to the success of all the trees in the Valley.
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