In the Casper area, the Ash Borers attack green or white Ash trees, European Mountain Ash, and Lilacs. The larvae bore into the wood of the host plant, creating holes in the trunk and main crotch area leading to swelling and cracking of the bark. Die-back of specific branches are then observed mid-summer or the following spring after the attack. A borer hole made by the larvae creates an entry for secondary infections by insects and disease organisms. Death to the host plant can occur if attacks go unchecked for continuous years.
Ash trees that are grown in a street or landscaped environment are highly susceptible to borer attack. Trees in unthrifty conditions from low fertility, drought, or defoliated by leaf eating caterpillars are especially vulnerable.
The insect over winters as a nearly mature larvae in the trunk of the host plant. In the spring the adults (wasp like moths) emerge, mate, and begin laying eggs on the host trees. The eggs hatch in approximately ten days and the larvae tunnel into the host plant. There is only one generation per year.
A spray application of Acme Borer spray or Astro can be applied to the trunk of the tree. Three times at two-week intervals, beginning approximately June 15th. The tree can also be injected with Bidrin or Dendrex by a certified arborist once a year, around mid June through the end of June, keeping the tree free if destructive insects and utilizing a good fertility program will keep the tree healthy.
If the tree has been attacked, it should be injected with Bidrin or Dendrex by a certified arborist. If the tree is in an unthrifty condition, a multi-nutrient should also be injected into the tree to give it a boost. In late fall or early spring the tree should be deep root fertilized with the above preventative measures taken the following spring.