Is there a way to treat an ash tree under attack?
We have an ash tree that has multiple holes from an insect. The bark is peeling off, and during the summer months, wasps are attracted to the tree. Our neighbor across the street lost an ash tree last year to the same ailment, but never removed the tree. Ours is not dead yet, but I am wondering if we should remove the tree before it fully dies. I would hate to be allowing the spread of these critters to other trees in the neighborhood. It still produces leaves, but they may be starting to thin. Or is there a way to treat this?
The borer you are referring to is probably the Lilac/Ash Borer (LAB), as the much-feared Emerald Ash Borer (EAB) has yet to be found in Denver. LAB is common along the front range, and tends to affect trees that are stressed from drought, damage or neglect. A stressed tree is easier for an insect to invade than a healthy tree. The adult stage of LAB is a clearwing moth that lays eggs, then in the larval stage the insect bores a hole and overwinters inside the tree. It then emerges the next spring as an adult, and the cycle continues. It is the larvae stage that is destructive to the tree.
There is not a 'cure' for LAB, but rather preventative treatments that are commonly applied as trunk sprays which prevents adults from laying eggs and repeating the lifecycle. It is important to treat this borer as it can eventually kill the tree.
The best time to spray for the Lilac/Ash Borer is April to June when the adults emerge from the holes and start mating and laying eggs around the tree.
No matter what tree you have in your landscape, it is important to keep your trees healthy and growing, with regular water, pruning and cultural practices. Healthy trees are more resistant to insects and disease.
Below is some additional information that might be helpful to you: