Mr. Goble, you asked a lot of questions about insect infestation.

Have you and your forester discussed the native Lilac Ash Borer, which commonly affects ash trees in Colorado? This common Colorado insect is similar, but not the same as, the imported Emerald Ash Borer (EAB). Refer to https://extension.colostate.edu/docs/pubs/insect/05614.pdf

To complicate things even more, Colorado State University says there are several kinds of borers. These other borers are not nearly as damaging as Emerald Ash Borer. If you have found sawdust and holes that are round and about 1/4 of an inch wide, it is probably Lilac ash borer or it could be a number of other insects

https://extension.colostate.edu/topic-areas/insects/recognizing-wood-boring-insects-of-ash-trees-in-colorado-5-620/

It’s hard to be a tree in Colorado. When trees get stressed, then insects invade.

For example, trees need water. Consistent watering during the growing season and winter watering is a task a homeowner can readily accomplish. Lawn irrigation is usually enough for ash in the growing season. In the dormant season, ash do need to be winter watered every 4 to 6 weeks when there is a lack of snow cover.

Drought stressed ash are prone to native borer attack and winter kill--like the winter kill damage you photographed at the edge of your tree’s canopy.

The effects of other tree stressors may not show up for years. You may want to recall when you first saw the damage. What stressors may have occurred before you recognized tree stress symptoms? Changes in the plant site, such as construction that disturbs tree roots? Wind damage? Irrigation changes?

So many things to consider.

If you wish to continue this discussion, please do not hesitate to contact the CSU Extension Service again.

Sue
Weld County Colorado Master Gardener