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Why Green Ash Trees From Fort Collins to Denver Look Unhealthy

Posted on: August 28th, 2014

Since the discovery of emerald ash borer (September 23, 2013) in Boulder Colorado, there has been a constant stream of news releases designed at educating the public about this destructive pest. There is no argument emerald ash borer (EAB) is the most destructive pest of shade trees in North America. EAB is currently in the City of Boulder and will spread throughout the Platte River Valley in the next few years, and likely eventually to most of eastern Colorado. The good news is there are well researched treatments which are very effective at controlling EAB.

The not so good news, or for some, the bad news is many green ash trees along the Front Range look poor this year. They have dead branches, branches with thin and sparse foliage, and sprout/sucker growth coming off the trunk. Some trees failed to leaf out altogether. Many green ash trees growing in Eastern Colorado are showing symptoms of emerald ash borer, but they are not infested with EAB, something else is the cause.

No one has a definitive answer as to what is causing the decline in the health of ash trees; however this is the most plausible theory. Likely, the weather events from 2012 had a lingering effect. Twenty-twelve was the hottest year on record, as well as one of the driest. This sent many ash trees into a state of drought stress. The drought stressed ash trees did not have sufficient sugars in their cells as they entered the winter season to lie dormant. As a result, the trees were severely damaged by single digit April 2013 freezes, which froze newly emerging ash foliage. Not only was the foliage frozen, but also the leaf bud, twigs, as well as some branches. Some ash trees only began to leaf out in late June. For these trees, their growing season was cut short by nearly two months. Weakened by the 2012 heat and a shortened growing season in 13’, the trees were exhausted as they entered the winter of 2013. Weakened, trees again suffered an April freeze in 2014 freezing their foliage. Some ash didn’t have enough resources to produce new leaf buds and foliage. In a last ditch effort, the trees produced trunk sprouts- this is the fastest mechanism for the tree to produce foliage.

For now, autumn purple ash trees are not showing these symptoms, but for the green ash- why should we be concerned?

For starters, emerald ash borer is difficult to detect. Trees exhibiting symptoms of EAB, but without the borer infestations, will make additional EAB detections all the more difficult to find as the borer is stealth. A Denver tree service can help you identify if your tree is effected by EAB or not. 

Weakened trees will attract EAB along with other pests and do not respond well to treatments designed to control EAB.

What should you do?

If your ash trees look healthy, this is good news! Remember to winter water your trees and seriously consider fertilization. Vigorously growing trees are much better candidates for treatments to prevent EAB. If your ash trees have dead branches or sparse canopies, have them inspected this fall by a tree service expert.

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