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Illinois Study Shows a Possible Lag in Visible Benefits for Ash Trees Undergoing EAB Treatment

October 20, 2011

Our resident master gardener, Pat Thomson, found the following article regarding the treatments for the Emerald Ash Borer:

If a tree has lost more than 50 percent of its canopy, it is probably too late to save the tree. Studies have shown that it is best to begin using insecticides while ash trees are still relatively healthy. This is because most of the insecticides used for EAB control act systemically — the insecticide must be transported within the tree. In other words, a tree must be healthy enough to carry a systemic insecticide up the trunk and into the branches and canopy. When EAB larvae feed, their galleries injure the plant’s circulatory system. This interferes with the ability of the tree to transport nutrients and water, as well as insecticides. As a tree becomes more and more infested, the injury becomes more severe. Large branches or even the trunk can be girdled by the larval galleries.

Studies have also shown that if the canopy of a tree is already declining when insecticide treatments are initiated, the condition of the tree may continue to deteriorate during the first year of treatment. In many cases, the tree canopy will begin to improve in the second year of treatment. This lag in the reversal of canopy decline probably reflects the time needed for the tree to repair its vascular system after the EAB infestation has been reduced.

Here’s the “executive summary”: if a tree has been treated for the Emerald Ash Borer, it may take more than one year’s treatment before there are visible signs of improvement in the tree’s appearance. It takes time for the treatment to fully circulate.

If a tree has already lost more than half of it’s canopy, it isn’t a good candidate for beginning treatment.

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