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Growing Concerns: Want to save that ash tree? Treat it now

December 17, 2018
The emerald ash borer will make S-shaped tunnels beneath the tree’s bark.

The Rochester Forestry Department is currently doing its annual inspections for ash borer-infested trees. While their primary responsibility is caring for trees on boulevards and in parks or other public spaces, they do also have jurisdiction to mark trees on private property. This is a common practice in municipalities when doing so helps with overall management of disease and insect problems or when it mitigates hazards.

The practice of condemning trees on private property has been integral to management of Dutch elm disease (DED) in our region because it facilitated removal of diseased trees that were a reservoir of the DED fungus and breeding habitat for the beetles that spreads DED.

This concept is being applied to emerald ash borer by removing trees that are infested to reduce insect populations which would infest more trees the next season. This does not eliminate the insect, but it does slow the pace at which they re-infest new areas. Infested trees also become brittle, making them higher risk to remove. This can increase removal costs considerably on trees that cannot be accessed with bucket trucks.

The ash borer is currently well established in Rochester and surrounding communities. Here in Rochester, the infestation started near the intersection of U.S. Highway 63 and Interstate 90. From there, it progressed into the southwest quadrant of the city. At this point, most trees that have not been treated in the southwest will have some level of infestation. Southeast and northwest also have significant infestations. Northeast Rochester also has infestations, but they are not as widespread.

I am getting frequent calls from homeowners who have had trees marked, asking if they can treat to save the trees. In many cases these trees can be treated, but some dieback should be expected because the insects have done significant damage by the time infestations can be identified. The borer feeds in the vascular system of the tree, which restricts movement of the insecticide into limbs with advanced damage. If you have ash trees and desire to protect them, it is advisable to treat them prior to infestations.

Treatment to protect from ash borer involves the infusion of insecticide into the vascular system, where it is translocated through the tree. Treatment controls adult beetles that feed on the leaves, and larva that feed in the vascular system. The chemical provides very effective control through a two-year period, after which it needs to be reapplied. Each treatment should be viewed as a two-year investment in preserving the tree. Anticipate treatment for as long as you choose to protect the tree.

All trees that are considered for treatment should be evaluated to determine if they warrant the investment. I always try to inform homeowners of any structural concerns or other tree-health related issues prior to recommending treatment. I also offer my perspective on how much landscape value the tree provides and treatment verses removal comparisons when requested.

Emerald ash borer is an unfortunate reality in our urban forest and I am finding many people have tried to ignore it until forced to deal with the problem. If you have ash trees, it is better to be proactive and treat trees that you wish to protect. Scheduled removal of trees that you do not plan to protect can save money because companies have more flexibility in scheduling removals and it reduces risk associated with declining trees.

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