Healthy ash trees on homeowner property or on public property adjacent to your property (on the city right of way) which provide beauty and/or shade will be good candidates for long term insecticide treatment.
That said, a cost comparison between treatment and removal/replacement, and a consideration of how long you will continue owning your property will be factors in your decision regarding treatment of your ash tree. Be aware that many trees are not worth protecting and you should prepare to remove the tree soon or when it becomes weak from EAB infestation.
Numerous analyses have concluded that the cost of treating your tree throughout the duration of the EAB threat and performing common maintenance (trimming) for the period is similar to the cost of removing it and planting a new tree. The difference of course is that if you treat your tree you enjoy a substantially larger tree in the meantime!
Trees that are not worth protecting include trees with major defects like wounds, cavities, significant lilac borer (or other insect) damage, and canker formations (irregularly formed and loose bark typically on stem base), and trees that are planted in a bad spot: too close to foundation or fence/property line or under power lines. If you don’t care if you keep the tree or get rid of it, this is a clear indication that the tree should be removed instead of treated.
Trees that need major pruning: If you are not dedicated to keeping the tree in top condition with routine trimming, it probably isn’t worth protecting it from EAB. It makes no sense to spend the money on treatments, yet to leave the tree unduly vulnerable to loss from storm damage or decay from unaddressed wounds. If you only want to enjoy your ash for a few more years, save your money to pay for its removal.
Trees that provide valuable shade from the setting sun or from mid-day sun over the house and driveway will often be worth treating for EAB. Trees that shade you from the afternoon sun are typically more valuable than ones that provide morning shade since the late day summer sun is more menacing than morning sun. Keep in mind a tree that provides morning shade for you may provide evening shade for your neighbor and vice versa.
At the end of the day, you the homeowner have the final say as to whether or not to protect your ash tree. There are also intangible reasons to protect your tree. Sometimes a tree has an emotional significance. If you are attached to your tree and it is healthy, well maintained and not a hazard, it is reasonable to protect it since cost is the only real impediment.
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