The next phase of the Emerald Ash Borer infestation –
One of my neighbors recently asked me what was causing the bark to fall off of his ash trees even though it did not have dead limbs at the top. I have to admit to some initial uncertainty about the cause. After all, by now we are aware of the warning signs of an EAB infestation – dying upper branches, water sprouts lower on the trunk, D-shaped holes in the bark, and girdling channels in the phloem underneath the bark left by hungry EAB larvae.
But what is causing the yellowing swatches of bark on the lower tree trunks? I am aware of a fungal infection that affects the lower bark on ash trees, and I can identify deer rub damage, but this is different. A closer look at the chunks of bark falling off his tree reveals the dreaded D-shaped holes.
The latest research indicates that the populations of the borer have grown so rapidly that infestations are occurring at any tree height rather than just at the top where the bark is thinner. What does this mean for the tree? Damage occurs above the point of the larvae channels since this cuts off the nutrient supply from the roots. Ash trees can have 33 – 50% damage in the upper branches but still survive if treated. But now, infestations at the base of the tree are blocking all upward flow of nutrients, and the trees are dying within a single season.
What does this mean for you? Your tree cannot be saved. Sorry. It will die far more quickly than when the damage occurred at tree-top level. If you have been treating your ash trees over the last few years, you still have hope, so continue applying your soil annual soil drench treatment or biannual trunk injections. As to how long you will have to continue treating your trees, there are several hypotheses:
- Once the majority of ash trees are dead, the EAB population will crash and die off.
- Small populations of the borer will survive in naturally resistant trees, but populations will not explode again.
- EAB host preferences will adapt to target other trees, so isolated EAB populations will survive.
I tend to support options 2 and 3 which means that I will continue to treat my trees until more research is available.
Submitted by Linda Hartmann, HVL Natural Resources Coordinator