If trees could talk, I would hope they would tell us what hurts, or where it hurts, or when a pest attack is getting the best of them. Their stories could help horticulturists, arborists, plant pathologists and others really get to the root of tree problems. Instead, we are left to rely on clues and what we know about plant growth to try to figure out what is going on and if there is a solution.
What I would ask of trees most recently is why some of them are losing patches of bark. In some cases, the phenomenon seems to be a combination of borers, drought and woodpeckers. The cottonwood and ash trees at Les and Sammie Conder’s residence southwest of Lawrence are a prime example. Both cottonwood and ash are especially prone to native borer species, and the Conders have observed red-bellied woodpeckers and northern flickers (a type of woodpecker) at work in the trees.
What the Conders really want to know is what can be done, if anything, to keep these trees alive. The bark loss in their case is minimal, but it is hard to tell how much damage borers may have done below the bark’s surface.
“We watered them all summer,” Sammie says, referring to the trees. She and Les, who are both Master Gardeners, understand the compounding effects of the drought and that keeping a tree healthy is easier than saving one that is already suffering.
They also wondered if they should try to discourage the woodpeckers from inhabiting the tree, even though they enjoy watching the birds.
The good news is that the woodpeckers are only bringing light to the problem in their search for the borers. Any bark loss from woodpecker pecking is less damaging to the tree than what the borers have already done. The Conders are on the right track with watering and keeping the trees mulched. Mulch reduces competition with lawn grasses and will reduce water loss in the trees’ root zones.
Insecticide treatments are another option. But the borer species must be identified so the insecticide can be applied at the proper time and through an appropriate method. Also, insecticidal treatments are preventative rather than curative.
For example, for the native ash/lilac borer, the trunk of the ash tree to be protected would need to be treated twice in the spring. The first application should be made when Vanhoutte spirea are in full to late bloom (late April to early May most years). The second application should be made four weeks later or per label instructions. Only use products that specifically list ash/lilac borer on the label. There are a few products containing the active ingredients bifenthrin and permethrin that are labeled for control of ash/lilac borer.
Cottonwood borer is active much later in the season. For preventative control, a borer-control product containing permethrin could be applied to the base of the tree and soil around it in late June or early July and again in late July per label directions.
There are also injectable insecticides and insecticides that can be applied as a soil drench. These are effective for borers that feed just under the bark, like the bronze birch borer, but are completely ineffective for borers whose adult versions are moths, like the ash/lilac borer.
The Kansas State University guide “Borers: Common Kansas Species” lists 22 species, many of which are indiscriminate to the trees they feed on. Because all borers are attracted to stressed trees, this is just one more reason to keep the tree healthy instead of trying to fix the problem later.
In a few cases, the reports of dislodged bark have come without observations of woodpeckers. Without seeing animal or insect activity, pinpointing the cause of the bark removal is difficult. But borer activity has been present in all cases so far.