JoAnne Skelly: Borer control in birch trees

After seeing my article last week on the efficacy of systemic insecticides for bark beetles and borers in pines, a reader, Ken, wondered whether a product he was using against bronze birch borers was working.

It has the same active ingredient, imidachloprid, as the systemic article I wrote about on pines, although it has a different brand name. Fortunately, the label does list bronze birch borers as one of the pests controlled.

However, there is a bigger issue with birch trees in our environment. Birch trees are native to areas with significant precipitation, not to arid areas. They grow best along rivers and waterways. They need water all year round, not just in the summer.

With our often-dry winters or with the length of time between snow or rain events in the winter, it is really challenging here to keep birch trees healthy. Ask yourself if you are willing to irrigate them every month of the year, even if it means dragging hoses to each tree in the cold of winter?

We started with six birch trees at our house in 1988, one of which was a huge tree. We lost every one of them to bronze birch borers, no matter how many times I augmented irrigation water with auxiliary sprinklers throughout the year and with the imidachloprid treatment.

The problem is that no matter how hard we work at it, birch trees are out of their element, so they struggle. This stresses the trees, which then releases stress hormones that attract the borers.

They then attack the trees year after year, until the trees have so little working vascular structure left that they die. An additional problem is the woodpeckers who girdle the trunk of trees going after the beetles. This accelerates vascular tissue loss and tree decline.

What I would tell Ken is that since the chemical is listed for bronze birch borers, he at least isn’t wasting his money. However, I would ask him how the trees are doing. If they are thriving, maybe his treatment is worth it.

If they aren’t, then perhaps he needs to increase the amount of water the trees receive all year. The soil out to the drip line of the branches needs to be kept moist to a depth of 18 inches. This combined with the chemical treatment may help keep his birches alive.

Remember though, that this active ingredient, imidachloprid, is highly toxic to bees and other pollinators. It’s a benefit-risk analysis.

JoAnne Skelly is Associate Professor & Extension Educator Emerita at University of Nevada Cooperative Extension. Email skellyj@unr.edu.