Homegrown: Nov. 12, 2011

Our 3-year-old Winter King Hawthorne has two places where the bark is gone. There is a small hole in each bare spot.

The southern exposure has been there awhile and appears to be healing. The eastern exposure is new this year.

What might cause this and should we be concerned? Is there any need to provide protection to the two spots this winter?

— Brad and Pam

You have a borer in the tree. In hawthorns, that’s almost always what’s called a flat headed borer. Before I get to specifics, let me talk a bit about borers in general.

Borers are almost always a stress-related problem. A tree that is weak and hurt for one reason or another is more likely to develop borer problems.

The long term solution to borer problems, whether it’s to minimize their damage or to prevent them, is to maintain the tree in a healthy, robust condition.

A newly planted tree such as yours is always under a little bit of stress, and it may be nothing more than that. However, I’d double-check the care of the plant just to make sure there’s nothing else going on.

Next spring, dig down and check on the water that the tree receives. Make sure that the soil is soaked deeply but then allowed to dry slightly before being soaked again.

Look also for sources of stress. One source of stress I see a lot in trees planted in the lawn is damage from the string trimmer or lawn mower. Wounding the plant at the base can be a significant stress.

Reducing stress is just the first step. You’ll need to plan on spraying your tree to help control the borer.

Keep in mind that careful timing of insecticide sprays is an important component of successful borer control. Once the insects are inside the tree, they are extremely difficult to reach with insecticides.

What we try to do is to take advantage of their life cycle. It’s the larval stage that is usually what we call the “borer.”

In due time, the larva will pupate and the adult insect, a small “metallic” beetle in this case, will emerge from the tree to find a mate. This is when they are vulnerable to insecticide sprays.

It’s important to know what specific borer you’re trying to control since different species of borer have different life cycles and therefore different spray schedules.

Also, certain borers will sometimes require different parts of the tree be treated. With the flat headed borer, the window is usually the middle to the end of May.

The timing will vary from year to year depending on how quickly or slowly the weather warms up in the spring.

Thoroughly and completely spray the trunk and the lower part of the main branches of the tree with a dilution of 38 percent Permethrin at that time of the year.

Usually, one thorough spray is enough to protect the tree for an entire year. If you want to be especially safe, you can do a second spray a month later but that’s usually not necessary.

Two other little helpful hints for flat headed borer is to be sure to avoid sun scald damage in the tree by wrapping the trunk in the fall when the leaves fall off and removing the wrap in the spring when new growth emerges.

Also, avoid pruning the tree in spring. Those fresh wounds can attract the borer. Any pruning should be done in late summer.

Don’t get discouraged. I had flat headed borer in a sycamore tree in my yard when it was first planted and now it is over 30 feet tall.

As long as the tree is looking good overall, this is a problem that can be fixed.

Dennis Hill is the nursery manager at Bookcliff Gardens, http://www.bookcliffgardens.com. Send questions to Bookcliff Gardens, 755 26 Road, Grand Junction 81506; or email .(JavaScript must be enabled to view this email address).


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