For Release May 1, 2005

Time to Protect from Borers

AGRI-VIEWS
by Chuck Otte, Geary County Extension Agent

It's the first of May and many homeowners aren't thinking, or even worried yet, about insect pests in the trees and shrubs around their home. But their is a group of insects called borers that can cause problems in certain plants and by the time you see the damage, it's too late to treat. They are called borers and just like their name implies, they bore into the trunks and stems of trees and shrubs.

There are several species of borers that will attack many different species of woody plants. Some become moths, some become beetles, and all can become destructive. What they have in common is that they are very specific about which species they attack, and what must be done to protect plants from them. They all start as an egg laid at the base of the plant, often behind loose bark. Upon hatching, the small larvae crawls a short distance up the tree and burrows into the tree taking up residence just underneath the bark. Once they are in the tree, you have little hope of controlling them.

Once inside the tree, the small larvae start feeding on the back side of the bark. Their feeding leaves little tunnels and severs the critical water and nutrient carrying vessels. If the plant is large and healthy this damage is may be dealt with by the plant. But if the plant being attacked is young, or stressed, or a shrub with small stems, the presence of even one borer can kill that stem.

Of particular interest this early in the season is the ash-lilac borer that will attack ash trees, lilacs and even privet hedges. You probably won't see anything in the shrubs until later in the summer when stems suddenly wilt and die, often falling out of the shrub crown with little effort. Close inspection usually will reveal a small tunnel in this dead stem. In ash trees, heavy infestations in young trees can kill part of the bark, causing portions of the tree to die or the top of the tree may break off in a strong wind.

Your one shot at controlling this pest is to treat BEFORE the young larvae burrow into the plant. The adult ash-lilac borer is a small wasp looking moth. They are emerging now and will soon be laying eggs. We could use scent traps to find out when the male moths are most active, which would indicate when we needed to spray. But it is probably easier to use a visual signal that we are all familiar with. Normally, the adults are most active when the old fashioned white spirea are in full to late bloom.

There are several products that are labeled for borer control, but probably the best is permethrin. Check the label of your product to make sure it has borers on the label. You don't need to spray the entire tree, in fact spraying the entire tree is a waste and probably won't control the small borer larvae. Since the eggs are laid at or near the base, you only want to spray the lower portion of the plant.

The spray needs to be applied heavily, to the point of runoff. Thoroughly soak all sides of the trunk or stems. In shrubs the lower two feet of the stems should be adequate. On small trees you will want to spray the lower ten feet of the trunk.. On shrubs, great care must be given to spraying all sides of all stems. Then mark your calendar and repeat this in four weeks.

Borers are quiet killers. If you had dead canes in your lilac or privet last year you probably had them and need to treat this year. If you have a small ash tree, I'd treat it whether you thought you had problems or not. Because if you don't treat and find you do have borers, it'll be too late for this year!

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