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Borers and their control
By John Fulton

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[May 10, 2014]  Few things strike fear in the hearts of tree owners like the mention of borers. Borers are most often the larvae of beetles or moths, and they do their damage where you can’t see it. The eggs are laid on or under the bark, and the small hatchling chews through to the part of the tree they feed on. They spend almost their entire lives inside the tree, where they can’t be seen or controlled.

May 24-30 has been selected as Emerald Ash Borer Awareness Week because it coincides with the time of year that the adult beetles will begin to emerge. These borers have gotten a lot of press the past few years, and have made ash trees undesirable for planting. They are metallic green, about a half inch long, and make “D” shaped exit holes (unlike the ash borers we have had around here for many years which make “O” shaped holes).

Most borers are named for their primary target, but they also affect other species of trees and shrubs. As an example, the flat-headed apple borer can also affect pin oaks and about 15 other species. Many borers leave a tell-take hole in the trunk, but some such as the ash borer are weak and have to enter through a pruning or mechanical injury.

Here is a listing of common borers and their control times: Common ash borers (early June and early July), emerald ash borer (mid May through early June), bronze birch borer (mid May and repeat two times at two week intervals), dogwood borer (mid May and mid June), flatheaded apple borer (late May and repeat in three weeks), lilac borer (early June and early July), locust borer (late August and mid September), mountain ash borer (early June and mid July), peach tree borer (mid June and mid July), viburnum borer (early  June and early July), and Zimmerman pine moth (April or August).

You can see borer control isn’t an exact science. Treatment times and re-applications are hopefully timed to catch the hatching eggs on the outside of the trunk, or discourage the adults from laying eggs. Some new research shows that trees that are under stress give off a certain pheromone that attracts more borers to the tree. So, keeping your trees in good growing shape will go a long way to helping the situation. Fertilizing with the same rate of broadcast fertilizer used for lawns will help (apply it early May and early September), and watering during extreme dry periods as well (with an inch of broadcast water per week.

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Some of choice for borer control include permethrin, bifenthrin, and acephate. Check the label for control on your target borer. Imidacloprid is fairly new on the market. One trade name is Merit (one example sold for homeowners is Bayer Advanced Tree and Shrub Insect Care). This product use rate is an ounce per inch of circumference of the tree trunk. You then mix it with three gallons of water and pour around the base of the tree. It may take a few months for it to translocate though the tree. A good time to apply it is in early spring when the sap rises. Each treatment lasts about a year. Fruit trees generally are treated differently with Sevin, or just using the regular spray program due to the possibility of residue in fruit

Zimmerman pine moth is one of those “kind of borers.” It generally affects only severely weakened trees, and goes just under the bark to girdle the cambium layer. It seems like older Scotch, red, and Austrian pines are favorites when they begin to decline. Bird damage from yellow bellied sapsuckers on trunks and main limbs also looks like borer damage to many. This bird damage is easily recognized by the evenly spaced holes in a straight line.

[By JOHN FULTON, University of Illinois Extension director for Logan, Menard and Sangamon counties]

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