May 20-26 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 this past year. 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
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 telltale hole in
the trunk, but some, such as the ash borer, are weak and have to
enter through a pruning or mechanical injury.
Painted hickory borer has been a common nuisance pest the
past week. These borers attack dead and dying trees and
firewood. They are not usually a concern in healthy trees. They
look very similar to the lilac borer, but the lilac borer adults
are out in the fall.
Here is a listing of common borers and their control times:
ash borers, early June and early July; bronze birch borer,
mid-May and repeat two times at two-week intervals; dogwood
borer, mid-May and mid-June; flat-headed 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. For the emerald ash borer,
although not confirmed in our area at this time, control time in
Michigan begins in mid-May and runs through mid-July.
You can see borer control isn't an exact science. Treatment
times and reapplications 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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The product of choice for many borers is now permethrin, since
Dursban is off the market. Imidacloprid is fairly new on the market.
One trade name is Merit, sold for homeowners as Bayer Advanced
Garden Tree and Shrub Insect Care. The use rate for this product 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. These
treatments need to be completed by late May to have a chance of
getting the current season borers. 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 kinds 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.
University of Illinois Extension, Logan County]