Fairy rings are caused by a fungus in the soil. Actually there
are about 50 fungi that can cause fairy rings. These fungi feed
on decaying organic matter such as large roots from trees that
were in the area or from buried lumber. The dark green circle
part of the equation comes from extra nitrogen that becomes
available as the organic matter is broken down by the fungus.
Some prevention will help keep the problem from occurring.
Simply removing stumps and large roots and not burying lumber
help prevent this type of problem. As for a cure, fungicide
drenches have been successful on a very limited basis. One
option is to mask the symptoms of the dark rings by fertilizing
the surrounding grass with a high-nitrogen fertilizer to make
that grass green also.
As for the puffballs, toadstools or mushrooms, they are part
of the same complex as fairy rings. They are part of the natural
decay process that helps break down large wood items in the
ground. There is no real control, so mowing them off or knocking
them loose with a garden rake is about the best thing going.
Here is a listing of common
borers and their control times:
Ash borers --
early June and early July
borer -- mid-May and repeat two times at two-week intervals
-- mid-May and mid-June
apple borer -- late May and repeat in three weeks
Lilac borer --
early June and early July
Locust borer --
late August and mid-September
borer -- early June and mid-July
borer -- mid-June and mid-July
-- early June and early July
moth -- April or August
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.
The products of
choice for many borers are now permethrin or bifenthrin.
Imidacloprid is fairly new on the market, and one trade name is
Merit (sold for homeowners as Bayer Advanced Garden 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. 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 and is more successful on younger trees.
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Fruit trees generally are treated differently, with Sevin or
bifenthrin applied to the trunk, or just using the regular spray
program, due to the possibility of residue in fruit.
Zimmerman pine moth, one of the borers, 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. Permethrin is recommended
for Zimmerman pine moth.
Bird damage on trunks and main limbs from yellow-bellied
sapsuckers also looks like borer damage to many. This bird damage is
easily recognized by the evenly spaced holes in a straight line.
Things to do
fruit spray programs. Because of pollinators, be careful with
insecticide applications during bloom periods.
The next couple of
weeks are ideal to fertilize the lawn and control broadleaf
weeds. Best to wait on the weed control if you have put down new
seed this spring.
tender vegetable and flower crops. Of course, it's best to check
the weather forecast for the next week.
For maximum bloom next year, prune
flowering trees and shrubs after they flower
University of Illinois Extension, Logan County]