Horticulture Hotline
03/09/20
By, Bill Lamson-Scribner
Bill,
After reading your articles for several years now, I’m going
to give you a shot at my problem. I have
these perfect circles in my yard.
Sometimes there are mushrooms growing in the circle and other times they
are just green grass followed by a dead area then green grass again. The circle looks like a halo or a ring around
Saturn. The dead areas are just a little
band about six inches around the circle.
These circles are amazing because you could take a compass, and they
appear to be perfect circles.
I know you have helped out many people including myself in
the past, any ideas on this problem?
Will you be offended if I tell you that you have fairy
ring? It is amazing how nature produces
these perfect circles! There are myths
about these rings going back to medieval times.
When I was in college (also the dark ages!), the only control for this
fairy ring was to dig up all the soil up to 20 ft. deep and replace it. Luckily science has advanced since then.
A fairy ring, in the old days, was believed to be where a
fairy danced around in your yard. It is
actually caused by decomposing organic matter either in the soil or in the
thatch. There is a certain class of
fungi (Basidomycetes) that are responsible for the rings that you see.
You described in your question the damage very
accurately. You have a band of green grass
and a band of dead grass then the center of the circle is usually green, next
to the dead area, and then just regular color in the middle. Under ground, the fungus is sending out
mycelium which are root like structures of the fungus that grow in a dense
mass. This mass doesn’t allow water to
penetrate it (think of a real pot-bound plant when you water it and all the
water goes to the outside edge of the pot and runs down the edges and out of
the holes in the bottom, without really wetting the plant). The mycelium mass is hydrophobic (water
hating), this results in the dead ring that you see above ground. The turf in this area is not getting any
water. Also the mycelium are constantly sloughing
off and dying and as they break down in the soil, they release nitrogen. This nitrogen can be in toxic levels,
resulting in the dead areas. Next to the
dead areas, the nitrogen causes the areas to be dark green. Think of an area where you have seen a dog
urinate. You have a dead area from too
much nitrogen, then a green halo where the nitrogen levels are ok for the
grass. The mushrooms are just a fruiting
body of the fungus that you see at different times of the year. It is amazing how they are in a perfect
circle.
To control fairy ring, unlike 20 years ago, you don’t have
to dig up your entire yard. A good
cultural practice is to apply a wetting agent, then aerate, and then reapply a
wetting agent. If that doesn’t give you
satisfactory results, you can also put out a wetting agent, aerate, drench in a
fungicide including a wetting agent, and see how your results are. It may take several cycles of this treatment
to be effective. Strobe G, Heritage
fungicide (derived from a mushroom), Fame and Pro-Star are fungicides that are
labeled to control fairy ring. Always
read and follow product label.
It is truly amazing how Mother Nature creates these perfect
circles. However, I don’t believe many
golf course superintendents are praising her when these circles show up on
their golf green.
Always read, understand and follow product label. The
product label is a Federal Law.
