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With the extreme hot temperatures of the past two weeks
we have been getting numerous calls regarding Poa annua
(annual bluegrass) decline/death on putting greens (Photo
1) and Poa trivialis (rough bluegrass) decline in the
fairways (Photo 2). These grasses are highly competitive
species during cooler spring and fall weather, are very
tolerant of low cutting heights, and make lots of seeds
to replenish their populations when under duress. Unfortunately,
these grasses are also shallow rooted and have very little
heat tolerance, and can die out quickly when extended hot
weather invades the upper Midwest.. With putting green soil
temperatures in some areas peaking in the low 90s (!) on
Sunday (July 21) many clumps of Poa checked out. In some
cases, symptoms were exacerbated by double cutting or rolling
of the greens in preparation for scheduled tournament play.
In some of these areas, we have also detected other pathogens
most notably anthracnose infection on foliage of these Poa
plants. In this case, however, anthracnose is probably only
a secondary pathogen, feeding on the dead or stressed leaf
tissue left behind by the heat. Anthracnose can be a devastating
disease especially when it is a basal rot, or infects the
plant crowns (Photo 3), but that type of symptom
is not occurring in these dying Poa patches.
So what to do? Probably the things you are already doing;
in this period of heat stress the only options require minimizing
stress on the plant. Hand-water or syringe hot spots just
enough to cool down the plant during the heat of the day
. If possible, raise mowing heights on the greens or skip
mowing altogether on the hottest of days. Other stress inducing
activities such as double cutting, rolling, topdressing
and fertilizing should also be curtailed..
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Photo 1
Photo 2
Photo 3
(click on image to enlarge
it.)
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