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SOLUTIONS
Some tests have
shown up to
three months
control of dollar
spot can be
attained with
early-sea<strong>son</strong>
fungicide
applications.
Midwest that occurs in the cold weather of
October.
For this rea<strong>son</strong>, it has been difficult to
develop a prediction model for dollar spot
because of different VCGs that occur under
the various environmental conditions.
The occurrence
For many years, dollar spot was only a problem
in the parts of the world where coolsea<strong>son</strong>
grasses were grown. With the introduction
of some of the new creeping bentgrass
cultivars, like Crenshaw, <strong>and</strong> the new
ultra-dwarf bermudagrasses, dollar
spot has now become a problem
in the areas of the
world where warm-sea<strong>son</strong>
grasses are grown.
In spite of its
proliferation, it is
rarely considered
a major disease.
You might say it is
the Rodney Dangerfield
of turfgrass
diseases: It
doesn’t get the respect
it deserves.
Over the years, when
golf course superintendents
are surveyed about
what they consider to be their
most important turf disease, they invariably
say Pythium blight. In recent years, their
top choice has been crown-rotting anthracnose.
But when the question is asked in another
way — “Which disease do you spend
the most money controlling?” — the answer
is usually dollar spot. This makes it a very
important disease from an economic point
of view.
Cultural management
Dollar spot outbreaks occur under conditions
of high humidity or when large
amounts of guttation water (dew) are present
on the turf.
Whereas little can be done about the high
humidity, a good cultural practice to reduce
the severity of dollar spot is to remove the
guttation water as soon as possible each
morning. This can be done by wiping the
guttation water off with a pole, dragging a
hose over the turf, or turning the irrigation
water on for a few minutes.
Another good cultural control that is
often overlooked is having adequate nitrogen
fertility. Nitrogen can help manage the
disease by encouraging growth, which in
turn increases mowing off infected leaves.
Studies at Michigan State University have
shown rolling the greens three times a week
following the morning mowing has also
suppressed the amount of dollar spot. Further
research needs to be conducted to determine
the mechanism involved in this
phenomena, however. In the meantime, for
the practitioner, it is enough to know that he
or she can reduce the incidence of dollar
spot by rolling in the morning immediately
after mowing.
Chemical management
The dollar spot organism starts out in the
spring as a tiny stroma (a cluster of mycelium).
It is much easier to control at this stage,
when it is small <strong>and</strong> slow-growing, than later
in the sea<strong>son</strong> when it gains mass <strong>and</strong> grows
more rapidly.
Several universities have been involved in
early fungicide application to delay the development
of dollar spot. Some tests have
shown up to three months control of dollar
spot can be attained with early-sea<strong>son</strong> fungicide
applications. However, more research
needs to be done to better determine the
exact timing of the early fungicide applications.
The current findings suggest the application
should be made between 150- <strong>and</strong>
200-degree days using a base 50.
Looking toward the future
Dollar spot will continue to be an important
disease. It appears that it is becoming widespread
in more areas <strong>and</strong> on more turfgrass
species. In addition, the resistance of certain
strains of R. floccosum to some fungicide
classes continues to be a problem. The future
of controlling dollar spot, then, may rely on
developing resistant species <strong>and</strong>/or cultivars.
One thing is for sure: The Rodney Dangerfield
of turfgrass diseases is not going away
anytime soon. ✹
J.M. Vargas Jr. is a professor in Michigan State
University’s Department of Plant Pathology.
36 Golf Advantage Winter 2006