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By Clint Waltz
and Gil
Landry
University of Georgia
Warm-season turf grasses such as Bermuda, centipede, zoysia and
St. Augustine suffer some common problems with springtime
green-up. Here are the ones we see most often.
Mowing height is the most common
problem as these grasses go from dormancy to active growth.
Scalping is more common in zoysia grasses, especially in the
denser-growth cultivars like Emerald.
Zoysia grasses don’t tolerate scalping as Bermuda will. As a
rule, zoysia will be set back anytime it’s cut low enough that
you can see the black mold under the leaf canopy. This is
generally below the node of the growing leaves. It can occur at
any mowing height from as low as 0.5 inches to more than 3 inches.
Regardless of the grass species and normal mowing height, taking
the grass down below the node will set it back. Generally, the
higher the mowing height, the more this is a problem.
Ideally, maintain Bermuda grass and centipede between 1 and 2
inches, zoysia from 0.5 to 2 inches and St. Augustine from 2 to 3
inches.
Mowing frequency is just as important as mowing height. If you
remove more than one-third of the leaf height at a single mowing,
the grass will be stressed.
Fertility requirements differ with
each grass. Consult your county University of Georgia Extension
Service agent or visit www.GeorgiaTurf.com for fertility
recommendations.
No matter what the species, though, fertilizing too early in the
season, before soils are warm enough to support continual growth,
can accelerate green-up but cause detrimental long-term effects.
Fertilizing these grasses in late-winter or early spring can
cause them to break dormancy. Then when the inevitable
late-season cold snap hits, they’ve used their stored food
reserves. They have no energy to withstand environmental
extremes. To avoid this, don’t fertilize until the soil reaches
65 degrees.
Thatch, as lawns get older,
becomes more problematic, particularly if the turf has been mowed
above its recommended height ranges. Increased thatch slows down
the turf’s spring transition. It makes it more susceptible to
disease, too.
Water — either too much or too
little or even a combination of the two — can cause problems
for grasses, especially zoysia.
Diseases can strike during spring
green-up. The most common is Rhizoctonia large patch, which
appears as large areas of blighted grass.
This disease is most active when night temperatures are between
50 and 60 degrees. When conditions are right, it’s common for the
disease to become active first in the fall and then again in the
spring.
You can see its typical “halo” when the disease is active. Fall
and spring fungicide applications can control it. Consult your
county UGA Extension agent for proper fungicides and rates.
Applying nitrogen just before or during active infection will
increase disease problems.
Cool temperatures make centipede
and zoysia slower to green up in the spring.
Microclimates can cause problems,
too. Emerald zoysia growing north of Atlanta has been killed by
the low temperatures in shaded sites that don’t get much winter
sun.
Varietal differences can be
troublesome. Some incidences suggest that many types of Emerald
zoysia exist in the landscape and green up at different rates.
Cooperative research with the Georgia Crop Improvement
Association and Auburn University is under way to evaluate these
grass differences.
(Clint Waltz is an Extension Service turf scientist and Gil
Landry the director of the Georgia Center for Urban Agriculture
with the University of Georgia College of Agricultural and
Environmental Sciences.)
