Red Thread – Common Plant Diseases in the Landscape and Garden

I’m Mary Ann Hansen extension plant
pathologist with Virginia Cooperative Extension and we’re out here today on
the Virginia Tech campus looking at a turf disease called red thread. This
disease is pretty common in the springtime and so it’s not unusual to
see it on May 9th. The disease affects a lot of different types of turf grass, so
it can affect Kentucky bluegrass, perennial ryegrass,
tall fescue, and what we have here is a mixture of grasses, and you see some of
these patches of pink straw colored grass appearing in the turf. They’re
usually between 4 to 8 inches in diameter. You can get a number of these
spots coalescing and forming a larger patch, and what’s diagnostic about the
red thread disease is these little pinkish or red threads that come out of
the tips of the leaves. These are structures of the fungus that cause
this disease and they’re called sclerotia, and they can actually survive
in the thatch layer when the grass gets cut and these fall down into the thatch
layer and can then reinfect the grass later. We often see this disease
showing up in the springtime and it’s most common on nutrient poor turf, so
usually by spring that fall application of nitrogen fertilizer has has worn off
and the grass is a little nitrogen deficient, and then the grass is more
susceptible to this disease. Red thread also occurs at cooler
temperatures, so we see it in the spring and in the fall, and under wet conditions
we can really clearly see those patches like we can today after we’ve had
a little bit of rain overnight. Types of controls that you might use for this
disease are basically cultural controls you can supply a little extra nitrogen
in the spring and that will help alleviate symptoms, and you also want to
avoid overhead watering late in the day, you don’t want to prolong that due period which will favor disease with a prolonged
moisture period. The fungus that causes this disease mainly is infecting the
leaf blades, and so you usually don’t get whole plants dying back, you just get
leaf blades dying back and then under warmer temperatures and higher nitrogen
conditions, that grass will come back and green up, so it’s mainly a cosmetic
problem and not something to really worry about. If you maintain your good
nitrogen fertility on an ongoing basis and you can avoid this disease–of
course you always want to base your nitrogen applications on a soil test
because if you end up applying too much nitrogen you can favor some other
diseases of turf that that also occur. There are some varieties of some of
these turf grasses that are less susceptible to red thread than others,
and to find out what some of the current currently available varieties are you
can look at the national turf grass evaluation program website, and you can
find some of those varieties that have performed better in their trials.

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