Red Thread Disease in Lawns
By: Sandy Feather
©2006
Penn State
Cooperative Extension
Q. My lawn
has patches of dead grass all over. They seem to have a reddish
color. Can you tell me what this is and how I can stop it?
A.
The writer enclosed a sample of damaged grass that showed classic
symptoms of red thread, a common fungal disease. It is especially
severe on perennial ryegrass and fine fescues, although Kentucky
bluegrass can also be infected.
The causal
fungus (Laetisaria fuciformis) overwinters on dead blades of
grass or clipping debris from last season. Air temperatures of 65 to
75 degrees and rainy or humid weather favor the development of red
thread. The disease is spread on turf equipment and by foot traffic.
From a distance, affected patches of grass have a reddish or pink
cast, and affected leaf blades dry out and take on a bleached-out
straw color. As the disease progresses, pink to bright red
thread-like fungal mycelia extend from the tips of infected blades,
giving the disease its common name.
Red Thread disease
Cultural
controls include
maintaining adequate fertility levels; red thread
can be indicative of low fertility. Be careful to use a moderate
amount of nitrogen, one-half to one pound of nitrogen per thousand
square feet. Too much nitrogen can create favorable conditions for
other, more serious diseases to develop. It is also important to
maintain a soil pH between 6.5 and 7.0. Avoid overwatering your
lawn, and water first thing in the morning so that the grass dries
off as soon as possible as the sun comes up. Do not water at night,
when the grass will stay wet all night until the sun comes up the
following morning.
Overseeding or
replacing susceptible grasses with resistant varieties is helpful in
controlling red thread. Resistant varieties of perennial ryegrass
include Assure, Derby Supreme, Gettysburg, Legacy, Loretta, Navajo,
Passport, Pinnacle, Precision, Riviera II, Sherwood and Shining
Star. Resistant varieties of fine fescues include Biljart, Bighorn,
Reliant and Waldina. Resistant varieties of Kentucky bluegrass
include Ascot, Classic, Dawn, Eclipse, Princeton and Trenton.
Fungicide
applications may be required to control severe outbreaks of red
thread. Products include Spectracide Immunox (myclobutanil),
Cleary's 3336 (thiophanate methyl), Bayleton (triadimefon), and
those fungicides containing mancozeb as the active ingredient.
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