These conditions include the susceptible host
(creeping red fescue), the disease-causing agent (causal fungi, Laetisaria fuciformis), and the correct environmental conditions
(67-75 degrees F, rain) over a period of time. All three legs of
the triangle must be present for red thread to develop.
Managing lawn diseases involves interrupting one or more of the
legs of the triangle.
The use of
resistant varieties of grasses disrupts disease development by
removing the susceptible host.
Cultural controls such as raising the mowing height, watering
deeply and infrequently, maintaining a balanced level of
fertility, periodic dethatching, and core aeration to alleviate
soil compaction disrupt some of the environmental conditions
required for red thread to develop. Finally, the use of
fungicides disrupts the causal fungi.
Classic red thread symptoms
is most severe on perennial ryegrass and fine fescues. It often
appears with another disease called pink patch, Limonomyces
roseipellis. Both diseases have similar symptoms. The causal
fungi overwinter on dead blades of grass or clipping debris from
last season. Air temperatures of 65 to 75°F and rainy or humid
weather favor the development of red thread and pink patch. Red
thread and pink patch are spread on turf equipment and by foot
traffic. From a distance, affected patches of grass have a
reddish or pink cast. Affected leaf blades dry out and take on a
bleached out straw color. Distinct symptoms appear as the
diseases progress. For red thread, reddish, thread-like fungal
mycelium extends from the tip of infected blades of grass. Pink
patch appears like pink cotton candy coating infected blades of
Cultural controls include
maintaining adequate fertility levels;
red thread and pink patch 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
such as leaf spot to develop.
Overseeding or replacing
susceptible grasses with resistant varieties is helpful in
controlling these diseases. Resistant varieties of perennial
ryegrass include Assure, Derby Supreme, Gettysburg, Legacy,
Loretta, Pinnacle, Regal and Sherwood.
While home lawns rarely warrant fungicide applications to
control red thread, it may be necessary when lawns are composed
of pure stands of perennials ryegrass or fine fescues.
Fungicides labeled to control red thread and pink patch on home
lawns include Cleary's 3336 (thiophanate methyl), Bayleton (triadimefon),
and those containing mancozeb as the active ingredient.