The windborne spores eventually may be deposited onto healthy grass and create new infections. The spores also may be washed down to the soil level and infect crowns and roots, initiating the melting out phase of the disease syndrome. The spots enlarge to span the width of the leaf, killing the tips of affected blades. The stand will thin as infections to crowns and roots kill entire plants. Prevention of leaf spot development is based on avoiding the application of excess nitrogen fertilizer in early spring.
Fungicides can be effective in minimizing the damage.
But, for satisfactory results, they must be applied early in the spring, as grass begins to turn green. A balanced nitrogen fertility program in the fall will eliminate the need for fungicide. Red thread may occur on all cool season turfgrasses used for Midwestern lawns. It is generally a disease of spring and fall, with symptoms often disappearing during the heat of the summer. Outbreaks occur in turf stands where nitrogen fertility is at less than optimum levels.