Tech Notes Issue 5

Autumn Spring Dead Spot Management

A chronic and difficult disease to control of couchgrass is Spring Dead Spot (SDS). Spring dead spot symptoms appear in late winter/early spring when couchgrass begins growth or "green up".

The circular patches of dead turfgrass normally 1 meter (3 feet) in diameter tend to reappear and expand in the same spot yearly. The turfgrass plants quickly slough-off causing the sunken patches. The patches can coalesce appearing as nonuniform areas. Three species of Ophiosphaerella - O. herpotricha, O. korrae, O. narmari - have been reported to cause spring dead spot. The pathogens of spring dead spot are considered ectotrophic root infecting (ERI) fungi. Species of Ophiosphaerella produce ectotrophic runner hypae along the surface of roots and stolons that lead to infection and eventually blackening and destruction of the root system.

These pathogens are thought to be most active in the fall and spring when the couchgrass is either entering dormancy in the fall or breaking dormancy in the spring usually when soil temperatures are below 21 C. It has been observed, and subsequently researched that freezing temperatures following pathogen infection and activity enhances symptom expression. Couchgrass freeze tolerance is decreased by infection by these ERI fungi making winter injury a greater possibility.

Some management suggestions:

1. Map severely affected areas (previous spring observations) for targeted fall fungicide applications
2. Aerify and/or spike severely affected areas every two weeks
3. Choose your nitrogen carefully. Some new studies (not well documented yet) have shown that ammonium sulfate is only suppressing spring dead spot caused by Ophiosphaerella herpotricha and is having NO EFFECT on O. korrae. Calcium nitrate, on the other hand, is doing an excellent job of controlling spring dead spot caused by O. korrae, but is having no effect on O. herpotricha. (Lane Treadway, North Carolina State University)

Chemical Control

Fungicide applications may be warranted in areas where SDS causes chronic severe disease. In these situations it may take the turf several months before the turf grows out of the symptoms. Fungicides like BANNER MAXX and HERITAGE MAXX are available.