Tech Notes Issue 9

Spring Dead Spot is Difficult to Control in the Spring… Manage it in the Fall

A chronic and difficult disease to control of couchgrass is Spring Dead Spot (SDS). Spring dead spot symptoms appear in spring when couch-grass begins growth or "green up". These conditions exist in the United States in the northern range of couchgrass adaptation.

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 non-uniform 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 de-struction 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 tempera-tures are below 21 C (70F). It has been observed, and subsequently researched that freezing tempera-tures following pathogen infection and activity enhances symptom expression. Couchgrass freeze tolerance is decreased by infec-tion by these ERI fungi making winter injury a greater possibility.

Some management suggestions:

1. Establishing cold tolerant va-rieties is probably the best practice

2. map severely affected areas (previous spring observations) for targeted fall fungicide ap-plications,

3. Aerify and/or spike severely affected areas every two weeks.

4. Choose your nitrogen care-fully. Some new studies (not well documented yet) have shown that ammonium sulfate is only suppressing spring dead spot caused by Ophi-osphaerella herpotricha and is having NO EFFECT on O. kor-rae. Calcium nitrate, on the other hand, is doing an excel-lent job of controlling spring dead spot caused by O. kor-rae, but is having no effect on O. herpotricha. (Lane Tread-way, North Carolina State Uni-versity)

Photograph: Spring Dead Spot symp-toms on couchgrass as it breaks winter dormancy. The nitrogen suppression affect on this disease is dependent on pathogen and nitrogen source.