Soil-borne diseases on turf can be among the most insidious infections that golf course superintendents will face and they often begin much earlier than symptom expression. To further complicate matters, symptoms caused by soil-borne diseases can be very general-looking, making identification and, ultimately, treatment, more difficult. Below are some common soil-borne diseases called ectotrophic root-infecting fungi:
Take-all patch, caused by Gaeumannomyces graminis f sp. avenae, is most common on creeping bentgrass but can occur on bluegrass, fescue and ryegrass. Symptom expression starts in spring/early summer and can persist into the fall. Patches can be large in size, up to three feet in diameter and often have a reddish-to-purplish hue visible on the expanding edges. Signs of the disease include roots colonized with black mycelium and perithecia present in plant crowns.
Necrotic ring spot, caused by Ophiosphaerella korrae, occurs on all cool season grasses. Patches caused by this disease are usually smaller in size (around 12 in. diameter) but can exceed three feet diameter. Cool, wet weather favors development of necrotic ring spot. As the name implies, the patches can have a ring-like appearance, but in some instances all of the grass within the patch may die. Roots may be colonized with dark brown mycelium.
Summer patch, caused by Magnaporthe poae, infects Kentucky bluegrass, annual bluegrass and fescue. Patches start as small areas of thin, slightly bronze-colored turf and then fade to a typical straw color. They are sometimes called frog-eyes because of their ring-like appearance. As with the previous two diseases, patches are usually small in size but can enlarge to be more than three feet in diameter, depending on the host, and dark brown-to-black-colored mycelium can be found growing on the roots.
With all of these diseases, recovery time is slow once the disease has developed and symptoms are apparent. The ideal treatment is a preventive fungicide, such as Tourney Fungicide from Valent Professional Products, applied with a high volume of water (3+ gallons/tsf) or watered-in after application early in the season. As always, please consult a plant disease diagnostic lab for help with identification.