AgWatch

Spring Dead Spot Of Forage Bermudagrass

 DR. RAY SMITH
LEXINGTON, KY.
   Last week, we diagnosed a case of spring dead spot from a bermudagrass hayfield in central Kentucky. With increasing interest in bermudagrass for forage production in the region, this is a disease producers should be aware of.
   Symptoms
   The disease appears in the springtime as dead patches of varying size that often are roughly circular. These patches simply fail to green up in the spring. When symptoms are severe, the patches can blend together, leaving large areas of dead forage. Bermudagrass will fill in the dead areas as the summer progresses, but regrowth can often be slow and weeds will compete to grow in the dead patches.
   Symptoms of the disease result from fungal infection in the roots, rhizomes and stolons which occurred during late summer and autumn of the previous year. The infections don’t kill the bermudagrass directly, but they predispose these infected patches to the cold temperatures that normally occur during Kentucky winters.
   Management
   Thus far, we have no direct research experience on spring dead spot in forage bermudagrass, but we have a fair amount of experience in research and management of this disease on turf-type bermudagrasses. In turfgrass situations, we know that one of the best practices the turf manager can do is to lower the pH of the soil, which significantly reduces disease activity (probably by enhancing resistance of the roots to fungal infection). However, we also know that, if the pH gets too low, forage bermudagrass becomes less productive and potassium and phosphorous become less available. The recommended pH for forage bermudagrass is 6.0 and above. If a forage producer has a severe enough problem with this disease, it may help to take a soil test and reduce the pH slightly, although it is important not to let the pH drop below 5.5-5.6.
   In turfgrass settings, we often see the disease diminish greatly from one year to the next, all on its own, through forces of nature that we do not fully understand. (It might be a form of natural biological control that is occurring in the complex microbial environment of the soil.) Thus, one option for a forage producer is to simply let the disease run its course, though it is important to recognize that disease severity could be higher next spring instead of lower.
   Producers of forage bermudagrass in Kentucky should be sure to select a variety that is proven to be winterhardy. ‘Wrangler’ is the only seeded variety proven to meet this standard. Examples of sprigged forage bermudagrasses proven to be winterhardy include ‘Tifton 44’ and ‘Quickstand’. Δ
Dr. Paul Vincelli is Extension Plant Pathologist and Dr. Ray Smith is Extension Forage Agronomist with the University of Kentucky at Lexington.

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