We have recently observed infections and symptoms of mini ring (leaf and sheath spot) in our TifEagle experimental green at the University of Georgia Griffin Campus. Environmental conditions characterized by hot spells, extended leaf wetness, and high humidity are favorable for disease development. While this week’s coolish temperatures are a temporary reprieve, turfgrass professionals should remain vigilant and continue scouting susceptible bermudagrass areas for early signs of infection.
Leaf and sheath spot (Mini ring), caused by Waitea zeae (Rhizoctonia zeae), initially appears as small circular patches ranging from a few inches to several feet in diameter. Symptoms often include yellowing, thinning, and chlorosis of turf within the affected areas. As the disease progresses, patches may develop a ring-like appearance with healthy turf in the center, giving rise to the name “mini ring.” Close inspection may reveal brown lesions on leaf sheaths and stolons. Symptoms can be mistaken for nutrient deficiencies, drought stress, or localized dry spots, making accurate diagnosis important.
Management Strategies
An integrated management approach is recommended for effective mini-ring suppression. Maintaining balanced fertility and adequate soil moisture can help reduce turf stress and improve recovery. avoiding excessive nitrogen fertilization. Urea-based nitrogen forms have been shown to ameliorate the disease, especially when applied preventively. Excessive thatch seems to be a principal factor in the onset of the disease (personal observation), therefore, implementation of dethatching procedures is a must for mini ring (LSS) management. Alleviating soil compaction through aerification and improving drainage may also reduce disease severity.
Preventive fungicide applications are often necessary in areas with a history of mini-ring. Fungicides in the strobilurin, demethylation inhibitor (DMI), and succinate dehydrogenase inhibitor (SDHI) chemical groups, and/or fungicide products containing combinations of these groups, have provided varying levels of control when applied preventively or at the first signs of disease. W. zeae is naturally resistant to methyl thiophanate-containing fungicide products. Precautions should be exercised when using DMI fungicides, as they can cause growth-regulating effects in ultradwarf bermudagrass under hot weather conditions. Water volume when applying the fungicide is important for adequate control. Usually, fungicides should be watered in using 1/8” to 1/10” irrigation shortly after application.
Check the Georgia Pest Management Handbook for a list of fungicides. Because fungicide efficacy can vary among sites and environmental conditions, turf managers should reach to your UGA county agent for locally-based recommendations. Always read the fungicide product label. Rotate fungicide modes of action to reduce the risk of resistance development. Continued monitoring throughout the growing season is essential, particularly on intensively managed bermudagrass putting greens, tees, fairways, and sports fields where mini ring has been problematic in previous years.