Mini Ring Information
Causal Agent(s)
- Rhizoctonia zeae
- Rhizoctonia oryzae
Hosts
- Hybrid bermudagrass
- Centipedegrass
- St. Augustinegrass
- Seashore paspalum
- Creeping bentgrass
- Tall fescue
Symptoms & Signs
Mini ring symptoms are most prevalent in the late summer to fall months (i.e., July through October). Depending on the timing and severity, symptoms may persist through the winter and into the following spring. Stand symptoms of mini ring manifest as frog eye, or ring-like, patches that range from a few inches to a few feet in diameter. The outer edges of these patches typically have a bleached or tan color, while the center of the patch appears generally healthy or unaffected. On individual plants, the older leaves may be entirely blighted. While under severe levels of disease, whole leaf sheaths, stolons, and nodes may be necrotic.
Images of mini ring symptoms:
When Does it Occur?
Air temperatures between 83° and 97° F are most conducive for R. zeae. However, infection can begin whenever air temperatures are consistently above 80° F. The pathogen was initially thought to only infect leaves and sheaths; however, recent research suggests the pathogen is more active in the crowns, nodes, and roots. Increases in plant stress, such as mechanical damage and low fertility, can increase disease severity. Extended periods of droughty conditions can also exacerbate symptoms.
Cultural Management
Reduce stress during conducive environmental conditions. Aggressive verticutting should be avoided. Nitrogen applications at rates between 0.1 – 0.3 lbs N 1000 ft-2 applied weekly can help reduce disease severity. Avoid ammonium sulfate as an N source as it has been documented to exacerbate disease severity, whereas urea reduced disease severity.
Chemical Management
Fungicide applications should be made preventatively for best results, since symptoms tend to manifest as environmental conditions become less favorable for hybrid bermudagrass growth. Begin preventative applications when daytime temperatures consistently break 80° F. Fungicide applications need to be watered in immediately with 1/8” irrigation to deliver the product to the crowns and upper rootzone.
