Mini Rings are now active on ultra-dwarf bermudagrass putting greens. The fungus also can be active on bentgrass putting greens at this time. According to Steve Kammerer, a University of Florida MS candidate and Syngenta Field Technical Manager, this is a fungus caused by Rhizoctonia zeae and it infects the sheaths of older leaf blades in the lower canopy. The outbreaks for some reason are a little later than normal, but perhaps the additional overcast skies the past few weeks has allowed the fungus to become more active. Seeing this fungus active now on putting greens is far better than in the cooler weather, as new growth can still happen. When the mini rings occur in the fall, during cooler weather, the rings can sometimes hang around until next spring when new growth resumes.
If you see the mini rings now, curative fungicide programs can work and kill the pathogen. It is important to apply both a systemic and contact fungicide together. Since the transportation system of the plant has been affected by the fungus, the contact does help with this situation. Dead tissue inside the plant causes some failure of the transportation system. The contact fungicides will also help to reduce the fungus on dead tissue outside the plant, while the systemic fungicide helps to reduce infection inside the plants. As long as the temperatures remain hot, keep applying the contact and systemic fungicides at 2 week intervals. Call or email the SE Region office for more information on curative fungicide programs.
It may take 4 to 6 weeks for the ring symptoms to disappear after the infection at this time of the summer. The fungus releases toxins, and it may take awhile for the toxins to degrade in the soil and new tissue growth happens. Also, with all the underground plant parts on an ultra-dwarf bermudagrass, it is more of a challenge to get the fungicides into the zone where they are needed, versus bentgrass. Since the Rhizoctonia zeae resides at soil level and not the aerial zone of the plant, it is important to irrigate the fungicides below the infection area.
The other key to this disease management besides curative fungicides, now, is fertility. This disease is worst on low fertility sites as opposed to higher fertility. Applying a little more nitrogen or fertility will promote new tissue growth, a big plus.
If we can do anything to assist with this disease issue, please call our office.