The Effects of Nitrogen and Trinexapac-Ethyl On the Severity of Brown Ring Patch On Annual Bluegrass Golf Course Putting Greens.

The effects of three nitrogen sources (calcium nitrate, ammonium sulfate or urea), the plant growth regulator trinexapac-ethyl (TE) and the fungicide azoxystrobin on brown ring patch were assessed on annual bluegrass putting greens. Waitea circinata var. circinata is a Rhizoctonia pathogen and the causal agent of brown ring patch. It causes yellow to brown rings or semi-circles that become necrotic or sunken over time on annual bluegrass (Poa annua) and rough bluegrass (Poa trivialis). Severely affected locations are associated with low nitrogen fertility, but guidelines for other Rhizoctonia diseases (such as brown patch) suggest high nitrogen fertility increases disease. In the first set of experiments, 240g/100 m² of the three nitrogen sources was applied with and without TE (0.048 g/100 m²) to replicated plots on a putting green developing brown ring patch. In a second set of experiments, azoxystrobin (0.43 g/100 m²) was applied to plots showing disease, alone or with nitrate, or nitrate plus TE. Plots were evaluated for disease and chlorophyll content. All three nitrogen sources increased chlorophyll readings and decreased disease severity. Amongst the sources, urea appeared to provide the greatest increase in chlorophyll. Applications of nitrogen and TE also reduced disease severity, and provided a higher chlorophyll reading than nitrogen used alone. TE used alone, increased chlorophyll readings but caused a very slight increase in disease severity. The addition of nitrate to azoxystrobin decreased disease severity and improved disease recovery as compared to azoxystrobin alone. Plots treated with azoxystrobin, nitrate and TE had slightly less disease than those treated only with azoxystrobin and nitrogen. Results demonstrated that adequate nitrogen fertility is an important aspect of brown ring patch management, especially when used in combination with TE. These results provide timely and practical information for the management of this new disease.