Potassium Fertilization Increases Microdochium Patch Incidence and Severity on Creeping Bentgrass.

Despite the many benefits associated with potassium (K) fertilization of turfgrass, few research studies have examined how the soil and tissue levels of potassium influence turfgrass quality, growth, and disease development. Turfgrass managers often apply large doses of potassium to turfgrass (>300 kg/ha) to putting greens. However, with more accurate information, turfgrass managers may be able to reduce their potassium applications, thus saving time and money, while not reducing and possibly enhancing the quality of the turfgrass they manage. The objective of this research is to evaluate putting green quality, growth, and disease incidence over a wide range of soil test and tissue potassium levels.

This project was initiated in 2011 on a USGA putting green with ‘A4’ creeping bentgrass. The experiment was a randomized complete block design with four replications. The treatments included five different levels of biweekly liquid potassium sulfate at rates ranging from zero to 30 kg/ha of K. Paired soil and plant tissue samples were collected monthly along with measurements of clipping yield. Turfgrass color and visual quality was evaluated biweekly. Disease incidence was quantified by counting Microdochium patch infection centers and disease severity was visually rated as percent area affected by using the grid intersection method.

Few, if any, differences in turf color, quality, or growth rate among the treatments were observed during the first four years of the study. In the fifth year, significantly lower turf quality was observed on the two no K treatments. However, these low K treatments had significantly less Microdochium patch than the treatments receiving K applications during the past three winters. Plant tissue K content was below 1.5% in treatments with the least Microdochium patch compared to tissue K content between 1.8-2.2% in K treated plots. Mehlich-3 K was near 20 mg/kg in the no K treatments and ranged from 25-50 mg/kg in the treatments receiving K. No significant differences in other diseases including dollar spot or brown patch were observed during the study. Results suggest that potassium fertilization can be manipulated to reduce Microdochium patch severity on creeping bentgrass putting greens.