Nitrogen Source Impact on Dead Spot (ophiosphaerella Agrostis) Recovery in Creeping Bentgrass

Dead spot is a relatively new disease of creeping bentgrass (Agrostis stolonifera L.) incited by Ophiosphaerella agrostis Dernoeden, M.P.S. Câmara N.R. O’Neill van Berkum et M.E. Palm. Limited information is available with regards to chemical and cultural management strategies for dead spot. Two field studies were designed to evaluate the influence of various fertilizers and iprodione on the recovery of dead spot when applied after or during peak dead spot activity. When applied after peak activity, all N-sources (ammonium sulfate, IBDU, SCU, urea, Ringer Greens Super, and methylene urea) aided in the recovery and healing of dead spot, but none provided for complete recovery prior to winter. Plots treated with ammonium sulfate and IBDU were among the fastest and slowest to recover, respectively. Iprodione (3-(3,5-dichlorophenyl)-N-(1-methylethyl)-2,4-dioxo-1-imidazolidinecarboxamide) failed to improve dead spot recovery when applications were initiated in late summer after most injury was evident. When applied during the early stages of symptom expression, none of five water soluble N-sources (Ca(NO3)2, KNO3, (NH4)2SO4, urea, and 20-2020) examined in a second study prevented new infection centers from occurring. The percent of plot area diseased, however, continued to increase in plots not receiving N and significantly less dead spot was observed in all N-treated plots by early to mid-September of the first year (2002). In the second year (2003), dead spot recurred in plots treated with KNO3, Ca(NO3)2, 20-20-20, and urea. Conversely, dead spot did not recur in plots receiving (NH4)2SO4 or the unfertilized plots. The number of dead spot infection centers per plot in 2003 was positively correlated with pH in plots receiving N and disease incidence appeared to be favored at a pH greater than 6.0 and 6.6 in the mat and soil, respectively.