Impact of Fertilization Programs and Preventive Fungicide Applications On Spring Dead Spot Pathogens.

Field studies were conducted in Raleigh, NC on ‘Tifway' bermudagrass that was artificially inoculated with the spring dead spot (SDS) pathogens Ophiosphaerella herpotricha (OH) and O. korrae (OK). Inoculation was performed in Oct 2005 using rye grain infested with each species. Fertilization and preventive fungicide treatments were applied in 2006 and 2007, and SDS symptoms induced by each species were evaluated in 2007 and 2008. Nitrogen source significantly impacted SDS development, but OH and OK responded differently. Ammonium sulfate and sulfur-coated urea suppressed OH as compared to calcium nitrate and urea. On the other hand, calcium nitrate significantly suppressed OK when compared to urea, ammonium sulfate, and sulfur coated urea. Fall applications of potassium chloride, dolomitic lime, gypsum, or elemental sulfur exhibited no effect on either SDS pathogen. Preventive applications of azoxystrobin + propiconazole, fenarimol, myclobutanil, or tebuconazole provided effective control of both species in 2007 and 2008. Propiconazole provided significant control only in 2007, and azoxystrobin did not suppress SDS in either year. While OH and OK were effectively controlled by several fungicides, these species responded very differently to nitrogen sources. Further research is needed to clarify the mechanisms by which SDS is influenced by nitrogen source. Fall applications of potassium and other nutrients may not be beneficial in spring dead spot management.