Assessment of Nitrogen Source, Sulfur, and Fall Fungicide Applications on the Management of Spring Dead Spot of Bermudagrass.

Abstract

Spring dead spot, caused by species of Ophiosphaerella, is the most serious disease of bermudagrass (Cynodon spp.) in regions where cold temperatures induce winter dormancy. Previous research indicates that soil pH reduction may reduce spring dead spot severity. Of the 165 isolates collected from 16 sites in Missouri and surrounding regions, Ophiosphaerella herpotricha was the most prominent spring dead spot pathogen found, with 154 confirmed isolates. Ten isolates were identified as O. korrae, being detected at a low incidence at 6 of 16 sites. In in vitro assays, most mycelial growth of both species occurred from pH 5 to 6, with more growth on calcium-nitrate-amended media than ammonium sulfate. In a naturally infested field study, nitrogen source alone did not affect spring dead spot severity. Less spring dead spot severity (P < 0.05) was observed in plots receiving tebuconazole but no treatment provided more than 38% control after 1 year. Three sulfur applications (each at 98 kg ha-1) provided as much control as a single fall tebuconazole application (0.28 kg a.i. ha-1) in the second year; however, significant phytotoxicity was observed in sulfur-treated plots thereafter. The suppression obtained from one fall tebuconazole treatment was as effective as two.