Diseases Caused by Dematiaceous Fungal Pathogens as Potential Limiting Factors for Production of Bermudagrass on Swine Effluent Application Sites

Abstract

Plant diseases that reduce the survival and productivity of forage crops on animal waste disposal sites may limit removal of waste‐derived nutrients in harvested hay. However, no studies have documented the occurrence and importance of plant diseases on waste disposal sites in the southeastern USA. During 1998, symptoms of leaf, stem, crown, and root necrosis were observed in common bermudagrass [Cynodon dactylon (L.) Pers.] on three swine waste disposal sites in Mississippi. Species of Exserohilum, Bipolaris, and Curvularia grew from 82 to 100% of leaf and stem tissues from symptomatic plants, and six species were identified among 266 isolates. E. rostratum (Drechs.) Leonard & Suggs and B. spicifera (Bainier) Subramanian were most frequent in samples from a severely diseased stand, and C. lunata (Wakk.) Boedijn and C. geniculata (Tracy & Earle) Boedijn were most frequent from moderately and slightly diseased stands. In inoculation experiments, E. rostratum was most virulent and caused extensive necrosis of bermudagrass leaves; B. stenospila (Drechs.) Shoemaker, B. cynodontis (Marignoni) Shoemaker, and B. spicifera were intermediate in virulence; and C. lunata and C. geniculata were least virulent. When samples of healthy and diseased bermudagrass from a severely diseased site were compared for forage production over three harvests in the greenhouse, mean dry matter yields of diseased grass were 37 to 52% of healthy yields. Results indicate that dematiaceous fungal diseases may cause stand decline and yield reduction of bermudagrass on swine effluent application sites, and that E. rostratum and Bipolaris spp. are the most damaging pathogens encountered to date.