Mustard Seed Meal (Brassica juncea) Biofumigation Controls Dollar Spot (Sclerotinia homoeocarpa) in Vitro and Has Low Phytotoxicity to Bentgrass Under Field Conditions

Dollar spot, caused by Sclerotinia homeocarpa F.T. Bennett, is a common disease of turfgrass.  It has become particularly problematic on creeping bentgrass (Agrostis stolonifera L.) putting greens. Dollar spot resistance to the fungicides Thiophanate-methy, iprodione, and propiconazole has been observed at a large number of golf courses sampled in Tennessee. An alternative control is needed for this disease.  We conducted  lab and field experiments to determine if the volatiles produced from Hydrated Indian mustard (Brassica juncea L. Czerniak) seed meal can provide a viable bio-control for dollar spot.  Lab studies determined that mustard seed meal at 0.05 g ml^-1 completely suppressed mycelial growth in vitro and that the LD50 was less than 0.02 g ml^-1.  In field studies we demonstrated that the low rates effective for growth suppression (< 0.05 g ml^-1) in vitro were not phytotoxic to established creeping bentgrass. In fact no phytotoxicity occurred until rates exceeded 1.0 g ml^-1 of mustard meal applied. These results warrant further research to determine if mustard meal can be an effective biofumigation treatment control strategy for managing dollar spot in field conditions.