Effect of Oriental Mustard (Brassica juncea) Seed Meal for Control of Dollar Spot on Creeping Bentgrass (Agrostis stolonifera) Turf

This research evaluated oriental mustard [Brassica juncea (L.) Czern.] seed meal (MSM) for safety and efficacy in control of dollar spot (Sclerotinia homoeocarpa F.T. Benn.) in vitro and on creeping bentgrass (Agrostis stolonifera L.) turf. As a plant residual, MSM is the seed fraction that remains after seeds are crushed and oil is removed. The meal contains both nitrogen and secondary compounds termed glucosinolates. When moist, glucosinolates convert to fungicidal isothiocyanates. The in vitro study determined that MSM at higher rates completely suppressed S. homoeocarpa mycelial growth. A field study was conducted for 2 yr with three sequential applications of MSM at seven rates ranging from 0 to 1680 kg ha^-1, in addition to the fungicide iprodione at 3.1 kg a.i. ha^-1. In 2007, the severity of dollar spot infections varied among MSM treatments, with greater rates reducing dollar spot up to 82% compared with untreated control. In 2008, MSM at 1680 kg ha^-1 reduced dollar spot by 60% or greater 8 to 14 wk after initial application (WAIA). After application of MSM at 1120 kg ha^-1 or greater, the color of creeping bentgrass color was reduced 1 point on a 1 to 9 scale, but this reduction in color only lasted for 2 wk, and turf color in treated plots increased significantly by 6 WAIA compared with the untreated plots. Collectively, our results suggest that MSM is an organic material that could be integrated into a dollar spot management program on turf for minimizing selection of pathogen resistance to fungicides.