Influence of Application Methods On the Phytotoxicity of Mustard (Brassica juncea L. Czern.) Seed Meal On Creeping Bentgrass (Agrostis stolonifera L.) Turf.

Mustard (Brassica juncea L. Czern.) seed meal (MSM) is a byproduct of oil extraction from seeds. This plant-based material contains a secondary compound, glucosinolate, that when exposed to moisture is converted into a group of biocidal compounds, including isothiocyanates. Previous research has shown that application of MSM can suppress a wide range of pests on a variety of crops.  However, its usage on turf has been limited due to potential phytotoxicity. The objective of this study was to investigate the influence of MSM application method and rate on phytotoxicity to foliar and root tissues of creeping bentgrass (Agrostis stolonifera L.). MSM was applied at rates of 0, 1000 and 3000 kg/ha to creeping bentgrass maintained as a putting green under field conditions or grown in the pots under greenhouse conditions. Two application methods were used to deliver MSM, including topdressing only or topdressing following aeration. In the greenhouse study, MSM applied by either method at 3000 kg/ha caused greater foliar phytotoxicity than did MSM applied by either method at 1000 kg/ha. However, when applied as a topdressing following aeration, MSM at 3000 kg/ha resulted in an acceptable foliar phytotoxicity rating over a 3-week period and 3.5 times higher percent living cover at 3 weeks after treatments (WAT), compared to MSM applied as topdressing only. In comparison, MSM applied at 3000 kg/ha as topdressing only resulted in unacceptable foliar phytotoxicity ratings.  A similar trend was found in the 8-week field study in which MSM applied at either rate as a topdressing following aeration consistently caused less foliar phytotoxicity than did MSM applied without prior aeration.  In addition, when MSM was applied at either rate as a topdressing following aeration, root dry biomass was statistically same to the root biomass of untreated control. In comparison, when applied as topdressing without prior aeration, MSM applied at 1000 or 3000 kg/ha significantly reduced root biomass by 23 or 64%, respectively, relative to biomass in control treatments. Our results suggest that application of MSM as a topdressing following aeration can significantly reduce phytotoxicity effects on foliage and roots of creeping bentgrass turf.