2017 ASHS Annual Conference

Metsulfuron-methyl (or MSM) is a sulfonylurea herbicide used primarily as a selective postemergence herbicide for broadleaf weeds in turf. Due to its low cost and high efficacy at low dosages, MSM has become one of the most widely used turf herbicides in the industry. While there has been extensive research published pertaining to efficacy and safety in turf, very little research has focused on the impacts of this herbicide to landscape plants growing in these turf sites. The objective of this project was to determine the impact of MSM on growth and establishment of live oaks and ligustrum following spring and summer applications to nearby turf. Quercus virginiana (live oak) and Ligustrum japonicum (ligustrum) (both in 11.4-L containers) were outplanted into the field at the Mid-Florida Research and Education Center in October, 2015, mulched, and drip-irrigated. In April 2016, directed applications of MSM were made to both species with a CO₂ backpack sprayer 2 inches outside of the initial root-ball zone so that no foliage was contacted and the initial root ball area (11.5 in. diameter pot size) was not directly contacted. Metsulfuron was applied at 8.9, 17.5, 35, 70, and 140 grams active ingredient per ha. Data collected included visual phytotoxicity ratings at 15, 30, 60, and 90 days after treatment (DAT) on both species. At 90 DAT, growth indices [(plant height + plant width1 + plant width2)/3] were taken on ligustrum and caliper and height were measured on live oak. Results showed that MSM reduced growth of both species at all rates tested with limited differences between the four lowest rates. The greatest growth reduction was observed in plants treated at the 2× rate. Both species exhibited injury at all rates, and injury increased with increasing MSM rate with the highest rate typically resulting in plant death. Results suggest that, as per label instructions, MSM should not be applied in areas where roots of ornamental plants extend. It is important to educate pesticide applicators on how far ornamental roots may extend into areas planted with turf.