Metsulfuron-Methyl Herbicides and Potential Concerns

Herbicides containing Metsulfuron-Methyl(MSM) are becoming more common to treat weed growth in lawns across the state. These herbicides are very effective at targeting and maintaining even the most stubborn types of broadleaf weeds and weed grasses such as Bahia, without damaging surrounding and desired turfgrasses like St Augustine and Bermuda. This effectiveness has led to MSM-containing herbicides becoming very popular among landscape and ground crews. However, the growing popularity of these herbicides is being linked to an observable pattern of decline in ornamental trees located close to MSM application areas.

Herbicides containing Metsulfuron-Methyl are systemic. Meaning, they enter the plant by absorption through the roots or foliage and then travel throughout the vascular tissue. This makes the herbicide very effective against their intended targets, while leaving more desirable turf grasses unharmed due to their natural resistances to MSM. Additionally, the targeted systemic nature of these applications means better results are achieved while needing to use much less of the actual product.

All these advantages have led to rapid growth in the number of lawns receiving these treatments. However, the increased use of these products are beginning to show links with rapid decline in certain ornamental trees located close to application areas. Specifically, when these applications happen during the warmer and dryer months of the year.

Although the common use of MSM-containing herbicides is still relatively new, only growing in popularity over the last decade or so, many observations have been made showing a direct correlation between MSM applications and ornamental tree and shrub decline. Most commonly within Oak species and Palms.

MSM products typically come in a dry, granular form and are mixed with water and applied with a sprayer. Rain or irrigation then helps the product work its way into the surrounding soil.

Trees and shrubs that have root systems extending beneath the soil into the treated turf areas have a potential to absorb these herbicides and fall into rapid decline. Additionally, when located in low-lying areas, these trees and shrubs appear to be even more affected due to rain runoff concentrating the herbicide around their root zones. Sudden and rapid necrosis of the vascular tissue, as well as a “scorched” or “fried” look to the foliage are signs often spotted in as little as 2-4 weeks after application.

Vascular tissue damage caused by MSM