Recent damage due to Metsulfuron-Methyl containing herbicides has shown up in Volusia County on our stately oaks. This time, a mature, well-loved Laurel Oak. The damage occurs when the herbicide is applied to St. Augustine grass from a commercial lawn service to eliminate broadleaved weeds in a neighboring yard. Unfortunately, certain ornamental trees and shrub roots have surface roots intertwined with turf roots and they too become damaged. Scorched, brown/red burned foliage shows up typically 2-4 weeks after exposure. In severe cases, entire branches, sections or the tree will die because of the exposure. Damage is most common in spring where the weather is hot, dry and new growth begins to flush out.
How it works
Dr. Jason Smith, Associate Professor (Forest Pathology) at the UF School of Forest Resources & Conservation has researched the problems with Metsulfuron methyl containing herbicides and their effects on oaks and other ornamentals. He maintains, “In addition to foliar absorption, metsulfuron-methyl is also rapidly absorbed by plant roots. Because it is systemic, it can move throughout the plant and accumulate in meristematic tissues.” The damage is more prevalent on oak species (Quercus spp.), Ligustrum (Ligustrum spp.), and certain palm trees.
Reducing the damage
According to Smith, “It is important not only to use an herbicide with the correct concentration of the correct active ingredient, but also the one labeled for a specific crop or site. For example, Nufarm’s Manor® and PurestandTM both contain 60% of metsulfuron-methyl, but the former is labeled for turfgrass and the latter for pastures. Thus, applying PurestandTM to turf would be an off-label use. Some metsulfuron herbicides labeled for turf are registered in the Crop Data Management Systems (CDMS) http://www.cdms.net/Label-Database . A web-wide search can yield equally suitable products (including generic options), like MSM Turf Herbicide Quali-Pro or Rometsol® by Rotam.”
It is important to READ THE HERBICIDE LABEL CAREFULLY, use the proper rate and avoid off-target damage. Always calibrate your equipment properly and avoid making applications during high ambient temperatures and low relative humidity. The label states “Do not plant ornamentals such as shrubs, and trees in treated areas for at least 1 year after the last application or bedding plants for at least 2 years.” For more information click on the link below or reach out to your local county extension agent.
Metsulfuron-Methyl-Containing Herbicides Potentially Damaging Ornamentals when Applied to Turfgrass1