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College of Food, Agricultural, and Environmental Sciences


Herbicide-Treated Mulches May Provide Good Weed Control

June 27, 2001

COLUMBUS, Ohio - Mulches pre-treated with herbicides may provide a new, better way to control weeds in nurseries.

Hannah Mathers, an Ohio State University Extension nursery and landscape specialist, along with graduate student Luke Case, is studying the effect of chemically treated mulches on ornamental plants. The researchers are trying to determine whether a type of mulch, pre-treated with a specific herbicide, would be an effective alternative to applying chemicals directly onto the soil or plant.

Mathers said there are problems associated with herbicide use in container production, including improper calibration, herbicide run-off from plastic or gravel, and the need for multiple applications.

"As with other crops, off-site movement of pesticides through herbicide leaching, run-off and spray drift is a concern facing nursery growers," said Mathers. "In addition, many container nurseries make three to five herbicide applications annually, resulting in significant non-target herbicide loss."

Previous studies indicate that depending on the growth habit and container spacing, non-target loss (herbicide falling between pots) can be as high as 86 percent.

Mathers and Case are evaluating whether the use of mulches pre-treated with herbicides reduces off-site movement and increases pre-emergent efficacy and duration. They are also studying the effect chemically treated mulches have on overall plant phytotoxicity.

"We speculate the mulch binds the herbicide up and acts as a slow-release carrier, releasing the herbicide over the entire growing season," said Mathers. "There is no direct application of herbicides on the soil or the plant, and the mulch itself determines how much of the chemical is applied to the surface."

The project, funded by the Horticultural Research Institute, Ohio Research Endowment, and Scarff's Nursery in the Dayton/Springfield area, is a spinoff of research Mathers conducted in Oregon that showed good weed control and low phytotoxicity with pre-treated Douglas fir bark.

The current project, which began in late June, focuses on mulches typically found in Ohio, including pine, palletized recycled paper (PennMulch'), cypress, hardwood, rice hulls and cocoa beans. Each type of mulch was treated with one of two types of herbicides, Surflan or Flumioxazin (not yet registered for ornamentals).

Mathers and Case will conduct three trials. One will track the performance of the herbicide-treated mulches over the normal life of herbicides, 40-45 days. Another trial will measure the effectiveness of the herbicide-treated mulches for the duration of the growing season, and a third will measure the effectiveness of pre-treated mulches into the next growing season.

Mathers hopes that if an effective herbicide-treated mulch is found, a company will be willing to market the product. "This could become something big. The product has potential beyond container plants. The ultimate market is the larger landscape industry. It's something the green industry is really interested in right now."

Candace Pollock
Hannah Mathers