Imprelis herbicide (active ingredient aminocyclopyrachlor) is being recalled by the E.I. duPont de Nemours and Company because of damage and death to nontarget trees. Homeowners, and landscape and pest control professionals are also being warned not to compost grass clippings from Imprelis-treated lawns.
Imprelis herbicide received conditional registration from the U.S. Environmental Protection Agency (EPA) in October 2010 as safe for use in residential, industrial, and institutional lawns and on golf courses to control broadleaf weeds. But applications adjacent to white pine, Norway spruce, and other evergreen trees have caused twisting and curling of new growth, which progressed to the browning and death of affected of trees. See photos below.
The U.S. EPA issued a 'stop sale' order for Imprelis (EPA Registration Number 352-793) effective August 11, 2011. This involves cease sale, use, and removal of the product. DuPont is planning a product return and refund program.
Damage to trees has been reported throughout the Midwest, in East Coast states, and along the Gulf Coast. New information provided to EPA by DuPont (July 2011) included thousands of reports of adverse incidents involving damage or death to trees associated with Imprelis applications. Test data from DuPont (also provided July 2011) showed phytotoxicity to Norway spruce and balsam fir, confirming damage reports.
Grass clippings from treated turfgrass should not be composted or used as mulch. From an EPA Pesticide Program Update (August 16, 2011): "As a part of EPA's efforts to minimize injury to trees following use of the herbicide Imprelis, EPA is reminding people that grass clippings that have been treated with Imprelis should not be used for composting or mulching, and trees that may have been injured from Imprelis should also not be used for compost or mulch. This is because clippings from grass treated with Imprelis or mulch from trees injured by Imprelis could continue to cause non-target plant damage."
"Specifically, the Imprelis label has the following restrictions on mulch and compost: Do not use grass clippings from treated areas for mulch or compost, or allow for collection to composting facilities. Grass clippings must either be left on the treated area, or, if allowed by local yard waste regulations, disposed of in the trash. Applicators must give verbal or written notice to property owner/ property manager/ residents to not use grass clippings from treated turf for mulch or compost."
Damaged conifer leader following Imprelis herbicide application.
Links to this article are strongly encouraged, and this article may be republished without further permission if published as written and if credit is given to the author, Horticulture and Home Pest News, and Iowa State University Extension and Outreach. If this article is to be used in any other manner, permission from the author is required. This article was originally published on August 24, 2011. The information contained within may not be the most current and accurate depending on when it is accessed.