Grass Clippings and Herbicides

I have received a few questions recently regarding the use of grass clippings on lawns treated with herbicides. Here is one of those questions: “Our Master Gardener Association will be working on a project in which they hope to use a great amount of lawn clippings to put down as compost in a large area. This will require lawn clippings donated from several different sites. Will they run into a problem with clippings from lawns that have been treated with Imprelis® this year? Would there be chemical residue which remains in the clippings and/or compost which should be avoided?”

The answer to that specific question is that we do not recommend that clippings from lawns treated with Imprelis® (aminocyclopyrachlor) be used in the composting. Even if Imprelis® was applied 6 months ago (applied in April, today’s date October 12) there still could be some Imprelis® residue present in the clippings or the soil. Although any herbicide residue may be minimal from a spring application, we 1) don’t fully understand how long Imprelis® lasts in the soil or the grass clippings and 2) Imprelis® is active at very low rates and thus even if just a little is left it could be enough to cause injury on a susceptible ornamental plant such as tomatoes in the garden or flowers in the landscape.

The Imprelis label states “Do not use grass clippings from treated areas for mulching 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.”

The Imprelis® label does not state how long not to remove clippings. Eternity, 1 year, 2 months? It simply does not say. Therefore, I recommend not to use clippings from Imprelis® treated lawns in compost.

What about other herbicides? Other herbicides applied to residential turf may have label language as well that restricts clippings from being collected. The Dimension® 2EW (dithiopyr) label also states “Do not use clippings from treated turf for mulching around vegetables or fruit trees.” Like the Imprelis® label, the Dimension® 2EW label also does not specify how long to wait after treating before clippings can be safely harvested. Another herbicide, Drive® XLR8 (quinclorac), states that “Clippings from the first three mowings after application should be left on the treated area”. This label makes it a little clearer when it is safe to harvest clippings. Most labels contain no reference whatsoever to “clippings”.

Therefore, language varies from label to label regarding the use of clippings for mulch or compost following a herbicide application. In most cases I would recommend not using clippings from a lawn treated with herbicide within one-month (approximately 3 mowings) unless the label states otherwise such as with Imprelis®.

Aaron Patton, Turfgrass Extension Specialist