Composting is great, but not if it has a toxic herbicide in it

Using grass clipping in your compost could pose a danger to evergreens if you're not careful

As the green movement continues to expand throughout the minds and practices of consumers, more people are aware of the advantages of composting. It cuts down on the amount of garbage we toss and it’s a great amendment for trees and home gardens.

But a darker side of composting has reared its ugly head.

If you’re been putting grass clippings in your compost, you may need to think again. Last month, the Environmental Protection Agency sent a letter to DuPont ordering the company “to immediately halt the sale, use or distribution of Imprelis, an herbicide marketed to control weeds that has been reported to be harming a large number of trees, including Norway spruce and white pine.” This order requires the chemical company to stop selling and distributing Imprelis in the United States and details specific steps to ensure its removal from the marketplace.

Imprelis was approved by the U.S. EPA in August 2010 to help control broad leaf weeds in turf grass. Originally thought to be environmentally friendly when it was introduced in 2010, landscapers who used the weed killer this spring have reported nearby evergreen trees began to die after its application.

DuPont originally said Imprelis´ key ingredient  aminocyclopyrachlor was used at lower rates than similar herbicides, and was less persistent in grass clippings and degrades in compost.

But on Aug. 4, a week before the EPA banned Imprelis, DuPont voluntarily suspended sales of the product and announced it would  implement a refund program.

White pine devastation from Imprelis use

In May, the U.S. Composting Council issued a warning to composters to watch out for grass clippings that were contaminated with Imprelis. At issue  the USCC said, is that unlike most herbicides,Imprelis will survive the composting process and still remain active. Preliminary research earlier this year by the USCC showed that Imprelis doesn’t break down significantly faster than the leaves and grass in the compost, so the concentration stays about the same.

On June 17th, DuPont sent a letter to professional applicators cautioning against the use of Imprelis where Norway spruce or white pine were nearby.

Dead trees caused by Imprelis use

As expected, there’s a class action suit in the works – with client groups in Ohio, Michigan, Indiana, Iowa, and Minnesota, with  plans to file additional actions in Wisconsin, Illinois, Kansas and South Dakota.  The EPA has received more than 7,000 reports of damaged trees so far. They’re continuing to assess whether the damages are the result of product misuse, inadequate warnings and label use directions, persistence in soil or plant material, uptake through root systems and absorption into plant tissue, environmental factors, potential runoff issues or other causes.

So buyers beware – again. You may need to check your garage to see whether the package of weed killer you’ve been using contains this apparently highly damaging toxic chemical. If it does, be careful of using that compost!

An Ohio State researcher quoted in a BioCycle special report said 60 percent of the active ingredient remained in compost after 200 days, enough to do damage to a number of susceptible garden plants including beans, cucumbers and tomatoes.

Is this another case of it’s better to go organic? As they say, it couldn’t hurt.


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