June 16, 2011 | General

DuPont Label Says "Do Not Compost" Grass Clippings

Dupont herbicide compost Imprelis aminocyclopyrachlorBioCycle June 2011, Vol. 52, No. 6, p. 23
Agricultural chemical company now partnering with Scotts to introduce fertilizer/herbicide product containing aminocyclopyrachlor to consumer market.
Dan Sullivan

Related article in this issue: The Aminopyralid Challenge Continues

Clopyralid, bifenthrin, aminopyralid. All of these agricultural chemicals have made headlines because they do not readily break down in compost. In some instances, they’ve been linked to major crop damage. In others, they’ve shut off commercial composters from some of their most lucrative markets. (See Table 1 for BioCycle coverage of these events, which started more than a decade ago.)
So when Wilmington, Delaware-based DuPont began aggressively marketing a new post-emergent broadleaf herbicide to landscapers, lawn maintenance professionals and turfgrass managers – under the name Imprelis and containing the active ingredient aminocyclopyrachlor – some organics recyclers became concerned. (An “active ingredient” is that part of a pesticide or herbicide product which performs the desired action, in this case killing off broad leaf weeds.) The red flag wasn’t so much that the active ingredient sounded to the ear very much like other chemicals that have plagued the industry in recent years (and is in fact quite similar chemically). It had more to do with an ominous label restriction, which states:
“Do not use grass clippings from treated areas for mulching or compost, or allow for collection to compost 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 owners/property managers/residents not to use grass clippings from treated turf for mulch or compost.”
This spring, Pennsylvania State University crop and soil scientist, turfgrass specialist and Extension agent Peter Landschoot, received a query from a commercial composter and landscaper in Pittsburgh expressing concern over the label. “I am hoping you can shed some light on the herbicide ‘Imprelis’ by DuPont and their composting restriction … Is this a public relations measure after the problems with clopyralid, or otherwise?”
Landschoot, in turn, sent an email to DuPont global products development scientist Charles Silcox. “I’m curious to know if this is just a precaution because the herbicide can damage sensitive plants, or if you have data from actual composting operations that it does not break down as quickly or as completely as other broadleaf herbicides,” he asked. “Is the chemistry similar to clopyralid?”

In 2000, the herbicide clopyralid began turning up in compost in levels that might have been considered negligible (around .03 ppm) had it not been for the fact that, even at these barely traceable amounts, the tainted compost severely damaged certain susceptible plants. (BioCycle aggressively covered the issue between 2000 and 2004.) To protect the compost industry, the states of California, Oregon and Washington banned clopyralid for use on residential and commercial lawns (but not parks and golf courses), and the product’s developer, Dow AgroSciences, amended the label to more clearly state that clippings from turf treated with clopyralid should not be used as mulch or diverted to commercial composting facilities.
The synthetic pyrethroid bifenthrin did not appear to be a problem for California composters until after it began showing up in retail products to control fire ants (previously it had required a pesticide applicator’s license). While bifenthrin has not been shown to be taken up by or damage plants, there is concern that the chemical may be harmful to certain juvenile aquatic species. Similar to clopyralid, aminopyralid and aminocyclopyrachlor, bifenthrin soon proved to be persistent in compost (Table 1.)
Dow-produced aminopyralid products, marketed in the U.S. under the brand-names “Milestone” and “Forefront,” bear similarity to both DuPont’s Imprelis and Dow’s clopyralid products in that label restrictions prohibit composting of organic materials where they are applied. (See accompanying article, “The Aminopyralid Challenge Continues.”)
Dupont herbicide compost Imprelis aminocyclopyrachlor
Another similarity between the active ingredient in Imprelis and its persistent predecessors is that it’s about to be introduced to the consumer market. DuPont is partnering with Scotts to add aminocyclopyrachlor to a new retail fertilizer/herbicide product targeted to homeowners (currently Imprelis/aminocyclopyrachlor requires a professional pesticide applicator’s license). The new product would offer a boost to turf grass while also controlling broadleaf weeds over time.
The consumer product label will carry a similar warning regarding mulching and composting. However, DuPont’s Charles Silcox says new data showing that the herbicide does indeed break down after a period of time could lead to modified label restrictions – at US EPA’s discretion – regarding the eventual composting or mulching with treated yard trimmings. “The plan is to submit to EPA a number of clipping residue studies that analyzed aminocyclopyrachlor and clopyralid at standard application rates.”
For now, he says, “the label is the law” and, if followed correctly, should circumvent any potential problems. “As the label states, you can not use or send clippings from treated areas for composting or mulching.” Silcox notes that DuPont has been actively working with entities such as the U.S. Composting Council and Washington State University (WSU) “to make sure word gets out [about the restrictions] as much as possible as part of our stewardship operation for the product.”
Varying degradation rates exist even within the same chemical class, explains Silcox, couching aminocyclopyrachlor as a step up environmentally since the active ingredient is present at a fraction of the level of active ingredients found in other broadleaf herbicides and requires only one application per year. For instance, he says, the application rate for clopyralid is 2.7 times more than for aminocyclopyrachlor. “And clopyralid has a higher residue profile,” he adds, referring to what he characterized as clopyralid’s tendency to remain present in clippings at higher levels over time. “After seven days it’s about eight times more prevalent than Imprelis, and after 30 days it’s about 12 times more. Imprelis is not as persistent in grass clippings.”
Unlike the spray-applied liquid Imprelis, the aminocyclopyrachlor in the granular fertilizer/herbicide products under development with Scotts will primarily be taken up by the target weeds systemically, according to Silcox, who adds that the active ingredient would peak about seven days after application at about 1 or 2 parts per million (ppm). “We’ve done a couple of compost trials with Fred Michel at Ohio State. It does degrade – I can’t say it’s a rapid degradation. We’re studying the various composting practices and different types of composting.”

Fred Michel, Jr., an associate professor of Biosystems Engineering at The Ohio State University, confirmed that he’d been running compost tests comparing the degradation rates of aminocyclopyrachlor and clopyralid. But, he says, until attending the BioCycle Global 2011 Conference in San Diego in April – he had never heard of the name “Imprelis.”
“I’m working with Scotts and DuPont – they have funded studies,” explains Michel. “I was unaware it was being used already. I found out after giving a presentation on the fate of persistent herbicides during composting at the BioCycle conference and somebody in the audience asked me if I was aware of a new product called Imprelis. I got back to the lab and, sure enough, it was the same thing we’d been working on. From my standpoint, it doesn’t look like a great product to put out there. I can see having some problems with this stuff when it gets to the consumer level.”
Their research found that aminocyclopyrachlor does degrade in compost by about 60 percent over 200 days. “That is under worse-case scenario conditions with application to grass following label guidelines and composting grass cut within days after application – the time when it peaks in clippings is seven days – together with leaves at a 2:1 ratio and with no dilution of other grass,” Michel notes. “We’re composting in lab reactors with defined temperature, moisture content and oxygen levels.” He says a case could be made that under more variable conditions the herbicides might break down more rapidly. The half-life for the compounds in soil has been found to be approximately 50 days, so the microorganisms involved in its degradation may be less active at high temperatures. Therefore, tests in full-scale windrows are being conducted this summer.
The researchers made a potting soil blend utilizing a soil media called Pro-Mix containing either 0, 2.5, 5 or 10 percent compost into which they planted beans, cucumbers or tomatoes and observed the effects on plant development. All three plants suffered damage at varying levels of exposure to the aminocyclopyrachlor-tainted composts. Beans were most sensitive to aminocyclopyrachlor, while tomatoes and cucumbers appeared to be more sensitive to clopyralid. As another control (in addition to growing plants in Pro-Mix only), the researchers used compost from grass that had not been treated with any herbicides. “Basically, this control shows that the leaf or grass compost itself didn’t have a high salt or ammonia content or some other immaturity issue that caused the plant damage,” Michel says. “It was definitely the herbicides.”
In an attempt to simulate a worst-case scenario, Michel says, the pots were not drained. This would simulate a greenhouse environment when no leaching is occurring, which is not usually the case. “Some water evaporates and some is taken up by the plant, but we didn’t let any of the herbicide leach out of the pot,” he explains.
As to how the DuPont products compared to clopyralid breaking down in compost, Michel reports that his lab saw similar rates of degradation during composting. He adds that compost shrinks by volume when it breaks down, so the same concentration of a chemical present in finished compost does not translate into a 100 percent failure to break down.

While DuPont continues to assert that label restrictions should take care of any potential contamination problems, the compost industry remains unconvinced. “They seem to think it’s going to be below the radar and diluted out to the point where there won’t be any effect,” says Michel. “The no effect level for beans, however, is very low and below the 2.5-percent level we tested. Beans are very sensitive to these compounds. Let’s say as a worst-case scenario one guy on the block is using it and the other nine aren’t and all the grass clippings go to a composting facility. It gets diluted and it does break down, but only by 40 to 60 percent. So problems may still arise.”
Michel also made the point that the compost cycles vary greatly in length from region to region and facility to facility. For instance, he says, it might be an annual cycle somewhere in the Midwest whereas a commercial composter in California might be processing material in as little as 60, 45 or even 30 days (Imprelis is not registered for use in either New York or California). These variances, Michel says, are bound to affect how fast the aminocyclopyrachlor breaks down. “We have been working with [DuPont and Scotts] and the USCC to try to develop guidelines for use of these compounds that may minimize the risks.” These, he says, include encouraging mulching of grass, providing clear label information about the compostability of the compounds, informing composters to thoroughly compost grass in spring, development of sensitive bioassays that labs can use to investigate contamination reports and discussing how impacted compost users may be compensated.
“Many compounds like this are already in the environment and used regularly by landowners, and they all potentially can cause problems,” adds Michel. “But with something like 2,4-D, it goes away fairly rapidly after it is used. The reason they want this new compound is it is persistent and is active at low levels. You can apply it one time and it lasts for a year or more. We need to develop strategies for these compounds as to how or if they can be integrated into the composting and recycling stream, because they will be in there, no matter what is put on the label.”
According to Scott Cassel, executive director of the Product Stewardship Institute, the problem lies in having the end-of-life discussion too late in the game. “There needs to be a feedback mechanism for those who have to deal with the back end to have input before the product is made,” Cassel told BioCycle. “Otherwise, it ends up becoming reactive and costing a lot of money. I think we have to have the debate way further upstream.”
Reflecting those words, composters like Carla Castagnaro of AgRecycle in Pittsburgh, Pennsylvania – the person who initially asked Michel about Imprelis at the BioCycle conference – are warning clients of the Imprelis label restriction and cautioning them not to bring in yard trimmings treated with the herbicide. “I have no idea why, with all the fuss we had about clopyralid, that we’re back to this again,” Castagnaro told BioCycle. “It’s just baffling to me.”
On May 25, the U.S. Composting Council (USCC) sent an alert to members. “One problem is that the warning is on page 7 of a 9-page label, and unfortunately not everyone reads or follows the label,” USCC Executive Director Stu Buckner stated in the memo. “We are requesting the USEPA initiate a special review of the registration due to the likelihood of residual herbicide levels in compost damaging non-target plants.”
“We’re working with the compost community and with the universities to make sure everyone understands there are a number of label restrictions regarding composting, the point being that DuPont believes in starting conservatively,” says Jon Claus, Global Technical Product Manager for DuPont. “If future data allows for us to lessen restrictions and EPA agrees with the label modifications, we will support that, as long as there is minimal risk to the compost community. Until we can demonstrate that, we have label restrictions that prohibit composting.”
Sidebar p. 26
Jon Claus, Global Technical Product Manager for DuPont, has been leading the global development of aminocyclopyrachlor as an herbicide to control broadleaf weeds in pasture and rangeland. He says the compound has both post-emergent weed control properties and the additional benefit of controlling weeds over time through the path of root uptake. “To do that you have to have some soil residual,” he explains.
Currently, aminocyclopyrachlor is registered for non-crop uses including vegetation management and turf, says Claus. “We’ve submitted an application to the US EPA for the use of aminocyclopyrachlor in pasture and rangeland; registration approval is anticipated in 2012.” The proposed label for rangeland and pasture use, he adds, reflects a “conservative and cautious approach” similar to the restrictions on the Imprelis label aimed at keeping aminocyclopyrachlor out of the compost stream.

As one of the country’s largest recycler of organics, Scotts Miracle-Gro Company could be causing problems for its own industry by introducing a product to the consumer market that could potentially harm the composting community, some composters have been quick to point out. The synthetic pyrethroid bifenthrin did not become a problem for composters until after it was introduced to the retail market. And clopyralid issues were largely managed by state regulators and the manufacturer itself pulling the product from use on residential lawns.
Now Scotts is partnering with DuPont to introduce a retail fertilizer/herbicide product containing the active ingredient aminocyclopyrachlor, which has been shown to be persistent in compost over time and at levels damaging to some crop plants. The company expressed confidence that its label restriction will keep treated clippings out of the compost stream.
“Aminocyclopyrachlor, or MAT28, will replace 2,4-D and atrazine in some of Scotts Miracle-Gro’s fertilizer and liquid lawn weed control products,” says Lance Latham, director of public affairs for Scotts. DPX-MAT28 is the free acid formulation and DPX-KJM44 is the methyl formulation of aminocylopyrachlor, which Latham described as “a unique molecule developed by DuPont,” stressing that it is neither derived from nor is a new generation of the active ingredient clopyralid.
“We believe MAT 28 represents a very innovative solution for weed control against homeowners’ most bothersome weeds,” Latham continues. “It is more effective than previous active ingredients and also marks a big step forward in our sustainability journey. As always, consumers must carefully follow the directions located on product labels when using any lawn and garden product.” This not only assures consumer and environmental safety, says Latham, but also the efficacy of the product.
“Based on our research, and as the largest marketer of growing media products in the U.S., we do not believe that consumer use of MAT28 will adversely impact commercial compost products,” he adds. “Additionally, the label instructions for consumers will instruct them to leave clippings on lawns as good source of added nutrients, which is a practice we’ve been advocating for years to help keep the clippings out of waste streams and ensure they are put to a sustainable use.”

Related articles from the BioCycle Archive:
Dow Restricts Use Of Aminopyralid, March 2011
Persistent Pesticide As Organics Recycling Foe, August 2010
Composters Off Bifenthrin Black List, May 2010
Certified Organic Compost Under The Gun In California, March 2010
Clopyralid Levels Decline, But Controversy Continues, May 2004

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