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DuPont Label Says "Do Not Compost" Grass Clippings :: BioCycle, 
Advancing Composting, Organics Recycling & Renewable Energy
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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:

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“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?”

DÉJÀ VU OR BETTER LIVING THROUGH IMPROVED CHEMISTRY?
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


RETAIL DEBUT FOR 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.”

COMPOST TESTS
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.

REACTIVE MODE
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
AMINOCYCLOPYRACHLOR POISED FOR AG MARKET
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.

SCOTTS CONFIDENT IN LABEL WARNING
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