Herbicide Carryover – Killer or Contaminated Compost

April 2, 2013

Spring is the time of year many gardeners amend their soils to improve organic content and soil structure. Although composted animal manures and composted plant material is considered to be the best soil amendment for general improvement of soil tilth, the use of a group of synthetic chemicals referred to as persistent herbicides gives rise to caution when procuring organic amendments. In particular, adding herbicide-exposed composted manure and other products to vegetable and ornamental beds can be devastating.

Farmers and home gardeners across the United States have reported damage to vegetable, flower and fruit crops after applying composted manure (whether from cows or horses) or composted hay, straw or grass clippings to the soil. Shortly after these applications as soil amendments or mulch, they noticed stunted growth, poor germination, death of plants, deformed plants and fruit. In most cases, the damage was caused by a group of synthetic chemicals known as pyridine carboxylic acids, sometimes referred to as pyralids, namely, aminopyralid, clopyralid, fluroxypyr, picloram, triclopyr and/or aminicyclopyrachlor. Products containing these chemicals include Curtail, Forefront, Grazon Next, Grazon P+D, Milestone, Redeem R&P, Surmount, Confront, Lontrel, Millennium Ultra Plus and Plus2, Clopyr AG, Stinger and Imprelis. These persistent herbicides stay active in the soil and in hay, straw and manures and composted manures exposed to the herbicides up to four years.

Grab 'n Grow

In September, 2009, Mother Earth News reported that a previously considered organic product, Grab 'n Grow, contained one of the above chemicals and caused damage to a vegetable garden of Grab 'n Grows manager, Don Liepold. Subsequently “I have been testing  and detecting herbicide residues and thus rejecting cow manure, horse manure, turkey mulch, rice hulls, mushroom compost and yard trimmings,” says Grab n’ Grow manager Don Liepold. “I spent $20,000 in lab fees in 2008, and am on the same track for 2009,” he says.”

The Mother Earth News article continues “It is extremely difficult to keep contaminated materials out of commercial compost. “One load of contaminated grass clippings can ruin a batch of compost,” says Eric Philip of Anatek Labs in Moscow, Idaho. Philip has seen so many positive tests for clopyralid residues in compost that he would not use untested compost in his own garden.

“When folks have plants die in their home gardens, their first assumption is that they did something wrong,” Philip says. “But with pyralid-laced commercial compost becoming more common, contaminated soil amendments could be the blame.

The source of pyralid pollution can be impossible to trace. For example, a horse stable may use hay brought in from a neighboring state, without knowing that it is laced with pyralid herbicides. If the horse’s manure or stable litter ends up in a garden, disaster is ready to strike. It’s better to be safe than sorry. Liepold stopped making one of Grab n’ Grow’s most popular products, Mango Mulch, for more than a year because he could not find an uncontaminated manure supply. Now he’s getting it from two local organic dairies.”

The effects of contaminated compost and composted manure might be transferred to foliar sprays as well, although I have not read any reports mentioning them specifically.

Dupont's Imprelis® Disaster

Mother Earth News first sounded the alarm on “killer compost” in 2008, and has continued to report as new information comes to light. In 2011, Dupont's Imprelis® an herbicide praised for being a “green alternative” because of its long residual (thought of as a greener alternative since it wouldn't have to be applied as often), made headlines as it killed trees and shrubs in numerous states from New England across the Midwest into the northern Plains States. Currently, the EPA put a Stop Sale Order on Imprelis®, but not on the other persistent herbicides by Dow AgroScience and Dupont.

Was this a case of unforeseen or unintended consequences by Dupont? Dupont did notice that Imprelis® could create killer compost. From Page 7 of the 9 page label on Dupont's Imprelis®: “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 managers/residents to not use grass clippings from treated turf for mulch or compost.”

It is well known that the “label is the law” for agriculture and landscape chemicals. How many people do you imagine read the entire label when purchasing herbicides? Although Imprelis® was sold only to licensed applicators, how many of them read the label or warned home or corporate owner/managers of the long term effects regarding compost, when they applied Imprelis®? In areas where community composting is practiced, it is easy to see how contamination of these resources can occur.

North Carolina University Cooperative Extension issued an excellent bulletin entitled “Herbicide Carryover in Hay, Manure, Compost and Grass Clippings” warning “farmers and home gardeners of reported damage to vegetable and flower crops after applying horse or livestock manure, compost, hay or grass clippings to the soil,” (http://www.ces.ncsu.edu/fletcher/programs/ncorganic/special-pubs/herbicide_carryover.pdf). Although the above mentioned products were licensed for use in agriculture by licensed applicators, Imprelis® was licensed for use on residential lawns by licensed applicators.

Home Landscapes Not Immune

Just because most of these products were for agricultural use, doesn't mean home gardeners are safe from persistent herbicides' long term effects. The warning for vegetable growers and home gardeners is to be aware of your source for hay, straw, manure or compost. These persistent herbicides can be active up to four years or more. The person you purchase or receive these products from may not even know this class of herbicides have been sprayed on them, or be aware of the long-term effects.

Here is an example of why it is difficult to find out. A friend of yours offers you horse manure that has been composted. You might ask him/her if herbicides were used, with the farmer replying the manure/compost is "safe" because the animal has not been effected. The horse or cattle were fed hay that was sprayed with one of these herbicides (it's reported not to be harmful to animals). The horse eats the hay, and the resulting horse manure contains active residues of the herbicide, even after it composts. If the composted manure is spread on your vegetable garden, your vegetables will be stunted, fail to thrive, or die outright.

You might think this couldn't happen to you, but a case very similar to what I described happened to a family member of mine in Wisconsin. After he did some research, he went back to the neighbor where he got the manure and found out the man did indeed spray his hay with one of these chemicals.

Unless you are absolutely sure hay or straw does not have a history with these herbicides, I would not use them in compost or on your garden soil or ornamental beds.

The exposed composted manure would be safe to spread on your turfgrass. To be safe, I would not compost the grass clippings or use the grass clippings in beds or borders. It would be safe to cut your turf with a mulching mow, returning the clippings to the soil if you had already used contaminated compost there. I'm unsure of the effects of these chemicals on trees (except for Imprelis®). The North Carolina Bulletin goes on to describe how to perform tests to determine whether the compost or hay/straw contains residues of one of these persistent herbicides.

New Warning about Livestock Feeds

This latest warning has come from Mother Earth News, published in the February/March 2013 issue. They noted that livestock feeds now contain the contaminated chemicals and are passed through the animal into the manure in this manner. Because of the growing contamination problem, Mother Earth News advises gardeners that “the time has come for the public to stop buying compost or manure products unless they come from suppliers that are able to afford testing and can screen feedstocks for herbicide residues.”

Once again, the buyer needs to be very aware.

Read More: a FAQ sheet from the US Composting Council on contaminated compost: http://compostingcouncil.org/persistent-herbicide-faq/

Read more: http://www.motherearthnews.com/Grow-It/Contaminated-Compost-Clopyralid-Aminopyralid-Pyralid-Dow-Chemicals-Toxins.aspx#ixzz2JNc6UOED
Read more: http://www.motherearthnews.com/Grow-It/Contaminated-Compost-Clopyralid-Aminopyralid-Pyralid-Dow-Chemicals-Toxins.aspx#ixzz2JNb7si5j

Angie Hanna, www.Highplainsgardening.com