One year after the Washington State Department of Agriculture (WSDA) restricted clopyralid use in the state, contamination of manure and compost is still widespread, according to testing by WSDA and others in Washington. While farmers and gardeners struggle with tainted manure, managers of compost facilities have filed a lawsuit seeking class action status to recover losses.

Clopyralid is a pyridine carboxylic acid herbicide registered by Dow AgroSciences for use in the United States since 1987. Clopyralid is used to control dandelions and clover in lawns, as well as thistles and knapweed in wheat, mint, timothy hay, corn, asparagus, sugar beets, and other crops. It is the active ingredient in 40 different pesticides registered in Washington State. Unlike some other herbicides, clopyralid is not readily bio-degraded and does not readily break down during composting. Compost contaminated with even extremely low levels of clopyralid can stunt or kill tomatoes, beans, peas, potatoes and many other sensitive plants.

Sampling in October 2001 identified grass clippings from lawn and turf as the major contributor to the contamination problem. An emergency rule in March 2002 eliminated, with the exception of golf courses, all turf applications of clopyralid.

Compost suppliers and buyers are not the only sector affected by clopyralid. Many small farmers and gardeners rely on manure and compost they make themselves to add organic matter and nutrients to their soil. WSDA has thus far chosen to make excuses for not acting to protect agricultural users of these materials instead of taking action. The manager of the WSDA pesticide compliance program, Cliff Weed, has argued that regulation of clopyralid use in cereal grains and grass hay is unwarranted and would not solve the problem. Specifically, Weed claims that 1) cereal grain is usually spot treated so not all grain is treated and 2) adoption of rules specific to WA would put WA grain and hay growers at a competitive disadvantage and would do little to stop contaminated grain, straw, or grass hay from entering the state from other states or Canada. As a solution, Weed proposed educational efforts aimed at Timothy hay producers and grain growers and developing a list of growers who can provide clopyralid-free grain straw and grass hay to interested buyers.

The extent to which hay or grain fields are spot treated versus broadcast treated has not been documented. However, the crops are not “spot harvested”, so the extent to which a field is sprayed is ultimately unimportant if an animal is fed hay or grain from a “spot” that was treated. The agency’s argument that state regulations would not prevent treated hay or grain from entering from other states or Canada is convincing and is a strong argument for nation-wide action on persistent herbicides threatening compost facilities and organic waste recycling.

Extremely low levels of clopyralid (10 parts per billion or even less) can cause damage to plants. Affected plants have twisted stems and cupped leaves. Badly damaged plants will never produce a crop or flower. Sampling programs throughout the state have demonstrated a high prevalence of clopyralid contamination.

Dairy manure and composted dairy manure were found to have clopyralid levels higher than 20 ppb in half of the samples tested. Of the animal manures tested, chicken manure had the highest clopyralid contamination, with levels greater than 100 ppb occurring commonly. Sixty percent of horse manure samples tested were contaminated, though the level of contamination was low, ranging from 2 to 8 ppb.
In yard waste compost, contamination is also the norm. WSDA tested 12 different compost facilities in Washington, with multiple samples taken from each facility, for a total of 34 samples. Of the 34 total samples, 25 did not mix any type of agricultural wastes in their feedstocks. Of these 25 non-agricultural samples, only 5 of the finished compost samples were non detects. Of the remaining 20 non-agricultural samples tested, 9 samples were below 10 ppb, 6 samples were between 11 and 20 ppb, and one sample contained 29 ppb. The compost sample with a stunning 333 ppb clopyralid is a glaring example of the continuing crisis for at least one compost producer.

In the absence of a complete nationwide ban on clopyralid it is difficult to conceive of manure without detectable levels of the herbicide. What does this mean for small farmers, organic agriculture and backyard gardeners? What is the threshold where we deem a material safe? In potting mix clopyralid can damage sensitive plants at levels below 10 ppb, a level much lower that other herbicides commonly found in manure.

Bioassays are an effective and cheap method for testing compost for herbicides. Researchers, compost facility operators, and state agency representatives in Washington State joined together to write a single bioassay protocol for testing compost for clopyralid or other phenoxy herbicides.

Doug Collins, Washington Toxics Coalition and Seattle Tilth Association; Art Biggert, Ocean Sky Farm; and Chrys Ostrander, Spokane Tilth Association