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Compost & Persistent Herbicides Fact Sheet

Much of the information contained in this fact sheet has been obtained from the U.S. Environmental Protection Agency (EPA), the State of Vermont, the UVM Extension Service and other sources CSWD believes to be reliable. CSWD, however, has not independently verified the information obtained from third parties.


General Background and Information about Persistent Herbicides

Information About CSWD Action and Impact on Compost Products

Information Specific to Managing Garden Impact

Looking Ahead

General Background and Information about Persistent Herbicides

Timeline Summary of Herbicides Issue

  • June 25th: We began receiving reports that certain plants weren’t doing well in gardens containing our compost. We visited the gardens reported and when we were unable to identify the issue, we contacted state agencies of Health and Agriculture. We voluntarily suspended sales of bulk compost.
  • June 27th: We identified a qualified laboratory and sent them 26 samples of various products, raw feedstocks (grass trimmings and manures), and compost samples from a variety of gardens for testing.
  • June 28th: We published this online fact sheet and an online reporting form for customers to register affected gardens.
  • July 3rd: Test results revealed the following:
    – Many samples tested positive for trace amounts (less than 16 parts per billion) of either of the herbicides Clopyralid or Picloram. In some cases, both were found to be present. Some samples showed no detectable levels of these herbicides.
    – The Vermont Health Department determined that, because only trace levels of these herbicides were found in our compost, they would not expect a health risk to arise from consumption of produce grown in it. Note: The Environmental Protection Agency considers drinking water acceptable for human consumption if Picloram is present in the water at up to 500 parts per billion. The EPA has not established a drinking water maximum allowable level for Clopyralid.
  • July 5th: CSWD sent additional samples of feedstock (farm manures and bedding, and yard debris) and all of our products to labs for  additional testing.
  • We contacted the VT Agency of Agriculture to work with them on identifying the source of these herbicides.
  • July 2oth: As the first step in our assistance program, CSWD begins deployment of trained field technicians to document any plant damage in gardens of customers who purchased a GMC product and are experiencing symptoms of persistent herbicides.
  • July 25th:  CSWD Board of Commissioners approves an assistance package for gardeners impacted by herbicides in compost.
  • August 10th: First checks mailed out to customers who qualified for financial compensation.
  • September 30th:  Deadline for submitting a report of abnormal plant growth associated with Green Mountain Compost and suspected effects of persistent herbicides.


What are persistent herbicides?

The Environmental Protection Agency (EPA) defines herbicides as chemicals used to manipulate or control undesirable vegetation. Persistent herbicides are a class of systemic herbicides that are used to control a wide variety of broadleaf weeds. These herbicides are formulated to survive multiple years of exposure in certain growing environments. They are typically designed for use in hayfields, horse pastures, golf courses, right-of-ways, and lawns to kill off unwanted weeds and to remain effective for several months to years. These herbicides do not impact grasses.

Chemical compounds in persistent herbicides

There are a number of compounds that fall into the category of persistent herbicides. The most prevalent are Clopyralid (Dow Agrosciences), Aminopyralid (Dow Agrosciences, 2005), Aminocyclopyrachlor (DuPont, 2010), and Picloram (Dow Agrosciences). Less prevalent compounds in the same class include fluroxypyr, dopyralid, and triclopyr. Many of these compounds appear on labels in slightly different variations making identification by the untrained applicator difficult.


Restrictions on compounds found in compost and compost feed stocks

  • The original two herbicides detected in some compost samples are Clopyralid and Picloram.  Subsequent testing by additional labs leads us to believe that Aminopyralid may also be present in some of the sampled compost.
  • The Vermont Agency of Agriculture regulates but does not prohibit the use of Clopyralid. Picloram is a restricted use product meaning that it can only be used by certified applicators. According to the Agency of Agriculture, there has been no reported commercial use of Picloram in Vermont from 2009 through 2011 on any potential compost feedstock.


How long do persistent herbicides last in soil?

Depending on the type of herbicide and the level of concentration in your soil, persistent herbicides can last anywhere from a month to three or more years before completely breaking down into inert compounds. The length of time depends upon a variety of factors, including the type of soil, and moisture content of the soil.  These herbicides all survive much longer in a pile of compost than they typically do when incorporated into other soils, such as in a garden.


Where do persistent herbicides come from and how did they get into compost?

The most common pathway known for persistent herbicides making their way into compost is through manures and bedding as well as leaf and yard debris. Depending on the region, these compounds are used in variable amounts on horse pastures, hay and grain fields, golf courses, right-of-ways, and lawns. The resulting hay, grass, or digested materials are required to be disposed of somewhere other than a garden or compost facility, or introduced back onto the land of original application. The labeling requirements for many of the persistent herbicides state that manures from animals grazing in treated areas or hay and grass clippings from treated areas are not to be sent to a compost facility.

We do not yet know the path of entry for possible entry of persistent herbicides contamination in our soil products, but it was likely introduced either through horse manure and bedding or leaf and yard waste. We are working with the Vermont Agency of Agriculture to help identify the source and to determine if the use of the herbicides in Vermont was in violation of state and federal regulations.


Why don’t persistent herbicides break down in the compost process?

Commercial composting involves a process of intense and prolonged biological activity at high temperatures. This environment not only results in rapid degradation of food scraps and other feedstocks, but is also extremely effective at degrading the vast majority of any potential herbicide and pesticide residues into their harmless constituent pieces. Persistent herbicides are relatively new compounds that have been formulated by the manufacturers specifically to be resistant to biological degradation.

While most residual traces of herbicides typically breakdown in a compost pile in a matter of days, the molecular bonds joining these particular compounds can be resistant for months or even years.


It looks like people have had problems with persistent herbicides in other states for several years. Why are they just now becoming a problem in Vermont?

New herbicides are introduced to the market regularly, and as with other products, they are often introduced in markets larger than Vermont. Persistent herbicide in compost problems starting popping up on the west coast of the United States about a decade ago. During that time, much attention was given to the legislation and regulation of these compounds in several western states, to the point where their use was greatly restricted in several states including California and Washington. Other problems have sprung up in more recent years, including multiple reports of persistent herbicides in the states of North Carolina, Idaho, and Minnesota.

Much attention was given to an Aminocyclopyrachlor-based product manufactured by DuPont and sold under the name Imprelis beginning in 2010. DuPont was ordered by the EPA to halt sales and remove this product from the market in 2011 after multiple complaints about the persistent herbicide having unintended consequences including in forestry applications. Since the withdrawal from the market of this product in 2011, there has not been much discussion of this issue in the northeast, presumably with the assumption that there were not any persistent herbicides being used in large enough volumes to warrant concern for the composters and home gardeners in Vermont.

It appears that usage  rates of persistent herbicides are on the rise nationwide, but particularly in regions of this country as well as Canada, where much of the land base is dedicated to commercial, large-scale agriculture.  Affected grasses and grains, particularly hay, is often sold far from their points of origin, and misuse (not following the provisions outlined on the labeling) leads to problematic quantities of these materials ending up affecting composters and gardeners in other parts of the country.


What is the scope of contamination? How many gardens are affected?

As of October 1, 2012, we have confirmed 505 cases of customers who reported that their gardens were affected by persistent herbicides in their soil.

The deadline for submitting a report of abnormal plant growth associated with Green Mountain Compost and suspected effectsof persistent herbicides was September 30th, 2012.  For any questions, please contact our office at (802) 660-4949.


Is compost from another source safe?

We are unable to answer this as it depends upon the intended use of the compost, the manner of adding it to soil, and the source of the compost and the materials used to make it. We have voluntarily undertaken testing of our compost products specifically for these herbicides and have made the results available to the public. Any compost containing manures, livestock bedding, or leaf and yard debris as ingredients may be vulnerable to persistent herbicides entering the mix.


Information About CSWD Action and Impact on Compost Products

What is CSWD doing to address this problem?

  1. Samples of suspected feed stocks and compost were sent to a lab for analysis as soon as the initial problem gardens were discovered.
  2. We  received official results from the lab analysis of our samples and and worked with the State of Vermont to provide guidance as how to best deal with gardens that may have trace amounts of the persistent herbicides.
  3. CSWD is leading the way on detection and analysis of persistent herbicides in compost.  At present, there are insufficient testing options on a national level for detection of minute quantities of persistent herbicides in compost.  GMC and CWSD have been working closely with the Vermont Department of Agriculture, the US EPA, the best private labs in the country, as well as the herbicide manufacturers to demand and ensure that accurate, reliable, and affordable testing is in place to identify the compounds in composts. As new and improved detection abilities are put in place, GMC will carry out regular chemical analyses on all compost produced to ensure that any material sold does not contain persistent herbicides.  Construction of a new greenhouse at the GMC facility is complete, and we have begun on-site growth trials on GMC soils.  In addition, Green Mountain Compost/CSWD is working hard to bring this issue to the forefront of national discussion and action.


What is CSWD doing to help those whose gardens may have been impacted?

We are working with the Vermont Agency of Agriculture and experts in plant and soil sciences to identify the source of the herbicides and their impact on gardens, as well as, more importantly, to help identify the ways to address soils in which the herbicides may be present.


I’m a commercial grower and I believe I have produce affected by persistent herbicides, what should I do?

Commercial growers who have grown produce in soils believed to be affected by persistent herbicides, regardless of the source, should contact Cary Giguere, Pesticide Program Section Chief at the Vermont Agency of Agriculture, (802) 828-6531.  Vermont Organic Farmers (VOF) has issued a statement that use of compost believed to contain persistent herbicides will not jeopardize the organic status of the farm that used the compost. If you purchased compost and are experiencing crop damage, NOFA suggests that you call their office immediately at 434-3821 to discuss the situation and report the issue. Please refer to NOFA’s July, 2012 memo: VOF Memo to Organic Farmers.


I believe my soil may be contaminated, will you come test it?

The deadline for submitting a report of abnormal plant growth associated with Green Mountain Compost and suspected effects of persistent herbicides was September 30th.  For any questions, please contact our office at (802) 660-4949.


Which compost products may be affected by persistent herbicide residue?

While many customers are reporting no evidence of the presence of persistent herbicides, CSWD has stopped sales of all compost products made in our facilities while we undertake this investigation.


Information Specific to Managing Garden Impact

How do I know if I have these persistent herbicides in my garden?

Broadleaf plants such as tomatoes, potatoes, eggplant, beans, peas, peppers, and sunflowers appear to be the most sensitive plants and will likely show the most impact. The pictures below show the typical symptoms of cupped leaves, tightly curled new growth and twisted or distorted stems.

Issues such as insect pests, fungus, virus, lack of fertility, water imbalance, light restrictions and other factors can contribute to problematic growth and poor germination.


What should I do if my garden is impacted?

The deadline for submitting a report of abnormal plant growth associated with Green Mountain Compost and suspected effects of persistent herbicides was September 30th.  For any questions, please contact our office at (802) 660-4949.

If you purchased soil products made by another manufacturer and believe it to contain persistent herbicides, contact the compost provider.


Will my garden be affected in future years? What can I do?

Persistent herbicides can be just that–persistent.  However, we have learned that in Vermont’s wet climate, and with hot conditions such as those we’ve experienced this summer, it is unlikely that the herbicides will affect negatively impact plants beyond the 2012 growing season.  To further decrease that likelihood, we have compiled a list of suggested guidelines to  hasten the process of persistent herbicide dissipation in your soil.


Are plants and vegetables grown in soil containing persistent herbicides safe to eat?

The Vermont Health Department has analyzed lab test results provided by Green Mountain Compost. The Health Department has indicated that levels of the herbicides detected in the compost, ranging from 1.7 – 15.3 parts per billion, are far lower than levels that would increase risk of harm to human health. Any concerns about the safety of eating produce grown in your garden should be directed to the Department of Health at 800-439-8550.


Is there anything I can do to save my tomato plants if they are showing signs of persistent herbicide damage?

Others who have experienced this problem have reported some success with carefully extracting tomato plants from affected soils, rinsing the roots clean with water, and replanting them in soil that does not contain the suspected herbicides. Further success may be achieved by removing any existing fruit and pinching blossoms to give the newly transplanted tomato plants more energy directed at root growth and leaf development.

Transplanted tomato plants will need to recover from the shock of being uprooted and will require frequent watering in well-drained soil until they reestablish. Typical transplanting guidelines would apply – avoiding transplants during periods of excessive heat or during parts of the day with full sun. Late-afternoon transplants would be the most likely to succeed.

Tomatoes are plants that will often survive a transplanting experience if proper precautions are followed. This would not likely work for bean plants as they do not typically survive once extracted from their original soil.


If my plants do not having leaf curling, is my compost is ok?

If you have a garden planted with Green Mountain Compost products and are growing tomatoes, potatoes, eggplant, beans, peas, peppers or sunflowers, and they are NOT exhibiting the symptoms described and shown elsewhere in this fact sheet, there’s a good chance that your soil does not contain persistent herbicides. Poor germination is not a reliable sign of damage from persistent herbicides.

If you don’t have any of these plant families represented in your garden, and are wondering whether or not you may have persistent herbicide residues, the best method for making that determination is to plant peas or beans (legumes) in the soil. A controlled bio-assay (growth trial) may be carried out using the methods described in this information sheet from Washington State University:


Can I replace plants that appear to have been affected by a persistent herbicide?

Persistent herbicides including Clopyralid and Picloram are formulated to remain in the soil for an extended period of time. Eventually they will be broken down into harmless constituents by microbiological processes in the soil, but this can take some time. The amount of time required for complete breakdown depends on a variety of factors, including how bioactive the soil is, drainage, and herbicide concentration, and moisture content. (See Recommendations for Accelerated Remediation of Persistent Herbicides.)

Affected gardens where minimal leaf curling is exhibited and plants otherwise thrived may be able to replant immediately with the same plant families. The risk is that you may not be free of all persistent herbicide residues and you may encounter similar, though likely diminished, growth defects on your plants.


Disposal options if you choose to remove plants and/or soils from your garden or property

Any plants removed from gardens that show symptoms of persistent herbicide exposure may be brought to the Green Mountain Compost facility in Williston or to any of the CSWD Drop-off centers free of charge. Do not add plants to a backyard compost pile or any on-site location that will be reincorporated into a garden within the next year.

CSWD does not recommend digging out soil that is believed to contain persistent herbicides, as extensive research into the effects of these compounds supports our belief that you will not see herbicide effects in any plants in the next growing season.  Please refer to our Recommendations for Accelerated Remediation of Persistent Herbicides for a compilation of our research on the best information and advice we have available on how persistent herbicides break down and disappear in soils, as well as how you can speed up the process.

CSWD will collect and refund unused bulk Green Mountain Compost product in quantities of ½ cubic yard or more. Please call or e-mail our office if you would like to schedule a collection time.


Looking Ahead

I heard there’s a new law that will ban leaf and yard waste from landfills throughout Vermont. If we can’t landfill them, how are we going to deal with persistent herbicides?

Vermont’s new universal recycling of solid waste legislation, Act 148, was unanimously passed by the house and senate and signed into law by Governor Peter Shumlin on June 7, 2012. This law will ban the landfill disposal of leaf and yard debris beginning in 2015 (landfill bans on food scraps will phase in beginning in 2014). We consider this a huge step forward for Vermont, where we recognize the greater common good of recycling materials into usable products instead of burying them in the ground as trash.

CSWD believes that leaf and yard debris are materials that should be returned to the soil rather than being landfilled.


This page was last updated 2/5/13 at 12:29 p.m. We will be updating this site with more information as it becomes available.