Fact Sheet Herbicide Residues in Compost Compost may contain herbicide residues. Here is what composters should know and how they can help prevent contamination.

During the spring and summer of 2020, a persistent herbicide called clopyralid showed up in test results of finished compost blends applied to gardens in Oregon and Washington. Clopyralid and other herbicides in the Materials Management same chemical family show up in finished compost Program every few years, according to the Oregon Department 700 NE Multnomah St., Suite 600 of Agriculture. These herbicides leave residues in Portland, OR 97232 compost that can damage sensitive garden plants, such Phone: 503-229-5696 as tomatoes, beans, peas, sunflowers, eggplant, parsley, 800-452-4011 potatoes, petunias, pansies, and cannabis even at low Herbicide damage on tomato leaf. Fax: 503-229-6124 Contact: concentrations of about two parts per billion. Bob Barrows, Eugene contaminated with clopyralid as it is made from [email protected] What is clopyralid? straw, manure and other agricultural materials. 541-687-7354 Clopyralid is the common name for a long-lived herbicide used primarily on agricultural land to kill Plant damage from compost contaminated with www.oregon.gov/DEQ broadleaf weeds such as clover, dandelion and thistle. It clopyralid is problematic for businesses, is the active ingredient in several pesticide products, residential gardeners, as well as the composting including Confront, Stinger, Redeem and Curtail. industry. Clopyralid contaminated compost DEQ is a leader in restoring, Products containing clopyralid are used on grain crops, hurts customer confidence in compost and if not maintaining and enhancing pastures, golf courses, cemeteries, rights-of-way and addressed could eventually negatively impact the quality of Oregon’s air, certain vegetables and fruits. State rules prohibit the use compost sales. land and water. of clopyralid on residential or commercial properties. Regulatory roles and responsibilities Clopyralid residue is the most commonly found Several state agencies have regulatory herbicide contaminating compost in the Northwest. responsibilities and respond collaboratively Testing in 2020 found the presence of clopyralid when gardens are harmed by compost residue in a number of agricultural crops and wastes, contaminated with clopyralid. including mushroom compost, dairy manure, straw and canola meal. Clopyralid residue may also be found in DEQ regulates composting facilities through straw used for dairy and horse bedding and grains fed to permits to ensure facility operations are livestock and poultry. protective of the environment and public health. DEQ collaborates with permitted composting Problems with clopyralid in compost facilities to minimize receipt of problematic Clopyralid residue may persist in plant material after it composting feedstocks and create quality has been harvested. Most herbicides break down in a compost products. composting process. However, clopyralid and other herbicides in its chemical family, which also includes The Oregon Department of Agriculture aminopyralid and picloram, are very slow to break regulates the sale and use of pesticides in down and residues may remain in finished compost. Oregon with the goals of protecting people and the environment from any adverse effects of Clopyralid contaminated compost can damage sensitive pesticide use while maintaining the availability plants. of pesticides. The agency investigates pesticide complaints to determine compliance with the Crops treated with clopyralid are banned as composting Oregon Pesticide Control Act, and initiates any feedstock, but those materials are indistinguishable necessary administrative actions. from crops not treated with clopyralid and sometimes still end up at composting facilities, which can The department also regulates the sale of contaminate finished compost. Manure may also fertilizer, agricultural amendments, agricultural become a contaminant because grain or hay crops minerals and lime to ensure that these materials treated with the herbicide passes through an animal’s are correctly labeled and registered; meet state digestive tract. Mushroom compost may be heavy metal requirements; and are not

Updated 2/10/2021 adulterated. Compost may be required to be registered Conduct regular plant growth bioassay testing using as an agricultural amendment or an agricultural mineral susceptible plant seeds on finished compost, depending on the product claims that are made by the particularly if using agricultural wastes or mushroom composter. Registered compost products would be substrate. Test compost or perform a bioassay on the considered adulterated if they contained pesticides that compost before delivering to customers. Several are not correctly listed on the label. websites provide lists of testing labs and instructions for performing bioassays. The Oregon Health Authority oversees Oregon's Pesticide Exposure Safety and Tracking (PEST) Educate compost users and gardeners about program, which seeks to reduce acute pesticide-related appropriate compost use. Compost is a soil illness or injuries in the state. OHA tracks acute amendment not a planting medium. Compost blended pesticide exposure and educates the public about safely with soil will be less likely to damage plants, even if using and storing pesticides. herbicides are present because soil microbes help break down herbicide residues. What can composting facilities and retailers do? Where to find more information? The US Composting Council provides a list of best • Oregon Department of Agriculture Pesticide management practices to minimize contamination of Complaint To report a complaint about an finished compost. A few of the recommendations are improper pesticide use or application. identified below. • Oregon Health Authority Pesticide Exposure Resources for investigating/tracking health effects reported by people exposed to pesticides. • Oregon State University Master Gardener Program Contains resources for gardeners. • US Composting Council Persistent Herbicides Contains factsheets about persistent herbicides; Best Management Practices to Minimize Contamination; guidance for conducting bioassays; lists of testing labs and Turning composting windrows. more. • Washington State University Clopyralid in How to prevent acceptance of clopyralid Compost Contains information about contaminated feedstocks clopyralid and other persistent herbicides; Before accepting agricultural wastes, golf course waste guidance for conducting bioassays; photos of or other wastes where clopyralid may be present, ask clopyralid damaged plants; and more. the following questions to determine if clopyralid has • Oregon State University Herbicide carryover been used on the plant material: in hay, manure, compost and grass clippings Information about clopyralid and other • If you’re using vegetative waste from herbicides of concern, including guidance on agriculture or landscaping, what herbicides bioassays. where used on the landscape, hay, pasture or • Improving Garden Soils with Organic Matter crop? OSU Extension guidance on importance and • If you’re using manure, what were the animals use of compost. fed? Was it clopyralid free? • Soil Test Interpretation Guide OSU Extension • If you’re using mushroom compost, were all guidance for gardeners and compost users. compost ingredients in compost clopyralid • Fertilizing Your Garden OSU Extension free? guidance for gardeners.

Alternative formats DEQ can provide documents in an alternate format or in a language other than English upon request. Call DEQ at 800-452-4011 or email [email protected].

Updated 2/10/2021