The Hidden Danger in Your Garden: Aminopyralids in Compost
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Collapse ▲As gardeners, we trust that compost is a safe, natural way to enrich our soil, improve plant health, and boost yields. However, there is a growing concern over the contamination of compost with herbicides, specifically aminopyralids. These chemicals, widely used in animal agriculture, can find their way into compost made from hay, straw, and manure, causing severe damage to garden plants. Even more troubling is the lack of regulation in the composting industry, which leaves gardeners unaware of the potential risks in the compost they buy or make.
What Are Aminopyralids?
Aminopyralids are a class of herbicides used to control broadleaf weeds in pastures, rangelands, and crops like hay. These chemicals are highly persistent and can remain active even after passing through the digestive system of animals. When manure or plant material treated with aminopyralids is composted, the resulting compost can still contain enough of the herbicide to harm sensitive plants like tomatoes, beans, peas, and many ornamental species. Symptoms of contamination include twisted or cupped leaves, stunted growth, and poor yields, sometimes leading to the death of the plant.
(University of Maryland Extension, 2021)
The Problem: Lack of Industry Regulation
One of the biggest challenges with aminopyralid contamination is the absence of strict regulations in the composting industry. In many regions, compost producers are not required to test for herbicide contamination, nor are they mandated to disclose the origins of the materials used in their compost. As a result, even well-meaning organic gardeners may inadvertently introduce aminopyralids into their gardens when they use manure or hay-based composts. While some companies voluntarily test for herbicides, this is not yet standard practice, leaving many gardeners vulnerable to contamination.
Testing for Contamination: The Plant Assay
Given the risks, it is essential for gardeners to take precautions when using new compost, particularly if it contains manure, hay, or straw. One of the simplest and most effective ways to check for aminopyralid contamination is to perform a plant assay. Here’s how:
- Fill containers: Use small pots filled with the compost in question, and fill additional pots with known, uncontaminated soil as a control.
- Plant seeds: Choose sensitive plants, such as tomatoes or beans, and plant them in both the compost and control pots.
- Monitor growth: Over the next three to four weeks, observe the plants for any signs of herbicide damage, such as distorted leaves or stunted growth. If the plants grown in the compost show abnormal symptoms, while those in the control soil do not, the compost may be contaminated with aminopyralids.
This simple test can save gardeners from the frustration of planting a season’s worth of crops only to see them destroyed by herbicide-laced compost.
(Michigan State University Extension, 2020)
What to Do If Contamination is Found
If your plant assay reveals aminopyralid contamination, all hope is not lost. Over time, aminopyralids break down naturally in compost. By allowing the compost to sit and decompose for a full 300 days, the herbicide will eventually degrade to levels that are safe for most plants. Additionally, gardeners can speed up this process by turning the compost regularly and ensuring that it remains moist and aerated, conditions that promote the breakdown of aminopyralids.
The presence of residual herbicides in compost highlights a serious gap in the regulation of compost production. Until stricter rules are put in place, gardeners must remain vigilant and take steps to protect their plants. By performing plant assays and allowing compost to fully decompose before use, gardeners can minimize the risk of contamination.
References:
- University of Maryland Extension. (2021). Understanding Herbicide-Contaminated Compost.
- Michigan State University Extension. (2020). Herbicide Carryover in Hay, Manure, Compost, and Grass Clippings.
Written by Angela Mason Foster
Extension Master Gardener Volunteer
If you are having an issue in your home garden or landscape, send your questions to Gene Fox, Consumer Horticulture Agent with the North Carolina Cooperative Extension Service, please email Gene at gene_fox@ncsu.edu or call at (252)946-0111. Check out our Facebook page, Beaufort County Master Gardeners, for The Plant of the Week and Finding Info Friday!