Gardener Alert! Beware of Clopyralid and Aminopyralid


“It all starts with the soil.” As many gardeners know,

improving soil quality with organic matter is essential for growing healthy plants. Many gardeners rely on manure and compost to improve soil structure and to add slow-release nutrients. Unfortunately, these natural materials can become contaminated with herbicides. Even the slightest trace of troublesome chemicals such as Clopyralid and Aminopyralid can quickly kill hearty plants such as peas, beans, peppers, lettuce, spinach, potatoes, and tomatoes when found in soil or compost.

Clopyralid and Aminopyralid are widely used herbicides that kill many species of broadleaf weeds growing in grain fields, hay fields, and along roadways. These man-made chemicals are easily absorbed by plants and remain chemically intact in live and dead plants. So, if an animal eats hay or grain from a producer who has used these herbicides to control weeds, the chemicals enter the animal’s digestive tract and do not breakdown. These toxic substances pass through the animal into manure, urine, and bedding, contaminating any organic material with which they come in contact, e.g. soil and compost. Clopyralid and Aminopyralid do not even breakdown in the high temperatures reached in a composting process and remain active plant killers for up to 24 months.

A concentration as low as one to three parts per billion will negatively affect the growth of plants in the nightshade category. Dow*, the manufacturer of these herbicides, claims that only a few plants are affected. These include some of our local garden favorites:

  • Nightshade family – including tomatoes, potatoes, peppers and eggplant.
  • Legume family – including lupines, peas, beans and clover.
  • Compositae family – including daisy, aster, sunflower and lettuces.
  • Umbelliferae family – including carrots.

Symptoms of herbicide poisoning include reduced seed germination, distorted/twisted leaves and stems, stunted growth, low yields, and death.

Herbicide injury; University of Maryland Extension

How do Clopyralid and Aminopyralid end up in our gardens?

Three main routes potentially bring these herbicides into gardens:

  • Contamination resulting from herbicide drift.
  • Contaminated manure and bedding from livestock fed crops treated with these herbicides.
  • Contaminated composts made from contaminated hay, bedding, or manure.


How to avoid Clopyralid and Aminopyralid

The only way to avoid this threat is to keep materials contaminated with Clopyralid and Aminopyralid out of our gardens in the first place.

When talking to a farmer, wholesaler, or retailer supplying hay or straw for your livestock it is a great start to ask about Clopyralid and Aminopyralid. However, the unsuspecting farmer or feed provider may not recognize these chemicals by their names as they are merely non-promoted ingredients. Therefore, asking about the specific product names that they are sold under might be more effective:

  • Clopyralid – sold as Curtail, Confront, Clopyr AG, Lontrel, Stinger, Millennium Ultra, Millenium Ultra Plus, Reclaim, Redeem, Transline.
  • Aminopyralid – sold as Milestone, Forefront, Pharaoh, Banish.

Distortion of tomato leaves caused by Clopyralid; University of Maryland Extension

Also, when you purchase finished soil blends or compost, inquire as to whether the manufacturer tests for Clopyralid and Aminopyralid.

What to do if your garden is contaminated

“This too shall pass”. It will take several years, but eventually the herbicides will disappear. In the meantime you can grow grass family crops. Yay!

Illustration from Dow AgroSciences’ label instructions for Aminopyralid

* Dow AgroSciences:


Get your clean compost here

A great local source for non-contaminated compost is Grab N’ Grow on Llano Rd. in Santa Rosa. They are the longest operating soil yard in Sonoma County and the proud manufacturer of Mango Mulch® Organic Compost. Grab N’ Grow takes pride in their testing process to ensure manures are free of Clopyralid and Aminopyralid BEFORE they are transported to their facility. The good folks at Grab N’ Grow are always on the look-out for “clean” manure, so they can keep supplying gardeners with non-contaminated compost. So, if you have horse, chicken or cow manure (at least 20 yards per month), please contact Grab N’ Grow at707-575 7275 or go to for more info.



Share with your friends!