Dow voluntarily suspended sales of herbicide containing aminopyralid in Great Britain in 2008 but began marketing it again in 2010, this time with stricter directions regarding barnyard manure management (Sullivan). Nevertheless, the problem of tainted manure and ruined gardens persists. Is new contamination occurring despite the new label directions? Does the destructive power of aminopyralid last much longer than formerly thought? Or does the interconnected nature of our world make containment measures moot?
The Scoop on Killer Poop
If you get barnyard manure for your garden from an outside source such as a local farm or stable, be sure to ask if herbicides have been used anywhere the animals have grazed. Also ask if the animals have been fed hay from farms that have or do use herbicides.
One herbicide in particular, aminopyralid, has such plant-killing power that it remains active for years, even after passing through an animal's digestive system.
Adding manure tainted with aminopyralid to your garden will damage and/or kill turnip greens, lettuce, cabbage, broccoli and other broadleaf vegetable crops not only this year, but for several years to come. It will also stunt the growth, deform and/or kill the fruit of other home garden favorites, including beans, peas, peppers and tomatoes.
Just as the digestive process does not lessen the herbicide's killing power, aging and/or composting aminopyralid-tainted manure doesn't make it any less harmful to your garden.
Furthermore, the herbicide's presence doesn't have to be great for it to do serious damage. According to a fact sheet from the University of Maryland, "concentrations [of aminopyralid] as low as 3 parts per million" is all it takes to turn barnyard manure into killer poop ("Gardener Alert").
Brandnames of Aminopyralid
Think packaged manure or compost from a greenhouse, garden center or discount house is safer than manure from a local source?
It's probably contaminated, too—if not with aminopyralid, then with clopyralid or some other herbicide. To check it or any other manure or compost for contamination, do a bioassay test before applying it to your soil.
Farmers may not be familiar with the name aminopyralid, but they'll know the name of the commercial herbicide that they used to kill weeds.
According to the Dow AgroScience website, these commercial herbicides from Dow contain aminopyralid: Chaparral, CleanWave, Forefront HL, GrazonNext HL, Milestone, Opensight and Pasturall.
A 2011 article in Mother Earth News as well as a more recent Mother Earth News article on the topic adds these comparable pyralid herbicides to the "beware list": Confront, Curtail, Forefront, Hornet, Lontrel, Millennium Ultra, Reclaim, Stinger and Transline.
If your source of barnyard manure has applied any of these herbicides to land where animals graze, or they have fed their animals hay and other forage from fields where aminopyralid has been used, the resulting manure will turn your garden into a broadleaf plant killing ground—one that won't produce a viable vegetable garden anytime soon.
Stories from Gardeners Who Have Inadvertently Tainted The Soil
How Aminopyralid Works
Ironically, those most adversely affected by aminopyralid damage are organic farmers and home gardeners who have inadvertently contaminated their soil, usually by fertilizing with aminopyralid-tainted manure and/or feeding livestock aminopyralid-contaminated hay.
Amish farmers and others who use livestock in farming have also unwittingly damaged garden soil when their plow animals, unknowingly fed on aminopyralid-tainted silage, defecate in fields as they work.
Is your garden at risk?
I use manure compost, tea, top dressing
Aminopyralid is an auxinic herbicide. It mimics plant auxins, a group of plant-produced hormones that stimulate cell growth and control the development of roots and lateral meristems while suppressing the formation of axillary buds.
If a plant is left to its own devices, auxins will determine its shape through apical dominance; however, gardeners frequently interfere with this by pinching off terminal buds, thus stopping the flow of auxins and allowing lateral buds to sprout so that the plant "bushes out." Aminopyralid interferes with plant growth in a much less benign fashion.
When plants take up the herbicide's fake hormone, its cells follow aminopyralid's cues for growth, which are aimed, of course, at the plant's malformation and ultimate destruction.
(For a highly technical explanation of how auxinic herbicides work, see Sterling and Namath's "Auxin and Auxinic Herbicide Mechanism(s) of Action - Part 2 - Advanced" in the Plant and Soil Sciences eLibrary.)
Following the Directions Doesn't Make It Safe
The labels on herbicides and pesticides (which include not only the actual label but also any fliers or brochures which accompany products) are considered legal documents. Not following label directions means one has no legal grounds for complaint if the product fails to perform as claimed.
Keep in mind, however, that herbicide labels are a combination of the manufacturer's knowledge and the regulator's knowledge of any given product's ingredients at the time of release. Sometimes, as in the case of aminopyralid, that knowledge is incomplete, downright wrong or, as some claim, intentionally misleading.
Furthermore, when actual use reveals the product's true nature, the label information may change. After the damage has been done, of course.
Although Dow AgroScience has changed its labels on pyralid products to address contamination issues, the chemical giant has assumed little or no responsibility for soil contamination and subsequent crop loss.
In thinking about these things, there are three questions I have pondered again and again. Here they are, considerably shorter after the removal of the expletives: Why does Dow persist in producing and promoting aminopyralid and other herbicides in the pyralid family despite continuing public outcry? Why do agrobusinesses purchase and use pyralid herbicides that could potentially ruin their soil and cause them grave financial loss? And why oh why doesn't the EPA demand the removal of aminopyralid and other pyralid herbicides from the marketplace?
Safe Composting & Mulching
If you've treated anything in your yard with any sort of herbicide, don't add it to your compost pile or use it as mulch. It could damage or even kill your garden.
"Weed & feed" products, for instance, may seem harmless enough. However, they leave residual amounts of herbicide in the lawn. Adding the grass clippings to your composter or piling them up around your vegetable plants could stunt and/or deform your plants and their fruits.
Also, if you've gotten manure from a source that's unsure about its safety or the chemicals that might have been in the livestock's feed, test the compost before using it by completing an at-home compost test.
TIPS ON USING (SAFE) BARNYARD MANURE IN THE GARDEN
More Articles About Herbicides in Manure & Compost
- Killer Compost Reports: Contaminated Manure & Herbicide Contamination Damaging Gardens
Many farmers and gardeners have unknowingly poisoned their crops due to a potent and persistent herbicide lurking inside contaminated manure, resulting in a killer compost that devastates crops.
- Pesticide Fact Sheet
This 2005 fact sheet from the EPA indicates a shorter active life for aminopyralid than occurs in real life.
- Plant and Soil Sciences eLibrary: Auxin and Auxinic Herbicide Mechanism(s) of Action
An interesting lesson in how auxinic herbicides like aminopyralid work.
- Herbicide Contamination of Dairy Derived Organic Matter in Whatcom County
Discussion of ongoing contamination problems in Whatcom County, an area of Washington State that has been particularly hard hit by aminopyrlid contamination. Includes pictures of damaged crops.
- Keep Your Garden Safe From Killer Compost
Killer compost containing aminopyralid herbicide has found its way into gardens in the United States and Europe alike, and the problem appears to be worsening.
- The Aminopyralid Challenge Continues
Herbicide sprayed on hay in 2008 remains active in horse manure three years later.
About the Author
The Dirt Farmer has been an active gardener for over 30 years.
She first began gardening alongside her grandfather on her parents' farm. Today, The Dirt Farmer gardens at home, volunteers at community gardens and continues to learn about gardening through the MD Master Gardener program.
© 2013 Jill Spencer