Composts and Herbicides Don’t Mix

This well written post on the Green Corn Project website details a problem we are having in compost in Texas. I have been getting some questioning emails about this and so below is what I wrote in an email to a concerned organic producer. I have tried to be fair but when it happens to you it is very frustrating and difficult not to lash out. Hopefully I won’t get beat down too bad for writing this blog!

Dow AgroSciences now known as Corteva makes the Grazon Next herbicide with aminopyralid and 2,4-D in a premix.  It has been on the market for years but was generally more expensive than a common pasture and hay field herbicide known as Weedmaster or its generics which is a premix of Banvel (dicamba) and 2,4-D.  Grazon Next is a popular herbicide but until the last few years the extra expense did slow its use somewhat.

Grazon Next has on its label below that it is only to be used on forage intended to be used on the farm and manure is not to be composted and used on vegetables. When a producer buys Grazon Next, they are required to be warned about this restriction. I really do believe that most producers who use the product know the danger, whether they abide by it or not. 

As a chemical used on hay or pasture crops and then fed to cattle it is really interesting because it does not break down in the animal but instead stays intact as aminopyralid. This is one reason why EPA has less trouble labeling it for animal feed, it is safe for animals and does what it says it will do in a pasture.  I am not justifying its use, only trying to understand why it is used.

Weedmaster is not persistent in the environment for more than a couple of weeks and certainly not persistent in manure used for compost. Grazon Next, on the other hand, can last up to 18 months in the environment, but generally speaking in my experience, only about 6 months or so.  Animals that eat treated grass will then excrete (poop!) manure with aminopyralid and that composted manure will have aminopyralid for about 6-10 months. The label says 18 months which is a field treatment at the highest rate of Grazon Next. There are all kinds of conditions that will speed up this breakdown process.

The past two years have been a perfect storm for this problem to get hugely worse.  The Weedmaster (or generics like it) has Banvel, and Banvel is now a common herbicide used in cotton because of GMO cotton with Banvel herbicide resistance.  This has significantly increased the use of Banvel and caused a shortage which caused the prices to go up.  This caused Weedmaster to be in short supply and more expensive than Grazon Next in many cases.  Also, Grazon Next or better said, the aminopyralid in Grazon Next, is available generically now which means more companies selling similar products at a cheaper price. 

So, the cheaper aminopyralid products and lack of supply of Weedmaster or Banvel caused many hay producers to switch and save money.  Hay has been in short supply and dairies have been getting it from anyone and anywhere they could, no questions asked.  Dairies, and to a smaller extent, feedlots are a big supplier of manure for compost operations all over the state and this perfect storm has opened up the potential for compost to have aminopyralid in it.  My local compost supplier had the same problem when they got manure with aminopyralid in it.  As a result, there was aminopyralid in the compost I bought, and it has lasted from May to September.  It is about over because I now have broadleaf weeds coming up in the compost pile!

One last thing that also makes this an issue, the compost industry has had a perfect storm itself.  The high synthetic fertilizer prices have caused all producers to search out cheaper sources of nutrients.  Compost suppliers usually have more than they can handle on their operations and want to sell it. Along comes field crop producers who are hit with high fertilizer prices, compost has what they need, and the price is low compared to synthetics.  This year compost has been hard to get because of demand. Compost yards have really pushed their compost process so that they are sending out compost/manure very fast after receiving it from the farm.  I have seen some compost that I think was just really mixed-up manure with no compost time or mixed with some small amount of compost.  Usually, the compost process and the time it takes, breaks down aminopyralid somewhat, but this year compost flew off the shelves because of high fertilizer prices. That has left very little time for the compost process to break down the chemical like there had been in years past.

I will close with this, there are some really great chicken compost facilities in East Texas making easy to spread compost crumbles. The cost is close to the same price as a few cow compost facilities are selling cow compost and chicken compost has more nutrients.  Chickens are not feed anything that contains aminopyralid – just sayin!

Author: Bob Whitney, Regents Fellow & Extension Organic Specialist

Agriculturalist, extension educator and researcher, organic agriculture enthusiast and promoter, international program developer, Christian, husband, father and friend.

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