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Aminopyralid contamination in garden soil

ZachS. z5 Platteville, Colorado
3 years ago
last modified: 3 years ago

I have been wondering why my potatoes look so bizzare are unhealthy for a while. At first I assumed it was related to the weather. But the twisting, curling, a cupping of the new growth got worse as the weather improved, and I started thinking about herbicide drift. I have only used glyphosate around the house/barn area, which doesn't cause the twisted leaves and stems, and the last time I sprayed around the house was before I had any plants growing in the garden anyhow. My neighbor uses 2, 4-d, which does cause the twisting, but if it was drift how did it magically miss my parsley, dill, and cabbage and only affect the potatoes? That's not right.

Then I began noticing a lot of weeds in my beds were also looking strange and dying. I wasn't too bothered by that, but still bizarre. More bizzarre, it was only certain weeds like the black nightshade, coltsfoot, and sunflowers. The grasses, amaranth, and purslane were all growing fine. The peas were another one that had me scratching my head. Why did only about 10% of them even germinate and why did all the ones that did all suddenly die?

Then I stumbled across something talking about the effects of aminopyralid contaminated manure, stating that nightshade and legume family crops are the most susceptible. I already know the effect of aminopyralid on asteraceae, we use it all the time to kill thistles and knapweed at work, and I know it doesn't harm grasses (one of the reasons we use it).

So I took a look at the label and started to piece together the weeds that were dying vs. the weeds it controls and looking through pictures of crops affected by it. My potato leaves are a dead ringer and the sudden death syndrome of my peas also matches. There is not a single brassica listed on the Milestone label and only one kind of amaranth which is not the one growing in my garden, explaining why my cabbages and broccoli and the pigweed all look fine, as do my onions which, like grass, are a monocot.

Now, I have a few beds that did not get any of the compost because I ran out or I had seeds/plants growing there already (the parsley and dill, apiaceae is another highly susceptible family). The weeds, all of them, not just the grass and pigweed, were growing just fine and so were the herbs. So the effects are seemingly only showing up in the places that got the compost which points to that being a likely source of entry.

I know Milestone has been used on a regular basis out here because it works great on the noxious and invasive thistles like Scotch, musk, and Canada. Shoot, I even still have a jug sitting on the shelf in the garage. The guy living here prior to me raised sheep and pastured them in areas that would have had these thistles growing in them. He also composted their manure. So all the pieces being put together by my master detective skills all point to the conclusion that my garden has been invaded by this powerful and persistent herbicide. I'm absolutely incised about it, but at this point, what is done is done. Amonipyralid will break down through microbial action in the soil and I will be able to plant again eventually, but it could take a couple seasons. In the meantime, I can grow corn and cabbage and use the beds that didn't get the compost added to them.

This is a major issue facing both home gardeners and farmers alike. Anyone who uses manure, compost containing manure, grain straw or grass hay, or who mulches with grain straw or grass hay can be affected by it. It is commonly used on rangeland and pastures and is persistant enough that any plant material that has come in contact with it and is grazed by livestock will pass through the gut and come out the other side still effective enough to kill crops. It is also used in grain and hay fields to kill weeds and any straw or hay that is used either as feed for livestock (who's manure is then used as an amendment) or for mulch will be contaminated and can kill crops. right in the Milestone label it states that any plant material that has been treated with that product cannot be used or sold outside the location where it came from, just for this very reason. However, there are a number brands of aminopyralid, as well as it's cousins clopyralid and picloram, and some of them must be labeled differently because mine is certainly not an isolated case. In 2014, the Durango Herald published an article about the pervasiveness of aminopyralid contaminated amendments and mulches in La Plata County and it was such a major problem across the pond that aminopyralid I believe is banned from use in the U.K.

This story is not to scare or alarm you, nor is it to say that aminopyralid ought to be banned. I do believe that the PROPER use of herbicides, including this one, has it's place. Unfortunately this was NOT the proper use of herbicide and even more unfortunate, I'm the one who gets to pay the price for that. Fortunately for me I have a tractor, a strong back, and plenty of other dirt just laying around. I can, and will, remove as much of the affected soil from my garden and replace it with new. It won't be in time to plant sensitive crops in those beds this year, but adapt and overcome as the Marines say. The loss of my potatoes and peas along with some adjustments to what, how much, and where I will plant things aren't the total end of the world I suppose.

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