Be conscious of your manure compost – by Tulsi French



Tomato with Herbicide Damage



After adding manure to our soil last year, our tomatoes have not had a chance.  We received slightly aged horse manure from a friend of ours in Gilpin County.  We were unaware the manure had small traces of Milestone herbicide (Aminopyralid). The herbicide was used in the horses’ grazing fields to treat noxious weeds. 

Milestone is a popular herbicide used throughout the county. It is not harmful to animals and does a great job at killing noxious weeds.  Livestock graze fields and munch on what is left of the noxious weeds.  The Milestone passes through their systems, and because it is persistent, it shows up later in manure, damaging sensitive crops like tomatoes and beans. It has much less effect on leafy greens. 

This is a photo of a tomato plant from a master gardener who had a similar issue.  The deformity starts at the top of the plant, usually with the leaves curling in any direction.  Eventually the entire plant looks like this. The symptoms are very similar to Tobacco Mosaic virus, Cucumber Mosaic virus, and Curly leaf top virus.  I had assumed all of these viruses were the issue, prior to having the plants tested at the Jefferson County extension office. Our results proved that we were in fact not dealing with a pest or disease.

Soil test for pesticides/herbicides are extremely expensive. For this reason, I planted a few bean seeds with some of this manure compost to test my suspicion.  Beans are highly susceptible to herbicides, especially Milestone. The bean plant looked just like the tomato plants and hardly came up.  Some of the beans never even sprouted.

Sadly enough, we also used this manure in some of our compost piles to give them some heat.  Now we have a large pile of Milestone-contaminated compost.  I am thankful that we caught the issue before further contamination. 

There might be a solution to this soil issue.  Activated charcoal was recommended to me by a farmer from Texas to treat the soil.  The charcoal is made up of hardwood trees and coconut shells (carbon).  The molecules of the charcoal bind with the herbicide to remove the product from the soil.  If you would like to read more about this product, check out this website: http://edis.ifas.ufl.edu/wg065

I have not tried this product yet since our tomato season is over. Thankfully our greenhouse moves on rails, so we will not be using the contaminated soil for the fall.    The persistence of Milestone lasts for a couple of years, so there is also the option of waiting it out for a few years.  To know when the herbicide is no longer active, test it with a bean see or two.   

            If you receive manure compost, ask if their grazing lands have been treated for noxious weeds with herbicides. If they are not sure, ask for a sample and have it tested or try the bean seed test. You may also choose to completely avoid foreign manures and stick to using familiar compost.