Herbicide Residues
Herbicides for weed control in pastures and hayland are generally very effective on the target weed species when applied as recommended. The safety of products on today’s market is reviewed and approved by the EPA and these products have practically no toxicity to humans, animals and the environment. They break down within a matter of days or weeks in the soil environment by design so that any lingering effects are minimized. Consequently cases of contamination of sensitive crops are practically infrequent.
However, hay, bedding, manure, straw or clippings from treated areas can be taken up by sensitive plants that are the unintended target of herbicidal response. Examples include broadleaf vegetable crops like tomatoes, peppers, legumes or agronomic field crops like tobacco, soybeans, cotton or sunflowers. Some pasture weed control chemicals have absolutely no residual activity while others can remain active in non-soil environments (such as bedding, manure, straw or clippings) for a month or two. In the case of manure, residues can pass harmlessly through grazing animals yet pass on residual activity that can affect sensitive plants. It is important to know what products are more risky than others and how to manage their unintended effects.
Products
Following is a brief description of a few primary pasture weed control products and how to address any concerns of residue being passed on to sensitive plants.
Forefront R&P® is of primary concern since the same residual activity that helps to control weeds can also allow it to be more easily passed to sensitive crops. It is recommended generally that product applied to pastures should remain on the farm – either by cycling manure, straw or clippings back to non-sensitive grass - or if moved off the farm should be used in a similar way. There are no grazing restrictions for any class of livestock, but there is a 7 day hay harvest restriction on the label. This restriction exists not because the product is toxic to animals; rather to allow the growing grass plant to metabolize the residue. The product Grazon P&D® is more restrictive but behaves similarly. Other products contain the same or similar active ingredients but aren’t used as widely. Their common names might include aminopyralid, picloram or chlopyralid. Forefront is the best product to use since its labeling contains descriptive stewardship guidelines that are most helpful to users as well as buyers and sellers of hay or manure.
Cimarron Plus® has no grazing or haying restrictions for any class of livestock and its use does not stipulate any such restrictions on residue.
Telar® or Pastora® do not have any issues with respect to residue.
2,4 D is generally not restricted for grazing by horses although formulations and brands do vary. It does not have residue issues when used according to the label.
Banvel® is more restrictive than 2,4 D to grazing depending upon the rate, but it does not restrict the use of hay, straw or bedding under normal usage.
Buying or selling
If you purchase hay, straw or manure it is well to consider the source before using on potentially sensitive garden or crop plants, and if you’re unsure, use the material on your own pasture. In soil environments the residues are readily broken down by sunlight, moisture or soil microbes usually in a matter of weeks. If you sell hay or manure on which sensitive products have been used, be sure to communicate to the buyer, and ask them to read the label or stewardship guidelines.
In agriculture, it is our collective responsibility to be good stewards so that we may retain these valuable herbicides in a productive and safe environment.