Fall herbicides & Grazing Corn Stalks

With the increasing problem of controlling weeds such as marestail (horseweed), UNL has recommended using fall applied herbicides to help control this in addition to winter annual weeds.  This practice usually does help with weed control, but I hadn’t thought about the considerations when grazing corn stalks until I received a recent question on it.  The farmer wanted to see if it was safe for his cattle to graze corn stalks after a fall herbicide had been applied.  The label wasn’t clear so he gave me a call. 

I won’t provide information for the various herbicides that can be applied in the fall, but I will recommend that if you are planning on having your cattle graze stalks, that you check to see if a fall herbicide was applied and check the pesticide label to determine if there are any grazing restrictions with that pesticide. 

If the label doesn’t specify any restrictions, then it should be ok.  If you want to be on the safe side, a rule of thumb many chemical reps use is to use the pre-harvest interval for the amount of time to wait before grazing stalks.  Some labels will say that residue should not be grazed or baled and fed to livestock.  Sometimes studies were actually conducted to know there is a safety concern.  In other cases, the chemical company may not choose to conduct all the studies the EPA required for labeling due to high costs.  If that’s the case, the EPA requires the strongest restrictive language be placed on the label.  Regardless, if it says there’s a grazing restriction on the label, the label needs to be followed.  Your cattle may not be affected by grazing stalks where a chemical with a grazing restriction is on the label, but there may be other concerns such as problems with the chemical affecting the calf or being retained in the cow’s milk.

I’m still recommending utilizing our corn stalks by grazing and utilizing fall-applied herbicides for weed control.  I just also recommend you check the pesticide labels on fields where a fall herbicide has been applied to determine any grazing restrictions or safety concerns.

About jenreesources

I'm the Crops and Water Extension Educator for York and Seward counties in Nebraska with a focus in irrigated crop production and plant pathology.

Posted on December 21, 2011, in Crop Updates, Livestock and tagged , , , , , , , . Bookmark the permalink. 1 Comment.

  1. Dear Jenn,

    As the Program Manager for the Pesticide/Fertilizer Program at the Nebraska Department of Agriculture, I tend to get a lot of label interpretation requests like the one you are talking about in this article. This is not the first time I have encountred the question, and while I have submitted a more detailed article to Crop Watch, I would like to provide some comments here, in general terms, regarding fall application of any pesticide (which includes herbicides).

    The U.S. EPA requires all pesticide manufacturers to provide data on how long their chemicals take to break down, both in the environment and in any domestic animal that might be eaten for food or produce a food product. A soybean herbicide applied in the fall to corn stalks might not have the necessary corn stubble residue data to support that use, especially if the chemical company doesn’t intend to register it for use on corn. The easiest way to determine whether a chemical can be applied in the fall is to check the label (just as you said in your blog article).

    If a herbicide label indicates it can be applied “pre-plant” or “pre-emergence”, that is NOT the same as a fall application, and should not be interpreted that it can be applied anytime before the next crop is planted. The label must say “fall application” for it to be legally applied in the fall. It must further indicate which crops can be planted in the spring after the fall application, and if the applicator doesn’t intend to plant one of those crops, he cannot apply the herbicide in the fall, since it will either cause crop damage the following spring, or exceed allowable residues in the following crop. EPA has determined that “pre-plant” applications must occur within 30 days of the intended planting date, unless the label specifically allows more than that. The term “pre-emergence” is interpreted as anytime after planting, but before the crop emerges from the soil surface. The term “fall application” is not defined by EPA, but has been interpted by our agency to mean after the previous crop is harvested and before winter commences, which is December 22nd. Anything after that date would be considered a “winter application”.

    If you or any of your readers would like to discuss this further, I can be reached at my Lincoln office at (402) 471-6882.

    Tim Creger
    Pesticide/Fertilizer Program Manager
    Nebraska Department of Agriculture

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