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.