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Updated: January 18, 2018
Most of the herbicides used for weed control in winter wheat and barley in the eastern Corn Belt do not persist very long, so there is flexibility in crop rotation. In the southern half of Pennsylvania and to the south, double-cropping soybean is quite common and typical herbicide use in wheat or barley does not generally limit this option. There are a few exceptions to this, but these herbicides are generally not commonly used in the mid-Atlantic region. Alfalfa would be one of the more susceptible crops to herbicide injury that could follow in rotation with a winter small grain, particularly if seeded in late summer a short time after small grain harvest. The restrictions for alfalfa and soybean are provided below for some common small grain herbicides. As with most herbicides, cover crop recrop intervals are not usually provided but can be estimated based on recrop intervals for other related crops. For example, the clovers and other small seeded legumes should respond similar to alfalfa. Remember that the recrop intervals stated on the herbicide labels may pertain to both the potential for allowable herbicide residues in the forage or grain as well as potential for crop injury. As long as the cover crop is not going to be consumed by livestock, the illegal residue issue should not be a problem, but rotational crop injury could still be problematic.
Table 1. Recrop intervals (months after application) for alfalfa and soybean for some common small grain herbicides. For Rotational Crop.
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