With harvest now in full swing, don’t forget to look at your fall weed control. What are the weeds that are left in your crop? Do you know what weeds they are? Is there a weed that you do not know? If so, how large is it? Does it look like the weed was not controlled at spraying time? Did you have an herbicide failure or is it a weed that your product does not control? As you move away from glyphosate products, it is important to read labels closely to make sure they control the weeds in your field. For example, you are using a program to control resistant waterhemp and now the field has a lot of lambsquarters in it, and upon reading the label, you determine lambsquarters is only suppressed and not controlled.
Now is the time to identify these problems so next year they are not a problem again. This year there was again a lot of late weed emergence after normal spraying was done. When there are wet August periods, it is likely that curtain weeds, like common waterhemp and velvetleaf, will emerge late and still put on seed before harvest. This only can be controlled if the herbicide products used have enough residual to keep these seeds from being able to emerge and grow. Back in the eighties and early nineties, this was very common in all fields and especially in soybeans. This year has also seen back isolated cases of black nightshade. Glyphosate has been very deadly on this weed, and still is, but where glyphosate was not used is where the problems showed up.
Taking a little time to answer these questions as harvest progresses can save a lot of time in the future. If you do not know which weed you are dealing with, get an ID done on it. We at the SDSU WEED Project would be happy to help you with this. There are two ways to get this done. You can send a high-quality digital picture to Paul O. Johnson or take the sample into your SDSU Extension Regional Center and they can help. Who knows, you may have the new weed to South Dakota that nobody knew was here yet. Or maybe you have Palmer Amaranth. For more info contact Paul O. Johnson.