Waterhemp leaves tend to be narrower and the seedhead is less coarse and somewhat thinner. The native habitats of waterhemp are flood plains and other wet, low-lying areas. Thus, wet areas of fields, soils with poor drainage, and fields bordering marsh areas are prime candidates for initial invasion by waterhemp. If you have any field where weed control is good with the exception of plants that look like pigweeds, it will be well worth an investigation to make sure it is not waterhemp. The question arises as to why we have found ourselves with a waterhemp problem now when it hasn't been in the past.
Several reasons come to mind.
There are several herbicides that have excellent activity on waterhemp, but no single one will provide consistent, full-season control. Experience from states like Iowa shows that an integrated weed control program will work the best. If possible, eliminate these plants before they go to seed. At this point, a cultivator may be the only options. Depending on the size of the corn or soybean crop, explore chemical options with your ag chemical dealer.