By Eric Jones and Philip Rozeboom et.al
Weeds are usually present at the time of harvest, and these weeds may have produced viable seeds. However, the severity of weediness can vary from “clean” to a “weedy mess” (Figure 1). Careful consideration should be taken to determine the order of fields to be harvested. What fields are “clean” and which ones are a “weedy mess” should be determined by preharvest scouting.
Fields that are very weedy should be harvested last. If weedy fields are harvested first, the weed seeds can become lodged into cervices of the combine and be transported to other fields. If the next field harvested happens to have low numbers of weeds present, the weed seeds deposited on combine could be become dislodged and get added to the soil seedbank. If the field with low weed pressure was harvested first, the field would have less weeds to control in the subsequent growing season. If a weedy patch is encountered in a field, this area can be avoided and combined later. Minimization of weed seed transportation via a combine is especially important if the field has herbicide-resistant weeds or weed species not common to other fields. If weed patches are small and isolated, then these areas can be hand weeded and removed from the field to ensure weed seeds are not returned to the soil or transported by the combine.
If a weedy patch is unavoidable, the combine should be cleaned before entering a different field. Regardless of the field harvest order, combines should be meticulously cleaned after harvest to remove weed seeds that may have become lodged into cervices. The residues from cleaning the combine should be contained and destroyed to ensure that any weed seeds removed do not inhabit fields in proximity. Weedy fields at the time of harvest should have the location and species present recorded. The records can be used as a reference to ensure that effective weed management is implemented for the next growing season by knowing where the weedy fields are at and what species are present.Source : sdstate.edu