Various 3-yr rotation sequences of 97- and 18-cm row spacings, with appropriate sicklepod control treatments within each row spacing, were implemented to evaluate sicklepod population and soybean yield at two locations. Alachlor plus metribuzin applied preemergence followed by either a postemergence-directed spray of metribuzin plus 2,4-DB or hand hoeing in 97-cm rows consistently reduced sicklepod populations. Reductions with 97-cm rows and preemergence-applied herbicides coupled with cultivation were not as great. At one location, using a split application of metribuzin preplant incorporated followed by preemergence with 18-cm rows reduced sicklepod populations if effective control measures had been used in wide rows the previous year, but the narrow-row treatments did not reduce sicklepod numbers if 18-cm rows had been used previously. Soil-applied metribuzin was more effective under high soil pH conditions, and sicklepod populations were reduced substantially whether the previous row spacing was 18 or 97 cm. After the third year, all plots were planted in 97-cm rows with no herbicides. No differences were found among sicklepod populations with any previous row spacing or sicklepod control program, indicating that, even with 3 yr of effective control, subsequent sicklepod populations were not affected.
