Abstract: Reduced herbicide inputs can diminish pesticide movement into water supplies, enhancing environmental quality. A 3-yr study was conducted to evaluate the efficacy and economic viability of reducing herbicide inputs by using ultra-low rates (ULRs), consisting of one-eighth the normal use rates of nicosulfuron plus thifensulfuron, delayed planting (DP), or both in corn and soybean. We compared the ULR treatment at the assigned cost of $12.35/ha with three other traditional types of weed management systems in both chisel plow and no-till production schemes. The ULR weed management system suppressed weeds enough to allow economical soybean production all 3 yr of the study, but this system proved viable only during the wettest year for corn. DP was economically competitive with the best systems in both crops under chisel-plowed tillage only in the driest year of the study.

Nomenclature: Nicosulfuron; thifensulfuron; corn, Zea mays L. ‘Pioneer 3417’; soybean, Glycine max L. Merr. ‘Williams 82’.

Additional index words: Delayed planting, drought, environment, low-rate input, no-till, tillage.

Abbreviations: DP, delayed planting; HI, high input; POST, postemergence; PPI, preplant incorporated; ULR, ultra-low rate.