Producers in the semiarid Great Plains are seeking management strategies to delay development of herbicide resistance. The objective of this study was to determine if cultural systems could control weeds in proso millet (Panicum miliaceum), thus eliminating the need for herbicides and removing selection pressure. Initially, we evaluated individual cultural practices for improving competitiveness of proso millet. Increasing seeding rate, banding N fertilizer with the seeds, growing a taller cultivar, and eliminating tillage favored proso millet over redroot pigweed (Amaranthus retroflexus). Combining several cultural practices with delayed planting in a cultural system reduced biomass and seed production of two pigweed species 85% or more in both tilled and no-till systems, subsequently eliminating proso millet yield loss. Density of the two pigweed species was sevenfold greater in the tilled system, yet the cultural system approach was still effective. Cultural system impact on seed production suggests that pigweed densities will not increase over time. With cultural systems, producers can minimize selection pressure, thus delaying development of herbicide resistance.

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.