Careful management will be needed to obtain successful weed control with these non-residual postemergence herbicides. There are a number of factors that influence effectiveness of postemergence herbicide programs. These include weed species in the field, weed size, herbicide rate, application timing, crop stage, crop species, tillage practices, weather conditions, row spacing, fertility, application equipment, additives, and possible herbicide interactions if tank-mixing. The last issue of Crop Insights on this subject concentrated on the effects of herbicide rate and weed height on the efficacy of postemergence herbicides. This issue will review the effects of tillage systems, crop row spacing and the difference in competitiveness of corn and soybeans on weed control with non-residual postemergence herbicides like Roundup and Liberty.
Most farmers are concerned about the effects of weeds on crop yields.
However, crops have an impact on the growth and development of weeds as well. Crop rotation has historically been an important tool for managing weed populations. Reduced crop rotation in many areas using continuous corn or soybeans allows weed populations to thrive and establish a permanent presence in the field. Competitive differences between crops are especially noteworthy if the same herbicide program can be used in both crops. The few studies available where a direct comparison has been made between weed competition in corn and soybeans all indicate that corn is a stronger competitor than soybeans.