The simplest part of weed management is selecting the right herbicide or mix of herbicides to control a specific weed complex. It is more difficult to understand and predict the timing and severity of weed competition with corn and soybeans. Given the uncertainty of weed growth and crop yields each year and the uncertainly of crop price, it becomes even more difficult to predict the most economically profitable weed management program that a grower should use in each field. I could argue that the investment in a good weed management program has the highest or one of the highest returns on investment next to purchasing seed (i.e., a given since a grower must purchase seed to get any return). Without weed management, corn and soybean yields can be reduced by 50% or more so weed management protects a substantial portion of gross returns. While it is wise to be as economical as possible with herbicide expenditures, the goal and achievement of yield protection cannot be forgotten and appropriate investments in weed management programs should be made. Even before the substantial increases in seed, fertilizer, and land input costs in 2008 and 2009, herbicide costs were a relatively small percentage of the total production costs of corn and soybean and herbicides protect a large percentage of the gross value relative to their costs (Table 1).
Soil Science Extension
University of Wisconsin Madison