Herbicide resistance in weeds, especially glyphosate resistance, has generated many recommendations from University Extension over the last several years to include more preemergence herbicides with residual weed control activity as a greater part of an Integrated Weed Management approach. Unfortunately, over the last many years the economics have favored the sole reliance on a postemergence glyphosate system. It is apparent that constantly ‘beating the drum’ to include residual herbicides as a way to prevent resistance falls on deaf ears unless economics favor the approach. Moreover, residual herbicides applied at the preemergence timing do not come without potential drawbacks. These drawbacks can include injury on young crop seedlings under adverse weather conditions, poor performance when rainfall does not occur to ‘activate’ the herbicide into soil-water solution, and potential carryover under prolonged dry soil conditions adversely affecting a sensitive rotational crop. Unfortunately, we experienced both of the latter of those three statements in 2012, even though the extent to the problems of carryover will not be clear until we’re into the 2013 season. So, in a dry year like 2012, it may easily leave some to question whether the risk of preemergence herbicides is worth the reward. With this background in mind, it is important to constantly evaluate the value of using preemergence herbicides with residual weed control activity for protecting crop yield, and ultimately producing greater economic returns. At the UW-Madison Arlington Agriculture Research station, we annually conduct several herbicide evaluation trials. This year we also conducted several trials that evaluated the impact of several other pest management treatments on the yield of corn and soybean. Several trials revealed the impact of early-season weed control through the use of residual herbicides this year, but to stay concise, I will summarize one corn trial and one soybean trial which demonstrated the effect of early-season weed control in a dry year (2012).
Soil Science Extension
University of Wisconsin Madison