Growers need to carefully evaluate the risks and benefits of different application timings to develop the most efficient weed management system. Benefits of early application All preemergence herbicides require rainfall to move them into the soil profile and make them available to emerging weeds. Applying the herbicide ahead of planting can reduce the risk of poor performance due to lack of rain after application because the herbicide is applied prior to major weed emergence events. In no-till systems, early preplant applications can eliminate the need for burndown herbicides such as Roundup, Touchdown, or Gramoxone Extra. The herbicides are applied prior to emergence of most species, and in many cases, the preemergence products also have some foliar activity on emerged weeds and will kill small seedlings.
Convenience is also a major driving force in the movement towards earlier applications.
Completing herbicide application in early April frees growers from this task when conditions become favorable for planting. Risks of early application Applying the herbicide ahead of planting reduces the length of weed control provided after the crop is planted. If the herbicide breaks down too quickly, the grower will be faced with making supplementary control strategies or accepting poor weed control. The length of control provided by the herbicide will be influenced by the herbicide's persistence, environmental conditions, and target weed species. The optimum application time for preemergence herbicides is dependent upon both the grower's management skills and environmental conditions.