Weed seed dormancy and escapes mean, in some cases, pre-emergent herbicide alone might not cut it, so have a post-emergent plan. In post-emergent spraying, herbicide options are limited. With your contingency plan in mind, make sure you don’t repeat herbicide groups multiple years or applications in a row. Just like in pre-emergent spraying, make sure you have at least two operative modes of action against any resistant weeds. After scouting to make sure you spray at the optimal time, Young finds post spraying in corn can cost $15 to $20 and $25 to $30 in soybeans, depending on chemistries.
Ideally, post-emergent spraying shouldn’t be necessary if you use a good pre-emergent herbicide with residual. With effective pre-emergent herbicide, the crop will canopy, and weeds will be under control. This could save farmers $15 to $30 per acre in post-emergent application. So, if you’re going to cut herbicide costs, plan to cut in the post-emergent application, not the pre-emergent.