Thus far in the spring of 2010, the weeds are looking quite healthy and did not suffer from the nasty winter. Planting has proceeded nicely, but the weather (the wind specifically) has (or at least should have) been an impediment to herbicide applications, says Mike Owen, an Iowa State University Extension weed scientist. If you have not yet planted soybeans, you still have time to apply a residual herbicide, says Owen. It is likely you will need to use a product that either has postemergence activity as well as residual characteristics or include a herbicide product to accomplish the needed postemergence control of emerged weeds.
If you are using a burndown, it's easy to rotate herbicides
If you are planting Roundup Ready soybean varieties and are planning to use a burndown herbicide, consider using Ignite instead of glyphosate. By doing that, you will help with glyphosate resistance management and you will likely improve your long-term weed management. Also, with postemergence treatments, remember the goal is to protect soybean yields not to "just" kill the weeds. Therefore, apply the postemergence treatment when weeds are very small (2-inch weeds are a good target), prior to when they have stolen some of your profit by reducing soybean yield potential. The use of the soil-applied, residual herbicide will help by controlling weeds long enough so that the postemergence application will be made later in the growing season and may be the only other weed management tactic you need.