I had the opportunity to travel via a rather circuitous route to NW Iowa last weekend and have a few observations.

First, there is still some planting to be accomplished, presumably in soybeans but likely also filling in some wet areas with corn. Second, weeds are doing extremely well and it appears that many fields have yet to be treated. I think that a number of the earlier-season annuals are ahead of the crops and already pose an issue for effective management. While you may control existing weeds with POST herbicides, now is not the time to skimp on the rates. While many/most of the soil-applied herbicides available for corn can be applied POST to the corn and weeds, recognize that there are size restrictions, particularly on the size of weed that will be consistently controlled. As a rule of thumb, smaller is better. The POST activity is typically from the “broadleaf” component of the herbicide combination (i.e. atrazine, dicamba, mesotrione). Annual grass control with many of these herbicides is a challenge with the exception of glyphosate and glufosinate products. Note the corn size restriction of 12” for atrazine application.

Another observation was that we essentially have four corn crops in the ground, based on the extended (due to wet conditions) planting season. This may represent an “opportunity” to spread out the work load over time, but again, keep on top of the weed management issues. Earlier is better than later – protect crop yields by managing weeds early!

We have received some questions and concerns about herbicide injury in corn. Notably the growth regulator products used in the burndown treatment may have created some issues. However, it often is difficult to differentiate the herbicide component from the environmental and management components. The weather did not lend itself to ideal crop planting and development, and some of the planting went into soils that were in poor condition at best. Honestly, we need some general (and gentle) rains to help things out. We have also heard about some injury from the pigment inhibitor herbicides (i.e. mesotrione) – here again, a bit of favorable weather should make this go away and no harm, no foul.

SOURCE: Mike Owen, ISU Weed Specialist

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