Weed Management In Sweet Corn: What's Working and What's Not?

During the latter half of the 20^th century, weed management systems changed dramatically in North America with widespread development and adoption of selective herbicides.  Relative to many other horticultural crops, sweet corn benefits from having a number of herbicides registered for use on the crop.  How close are we to optimizing weed management in sweet corn?  Recent surveys of growers’ fields indicate that while weed frequency and density in fields have declined in recent decades, weed interference continues to cause yield losses in a majority of fields.  Use of interrow cultivation has declined considerably, crop rotations largely lack diversity needed to disrupt weed life cycles, and weed management systems are dominated by a single, at best two, applications of herbicides.  Atrazine, one of the oldest herbicides registered in sweet corn, is by far the most widely used.  Some of the most abundant weeds have been problems for decades, including common lambsquarters (Chenopodium album), velvetleaf (Abutilon theophrasti), and fall panicum (Panicum dichotomiflorum).  Of limited concern 20 years ago, wild-proso millet (Panicum miliaceum) ties with giant foxtail (Setaria faberi) as the 2^nd most abundant weed in sweet corn.  An analysis of the weed community, management tactics and environmental conditions during crop growth revealed several characteristics associated with improved weed management in today’s production.  First of all, weeds need to be managed for the long-term; weedier fields receive some of the greatest herbicide use but these additional inputs do not protect yields relative to fields with less of a weed problem.  Secondly, aim for maximum herbicide activity; adequate precipitation or irrigation dominates weed control potential.  Finally, a less obvious finding was that the extent to which weeds are a problem in sweet corn are affected by planting date and latitude within the north central U.S. production region.