From reports of soybean fields near St. Louis destined for mowing rather than harvest to thick lawns of waterhemp beginning to emerge from soybean fields nearer to the Northwestern Illinois Ag R&D Center, weeds are a major problem in many Illinois farm fields in 2016.
What in the world is going on? Why have weeds become such an urgent issue this year?
There are likely several factors converging at once.
2015 left a large soil seed bank. An abnormally wet spring resulted in out-of-control weeds in many fields last year. This was particularly true in those fields in which soil-applied residual herbicides were not a part of the weed management plan. Even with residual herbicides, activity may have dissipated by the time that soils were firm enough to get machinery back into fields. Additionally, in some fields herbicide resistance issues may have led to a situation where no post-emergence herbicide options were available. Other issues such as surpassing pre-harvest intervals or weeds too large to manage with herbicides may have contributed to the abundant weed seed bank going into the 2016 growing season.
Palmer amaranth is no joke. Robert Bellm, retired Extension Educator recently shared the news that in West-Southwest (the Madison County area) Illinois where he spends time field scouting, Palmer amaranth is abundant. Severe Palmer amaranth infestations have left some producers with little choice but to mow the crop rather than harvest an already yield-compromised crop and risk spreading weed seed with harvest equipment.
Diversifying weed management strategy is key. Regardless of dire warnings by university weed scientists, many producers continue to rely on glyphosate-only, post-emergence-herbicide-only strategies for weed management. While this strategy may have been effective 10 or 15 years ago, it was never sustainable.
One positive development has been that I have personally witnessed or heard many more people talking about 'walking bean fields' this year than I have in the past 5 years. While not necessarily everyone's favorite activity, mechanical weed control was a common occurrence in the recent past and over several years can reduce the number of weeds seeds in the soil.
Last fall, University of Illinois Extension Weed Specialist Dr. Aaron Hager penned a series of articles about weed management considerations for 2016 in the Bulletin. The topics and themes covered in these articles are of continued relevance and value: