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One of the founding fathers of the United States is often credited as the source of the phrase “in this world nothing can be certain, except death and taxes.” Scholars and pundits alike have added other “certainties” to this relatively short original list, so perhaps we can enjoy a sense of serenity to suggest another: weeds. Even with all the time and resources expended to control weeds in 2015, one can be reasonably confident this persistent foe will again plague Illinois fields in 2016. As weed management practitioners begin to contemplate plans and programs for next season, a review of weed management in 2015 could provide a bit of sage counsel. We will publish several short blogs over the next several days that both review 2015 and provide suggestions for 2016.

Challenges caused by weather
Weather patterns during portions of the 2015 growing season once again demonstrated the inherent perils of weed management programs that rely exclusively on one tool or tactic. These perils were often highlighted in soybean fields not treated with soil-residual herbicides. Applications of postemergence herbicides were often delayed by frequent precipitation and persistently wet field conditions until well beyond the point when weed interference began to reduce soybean yield. This provides a reminder of a very important central tenent of weed management: resources expended to keep weeds under control do not increase crop yield. Increases in crop yields are accomplished though plant breeding; weed management, on the other hand, preserves the genetic yield potential achieved through breeding. Put another way, weeds and crop plants require the same resources for growth. Any resource consumed by competing weeds becomes a resource unavailable for the crop to use to express its genetic yield potential. Once weed interference has persisted long enough to adversely impact crop yields, nothing can restore the lost yield.

Be cautious about which expenditures you trim
Lower commodity prices have many contemplating ways to reduce input costs in 2016. There are several viable options to reduce herbicide costs, but remember that hybrids and varieties, even those with the highest yield potential, will not realize their yield potential if weeds are not adequately and timely controlled. For example, assume a soybean farmer did not realize (or refuses to accept the fact) that glyphosate-resistant waterhemp infests a particular 60-acre field. The decision is made not to invest in an effective soil-residual herbicide; the farmer believes glyphosate alone will control the waterhemp. Following the in-crop application of glyphosate, two outcomes of this decision become rather obvious: poor control of waterhemp, and weed interference that continues to reduce soybean yield for much of the growing season. With a soybean yield potential of 65 bushels per acre, a modest yield loss of 20% due to weed interference, and a soybean market price of $9 per bushel, the decision to save a few dollars in weed control costs at the beginning of the season actually resulted in a revenue loss of over $100 per acre through reduced soybean yield. Keep in mind, especially while planning 2016 weed management programs, that wise investments to manage weeds before interference reduces crop yields will realize a return through more bushels harvested at the end of the growing season. An investment in high-yielding hybrids and varieties should be coupled with an investment in weed management that adequately protects yield potential.

Aaron Hager is an Associate Professor in the department of Crop Sciences at the University of Illinois. This article originally appeared on The Bulletin, which is part of the U of I Extension website, and has been reposted with permission.