DECATUR, Ill. (DTN) -- Entering a field to take photos or pull yield samples generally involves what amounts to gymnastics on my behalf -- especially as the soybean crop starts to take off. I can't stand to step on the crop or harm it in any way.
While my steps may not result in much yield loss, it turns out sprayers can and do take their toll. Research by agricultural engineer Mark Hanna at Iowa State University indicates sprayer wheel traffic from first flower (R1) through harvest can damage soybean plants and reduce yield.
University of Wisconsin soybean specialist Shawn Conley has found that an adequate soybean stand (more than 100,000 plants per acre) planted in late April through mid-May can compensate for wheel tracks made when a field is sprayed at R1. "Yield loss can occur, however, when wheel tracks are made at R1 or later in thin soybean stands (less than 100,000 plants per acre) or late planted soybeans," said Conley.
"Regardless of stand, plants could not compensate for wheel tracks made at R3 (early pod development) or R5 (early seed development)," Conley reported. In Conley's trials, yield losses averaged 2.5%, 1.9% and 1.3% when sprayer boom widths (distance between wheel track passes) measured 60, 90 and 120 feet, respectively. Multiple trips along the same wheel tracks did not increase yield loss over the first trip.
Wet conditions have delayed postemergence herbicide applications this year, so sprayer tracks are going to happen. With resistance to herbicides swirling and aggressive weeds such as Palmer amaranth looming, letting weeds go to seed is not a good option.
In addition, fungicide applications are generally in the R3 timeframe. Conley said they did not see an economic response to fungicides in his studies. However, fungicides in the presence of disease are another matter and this year's wet conditions favor disease pressure. University of Illinois plant physiologist Fred Below gives fungicides and insecticide applications a 3.6 bushels per acre yield credit when other high yield practices are in place. Obviously, pest problems need to be addressed if they are challenging yield.
Just watch your step -- all these maybes need to be weighed with the potential losses of running the sprayer through a standing crop.
For more reading on this topic go to:
Pam Smith can be reached at email@example.com
Follow Pam Smith on Twitter @PamSmithDTN
© Copyright 2014 DTN/The Progressive Farmer. All rights reserved.