Lambsquarter is easily controlled with tillage and many soil-applied herbicides, so effective management is not difficult if one doesn’t rely solely on postemergence herbicides. If you will be relying on glyphosate in Roundup Ready (RR) corn and the field has lambsquarter and giant ragweed, the labels for RR corn limit the glyphosate rate to 0.75 lb. ae/acre.

We have shown that it is critical to use a rate and tankmix partner which is most likely to be effective with the first postemergence treatment, rather than trying to control escapes with higher rates in a second postemergence treatment. You can use state weed control guides, such as the Weed Control Guide for Ohio and Indiana – Bulletin 789 (Loux, et. al., 2007), to determine the most appropriate tankmix partner with glyphosate to provide effective control of emerged lambsquarter and giant ragweed.

For more information on glyphosate-resistant weeds and specific recommendations on tough-to-control weeds in RR cropping systems, weed scientists in the North-Central region began producing publications on this topic and launched a Web site to distribute this information. The Glyphosate, Weeds and Crops Group Web site can be found at <http://www.glyphosateweedscrops.org> (URL accessed 11/1/07).

Harvest Season Issues

Obviously, planting more corn acres will effectively lengthen the corn harvest season because of time and capacity demands on harvest machinery, drying facilities, transport and storage. Some portion of the corn crop will likely remain in the field longer into the fall. Deterioration of mature stalk tissue, especially if already stressed with stalk rots, greatly increases the risk of stalk breakage and mechanical harvest loss if fields suffer severe wind damage prior to harvest. The greater risk of leaf diseases in corn following corn also indirectly increases the risk of stalk rot development if photosynthetic output is severely compromised during grain fill. Excessively dry grain may lead to greater-than-normal mechanical harvest loss at the header.

Mitigate the risk of stalk breakage by selecting hybrids with superior overall plant health and stalk strength characteristics. If you will be switching only part of your soybean acres to second-year corn, target better-drained fields in your farming operation. Scout fields for the occurrence of stalk rots prior to harvest and prioritize their harvest schedule if necessary to harvest “weak-kneed” fields early. Consider beginning harvest earlier than usual to avoid finishing in late fall when rain and snow prospects typically increase.

Bottom Line

The decision to switch significant soybean acres to second-year corn acres should be made cautiously with careful attention to both the economics and agronomics of such a choice. While short-term economics may favor second-year corn over soybean production (Schnitkey & Lattz, 2005), long-term economics are very much dependent on the economic assumptions made when calculating comparative crop budgets. Growers should recognize that second-year corn yields will range from 7 to 10% less than corn following soybean. Consideration of the risks outlined in this article will help minimize the downside dollar potential of second-year or continuous corn relative to corn following soybean.

Related References

Butzen, Steve. 2006. Best Management Practices for Corn-After-Corn Production. Crop Insights vol. 16, no. 14. Pioneer, a Dupont Company, Johnston, IA. [On-line]. Available at <https://www.pioneer.com/growingpoint/agronomy/library_corn/management/corn_follow_corn.jsp> (URL accessed 10/31/07. Access requires free registration to Pioneer Growing Point™ Web site).

FAST Tools. 2007a. Corn-Soybeans Rotation Tool. Univ. of Illinois Farm Analysis Solution Tools. [On-line]. Available as a downloadable Excel file at <http://www.farmdoc.uiuc.edu/fasttools/index.asp> (URL accessed 10/31/07).

FAST Tools. 2007b. Crop Budgeting Tool. Univ. of Illinois Farm Analysis Solution Tools. [On-line]. Available as a downloadable Excel file at <http://www.farmdoc.uiuc.edu/fasttools/index.asp> (URL accessed 10/31/07) or as an online calculator at <http://www.farmdoc.uiuc.edu/manage/crop_budgets.asp> (URL accessed 10/31/07).

Lauer, Joe, Paul Porter, and Ed Oplinger. 1997. The Corn and Soybean Rotation Effect. Agronomy Advice. Univ. of Wisconsin. [On-line]. Available at <http://corn.agronomy.wisc.edu/AAdvice/1997/A014.html> (URL accessed 10/31/07).

Loux, Mark, Jeff Stachler, Bill Johnson, Glenn Nice, Vince Davis, and Dawn Nordby. 2006. Biology and Management of Horseweed. Purdue Extension Pub. GWC-9. A collaboration of Ohio State University Extension, Purdue University Extension, and University of Illinois Extension. [On-line]. Available at <http://www.ces.purdue.edu/extmedia/GWC/GWC-9-W.pdf>. (URL accessed 11/1/07).

Loux, Mark, Jeff Stachler, Bill Johnson, Glenn Nice, and Tom Bauman. 2007. Weed Control Guide for Ohio and Indiana (Bulletin 789). Ohio State Univ. and Purdue Univ. Available from the Ohio State Publications distribution center (ph. 614-292-1607) or online at <http://www.btny.purdue.edu/Pubs/WS/WS-16> (URL accessed 10/31/07).

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