Subscribe and stay up-to-date with the latest news and great offers from DEKALB, Asgrow and Deltapine.
Don't miss out on the latest agronomic news.
Local agronomic alerts.Delivered straight to your inbox.
The objective of weed management is to not only control weeds, but also to protect corn yield potential. Timely use of postemergence and preemergence herbicides, using a product mix that provides multiple sites of action, is key to weed management in corn.
Figure 1. The influence of time of weed removal on corn ear size, with herbicides applied PRE or at various corn vegetative stages compared to no herbicide treatment. Corn plants can detect the presence of weeds very early in their growth cycle and make reproductive adjustments that are not altered by subsequent ideal growing conditions.2 (Photo courtesy of Dr. Phil Westra, Colorado State University).
Weeds can compete with corn for space, light, water, and nutrients. A recent survey across North America concluded that weeds can cause more than 50% yield loss in corn without the use of herbicides in weed management.1 The timely use of herbicides is important to maximize corn yield potential (Figure 1).
Starting with a clean field, either through tillage or a burndown herbicide application, is the best approach to begin weed management in corn. This helps to reduce competition from weeds as corn emerges and becomes established. Weeds that germinate early in a corn crop can be the most competitive. Applying residual herbicides preplant or preemergence (PRE) in corn prior to postemergence (POST) in-crop treatments usually provides better weed control at the end of the season. Residual herbicides applied preplant or PRE can also provide more flexibility for timely in-crop POST herbicide applications.
Situations arise where total POST herbicide programs may be utilized. When making an in-crop POST application in glyphosate-tolerant corn, a Roundup® brand glyphosate-only agricultural herbicide should be applied in a tank-mixture with recommended herbicides when weeds are 2 to 4 inches tall. Delaying an application to weeds that are more than 4 inches tall can result in significant yield loss, especially when no residual herbicide is applied in a tank-mixture to control weeds that can emerge after application (Table 1).3
There can be a greater risk of yield loss when using total POST herbicide application programs. Weeds grow rapidly, and weather can delay POST applications. Surveys have shown that when weeds are managed with only POST herbicides, that application timings often occur too late to protect the full yield potential of corn from early weed competition.4
Remember to control weeds when they are small (less than 4 inches) with POST applications in corn, and use residual herbicides in the program. Herbicide programs that provide multiple sites of action also help in the management of weed resistance. Visit www.RoundupReadyPLUS.com for more information on weed management solutions.
1 Dille, J.A., Sikkema, P.H., Everman, W.J., Davis, V.M., and Burke, I.C. 2015. Perspectives on corn yield losses due to weeds in North America. WSSA abstracts. http://www.wssa.net. 2 Westra, P., Swanton, C., Page, E., Loux, M., Dobbels, A., Smith, K., Bullington, J., Wright, H., and Foresman, C. 2011. Colorado light avoidance corn ecology study. WSSA abstracts. http://wssaabstracts.com. 3 Gower, S.A. et.al. 2003. Effect of postemergence glyphosate application timing on weed control and grain yield in glyphosate-resistant corn: Results of a 2-year multi-state study. Weed Technology 17: 821-828. 4 Fickett, N.D., Boerboom, C.M., and Stoltenberg, D.E. 2013. Predicted corn yield loss due to weed competition prior to postemergence herbicide application on Wisconsin farms. Weed Technology 27: 54-62. Web sites verified 6/9/16. 160608214112