This article was written collaboratively by Mark Rosenberg, former SDSU Extension Agronomy - Weeds Field Specialist, and Darrell Deneke, former SDSU Extension IPM Coordinator.
In 2007, researchers at South Dakota State University indicated that volunteer corn is much less competitive in corn than soybean. The South Dakota study (Alms et al. 2007) evaluated the full season effect of a range of volunteer corn densities (800-14,000 plants/acre) on both corn and soybean and reported yield losses that ranged from 0% to 13% in corn and 0% to 54% in soybean. A 2007 University of Minnesota (U of M) study reported yield loss potential in corn that was very similar to the South Dakota study.
A study conducted in Minnesota in 1979 and 1980 (by Andersen et al. 1982) evaluated the effect of clumps of volunteer corn per row of soybean (approximately 8 plants/clump) on soybean yield. When averaged over six experiments, soybean yield was reduced 1% for every 75 clumps/acre. The authors also indicated that at a density of 75 clumps/acre or greater, delays in herbicide application of approximately three weeks (from mid-June into July) resulted in a reduction in soybean yield.
Like any weed, early emerging volunteer corn that competes longer into the growing season with soybean will have a greater impact on yield, especially if drought conditions persist. However, volunteer corn emergence is often delayed and extends throughout the growing season making the timing and economics of the time of weed removal more difficult to determine.
In soybeans, producers have the herbicide options of the ACCase inhibiting herbicides such as: Select Max (clethodim), Fusilade DX (fluazifop-P), Fusion (fluazifop-P & fenoxaprop) and Assure II (quizalofop); NOTE: Poast Plus (sethoxydim) is not as active as the other herbicides on volunteer corn. The ACCase inhibiting herbicides are generally targeted on 12-24-in.-tall volunteer corn. The ALS herbicide Raptor can also effectively control smaller (2-8 in.) volunteer corn.
To save a trip across the field the ACCase inhibiting herbicides mentioned previously can be tank mixed with glyphosate, but adjuvant requirements may need to be adjusted depending upon the glyphosate and ACCase herbicide formulations used (see specific labels for details). Also, different ACCase rates are associated with different volunteer growth stages. Often growers would like to wait later into the growing season before treating for volunteer corn, to allow for the extended emergence period. This response is understandable but must be tempered by the fact that the early emerging volunteer corn plants will cause the greatest yield loss and extending the herbicide application too late into the growing season can diminish herbicide effectiveness, potentially resulting in reduction in soybean yield.
Volunteer conventional corn can be controlled with glyphosate or Ignite; volunteer Liberty Link (LL) corn can be controlled with glyphosate; volunteer Roundup Ready (RR) corn can be controlled with Ignite.