Late Emerging Weed Suppression by Interseeded Cover Crops Planted At V6 Corn Growth Stage.

Late emerging weeds are a common problem in corn production systems.  Suppression of late emerging weeds typically is achieved using glyphosate applications.  With the increasing use of glyphosate, glyphosate-resistant weeds have become problematic.  The goal of this study is to determine if cover crops can be an alternative solution to suppress late emerging weeds without compromising corn yield.  The cover crops interseeded by broadcast and drill applications, in four replications, at the V6 growth stage at the footslope and summit locations were 9.8 kg/ha of Lens culinaris (lentils), 8.9 kg/ha of Triticum aestivum (winter wheat), and 5.4 kg/ha of Trifolium incarnatum (crimson clover).  The test plots were 24 m long and six rows wide on 76 cm row spacing.  Each plot was subdivided into four nitrogen treatments, 0, 33, 67, and 134 kg N/ha, which were 6 m long and six rows wide.  Three 1/10^th m² areas were harvested for cover crop and weed samples after corn maturity but just before corn harvest.  Samples were separated into cover crop, broadleaf weeds, and grass weeds.  Samples were dried at 60 C, weighed, and data were analyzed by using PROC GLM in SAS.  Nitrogen rate was not significant for any of the measured parameters at either field location.  In the experimental plots the mean cover crop biomass 40 kg/ha (drilled) and 23 kg/ha (broadcast) in the footslope, and 118 kg/ha (drilled) and 120 kg/ha (broadcast) in the summit location with the most prolific species was crimson clover.  Cover crop applications did not influence the broadleaf weed biomass in either the footslope or summit location.  The mean grass weed biomass in footslope was 388 kg/ha (control), 225 kg/ha (drilled) and 261 kg/ha (broadcast), whereas at the summit, grass biomass was 604 kg/ha (control), 118 kg/ha (drilled) and 160 kg/ha.  The main grass weeds in each location were Setaria pumila (yellow foxtail), Setaria viridis (green foxtail), and Echinochloa crus-galli (barnyardgrass).  In the footslope, grass biomass decreased by 33% when broadcast interseeded and 42% when drilled compared to the control.  Broadcast application of the cover crop at the summit reduced grass biomass by 73% and the drilled application reduced grass biomass by 80% when compared with the control.  Cover crops had no impact on crop yield.  These data indicate cover crops interseeded at the V6 stage has the potential to suppress grasses, but was influenced by field location and planting procedure.