Late-season glyphosate applications in glyphosate-tolerant soybean to reduce soil seedbank

The ability of glyphosate to reduce weed seed production when applied at flowering and the adoption of glyphosate-tolerant soybean enables soil seedbank reduction. The objectives of this research were to determine the effects of late-season glyphosate applications on seed production of a weed community, document 14C-glyphosate movement within flowering sicklepod, and evaluate effects of late-season glyphosate treatments in glyphosate-tolerant soybean on the soil seedbank and soybean yield components.;The most effective treatment to reduce seed production of a weed community consisting of banyardgrass, Palmer amaranth, pitted morningglory, prickly sida, and sicklepod was a 0.84 kg ae/ha glyphosate application at pitted morningglory flowering, resulting in seed reductions of 90, 83, 98, 96, and 99%, respectively. Although only 2% of the recovered 14C-glyphosate accumulated in sicklepod flowers and buds, extensive bud and flower abscission drastically reduced sicklepod seed production.;Results from a 3-yr continuous field study revealed that a 0.84 kg/ha glyphosate application at soybean V3 followed by 10-d sequential 0.42 kg/ha glyphosate applications initiated by the first flowering weed species effectively reduced barnyardgrass and prickly sida seed production. Glyphosate applied at 0.84 kg/ha at soybean V3 followed by 10-d sequential 0.21 kg/ha glyphosate applications effectively reduced pitted morningglory seed production, and 0.84 kg/ha glyphosate at soybean V3 and V6 managed broadleaf signalgrass and hophornbeam copperleaf seed production. Glyphosate applications of 0.84 kg/ha at soybean V3 followed by 10-d sequential 0.42 kg/ha glyphosate applications for three consecutive years reduced the soil seedbank by 84 and 50%, compared to the nontreated check and the standard treatment, respectively.;Yield components of glyphosate-tolerant soybean cultivars treated with 10-d sequential 0.84 kg/ha glyphosate applications throughout flowering, resulting in a combined in-crop glyphosate rate of 6.72 kg/ha, were equal to yield components of soybean receiving 0.84 kg/ha glyphosate at soybean growth stages V3 and V6.;The planting of a late-maturing glyphosate-tolerant soybean cultivar and application of 0.84 kg/ha glyphosate at soybean V3 followed by 20-d sequential 0.42 kg/ha glyphosate applications initiated at pitted morningglory flowering will maximize soybean yield, reduce the soil seedbank, and limit the total in-crop glyphosate rate to 2.10 kg/ha or less per season.