Effect of Three Desiccant Herbicides on Soybean (Glycine max) Seed Quality

Soybean [ Glycine max (L.) Merr.] cultivars ‘UFV 1 ’ and ‘UFV 2 ’ grown at Viçosa and Florestal, Brazil, and ‘Bonus' and ‘Wells' at Urbana, Illinois, were sprayed at growth stages R 5.5 to R 6 (full-pod) or R 7 (50% defoliation) with the desiccant/herbicides glyphosate [ N -(phosphonomethyl)glycine], paraquat (1,1′-dimethyl-4,4′-bipyridinium ion), or sodium chlorate:sodium borate (50:50, w/v). Desiccation of plants by paraquat significantly reduced seed weight and germination at all locations and increased the incidence of Alternaria and Phomopsis spp. at Urbana. Analysis of the combined data from the Brazilian locations showed a significant decrease in seed germination for all treatments except paraquat sprayed on the UFV 2 at R 7 and sodium chlorate: sodium borate sprayed on UFV 1 at R 7 . Herbicide application at R 7 did not result in consistent increases in seedborne Fusarium or Phomopsis spp. at any Brazilian location. Rainfall and temperature at seed maturation were more important variables in pod-to-seed infection by these fungi than increased rates of tissue senescence caused by the desiccants.