Influence of formulated glyphosate and activator adjuvants on Sclerotinia sclerotiorum in glyphosate-resistant and -susceptible Glycine max

Two Glycine max near-isolines, GL2415 (glyphosate sensitive) and GL2600RR ( glyphosate resistant), were compared for susceptibility to Sclerotinia scle rotiorum, the fungus that causes white mold disease (also known as Scleroti nia stem rot). A formulated isopropylamine salt of glyphosate (RU) at 840, 1,680, and 2,520 g ae ha(-1) the RU formulation blank containing only adjuv ants (RUFB) at 0.4% (v/v); organosilicone at 0.3% (v/v); a crop oil concent rate at 1.0% (v/v); and a nonionic surfactant at 0.5% (v/v) were evaluated for their influence on V5 G. max susceptibility to S. sclerotiorum in the f ield. The same treatments plus a formulated isopropylamine salt of glyphosa te lacking adjuvants at 2,520 g ae ha(-1) and a formulated trimethylsulfoni um salt of glyphosate at 2,520 g ae ha(-1) were applied to GL2600RR G. max in the greenhouse. Results from these studies indicated no differences in f ungal growth, disease development, or G, max yield for any of these treatme nts. To determine if any interaction occurred between the chemicals, plants , and S, sclerotiorum, leaflets from both cultivars were dipped into and im mediately removed from solutions of the RU at 4, 7, and 10% (v/v) and the R UFB and adjuvants at the rates described. The resulting lesion developments were similar across both cultivars but not across chemical treatments. Les ion developments were smaller on leaflets treated with RUFB and RU, but lar ger on leaflets treated with the other three adjuvants. Sclerotinia sclerot iorum mycelia growing on potato dextrose agar were inhibited by high concen trations of RU and of RUFB at 100 mM ae glyphosate and by the three adjuvan ts at 1% (v/v). Formulated glyphosate lacking adjuvants did not inhibit, my celial growth on potato dextrose agar. The glyphosate resistance trait did not appear to be associated with the susceptibility of G. max to S, sclerot iorum. Neither the glyphosate resistance trait nor the applications of glyp hosate and adjuvants influenced G. max susceptibility to S. sclerotiorum.