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 sclerotiorum, the fungus that causes white mold disease (also known as Sclerotinia 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 adjuvants (RUFB) at 0.4% (v/v); organosilicone at 0.3% (v/v); a crop oil concentrate 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 field. The same treatments plus a formulated isopropylamine salt of glyphosate lacking adjuvants at 2,520 g ae ha^-1 and a formulated trimethylsulfonium 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 fungal growth, disease development, or G. max yield for any of these treatments. To determine if any interaction occurred between the chemicals plants, and S. sclerotiorum leaflets from both cultivars were dipped into and immediately removed from solutions of the RU at 4, 7, and 10% (v/v) and the RUFB and adjuvants at the rates described. The resulting lesion developments were similar across both cultivars but not across chemical treatments. Lesion developments were smaller on leaflets treated with RUFB and RU, but larger on leaflets treated with the other three adjuvants. Sclerotinia sclerotiorum mycelia growing on potato dextrose agar were inhibited by high concentrations of RU and of RUFB at 100 mM ae glyphosate and by the three adjuvants at 1% (v/v). Formulated glyphosate lacking adjuvants did not inhibit mycelial growth on potato dextrose agar. The glyphosate resistance trait did not appear to be associated with the susceptibility of G. max to S. sclerotiorum. Neither the glyphosate resistance trait nor the applications of glyphosate and adjuvants influenced G. max susceptibility to S. sclerotiorum.