Foliar Application of Manganese Sulfate Alleviates Detrimental Effects of Glyphosate Drift on Wheat Growth

Glyphosate drift can severely reduce nontarget crop growth, such as wheat (Triticum aestivum L.). However, it is unclear whether different foliar manganese (Mn) formulations can alleviate this damage. In this study, different Mn formulations (MnSO4, fulvic acid + MnSO4, Mn-ethylenediamine tetra-acetic acid (Mn-EDTA) and MnSO4 + Mn-EDTA) were foliar-applied either as tank mixtures with glyphosate, or separately 3 days prior to glyphosate application. Simulated glyphosate drift was applied at Zadok 13 stage of wheat at 2%, 5% and 10% v/v of the recommended rate for weed control (equivalent to 18, 45, and 90 g ae ha−1, respectively). SPAD values declined progressively with increasing glyphosate rate, indicating reduced leaf greenness. At the highest glyphosate rate, all Mn formulations reduced shikimic acid accumulation compared with the glyphosate-only treatment, regardless of application method. The tank-mixed applications of all Mn formulations alleviated glyphosate phytotoxicity on wheat growth at 10% v/v of the recommended glyphosate rate. In contrast, when applied separately, alleviation was only observed with MnSO4 alone and only at 2% v/v of the recommended glyphosate rate, resulting in a 40% increase in shoot dry weight compared with the glyphosate-only treatment. The protective effect of MnSO4 is likely a result of an interaction between Mn2+ and glyphosate on the leaf surface, potentially limiting glyphosate absorption or bioavailability. These findings suggest that MnSO4 may provide limited protection against low-level glyphosate drift injury in wheat.