Changes in manganese concentration and content by wheat (Triticum aestivum) and conventional canola (Brassica napus) following simulated glyphosate drift with and without foliar applications of manganese and fulvic acid

Context Several studies have shown that glyphosate application can reduce manganese (Mn) concentration and content in plants. Aims We investigated the potential of foliar application of Mn prior to glyphosate to alleviate glyphosate drift damage in non-target crops. Methods Simulated glyphosate drift of up to 10% v/v (90 g ae ha−1) of the recommended application rate for weed management was applied to wheat (Triticum aestivum) and canola (Brassica napus) at two growth stages: (1) Zadoks 13 and 16 stages for wheat; and (2) 2-leaf (BBCH 12) and 6-leaf (BBCH 16) stages for canola. We assessed how sole and combined foliar application of Mn (20 mg Mn L−1) and fulvic acid (FA, 9 g L−1) at 3 days prior to glyphosate spraying influenced plant growth, chlorophyll content, Mn concentration, and Mn content. Key results Glyphosate drift at 10% v/v of the recommended application rate significantly reduced shoot dry matter in young plants (wheat at Zadoks 13 and canola at BBCH 12), but had no effect at the later stages. Mn application alone or in combination with fulvic acid (FA) prior to glyphosate decreased shikimic acid accumulation, and increased shoot Mn concentration and content in wheat. Conclusion Foliar application of MnSO4 alone or in combination with FA prior to simulated glyphosate drift provided no protection for young plants (wheat at Zadoks 13) from a glyphosate-related decrease in dry weight. Implications Increasing Mn supply is unlikely to provide protection against glyphosate in canola or wheat.