The influence of calcium, iron, magnesium, other cations, and mixtures of cations on the activity of glyphosate and the interaction with pH is reviewed, discussed, and demonstrated with laboratory data. The strategy to overcome antagonistic effects of the cations via use of adjuvants is discussed and illustrated with data.
The influence of calcium concentration on glyphosate efficacy was investigated on black nightshade (Solanum nigrum L.) by monitoring glyphosate activity via fluorescence technology and inhibition of growth. Giant foxtail (Setaria faberi Herrm) was also used for biological evaluation. Calcium concentrations equal to the glyphosate concentrations were most antagonistic; higher concentrations of calcium were less antagonistic.
Different adjuvants were tested to overcome the antagonistic effect of calcium. Results are discussed in relation to the physical chemical properties of the adjuvants. With a more appropriate scientific base, remedial measures may protect field performance of glyphosate and reduce farm costs.