The effect of droplet size on retention, absorption, and translocation of 14C-glyphosate was studied in glyphosate-resistant corn. Fine, medium, and coarse spray droplets were studied using a track-sprayer equipped with commercially available nozzles. Glyphosate-resistant corn was used to obtain measurements at field use rates in the absence of phytotoxicity. Spray retention on corn leaves was calculated based on recovered glyphosate per leaf area, and retention was higher with application of fine droplets (47%) than with application of coarse (38%) and medium (37%) droplets. Absorption in corn leaves was directly correlated with droplet size and reached a plateau 1 d after treatment (DAT) for all droplet sizes. Based on glyphosate recovered 3 DAT, coarse droplets showed the highest absorption (49%), followed by medium (35%) and fine (30%) droplets. Percentage of translocation also increased with droplet size, and translocation was primarily toward strong sink tissues such as roots and young leaves. Our results show that large droplets have slightly reduced retention in corn but have increased absorption resulting in increased translocation of glyphosate to growing sink tissues.
Nomenclature: Glyphosate; glyphosate-resistant corn, Zea mays L. ‘Roundup® Ready’.