Droplet Size and Phytotoxicity of Herbicides1

An oil soluble formulation of the dodecyl (51% w/w) and the tetradecyl (13% w/w) amine salts of (2,4- dichlorophenoxy)acetic acid (2,4-D) was diluted with diesel oil and applied in homogeneous sprays of 100, 200, and 400-p droplets to seedlings of sunflower (Helianthus annuus L. 'Peredovik'). At each droplet size all combinations of five dosage levels and five spray volumes were compared. For the same applied dosage the amount of stem curvature increased as droplet-size was decreased. When compared with 100-t droplets, approximately three times and six times as much active ingredient was needed to produce the same effect with 200-is and 400-Rs droplets, respectively. For a fixed droplet- size, the effective dosage could be increased equally well by increasing the concentration or by increasing the number of droplets per unit area.