SPREAD OF WATER AND OIL DROPLETS ON JOHNSONGRASS (SORGHUM-HALEPENSE) LEAVES

Comparative spread of droplets of several different oils and water wit h different adjuvants on leaf surfaces was investigated. Spread was be tter on the lower surface of johnsongrass leaves than on upper leaf su rfaces with nine of 14 oils studied; two spread best on upper leaf sur faces, and three were equal in spread on both surfaces. Differences in spread coefficients did not appear to be directly related to surface tension, viscosity, or mid-boiling point of the oils. Soybean or cotto nseed oils did not spread as well as petroleum oils but methylated soy bean and sunflower oils had high spread coefficients on both upper and lower leaf surfaces. All but one petroleum-base oil spread three to f our times better on leaf surfaces than on oil-sensitive paper. Water m ixtures of an organosilicone surfactant spread much better on water-se nsitive paper and on johnsongrass leaves than water with conventional adjuvants, but spread of paraffinic oils exceeded that of any water-ad juvant mixture. Spread coefficients of most petroleum-base oils were b etter on lower than upper leaf surfaces. Spread usually increased as t he age of leaves increased from 14 to 56 d. Water droplets with adjuva nt had at least an 86% weight loss after 6 min, but low volatile paraf finic oil droplets had little weight loss 2 d after application.