Time of day at which a herbicide is applied can affect efficacy, and variab
ility may be attributed to leaf angles at application. Spray interception b
y hemp sesbania (Sesbania exaltata), sicklepod (Senna obtusifolia), and pri
ckly sida (Sida spinosa) under day and night conditions was quantified by m
easuring interception of a 2-M potassium nitrate solution. Following the ni
ght application, interception by prickly sida, hemp sesbania, and sicklepod
was reduced 17, 67, and 70%, respectively. In a second study in the greenh
ouse, glyphosate was applied to hemp sesbania, pitted morningglory (Ipomaea
lacunosa), prickly sida, and sicklepod at 6:00 and 11:00 A.M, and 4:00 and
9:00 P.M. Control of all species was dependent on the time of day treated,
with night applications generally being less effective.