| Summary: | Laboratory and greenhouse studies were conducted to examine the leaf surface, epicuticular wax content, spray droplet behavior, and primisulfuron activity (with and without surfactants) on common lambsquarters, common purslane, velvetleaf, barnyardgrass, and green foxtail. Adaxial and abaxial leaf surfaces were examined using scanning electron microscopy. Leaf wax was extracted and quantified. The spread of 1μl droplets of distilled water, primisulfuron solution (without surfactant), primisulfuron solution with a nonionic surfactant and with an organosilicone surfactant was determined on the adaxial leaf surfaces of each of the weed species. The activity of primisulfuron without or with surfactants was assessed 3 weeks after treatment in terms of percent injury and plant fresh weight. Greenhouse studies were also conducted to investigate the bioherbicidal activity of Alternaria helianthi (Hansf.) Tubaki & Nishih. on multiple-seeded cocklebur as affected by various surfactants. The number of stomata per unit area on abaxial surface was more than on adaxial leaf surface of barnyardgrass, common lambsquarters and velvetleaf, whereas, common purslane and green foxtail had more stomata on adaxial surface than abaxial. Common lambsquarters had the highest wax content per unit of leaf area (274.5 μg cm-2) and velvetleaf had the lowest (7.4 μg cm-2). Wax content of common purslane was 153.4 μg cm-2. The mean values of the wax content per unit of leaf area in barnyardgrass and green foxtail were 35.91 μg cm-2 and 19.14 μg cm-2, respectively. Surfactants increased primisulfuron activity on common lambsquarters, common purslane, velvetleaf, and green foxtail. In general, organosilicone surfactant reduced the contact angle with increased spread area of the primisulfuron droplets more than the nonionic surfactant treatments and resulted in enhanced activity of primisulfuron. Alternaria helianthi resulted in significant reduction of fresh weight of multiple-seeded cockleburs when followed by a 12 h dew period as compared to a 6 h dew. Under short dew period (6 h), greater control of multiple-seeded cocklebur was achieved using higher rates of Activator 90 and Silwet L-77 and may have great potentials for achieving effective biological control.
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