The Influence of Spray Tank Turbidity on Chemical Management Efficacy of Barnyardgrass [Echinochloa crus-galli (L.) P. Beauv.], and Velvetleaf (Abutilon theophrasti Medicus.) at Greenhouse Conditions

The influence of spray tank turbidity on glyphosate (Roundup®, 41% SL) and nicosulfuron (Cruse®, 4% SC) performance on barnyard-grass and velvetleaf was examined in a greenhouse study as a factorial arrangement of treatments 2×6 based on a completely randomized design with six replications (+six control pots) for each weed species at Ferdowsi University of Mashhad, Iran during 2008-9. Factors were included turbidity at six levels (0, 100, 200, 300, 400, 500, and 600 ppm sieved soil particles containing 31.7% clay into deionized water (w/v)), and two herbicides (glyphosate and nicosulfuron). In a preliminary test, a dose-response experiment was carried out to estimate the ED50 doses of the herbicides at greenhouse. The glyphosate and nicosulfuron solutions were applied as post emergence at 3 to 4 leaf stage of the weeds at the estimated ED50 doses in the preliminary experiment (158 and 22 g ai ha-1, respectively) based on spray volume of 250 L ha-1. The results showed that adding soil particles (turbidity) into spray tank was reduced herbicides performance significantly (P≤0.01), whereas, survival, plant height, leaf area, and shoot dry weight of weeds (% control) were increased. The antagonistic effect of turbidity was higher with glyphosate than with nicosulfuron for barnyard-grass, but for velvetleaf the results was reversed. In conclusion, the results have highlighted the importance of spray tank turbidity on herbicide performance.