Glyphosate efficacy on eastern Canadian forest weeds. I. Experimental design and on-target deposit

Experimental methods and resulting on-target deposit data are presented for an operational field trial designed to evaluate glyphosate (Vision) efficacy using two different dispersal systems (AU5000 Micronairs and conventional hydraulic nozzles). A range of glyphosate rates (0, 0.25, 0.50, 0.75. and 1.00 kg acid equivalent per hectare) was aerially applied in a randomized complete block design to four cutover sites in New Brunswick. Formulation, tank-mix, droplet, and chemical analyses were conducted to quantify actual on-target deposit for each treatment. Data for the calibrated portion of each swath suggested that the Micronair system produced a slightly narrower drop-diameter spectrum (0-677 micrometer, volume median diameter = 300 micrometer) than the hydraulic system (0-1085 micrometer, volume median diameter = 425 micrometer). Analysis of variance and orthogonal contrasts indicated that on-target deposit for the Micronair system (average accountability = 71%) was not significantly different from that of the hydraulic system (average accountability = 82%) for three of four rates tested. Unrepresentative meteorological and site conditions affecting Micronair treatments in two blocks resulted in reduced deposit for the treatment of 1.00 kg acid equivalent per hectare. Substantial variability within treatments was observed for both dispersal systems (41 and 47% coefficient of variation for Micronair and hydraulic systems, respectively). Overall, results suggest no significant differences between the two dispersal systems (as calibrated) in terms of on-target deposit efficiency or variability. Both on-target droplet density and chemical deposit data reflected differences associated with blocks. This fact highlights the need for further studies on meteorological and operational factors on deposit.