UPTAKE, TRANSLOCATION, AND METABOLISM OF DITHIOPYR IN LARGE AND SMOOTH CRABGRASS AS INFLUENCED BY ENVIRONMENT, GROWTH STAGE, AND ADJUVANTS. D. Gómez de Barreda, Polytechnic University of Valencia, Spain; P. McCullough and J. Yu, Department of Crop and Soil Sciences, University of Georgia, Griffin, GA 30223.

ABSTRACT

Dithiopyr provides preemergence and early postemergence control of crabgrasses (Digitaria spp.) in turfgrass but postemergence applications often have inconsistent efficacy.  Experiments were conducted to evaluate effects of growth stage, temperature, and adjuvant use on absorption and translocation of dithiopyr in smooth and large crabgrass (Digitaria ischaemum and D. sanguinalis).  Multi-tiller smooth crabgrass absorbed more root-applied ¹⁴C-dithiopyr than multi-leaf and one-tiller plants but radioactivity concentration (Bq/g) across growth stages from high to low measured: multi-leaf > one-tiller > multi-tiller.  Smooth crabgrass had approximately twofold more total radioactivity concentrations at 15/10 C compared to 30/25 C from root applications.  Distribution of root-applied dithiopyr to shoots was twofold greater in multi-leaf smooth crabgrass compared to multi-tiller plants and increased at 30/25 C compared to 15/10 C.  Across growth stages, smooth crabgrass had more foliar absorption of ¹⁴C-dithiopyr at 15/10 C compared to 30/25 C and >90% of absorbed ¹⁴C was retained in shoots.  The addition of a nonionic surfactant (Activator 90) at 0.25% v/v increased foliar absorption of ¹⁴C-dithiopyr in large and smooth crabgrass at one-tiller compared to treatments without a surfactant.