Abstract

Three experiments were conducted to evaluate the influence of alternative substrates on herbicide efficacy in container grown nursery crops. In Experiment 1, alternative substrates evaluated were either pine wood chips hammer-milled, to pass between 0.48 cm (0.19 in) screen (PWCH1) or 0.64 cm (0.25 in) screen (PWCH2), whole pine trees chipped or hammer-milled (WTCH), to pass between a 0.48 cm (0.19 in) screen, or the previously mentioned combined with pinebark. A commercial pine bark substrate (PB) with a 6: 1 (by vol) ratio of pine bark to sand was maintained as a control treatment. Rout® at 3 lbs aia (oxyfluorfen + oryzalin at 2.24 + 1.12 kg·ha⁻¹) and Ronstar at 4.0 lb aia (oxadiazon at 4.48 kg·ha⁻¹) were applied at recommended label rates. Herbicides were applied and irrigated, and each container was overseeded with 25 spotted spurge (Euphorbia maculata) seed per container. In general, the greatest spurge numbers occurred in PB substrates. Rout provided superior spurge control compared to Ronstar. In Experiment 2, substrates evaluated were PWCH2, WTCH and PBS with 7.0 kgm⁻³ (12 lbsyd⁻³) of Polyon 17-6-12 or with an additional 8 lbs·yd⁻³ of Polyon 17-6-12, or PWCH2 and WTCH combined with composted poultry litter (CPL). PWCH2 tended to have the fewest spurge numbers throughout the experiment, while WTCH and PBS tended to have similar spurge numbers and spurge fresh weight. Addition of CPL and additional fertilizer tended to increase spurge numbers and spurge fresh weight in all substrates. Rout and Ronstar provided similar spurge control in this study. In Experiment 3, substrates evaluated were PB (100%), WTCH (100%), CCR (100%), and PB: S (6: 1 vol), WTCH: S (6: 1 vol), and CCR: S (6: 1 vol). Rout and Ronstar were each applied at 0.25×, 0.50×, 075×, and 1.0× label rate. There was a significant substrate affect on all dates except 14 DAT. Spurge numbers and spurge fresh weight were greatest in PB or PB: S substrates. Spurge numbers and spurge fresh weight in general decreased with increasing herbicide rates. At 45 DAT and 60 DAT, Rout had superior spurge control compared to Ronstar. With WT and CCR substrates, Rout provided excellent control (less than 1.0 gram fresh weight) at the 0.50× and 1.0× rates. In general, weed control in alternative substrates was superior to that obtained in commercially used pinebark.