Safety of Preemergence Herbicides Applied during Propagation of Three Woody Nursery Crops

Currently there are no preemergence herbicides labeled for use during propagation of ornamental crops. In propagation, weed control can be one of the most expensive production problems during due to lack of herbicide options. Weeds compete with cuttings for water, light, nutrients and also significantly reduce the marketability of liners. Once weeds have begun to germinate in propagation flats the only method of removal is typically hand weeding which is extremely expensive from a labor standpoint and can also disrupt or delay the rooting process as the cuttings are often disturbed. Past research has shown varying levels of success with multiple species-herbicide combinations at different stages of propagation. The objective of this study was to investigate the impacts of herbicides on rooting and quality of three woody nursery crops. Four different herbicides were evaluated for use during propagation of Loropetalum chinense ‘Sizzling Pink’ (loropetalum), Viburnum odoratissimum (viburnum), and Rosa ‘Radrazz’ (rose) in various combinations. Loropetalum cuttings were treated with Marengo G (indaziflam), Rout (oxyfluorfen + oryzalin), or Tower (dimethenamid-p), viburnum cuttings were treated with either Gallery SC (isoxaben), Rout, or Tower, and rose cuttings were treated with either Marengo G or Gallery SC. All herbicide treatments were applied at 0.5, 1, or 2× their label rate. For rose and loropetalum, herbicide treatments were either applied 14 days before sticking (DBS), on the day of sticking (0 DAS), or at 30 or 60 DAS. Viburnum cuttings were treated at 14 DBS, and at 0, 30, 60, and 90 DAS. Data collected included phytotoxicity ratings at 1, 2, and 4 weeks after treatment and shoot and root fresh weights at study conclusion. Herbicide rate had little impact on trial results. Loropetalum cuttings performed best when treated with Marengo G at either 30 or 60 DAS in which there were no significant reductions in shoot or root FW, although there was a numerical reduction in shoot and root weight. For rose, cuttings performed best when treated with the lowest two rates of Gallery SC or Marengo at 30 and 60 DAS. For viburnum, cuttings grew similarly to non-treated controls when Gallery SC was applied at 14 DBS, 0 DAS, and 90 DAS. Viburnum cuttings were also similar to non-treated controls when Rout was applied at 14 DBS or 90 DBS. Viburnum cuttings were most impacted by applications of Tower which reduced shoot and root FW at most timings.