SCREENING HERBICIDES FOR INJURY TO THREE CONTAINER-GROWN PANSY CULTIVARS

in HortScience

Little information is available on phytotoxic effects to annual bedding plant species from herbicides commonly used on container-grown woody plant species. Viol×wittrockiana `Crystal Bowl True Blue', `Imperial Antique Shades', and `Maxim Orange' were grown in 2.54-liter (#1) containers using an amended 6 pine bark: 1 sand medium. Five days after containerizing, each cultivar was either hand-weeded or treated with one of 13 granular or spray, pre- or post-emergence herbicides, within recommended rates in two separate studies. Herbicide phytotoxicity ratings were made 15, 30, 60, 90, and 120 d after treatment. Shoot dry weights were taken 120 d after treatment. Most injurious and persistently injurious herbicides were Rout 3G (oxyfluorfen + oryzalin), Pendulum 60 WDG (pendimethalin), and Ronstar 2G (oxadiazon). Low shoot dry weights closely correlated to injury rating. Least injurious herbicides included Pennant 7.8E (metolachlor), Surflan 4AS (oryzalin), Stakeout (dithiopyr), Pennant SG (metolachlor), and Derby SG (metolachlor + simazine). Southern Weedgrass Control, a granular formulation of pendimethalin, was among the least injurious, while Pendulum 60 WDG, a liquid formulation of pendimethalin, was most injurious. Evidence suggests that phytotoxic injury was greater on small, newly transplanted plants, though in some cases they were able to outgrow the injury.

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