Effective Non-Traditional Weed Control in Container-Grown Nursery Crops

Abstract

A series of experiments were conducted to evaluate container nursery crop tolerance and oxalis control with postemergence applied diuron as influenced by timely overhead irrigation. Intent was to identify an interval between application and irrigation that may reduce crop injury without compromising oxalis control. Diuron was applied at a common rate of 1.0 lb ai/A to oxalis and two nursery crops (Camellia sasanqua ‘Alabama Beauty’ camellia, and Rhododendron indicum ‘G.G. Gerbing’, azalea). Treatments consisted of irrigation at 1, 2, 4, 8, 12, 24, or 48 hr after application. Oxalis control was equivalent whether treated plants were irrigated within either 1 hr or 48 hr after application. Camellia exhibited no visible injury regardless of treatment. Azaleas exhibited diuron-induced injury, however injury was reduced if plants were irrigated within 1 hr of diuron application. 14C-diuron was used to determine the absorption rate of foliar-applied diuron into oxalis, camellia and azalea. Absorption by oxalis was relatively rapid, and reached a maximum (~68% of applied) within 8 hr after application. Camellia and azalea absorbed a smaller percentage of the amount applied, and absorption was more protracted over time compared to oxalis. Azalea absorbed slightly more than camellia. Diuron has potential for use as an over-the-top application for postemergence oxalis control and timely irrigation has the potential to reduce injury to sensitive crops. Another set of experiments were conducted to evaluate fresh pine bark nuggets for cool season weed control (oxalis and bittercress) in 11 and 27 L (3 and 7 gal) containers. In October 2004, gardenias were seeded with oxalis, and crapemyrtle with bittercress in 27 L (7 gal) containers. In March 2005, oakleaf hydrangeas were seeded with oxalis and ternstroemia with bittercress in 11 L (3 gal) containers. Treatments consisted of mulch applied at depths of 0, 3.8, and 7.62 cm (0, 1.5 and 3.0 in.), and seeded either before or after mulch application. A separate group of treatments were included similar to the above except that a granular preemergence herbicide was applied after mulch application. Growth of crapemyrtle and ternstroemia were similar regardless of mulch depth. With gardenia and oakleaf hydrangea growth differences existed but there was not a consistent trend with any of the treatments. Season long weed control was obtained in all treatments that included 7.62 cm (3 in.) mulch depth. The final series of experiments evaluated fresh pine bark nuggets for warm season weed control (spurge and eclipta) in 27 L (7 gal) containers. In 2004 lilac chaste tree were seeded with spurge and dwarf burford holly were seeded with eclipta. In 2005, natchez crapemyrtle were seeded with spurge and willowleaf cotoneaster were seeded with eclipta. Treatments consisted of mulch applied at depths of 0, 3.8, and 7.6 cm (0, 1.5, 3.0 in.), and seeded either before or after mulch application. A separate group of treatments were included similar to the above except that a granular preemergence herbicide, flumioxazin (Broadstar 0.25G) (Valent. Walnut Creek, CA) was applied at 0.40 kg ai/ha (0.375 lb aia or 150 lb product/A) after mulch application. Growth of all species was similar except dwarf burford and cotoneaster where non- mulch treatments were slightly smaller. Season long weed control was obtained in all treatments that included mulch at 7.6 cm (3 in.) depth.