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ARS Home » Southeast Area » Poplarville, Mississippi » Southern Horticultural Research » Research » Publications at this Location » Publication #169165

Title: MINIMUM DURATION OF DIURON EXPOSURE FOR OXALIS CONTROL

Author
item RICHARDSON, BEN
item WEHTJE, GLENN
item GILLIAM, CHARLES
item Fain, Glenn

Submitted to: Southern Nursery Association Research Conference
Publication Type: Proceedings
Publication Acceptance Date: 8/1/2004
Publication Date: 8/1/2004
Citation: Richardson, B.M., Wehtje, G.R., Gilliam, C.H., Fain, G.B. 2004. Minimum duration of diuron exposure for oxalis control. Southern Nursery Association Research Conference. 49:370-373.

Interpretive Summary: Oxalis stricta is a common nursery weed that has been identified as difficult to control. Previous research has shown that diuron provided excellent oxalis control and that crop tolerance was good with dormant nursery crops. The objective of this study was to determine the minimum time duration of diuron exposure between application and irrigation to result in postemergence oxalis control while causing little or no injury to actively growing nursery plants. Results show that irrigating one hour after diuron application has minimal impact on diuron activity on oxalis. Camellia plants were actively growing at the time of diuron application and no visible injury occurred at any time during the study. Azaleas were also actively growing at time of diuron application and were injured in all treatments across all dates; however the least injury occurred with the azaleas irrigated within one hour of application at 28 days after treatment. This research shows that properly applied, diuron could be a postemergence herbicide option for growers to control oxalis in container crops.

Technical Abstract: Oxalis stricta is a perennial weed which spreads rapidly by seed. In a survey of nurserymen it was identified as being very difficult to control in container crops. Diuron has been shown to provide excellent oxalis control and that crop tolerance was good with dormant nursery crops. However injury occurred if crops were actively growing. Other work evaluating diuron as a preemergence herbicide has shown that nursery crop tolerance is improved with overhead irrigation soon after diuron application. The objective of this study was to determine the minimum time duration of diuron exposure between application and irrigation to result in postemergence oxalis control. This experiment was conducted in Auburn, Alabama in 2004. Oxalis were seeded and grown in a standard nursery substrate in 7.5cm containers and thinned leaving one uniform sized oxalis plant per container. At time of treatment, approximately five weeks after seeding, oxalis plants were 8-12cm wide and 4-6cm tall. Direx 4L (diuron) at 1.1kg ai/ha plus 0.25% Agridex non-ionic surfactant were applied to the oxalis using a spray chamber. The chamber was calibrated to deliver 30 gal/A (284 l/ha) with an 11002 nozzle. Application was at 7:00 A.M. Treatments consisted of irrigation intervals of 0.5, 1, 2, 4, 8, 12, 24, and 48 hours after diuron application with 7 replications for each treatment. Crop tolerance was evaluated for azalea (Rhododendron indicum 'G. G. Gerbing') and camellia (Camellia sasanqua 'Alabama Beauty') liners. Each species was transplanted into four inch containers in a standard nursery media. Treatments were the same as described above. This study shows that irrigating one hour after diuron application has minimal impact on diuron activity on oxalis. There was no significant difference among irrigation intervals at anytime throughout the study. Camellia plants were actively growing at the time of diuron application and no visible injury occurred at any time during the study. Azaleas were also actively growing at time of diuron application and were injured in all treatments across all dates; however the least injury occurred with the azaleas irrigated within one hour of application at 28 DAT. These data concur work by Ahrens et al. and Barolli et al., who reported that overhead irrigation soon after diuron application for preemergence weed control increased crop tolerance of landscape plants. Additional research is needed to evaluate tolerance of diuron and timing of application to nursery crops.