Evaluation of Dichlobenil and Flumioxazin Preemergent Formulations for Ornamental Weed Control

Abstract

The objective of this study was to evaluate the extent and duration of efficacy and phytotoxicity of two new formulations of dichlobenil (Casoron 50WP and Casoron CS), applied alone or onto two bark mulches, pine nuggets or shredded hardwood. The herbicide treated bark was compared to a control (weedy check), direct sprays of the herbicides and mulch alone. Three granular preemergent herbicides, dichlobenil (Casoron 4G) and two formulation of flumioxazin (Broadstar 0.17G, VC1351, and VC1453) were also evaluated for a total of 12 treatments. The trial started on May 23, 2003. Visual ratings and dry weights were evaluated for efficacy at 4, 8 and 16 weeks after treatment (WAT) and phytotoxicity 2, 4, 8, and 16 WAT. Ratings of efficacy were based on a 1-10 scale where, 0 represents no control, 10 represents complete control. Visual rating scores of 1 (no injury) to 10 (complete kill) were used for phytotoxicity on Salvia May Night. The two most efficacious treatments are Casoron CS as a directed spray (7.9) and treated on pine nuggets (9.0). The hardwood bark with Casoron CS also was providing an efficacy rating of 7.75 in the analyses of combined dates 4 and 8 WAT. The weed control provided by the untreated hardwood bark and pine nuggets was not significantly different from the control. Four treatments—Casoron CS and 4G, Casoron CS on pine, and CS on hardwood—provided ratings of 3 and above for phytotoxicity, in the analyses of combined dates 2, 4, 8, and 16 WAT. Although the Casoron CS was the second most efficacious treatment it had a phytotoxicity rating of 9.25 over combined dates. The CS on pine, however, had a significantly reduced phytotoxicity rating (3.5) and superior efficacy.