Evaluation of Selected Preemergence Herbicides in Field-Grown Landscape Crops in Kentucky

Abstract

Abstract Research was conducted during 1990 and 1991 at the Horticultural Research Farm in Lexington, Kentucky, to evaluate the efficacy of herbicides available for use on woody landscape plants (simazine and oryzalin), newly labelled herbicides (isoxaben, isoxaben plus oryzalin, metolachlor and metolachlor plus simazine) and those not widely labelled for the nursery industry (oxyfluorfen and dithiopyr). Herbicide phytotoxicity was also evaluated in 10 species of woody nursery crops. Results 6 WAT (weeks after treatment) indicated that the standard of simazine at 1.1 kg ai/ha (1.0 lb/A) plus oryzalin at 3.3 kg ai/ha (3.0 lb/A) provided adequate control of most common broadleaf weeds (98%) and annual grasses (98%) but not yellow nutsedge (31%). Isoxaben plus oryzalin at 4.2 kg ai/ha (4.0 lb/A) (DF formulation) and isoxaben plus trifluralin at 4.2 kg ai/ha (4.0 lb/A) (granular formulation) gave excellent full-season control of nearly all broadleaf and grass weeds with the exception of galinsoga and field bindweed. In addition, yellow nutsedge control was acceptable, ranging from 63 to 96% in these treatments. Isoxaben alone also provided excellent broadleaf control (93%) 6 WAT in 1990 but poorer (<70%) control of giant foxtail, galinsoga and velvetleaf by 12 WAT. Dithiopyr (granular formulation) provided excellent full-season residual control of broadleaf weeds, nutsedge and grasses at the highest rate of 2.2 kg ai/ha (2.0 lb/A). Oxyfluorfen at the higher rate (2.2 kg ai/ha) (2.0 lb/A) also controlled all species except yellow nutsedge. Poor broadleaf control was obtained 12 WAT with 3.3 kg ai/ha (3.0 lb/A) metolachlor or metolachlor plus simazine at rates up to 4.4 kg ai/ha (4.0 lb/A) in both 1990 and 1991. Pronamide at 2.2 kg ai/ha (2.0 lb/A) did not provide adequate control of either broadleaf or grasses at 6 or 12 WAT. No visible phytotoxicity to woody ornamentals was observed in either season up to 8 weeks after application. However, growth reductions were noted in both common lilac and red oak stem or trunk diameter following treatment with isoxaben at 1.1 kg ai/ha (1.0 lb/A).