014 Effects of Preemergence Herbicides on Weeds and Eighteen Containerized Crops

Abstract

Five preemergence herbicides (prodiamine 0.5 G, prodiamine 65 WDG, dithiopyr 0.27 G, thiazopyr 2.5 G, and oxyfluorfen + pendimethalin 3 G) were evaluated for weed control and crop safety on 18 plants (Acer rubrum, Agapanthus africanus, Asparagus densiflorus, Camellia sasanqua, × Cupressocyparis leylandii, Cycas revoluta, Galphimia gracillis, Gelsemium sempervirens, Illicium parviflorum, Lantana camara, Loropetalum chinense, Myrtis communis, Ophiopogon jaburan, Plumbago, Quercus virginiana, Rhododendron, Viburnum suspensum, and Zamia floridana. Herbicides were applied at 1.7 kg a.i./ha, except for oxyfluorfern + pendimethalin, which was applied at 3.4 kg a.i./ha. Treatments were applied twice at 4-month intervals. Untreated and weed-free controls were used to determine herbicide effects on weeds and crops, respectively. All herbicide treatments reduced weed growth (dry-weight basis) and weeding times. Major weeds were dogfennel [Eupatorium capillifolium (Lam.) Small], southern crabgrass [Digitaria ciliaris (Retz.) Koeler], yellow woodsorrel (Oxalis stricta L.), tasselflower (Emilia spp.), and hairy crabweed [Fatoua villosa (Thumb.) Nakai]. Based on weed dry weights, overall weed control for the first 4 months was higher for diazopyr, thiazopyr, and prodiamine G than for the combination treatment. At 8 months, weed growth was similar for all herbicide treatments. The combination treatment was acutely phytotoxicity to more crops than the other treatments; however, phytotoxicity varied with crop, active ingredient, and formulation.