Evaluation of Weed Control and Phytotoxicity of Preemergence Herbicides Applied to Container-grown Herbaceous and Woody Plants

Abstract

Abstract Six different preemergence herbicides were used with eight different plant species to evaluate weed control efficacy and possible phytotoxicity. The species used were Stachys byzantina C. Koch (lamb's ears), Campanula persicifolia L. (peachleaf bellflower), Achillea millefolium L. ‘Summer Pastel’ (common yarrow), Coreopsis lanceolata L. (Lance coreopsis), Gypsophila pacifica Kom. (baby's breath), Wisteria sinensis Sims (Chinese wisteria), Syringa vulgaris L. (common lilac), Phlox paniculata L. (perennial phlox), Dahlia Cav. x hybrida (garden dahlia). Herbicides were applied to the soil surface at rates of lx and 2x as recommended by the label. The herbicides and rates were as follows: Pennant (Dual) 7.8 Liquid, 4.6, 9.1 kg ai/ha (4, 8 lb ai/A); Gallery 75DF, 1.1, 2.3 kg ai/ha (1, 2 lb ai/A); Ronstar 2G, 4.5, 9.0 kg ai/ha (4, 8 lb ai/A); Rout 3G, 3.4, 6.8, 13.6 kg ai/ha (3, 6, 12 lb ai/A); Surflan AS, 2.3, 4.6 kg ai/ha (2, 4 lb ai/A); and Treflan 5G, 4.5, 9.0 kg ai/ha (4, 8 lbs ai/A). Weed seeds of Setaria glauca (L.) Beauv. (yellow foxtail), Echinochloa crus-galli (L.) Beauv. (barnyardgrass), Poa annua L. (annual bluegrass), Capsella bursa-pastoris (L.) Medik. (shepherdspurse), Senecio vulgaris L. (common groundsel), and Amaranthus retroflexus L. (redroot pigweed) were sown on the soil surface. Two control treatments (no herbicide and no weed seeds applied, or no herbicide but with weed seeds) also were evaluated. Plants were grown in #1 black plastic containers in a medium of clay loam soil, plaster sand and sphagnum peat (1:1:2 by vol). Weed counts at the end of the season indicated that weed control was variable according to the herbicide used. Rout and Ronstar at both the lx and 2x rates controlled over 99% of the weeds (compared to the control treatment with weeds). Weed control for the other herbicides were as follows: Surflan lx = 92%, Surflan 2x = 95%, Pennant lx = 93%, Pennant 2x = 98%, Gallery lx = 35%, Gallery 2x = 43%, Treflan 1x = 88%, and Treflan 2x = 96%. Evaluations also indicated that herbicides utilizing oryzalin resulted in phytoxicity or stunting to Phlox (appearance declined 88% at the 1x rate and 93% at the 2x rate compared to the control treatment), Gypsophila (dry weights for Surflan 1x was 27% less and Surflan 2x was 39% less compared to the control treatment), and Stachys (appearance declined 55% for 1x rate and 60% at the 2x rate). Gallery (isoxaben) resulted in stunting in Stachys (dry weights for Gallery 1x were 75% less compared to control plants and Gallery 2x was 80% less).