Six herbicides were applied to four woody and two herbaceous plant species to evaluate weed control effectiveness, effect on plant growth and phytotoxicity level. Surflan (Oryzalin) at 2.3, 4.5, 6.8 kg ai/ha (2, 4, 6 lb ai/A), Devrinol (Napropamide) at 5.5, 9.1, 13.6 kg ai/ha (4, 8, 12 lb ai/A) and Dual (Metolachlor), Rout (Oxyfluorfen + Oryzalin) and Snapshot (Isoxaben + Oryzalin) at 3.4, 6.8, 10.2 kg ai/ha (3, 6, 9 lb ai/A) were applied to container-grown Fraxinus pennsylvanica var. lanceolata (Borkh.) (green ash) and Betula pendula (Roth.) (European white birch). Additionally, Surflan at 2.3, 4.5 kg ai/ha (2, 4, lb ai/A), Ronstar (Oxadiazon) and Devrinol at 5.52, 9.1 kg ai/ha (4, 8 lb ai/A), Dual and Rout at 3.4, 6.8 kg ai/ha (3, 6 lb ai/A) were applied to container-grown Acer tataricum L. (Tatarian maple), Philadelphus virginalis L. (virginal mock orange), Hemerocallis L. sp. (daylily) and Clematis recta L. (clematis). Weed seed sown in both experiments included: Setaria glauca (L.) Beauv. (yellow foxtail), Echinochloa crusgalli (L.) Beauv. (barnyardgrass), Poa annua L. (annual bluegrass), Stellaria media (L.) Vill (common chickweed), Capsella bursapastoris (L.) Medic (shepherdspurse) and Senecio vulgaris L. (common groundsel).

Plants were grown in 2.5 1 (# 1) black plastic containers in a medium of sandy loam topsoil, plaster sand and sphagnum peat (1:1:1 by vol). Good weed control occurred in most cases with all herbicides except Devrinol and Dual. No visual foliage injury occurred in any treatment but significant growth reduction was observed with the 10.2 kg ai/ha (9 lb ai/A) rate of Snapshot with Betula pendula (white birch). Growth reduction of tatarian maple was also observed with 6.8 kg ai/ha (6 lb ai/A) rate of Dual and 4.52 kg ai/ha (4 lb ai/A) rate of Surflan.

Author notes

Funding was provided by Colorado Agricultural Experiment Station (Project 713) and Western Regional Pesticide Impact Assessment and IR-4 Minor Use Programs.

2Graduate Research Assistant and Associate Professor, respectively.