Preemergence Weed Control in Container-Grown Herbaceous Perennials

Abstract:  During the 2009 season, two preemergence herbicides were applied to twelve container grown herbaceous perennials and evaluated for weed control, phytotoxicity, and effect on plant growth.  The herbicides and rates were:  BAS 659H G (dimethenamid-p + pendimethalin) 2.97, 5.94 and 11.88 kg ai/Ha and Certainty (sulfosulfuron) 91.2, 182.6 and 365.3 ml product/Ha.  Herbicides were applied to Clematis integrifolia;  Anemone x ‘Little Princess’; Armeria maritima compacta ‘Rubrifolia’; Asclepias tuberosa; Astilbe sp.; Dendranthema x morifolium; Gaura lindheimeri; Lamium maculatum ‘Orchid Frost’; Liatris spicata ‘Kobold’;  Nepeta x faasseni ‘Walker’s Low’; Pennisetum setaceum and Lavandula angustifolia ‘Hidcote Blue’.  Treatments were applied twice with six weeks between applications.  The entire experiment was repeated twice with two weeks between the experiments.  Plants were evaluated for phytotoxicity after one week, two weeks and four weeks after applying herbicide treatments In this study, BAS 659H G (dimethenamid-p + pendimethalin) was safe to use on Anemone, Clematis, Dendranthema and Nepeta at all rates.  However, BAS 659H G produced phytotoxic symptoms at all rates in Asclepias, Astilbe, Lamium, Liatris and Pennisetum.  It was safe at the 1x (label) rate but not at the  2x or 4x rates for Gaura and Lavandula.  Certainty (sulfosulfuron) produced phytotoxic symptoms in Armeria, Clematis, Lamium and Lavandula at all rates and would not be recommended for use with these plants.  Effective weed control was provided BAS 659H G and sulfosulfuron with all but one treatment controlling more than 97 percent of the weeds.