Weed Control Efficacy and Ornamental Plant Tolerance to Dimethenamid–p + Pendimethalin Granular Herbicide

Weed control efficacy and ornamental plants tolerance to dimethenamid–p (0.75%) + pendimethalin (1%) granular herbicide was evaluated in flat tray-grown weeds and container-grown ornamental plants. Dimethenamid – p + pendimethalin at 2.94 kg ai.ha–1 (2.62 lb ai.A–1) controlled the tested broadleaf and grassy weeds >80% for up to 8 wk following herbicide application. The higher dimethenamid–p + pendimethalin rates of ≥5.88 kg ai.ha–1 (≥5.25 lb ai.A–1) provided 94% to 99% control of the tested weed species but caused commercially unacceptable injury to pygmyweed [Crassula radicans (Haw.) D. Dietr. ‘Red carpet']. Chocolate flower (Berlandiara lyrata Benth.) tolerated dimethenamid–p + pendimethalin at 2.94 kg ai.ha–1 (2.62 lb ai.A–1) and 5.88 kg ai.ha–1 (5.25 lb ai.A–1) but the 11.77 kg ai .ha–1 (10.5 lb ai.A–1) rate was injurious in one of the two study years. Leucothoe [Leucothe fontanesiana (Steudel) Sleumer ‘Rainbow'] showed excellent tolerance to dimethenamid–p + pendimethalin at rates up to 11.77 kg ai.ha–1 (10.5 lb ai .A–1). Herbicides used in this study: 0.75% Dimethenamid–p + 1% pendimethalin (Freehand 1.75 G), (S) 2-chloro-N-(2,4-dimethylthiophen-3-yl)-N-[(2S)-1-methoxypropan-2-yl]acetamide] + N-(1-ethylpropyl)-3,4-dimethyl-2,6- dinitrobenzenamine]. Ornamental plant species used in this study: chocolate flower (Berlandiara lyrata Benth.), leucothoe [Leucothe fontanesiana (Steudel) Sleumer ‘Rainbow'], and pygmyweed [Crassula radicans (Haw.) D. Dietr. ‘Red Carpet']. Weed species used in this study: barnyardgrass [Echinochloa crus-galli (L.) Beauv.], fringed willowherb (Epilobium ciliatum Raf. ssp. ciliatum), giant foxtail (Setaria faberi Hermm.), goosegrass [Elusine indica (L.) Gaertn.], hairy bittercress (Cardamine hirsuta L.), large crabgrass [Digitaria sangunalis (L.) Scop.], redroot pigweed (Amaranthus retroflexus L.), and yellow woodsorrel (Oxalis stricta L.).