Ornamental Plant and Weed Response to Oxyfluorfen Plus Prodiamine

Ornamental plant and weed response to oxyfluorfen + prodiamine herbicide was evaluated in Connecticut and Tennessee, USA, in 2017 and 2018. Preemergence application of oxyfluorfen + prodiamine was made at 0 lb/acre, 2 + 0.75 lb/acre, 4 + 1.5 lb/acre, and 8 + 3 lb/acre to container-grown ornamental plants on an outdoor gravel pad and weeds in greenhouse experiments. Ornamental plants were treated first within a week after transplanting and again 6 weeks after the first treatment. Asiatic jasmine (Trachelospermum asiaticum), candlestick plant (Senna alata), and English ivy (Hedera helix) in Tennessee, USA; and ‘Blue Flag’ iris (Iris sp.), ‘Firecracker’ gladiolus (Gladiolus sp.), and ‘Green Carpet’ Japanese pachysandra (Pachysandra terminalis) in Connecticut, USA, were not injured with oxyfluorfen + prodiamine regardless of rate applied. Lily-of-the-Nile (Agapanthus africanus) in Tennessee, USA, and ‘Bowles’ periwinkle (Vinca minor) in Connecticut, USA, showed minor but commercially acceptable growth reduction with oxyfluorfen + prodiamine up to 4 + 1.5 lb/acre. Shasta daisy (Leucanthemum ×superbum) in Connecticut, USA, was the most sensitive ornamental plant. After the first application, average necrotic injury to Shasta daisy varied from 24% with 2 + 0.75 lb/acre to 31% with 8 + 3 lb/acre of oxyfluorfen + prodiamine. After the second application, necrotic injury was ≤ 5% with all oxyfluorfen + prodiamine rates tested and was commercially acceptable (≤ 20%). Oxyfluorfen + prodiamine reduced densities of creeping woodsorrel (Oxalis corniculata), hairy bittercress (Cardamine hirsuta), giant foxtail (Setaria faberi), and large crabgrass (Digitaria sanguinalis) ≥ 80% by 4 weeks after treatment. The fresh weed biomass 6 weeks after treatment indicated an 88% to 99% reduction compared with the untreated control.