Preemergence Weed Control in Direct-Seeded Watermelon1

Studies were conducted at eight sites during a 3-yr period in Oklahoma and Arkansas to determine the effectiveness and safety of preemergence applications of halosulfuron both alone and in tank mixtures with bensulide, clomazone, ethalfluralin, and naptalam. Ethalfluralin, naptalam plus bensulide, and sulfentrazone also were applied alone. Although halosulfuron caused up to 20% seedling stunting, watermelon plants recovered by 5 to 7 wk after planting, and yield was similar to that of hand-weeded plots. Halosulfuron treatments controlled hophornbeam copperleaf, Palmer amaranth, carpetweed, and cutleaf groundcherry 80 to 100%. Control of goosegrass was at least 97% with clomazone plus ethalfluralin plus halosulfuron. Injury to watermelon treated with sulfentrazone ranged from 76 to 98% at 2 to 4 wk after treatment. This was reflected by yields that were lower than any other herbicide treatment in the studies. Nomenclature: Bensulide; clomazone; ethalfluralin; halosulfuron; naptalam; sulfentrazone; hophornbeam copperleaf, Acalypha ostryifolia Riddell #3 ACCOS; Palmer amaranth, Amaranthus palmeri S. Wats. # AMAPA; goosegrass, Eleusine indica (L.) Gaertn. # ELEIN; carpetweed, Mollugo verticillata L. # MOLVE; cutleaf groundcherry, Physalis angulata L. # PHYAN; watermelon, Citrullus lanatus ‘Jubilee’, ‘XIT 101’, ‘Crimson Sweet’. Additional index words: Broadleaf weed control, watermelon injury. Abbreviations: PRE, preemergence; WAT, weeks after treatment.