CRITICAL WEED-FREE PERIOD FOR LARGE CRABGRASS (DIGITARIA-SANGUINALIS)IN TRANSPLANTED WATERMELON (CITRULLUS-LANATUS)

Removal and plant-back studies were conducted in North Carolina in 199 1 and 1992 to determine the critical period of large crabgrass competi tion in transplanted triploid (seedless) watermelon. For every week th at large crabgrass remained in watermelon, medium (3.6 to 7.3 kg) melo n yield decreased 3,996 kg and 716 fruit ha(-1). For every week that l arge crabgrass emergence was delayed, yield increased by 814 kg and 14 2 fruit ha(-1). Likewise, for every week that large crabgrass remained in watermelon, marketable (3.6 kg and over) yield decreased 5,582 kg and 911 fruit ha(-1). For every week that large crabgrass emergence wa s delayed, yield was increased 881 kg and 151 fruit ha(-1). Large crab grass emerging after 6 wk had no effect on marketable fruit or number of watermelon. To achieve the greatest quality or quantity of medium o r marketable fruit, a large crabgrass-free period between 0 and 6 wk a fter transplanting was necessary.