Season-Long Interference of American Black Nightshade with Watermelon

Field trials were conducted over two spring seasons (2005 and 2006) to investigate the interference between American black nightshade and watermelon in polyethylene-mulched and nonmulched (bare ground) trials. Competition studies were performed with watermelon at 1 plant/m in-row and American black nightshade grown at 0, 2, 4, 6, and 8 plants/m2 in-row. Watermelon yield reductions started to plateau at only 2 American black nightshade plants/m2. Yield reduction was 80, 89, 96, and 98% and 54, 67, 81, and 85% at 2, 4, 6, and 8 American black nightshade plants/m2 in mulched watermelon production in 2005 and 2006, respectively. When watermelon was grown on bare ground, yield reduction was 100% at 2 American black nightshade plants/m2 in 2005 and 68, 81, 89, and 93% at 2, 4, 6, and 8 American black nightshade plants/m2 in 2006, respectively. Watermelon fruit numbers were reduced due to American black nightshade interference, but no significant differences in individual fruit weight were observed.Nomenclature: American black nightshade, Solanum americanum Mill., SOLAM, watermelon, Citrullus lanatus (Thunb.) Matsum. & Nakai. cv. ‘Mardi Gras’