|Biernacki, Maciej - OKLAHOMA STATE UNIVERSITY|
|Roberts, Warren - OKLAHOMA STATE UNIVERSITY|
Submitted to: Weed Science Society of America Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: March 20, 2000
Publication Date: N/A
Technical Abstract: Although it is clear that weed competition can reduce watermelon yields, it is still unclear the precise competition mechanisms involved with specific weed species. A field study was conducted at Lane, OK to determine the effect of pigweed (Amaranthus albus L.) competition on watermelon yield parameters over a 14-week period. Watermelon plants were grown surrounded by pigweed seeded in 5 radial distances from 0 cm to 160 cm and at 5 densities ranging from 2 to 64 plants. The control treatment was maintained weed free. Watermelon performance and biomass were suppressed by increasing pigweed plants and by shorter distance to weeds. Distance between watermelon leaves increased up to 3 times for vines surrounded by pigweed compared to the control. Leaf number increased and their surface area decreased from over 250 cm**2 to below 20 cm**2 on vines shaded by pigweed. Mean lifespan of watermelon leaves decreased from over 80 to 28 days with greater weed numbers and shorter distance to weeds. Watermelon flowering was delayed, and total leaf surface area and leaf area index were decreased with increasing pigweed populations and as the distance between the watermelon and weeds decreased. Shading of watermelon vines produced a greater proportion of male flowers than female flowers when compared to the control. Date of flower and fruit production were delayed in watermelon exposed to greater pigweed populations and grown closer to pigweeds. Watermelon plants exposed to pigweed plants grown at distances from 0 cm to 20 cm did not produce any fruit. The research determined that watermelon is a weak competitor and that greater densities of nearby pigweed plants increase the watermelon vegetative growth period and delayed flowering and reproduction.