A Model of Competition for Light Between Peanut (Arachis hypogaea) and Broadleaf Weeds

A model of competition for light between peanut and three broadleaf weed species has been developed to run with the PNUTGRO model. The model simulates shading of the peanut canopy by reducing the total daily PAR received by the peanuts in a manner that realistically represents timing and quantity of light capture by the weeds. Data were col- lected in nursery plots of Florida beggarweed, sicklepod, and wild poinsettia in 1989,1990, and 1991. These data provided the values for the critical parameters: maximum attenuation of PAR by the weed, time when the weed overtops the peanut canopy, time when maximum attenuation is reached, and the distance of influence of the weed. Florida beggarweed over- topped the peanut canopy 52 DAP, and reduced PAR reach- ing the peanuts 45 % by 73 DAP. Sicklepod overtopped the peanut canopy 42 DAP and reached an attenuation of 41% 79 DAP. Wild poinsettia overtopped the peanut canopy 44 DAP, and had an attenuation value of 39% 85 DAP. The distances of influence were 162, 150, and 192 cm for Florida beggarweed, sicklepod, and wild poinsettia, respectively. Ob- served yield losses in the distance of influence were 26, 27, and 22%, respectively. The model predictions accounted for at least 90% of the yield losses observed in field studies. The model also proved capable of simulating competitive differ- ences between morphologicaily and phenologically different populations of Florida beggarweed. Simulation models will play an important role in reducing the expenditure of time and resources required to document yield losses due to weeds in peanuts. Nomenclature: Florida beggarweed, Desmodium tortuosum (Sw.) DC. #3 DEDTO; sicklepod, Cassia obtusifolia L. # CASOB (now-Senna obtusifolia); wild poinsettia, Euphorbia heterophylla L. # EPHHL; peanut, Arachis hy