A MODEL OF COMPETITION FOR LIGHT BETWEEN PEANUT (ARACHIS-HYPOGAEA) AND BROADLEAF WEEDS

A model of competition for light between peanut and three broadleaf we ed species has been developed to run with the PNUTGRO model. The model simulates shading of the peanut canopy by reducing the total daily PA R received by the peanuts in a manner that realistically represents ti ming and quantity of light capture by the weeds. Data were collected i n nursery plots of Florida beggarweed, sicklepod, and wild poinsettia in 1989, 1990, and 1991. These data provided the values for the critic al parameters: maximum attenuation of PAR by the weed, time when the w eed overtops the peanut canopy, time when maximum attenuation is reach ed, and the distance of influence of the weed. Florida beggarweed over topped the peanut canopy 52 DAP, and reduced PAR reaching the peanuts 45% by 73 DAP. Sicklepod overtopped the peanut canopy 42 DAP and reach ed an attenuation of 41% 79 DAP. Wild poinsettia overtopped the peanut canopy 44 DAP, and had an attenuation value of 39% 85 DAP. The distan ces of influence were 162, 150, and 192 cm for Florida beggarweed, sic klepod, and wild poinsettia, respectively. Observed yield losses in th e 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 competitiv e differences between morphologically and phenologically different pop ulations of Florida beggarweed. Simulation models will play an importa nt role in reducing the expenditure of time and resources required to document yield losses due to weeds in peanuts.