Competition for Light Between Tomatoes and Nightshades (Solanum nigrum or S. ptycanthum)

The effect of black and eastern black nightshade on the amount of photosynthetically active radiation (PAR) intercepted by a processing tomato canopy was studied along with the correlation between PAR and tomato growth and yield. During 1989 and 1990, black and eastern black nightshade were established at densities of 0 to 4.8 m-2 within rows of transplanted, irrigated processing tomatoes. Increasing the density of either nightshade species decreased the number of tomato fruit; however, eastern black nightshade reduced tomato yield more than black nightshade. Eastern black nightshade was taller than the tomatoes, reducing PAR reaching the top of the tomato canopy. PAR reaching the top of the tomato canopy was positively correlated with yield and negatively correlated with eastern black nightshade density. Eastern black nightshade intraspecific competi- tion decreased both stem and berry weight. Black nightshade was never taller than tomatoes and did not affect PAR reaching the top of the crop canopy. Increasing the density of black nightshade decreased berry dry weight but increased the weight of stems and leaves. Nomenclature: Black nightshade, Solanum nigrum L. #3 SOLNI; eastern black nightshade, S. ptycanthum Dun. # SOLPT.; Tomato, Lycopersicon esculentum Mill. 'Heinz 6004'. Additional index words. Canopy structure, fruit set, specific leaf area, intraspecific and interspecific competition, SOLNI, SOLPT.