Effects of shading and soybean Glycine max (L.) interference on Solanum ptycanthum (Dun.) (eastern black nightshade) growth and development

Summary. Solanum ptycanthum (Dun.) vegetative and reproductive growth was evaluated under shade and in the field with soybean interference. In full sunlight without soybean interference, a S. ptycanthum plant produced 243 g shoots and 5957 berries in 20 weeks, but only 38 g and 576 berries in 11 weeks. Plants grown in 94% shade produced 3 g of shoots and 23 berries in 20 weeks, and 1 g and 1 berry in 11 weeks. S. ptycanthum plants that emerged with the soybeans and were positioned between 75‐cm rows produced 43 g shoots and 264 berries, whereas plants positioned in 75‐cm rows and emerging 6 weeks after the soybeans produced 1 g and 16 berries. When grown between 37·5‐cm rows for the same period of time this weed produced 12 g and 2 berries plant−1; plants positioned in 37·5‐cm rows produced shoots less than 1 g in weight and one berry plant−1. Shoot growth and berry production of S. ptycanthum increased from 80 to 200% in a 2‐week period between the initiation of soybean leaf abscission and maturity. In a season about 50 000 seeds weed−1 were produced in full sunlight; 20 000 or less were produced under soybean interference. When grown in irradiance levels from full sunlight to 94% shade, viable seeds were first detected 10 days after anthesis and essentially all seeds in the berry were viable 24 days after anthesis