Black nightshade (Solanum nigrum L.) is a major problem in gardenpea cultivations contracted by Findus AB, a Swedish food processing company. The main problem is that the nightshade berries contain solanin and, thus, are not tolerated in the marketed product, which is fresh frozen peas. In addition, berries have the same size and color as the peas and cannot be separated at the factory. Black nightshades have the last ten years become a more common weed in field grown vegetables in the southern parts of Sweden. This MSc thesis presents an experiment conducted in 2005, aiming at developing a tool for predicting the need for control of black nightshade in peas.