Effects of Intercropping on Growth and Reproductive Capacity of Late-emerging Senecio vulgaris L., with Special Reference to Competition for Light.

Due to increased emphasis on long-term management of weed populations in cropping systems with a reduced reliance on herbicides, the production of seeds by weeds that emerge after the critical period for weed control is increasingly important. It was hypothesized that increased soil cover and light interception by a crop canopy would shorten the critical period for weed control and reduce growth and fecundity of late-emerging weeds. This hypothesis was tested in a series of field and glasshouse experiments in which competition for light was manipulated. Senecio vulgaris , an important weed in vegetable production systems, was chosen as the target plant, and canopies of pure and mixed stands of leek and celery were used to provide shade. The time course of light interception differed among the crop canopies. Increasing competition for light caused morphological changes to S. vulgaris , including a vertical shift in leaf area distribution. Increased shading reduced biomass, capitula:shoot ratio and seed production of S. vulgaris . However, the viability of seeds produced by the shaded weed plants was not affected. Results indicate that intercropping can increase light interception in a weakly competitive crop such as leek and can contribute to weed suppression in a long-term strategy for weed management.