Weed suppression and weed tolerance of wheat cultivars - relevant traits for Integrated Pest Management

An assortment of 10 winter wheat cultivars was tested for specific effects on weed suppression. Furthermore cultivar specific effects of weed infestation and weed control measures on the crop yield were investigated. Two trial series conducted from 2005 to 2010 demonstrated a wide cultivar specific range of shading capacity and weed suppression. Light penetration and the dry matter of the model weed Sinapis alba were highly correlated (r = 0.87) in trial series A (2005-2007). Consequently, the weed dry matter in the less competitive cultivar Dekan was 5 times higher compared to the weak competitor Cubus. Mechanical weed control by harrowing reduced ears density of all cultivars tested in trial series A. These reductions were significantly higher in the cultivars Bussard and Pegassos compared to the other cultivars. Since the weed infestation was low and negative crop effects by harrowing could be compensated by a higher number of kernels/ear, the yield effects were the same for all cultivars. Contrary to the hypothesis, a cultivar specific yield response by harrowing could not be assessed. Higher competition effects by sowing the model weed Sinapis alba could be realised in trial series B (2008-20120). Consequently, the control measures (a) harrowing (b) 50% herbicide (c) 100% herbicide resulted in significantly higher crop yields ranging from 1.23 t*ha-1 (harrowing) to 2.08 t*ha-1 (100% herbicide). The yield reduction caused by the model weed was not the same for all cultivars and was lower for the cultivars Cubus and Limes (6% and 7%) compared to Boomer (15%). Thus, weed tolerance could be identified as a cultivar specific trait. There were significant interactions between cultivar and weed control measures: The yield increase (relative to model weed) was 5% for Bussard, which was much lower compared to the treatment effects on the cultivar Impression (11%). The hypothesis that yield effects by mechanical and chemical weed control may be affected by the wheat cultivar, could be confirmed. These yield effects by trend increased while the competitiveness of the cultivar decreased.