Evaluation of cropping systems for management of herbicide-resistant populations of blackgrass (Alopecurus myosuroides Huds.)

Simplification of cropping systems often leads to an increase in weed popul ations which require an intensive use of herbicides to maintain populations at an acceptable level. Due to a heavy reliance on herbicides and a lack o f cultural control measures, herbicide-resistant blackgrass (Alopecurus myo suroides Huds.) biotypes appeared recently in France. An experiment was con ducted to evaluate the effects of different cropping systems on a populatio n of herbicide-resistant blackgrass. Two crop rotations, one consisting exc lusively of winter crops and another including spring crops, were assessed over a three-year period. Crop rotation was combined with different cultura l practices (mouldboard plough, delayed sowing dates, reduced nitrogen fert iliser applications and effective herbicides on resistant blackgrass). Blac kgrass densities decreased in all the cropping systems, but blackgrass cont rol by herbicides was most effective when combined with non-chemical practi ces. The benefits of the different weed management systems are discussed in relation to their effect on blackgrass density and their cost to the farme r. In our conditions, the introduction of spring crops into the rotation ga ve the best results, both from an economical and weed management point of v iew. (C) 2001 Elsevier Science Ltd. All rights reserved.