Ambrosia artemisiifolia growth as affected by winter wheat and barley density and harvesting period

Common ragweed (Ambrosia artemisiifolia L.) is a plant native to America that has become a troublesome weed in European field crops such as maize, soybean, wheat. Field experiments were conducted from 2009 to 2011 in a field highly infested by A.artemisiifolia (more than 200 seedlings/m2 in 2009) to assess the effect on the weed of wheat (Triticum aestivum) and barley (Hordeum vulgare), seeded at a density of 280 or 230 kg ha-1 and 260 or 180 kg ha-1 respectively, and harvested at 35% and 14% grain moisture maturity (for silage forage or grain production, respectively). Crops were seeded in autumn on 2 x 25m plots, with 3 replicates. Treatments were maintained in the same plots over 3 growing seasons. Weed control was carried out in post-emergence against monocot species only. A. artemisiifolia emerged already during cultivation of the winter cereals, during the first decade of April in 2009 and 2010, and in the last decade of March in 2011. All combination of treatments (crop species, crop densities and harvesting period) demonstrated to reduce A. artemisiifolia biomass by up to 60% (wheat grown for silage forage) in comparison with the untreated (no crop presence). Harvesting period resulted in the highest effect on the weed growth over the 3 growing seasons. In the last year A. artemisiifolia density and soil coverage recorded in winter wheat were 30% higher than in barley, with differences between crop densities lower than 5% in both crops. In all considered years, higher A. artemisiifolia biomass (30% and 50% for wheat and barley, respectively) was recorded at the end of the season (September) in the plots where crops were harvested earlier.