IWMS in maize weed control - the role of crop rotation and herbicides

The Integrated Weed Management System has been applied with variable success in many crops since its establishment in 1991. Environmental awareness, growing problems with herbicide resistance and a lack of new active ingredients, resulted in weed control not only with chemicals but also other measures. The aim of the study was to examine long-term IWM measures - combined application of crop rotation and herbicides on weed biomass and maize yield. The trial has been conducted since 2009, encompassing maize continuous cropping (MC), maize-winter wheat (MW), maize-soybean-winter wheat (MSW) and maize-winter wheat-soybean (MWS) rotations. The isoxaflutole + acetochlor mixture at recommended (RR), half of the recommended rate (0.5RR) and no-herbicides (C) were preemergence treatments applied in maize. Weed biomass was recorded from two randomly selected sites in the middle of each plot by square meter method, 6-7 weeks after the application of herbicides. Maize grain yield was calculated at 14% moisture at the end of the growing season. The data were processed by ANOVA and LSD-test (α = 0.05). According to the 10-year average, weed biomass had decreased with the application of herbicide 0.5RR by 69.2%, 90.0%, 83.2% and 70.9% and of RR by 79.2%, 94.2%, 93.9% and 81.3% in MC, MW, MSW and MWS rotation, respectively. Herbicide RR was in average more effective than 0.5RR by 8.8% while the most effective in weed biomass reduction in average for both herbicide rates were MW and MSW rotations - 94.2% and 93.9%, respectively. Herbicide weed control contributed to the grain yield increase even in MC by 31.0% and 43.1% with 0.5RR and RR, respectively, while MSW was the most effective rotation and increased yield by 36.1% and 30.5% with 05.RR and RR, respectively. This indicates a significant correlation between the weed biomass decrease and the maize yield increase, as well as the importance of a preceding crop for maize productivity in integrated crop production systems with reduced herbicide use