Changes in weed community composition in a long-term trial with different crop rotations and herbicide treatments
The impact of herbicide application on weed community changes was studied in a long-term field experiment conducted since 1972 at two sites in the Czech Republic; Pernolec and Hněvčeves. The ongoing trial comprises multi-crop and simple crop rotations with 50 and 75% cereals, respectively. Three herbicide treatments were used: (1) untreated; (2) synthetic auxins (MCPA; 2,4-D; only in simple crop rotation) and (3) targeted herbicide combinations, including especially sulfonylureas, triazines, ureas and synthetic auxins. Weed species composition and weed density were assessed at the trial beginning, during the trial and in the present (2013- 2016). Changes in weed flora composition were found out. In Hněvčeves, abundance of some species such as Galium aparine, Stellaria media, and Vicia spp. increased on untreated plots; the abundance of Apera spica-venti, Fumaria officinalis, and Tripleurospermum inodorum increased on treated plots. In Pernolec, some species receded in all variants, e.g. Myosotis arvensis, Raphanus raphanistrum, and Scleranthus annuus; the abundance of Centaurea cyanus, Tripleurospermum inodorum, Veronica spp., and Spergula arvensis increased in untreated plots. No significant differences affected by time and treatment were detected in population densities of Apera spica-venti, Arabidopsis thaliana, and Stellaria media. The species composition of the weed community was affected by explanatory variables in the following order: treatment < time < type of cultivated crop. The longterm study confirmed weed population shifts over time were caused by interaction between the management factors and environmental conditions.