Invasive weeds in Hungarian agriculture.
Out of the invasive alien plants at present ca. 20 species have a great importance in the Hungarian agriculture. Some of them were intentionally introduced earlier, others randomly. Their presence and harmful effect have a great importance, especially in root crops. The gene centre most of them is North America. Majority of them belongs to summer annuals (T4 life form). Allogamy, considerable seed production, considerable generative and vegetative reproduction (in case of perennials), large persistent weed seed bank of the soils, strong dormancy, intensive early development, large biomass production, good competitve ability and allelopathy help their intensive spreading. Good drought tolerance and nutrient utilizing ability, broad ecological amplitude, morphological-genetic variability ensures a good adaptive ability and effective survival strategy even under stress conditions. Their natural monophagous enemies causing considerable biological decline arc missing. Some of them developed resistant biotypes to herbicides. In agrarecosystems their control can be classified according to the elements of the integrated weed management. Due to the spreading of uncultivated tillage the enhanced importance of perennials will be predicted in the future.