The Contribution of Biological Control to the Integrated Weed Management of the Invasive Alien Common Ragweed (Ambrosia artemisiifolia L.)

Ambrosia artemisiifolia L. (common ragweed, Asteraceae), native to North America, is a highly invasive weed causing substantial agricultural losses and serious human health problems due to its allergenic pollen. In several countries, legal regulations require its active management. The North American leaf beetle Ophraella communa (Coleoptera: Chrysomelidae) is a biological control agent that can suppress ragweed growth and pollen production. This study evaluated the effectiveness of a synthetic herbicide, a bioherbicide, mowing, and O. communa releases at different densities and timings, applied alone or in combination under field conditions. Three field experiments were conducted in a major European hotspot of A. artemisiifolia in the Pannonian region of Hungary during the 2024 and 2025 growing seasons. Both herbicides, as well as mowing, reduced A. artemisiifolia growth and, to some extent, flower head formation, but not flowering intensity. Ophraella communa established at low densities regardless of the number and timing of released beetles, and despite the hot and dry summer climate of the region. The highest abundance and most damage were observed following medium-density early-season releases (4 beetles per m2) and high-density mid-season releases (32 beetles per m2). The results suggest that repeated or more intensive management may be required for an effective season-long suppression of A. artemisiifolia, and that early, higher-density O. communa releases under different local climates may warrant further investigation.