Researchers: Only a Combination of Methods Gives Lasting Results Against Invasive Species
Experts in the “Invago” project of Zemgale and Lithuanian municipalities conclude that no single universal solution exists for controlling invasive species. Lasting results come only from combining methods adapted to each site.
A cooperation project of Latvian and Lithuanian municipalities, “Invago”, led by the Zemgale Planning Region (ZPR), has concluded that lasting control of invasive species is achieved only by combining different methods. The information comes from ZPR public relations specialist Agnese Launerte. In late September, the project's cycle of demonstrations ended in six municipalities in Latvia and Lithuania, where methods against giant hogweed, Canadian goldenrod, Himalayan balsam and the Spanish slug were tested in practice.
Drones help but cannot replace specialists
Drones helped determine the spread and density of species, allowing large areas to be mapped quickly before and after work. However, plants hidden under tree and shrub canopy cannot be seen from the air. At the Līrumi quarry in Bauska municipality, a drone initially recorded only 0.1 hectare of Canadian goldenrod, but an on-site inspection showed it covered 1.45 hectares of scrubland.
Methods in different places
In Bauska and Šiauliai, massive stands were tackled with deep soil milling, followed immediately by sowing clover or a grass mixture that grows over quickly and suppresses invasive plants. In Dobele municipality, herbicides were sprayed against giant hogweed in open areas, while near water bodies, where chemicals are prohibited, the plants were cut with brush cutters before flowering.
In Jelgava municipality, at the Bērvircava pilot site, the Spanish slug was controlled by mowing the lawn every two weeks, hand-collecting pests and working in professional granules. Counts showed slug numbers falling in the tended zone, but the risk remains in riverside scrub, which serves as shelter and a breeding place. Experts stress clearing undergrowth, not dumping garden waste on the riverbank, and cleaning equipment and footwear after work to avoid spreading eggs.
Public involvement and equipment
ZPR notes that municipal work yields results only if neighbouring private land is also managed, so informing and involving residents is important. The Pakruojis district municipality in Lithuania asked people on social media to report slugs they spotted, which helped find new sites and move the demonstration to a more relevant area.
Because control takes several years and seeds in the soil stay viable for years, the municipalities bought ride-on mowers, brush cutters and soil-processing equipment with project support. The equipment stays with the municipalities so the work can continue after the project ends.
