Control of Centaurea stoebe using solarization in preparation for pollinator meadow creation

Abstract

This study follows the first year of the Wasa Slough Dike Pollinator Meadow project. The first year's focus was to evaluate the nature and abundance of native and invasive vegetation, reduce the cover of Spotted Knapweed and Alfalfa, and examine the status of the biocontrol agents previously released on site. Vegetative analysis showed that althought the banks of the dikes housed 22 native species, only 13 grew on the top of the dike. 83% of the top of the dike was covered either by bare ground or invasive species, perhaps even highter if invasive grasses were included. Solarization reduced the Spotted Knapweed and Alfalfa populations to 0% and 1% in solarized zones from 16% and 25% to 11.6% and 20% overall. Though the preliminary reduction in invasive species is hopeful, more information is needed about the effect of solarization on this seed bank to predict long term effects of the treatment. Evidence of root-boring biocontrol was found in 62.7% of Knapweed plants, and flower-eating evidence was found in 50-60% of Spotted knapweed.