Spotted knapweed (Centaurea biebersteinii) exists in dense patches despite the presence of biological control (biocontrol) agents that have been released and have spread into the area for potentially 35 years at the Lundbom Commonage grasslands near Merritt, B.C. Biocontrol agents will not eradicate the target invasive plant population but are intended to decrease the quantity to below a deleterious threshold. Spotted knapweed and its biocontrol agents were counted in 2015 and 2016 at three sites in the Lundbom grasslands to identify and quantify the biocontrol agent species present. The population of biocontrol agents should be reducing the spotted knapweed seed bank and thus reducing the plant numbers in the long term. The average number of rosettes and bolted plants over 2 years for two sites was 36/m2 and 25/m2, respectively. In 2016, the average number of seedlings for three sites was 359/m2 and seed heads was 413/m2. The average number of seeds per seed head was 2.8, and the average number of viable seeds produced per plant was 42.4. The soil seed bank held an average of 153 seeds/m2 to a 5 cm depth. Ninety-five percent of seed heads were occupied by biocontrol seed-feeding agents in 2016, with an average of 3.6 agents per seed head. Despite seed counts in seed heads and soil in the Lundbom grasslands being below counts of other studies, the spotted knapweed seed bank at our study sites has not yet reached a tipping point to cause a landscape decline in spotted knapweed.
Turner, Susan C., Bassett, Eleanor; and Cesselli, Sandy C.. 2023. Spotted Knapweed Biological Control in Lundbom Commonage, British Columbia. Ministry of Forests. Technical Report (FLNRORD). TR143
Topic: FLNRORD Research Program
Scientific Name: Centaurea biebersteinii
English Name: Spotted Knapweed
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