Impact of a native hemiparasite and mowing on performance of a major invasive weed, European blackberry

O_LIPlant invasions are a major global threat to biodiversity. Traditional methods of weed control are falling short, and novel and environmentally friendly control tools are needed. Native parasitic plants are showing promise as effective biocontrols for some of the worst weeds, however, their application is in its infancy. C_LIO_LIFirst, we established the native parasitic plant, Cassytha pubescens on unmown invasive European blackberry (Rubus anglocandicans), at three field sites (Belair, Horsnell and Blackwood) in South Australia to measure the impact of infection host performance. Concurrently, we established the parasite on hosts that were mown at two of these sites (Horsnell and Blackwood), to determine the impact of mowing, a commonly used control method, in conjunction with infection by C. pubescens. C_LIO_LIFruit production, midday quantum yield and electron transport rates of infected R. anglocandidans were significantly lower than uninfected plants at only one site, Blackwood. Predawn quantum yield, and foliar nitrogen and phosphorus concentrations of infected plants were significantly lower than uninfected ones across all three sites. Stomatal conductance was negatively affected by infection at one site (Belair). Mowing enhanced parasite impact on host nitrogen concentration at one site (Horsnell), and infection negatively affected host stomatal conductance at the same site, irrespective of whether plants were mown or not. C_LIO_LIWe have demonstrated that this native biocontrol can be artificially established on invasive European blackberry in the field, with negative consequences for its performance. Our results demonstrate the feasibility of implementing native parasitic plants as weed biocontrols to protect biodiversity, and are aligned with the Biotic Resistance hypothesis that invasive species are susceptible and sensitive to enemies native to their newly invaded habitat. C_LI