Novel and conventional control of Linaria genistifolia ssp. Dalmatica in a semi-arid grassland of British Columbia's southern interior

Dalmatian toadflax (Linaria genistifolia ssp. Dalmatica) is a major concern in disturbed areas of British Columbia’s interior due to its pronounced ability to displace native vegetation. To investigate the most appropriate control method, including efficiency, a study was established in Kenna Cartwright Nature Park, Kamloops, BC in 2016. Manual removal and three herbicide treatments were compared by collecting live and dead stem count in 6m by 6m replicates (n=30) during baseline, post-treatment and end-of-growing season assessments. Tordon 22K was applied at 213 g a.e. ha-1 picloram mixed with Agral 90 surfactant (0.025% by volume) using broadcast spraying, spot spraying and hand wicking (August 23rd). Treatment had a significant effect; broadcast and spot spraying provided the highest overall success resulting in mean stem counts of 1.7 ± 1.07 and 6.33 ± 2.67 at the end of the growing season, respectively. Wicking offered the same overall success as spot spraying in reducing total live stems. However, wicking contained 61% of the live stems at the end of the growing season, relative to baseline, whereas spot spraying only contained 31%. Broadcast spraying offered the greatest success in which survivorship was 13%. Only broadcast and spot spraying provide statistically significant reduction in vegetative stems from baseline to end-of-season; broadcast spraying contained zero stems in this life stage. Despite eliminating all stems at time of treatment, manual removal experienced high regrowth which resulted in statistical similarity to the control and appeared to encourage vegetative regrowth. Nearly all of the regrowth experienced in the control, manual removal, spot spraying and wicking at the end of the growing season were rosettes. Seedlings did not greatly contribute to reproduction in any treatments and were absent from broadcast spraying. For high density sites (>31 stems/m2), broadcast spraying offers the greatest chance of success based on both success and efficiency. Low to medium density sites can be controlled by spot spraying, however the lower residual soil activity must be considered. Ultimately, the effect on the native plant community must be evaluated when selecting one of the recommended treatment methods and future research should focus on tracking the communities through time.