Efficacy of dormant season herbicide application on control of Japanese honeysuckle (Lonicera japonica) in Kentucky.
North America's remaining natural grassland communities provide habitat for native flora and fauna. We conducted a study to compare the efficacy of herbicides in control of the invasive Japanese honeysuckle (Lonicera japonica Thunb.) applied at times when most native plant species are dormant. Six herbicide mixtures (glyphosate, glyphosate+imazapyr, glyphosate+imazapic, imazapyr, triclopyr+diflufenzopyr, and metsulfuron methyl+diflufenzopyr) were applied once each in three seasons to assess the effect of application timing of each mixture on honeysuckle control. Herbicides were applied with a CO2 pressurized sprayer at three sites in a randomized complete block design. Pretreatment sampling indicated that Japanese honeysuckle constituted over 70% of plant cover at the study sites. Post-treatment sampling was conducted 60 days, 180 days, 420 days, and 540 days after the final application. All mixtures in all application seasons decreased percent cover of honeysuckle with varying effectiveness. Results indicate that the glyphosate, imazapyr, and metsulfuron methyl+diflufenzopyr mixtures are particularly effective at controlling Japanese honeysuckle when applied at any time between October and April with suitable temperatures. Many native grasses and broadleaf forbs not found during pretreatment sampling also emerged post-treatment, benefiting from either application timing or indicating herbicide tolerance.