The efficacy of controlling <i>Lonicera maackii </i>(Amur honeysuckle) with basal bark herbicide application

Background/Question/Methods Amur honeysuckle ( Lonicera maackii ) is a perennial shrub native to temperate Asia and is invasive in the Midwestern United States. It now infests many savannas and woodlands and is difficult to eradicate. This study looks at the efficacy of basal bark application, where a mineral oil solution of herbicide is sprayed on the bark without cutting the plant.  The three treatment plots (each 30.5 m /15.2 m) were randomly chosen from an oak-hickory woodland on The Nature Conservancy’s Nachusa Grasslands preserve in 2014. The study tract had an understory of Amur honeysuckle shrubs. The treatments were conducted on May 22-25, 2014, as follows:  Live shrubs were chosen and marked with a stripe of tree-marking paint (3 separate colors). For treatment 1 basal bark herbicide with mineral oil as carrier was applied to the stems with a Birchmeier Flox backpack sprayer. To test if it had any effect on mortality, mineral oil alone was applied to the stems of another set of shrubs. On September 13-14, 2014 the results were gathered. Mortality was confirmed by observation of complete loss of leaves. Data was collected using tallies on graphing paper. Each plant was then flagged with tape so as not to repeat data. Results/Conclusion The literature is sparse on the efficacy of basal bark application on Amur honeysuckle. We found only two relevant papers. One study notes inconsistent results of basal bark application and the other study notes 95% control. Our basal bark application yielded 97% mortality. Applying only mineral oil yielded 11.7% mortality, essentially little or no effect on honeysuckle. This highlights that the herbicide triclopyr was the main cause of shrub mortality. Nearly all the control survived. The herbicide was effective on all diameters of honeysuckle encountered, from 0.25 cm to 15 cm. Basal bark application is efficacious in that the mortality is very high, the work is physically easier than cutting the shrubs, and the damage to nearby desirable plants is limited to several inches surrounding the shrub. The herbicide mix is expensive, but time and safety gains make the treatment cost competitive. For areas that have had Amur honeysuckle invasion for years where the native understory has been destroyed it will take more than one year of treatment.