The effect of a novel herbicide adjuvant in treating Amur honeysuckle (Lonicera maackii)

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Ben J. Rivera, Michael A. Jenkins and Richard Meilan, Forestry and Natural Resources, Purdue University, West Lafayette, IN

Background/Question/Methods
Invasive woody perennials pose a serious threat to the diversity and function of forests in the eastern United States. While herbicide treatments have proven effective in controlling invasions, there is concern about non-target environmental effects and potential health risks associate with widespread herbicide use. We used ‘2XL’ – a cellulase enzyme derived from termites – as a potential herbicide adjuvant in order to increase the efficacy of glyphosate, allowing the use of lower concentrations of herbicides in treatment efforts. To test whether the addition of 2XL on a treated woody stump would increase the efficacy of glyphosate treatment, we conducted a controlled field-based experiment using the ‘cut-stump’ method of treatment on a particularly problematic invasive shrub, Amur honeysuckle (Lonicera maackii [Rupr.] Herder). Given its ability to degrade a critical cell-wall component, it was thought that 2XL would affect glyphosate uptake by vascular tissue(s). In our experiment, we tested combinations of three concentrations of 2XL with five concentrations of glyphosate and predicted that low concentrations of glyphosate combined with 2XL would be as effective in limiting the sprouting of Amur honeysuckle as higher concentrations of glyphosate without the enzyme.
Results/Conclusions
A negative binomial mixed-effects model on the number of sprouting stems revealed that 2XL actually decreased the effectiveness of glyphosate. The number of sprouting stems predicted by this model showed a consistent pattern of 2XL addition leading to one to five more sprouting stems in all concentrations of glyphosate treatment. Additionally, in a type III ANOVA, neither the interaction between 2XL and glyphosate nor 2XL alone had a significant effect on the height of the tallest sprouting stem after treatment. All of these patterns were consistent within in the same year as application of the treatment, as well as in the following year. These results suggest that the walls of the cells responsible for distributing glyphosate may have been compromised in some way, leading to less herbicide being absorbed. While 2XL may not be effective in this context, our study shows that the preservation of cell walls may be important for finding a better herbicide adjuvant to help control invasive shrubs.