Effects of Aerial Glyphosate Applications for Controlling Lonicera maackii

Lonicera maackii (Amur honeysuckle) is a non-native species that has invaded forest stands throughout the eastern United States. This research examined using aerially applied glyphosate in autumn 2013 to control L. maackii in oak-hickory forest stands in Missouri, U.S.A. We targeted the spraying time period when L. maackii was still green and most native plants were dormant. Across treatment units, the mean difference in L. maackii stem density significantly declined (p = 0.004) by 5.4 stems per plot from spring 2013 to summer 2014 when compared to control units which increased by 1.8 stems per plot. Treated units with a high initial infestation level of L. maackii (>50% cover) had a significant (p = 0.004) decline in the mean difference in L. maackii cover of −50.0% per plot between spring 2013 and summer 2014 compared to an average increase of 9.2% in the controls. Similar results were found for treated units with a low initial infestation level of L. maackii (10–50% cover). Mortality of native overstory and understory trees post-treatment was negligible. In the ground layer of forest stands with a low initial L. maackii infestation level, native non-spray-sensitive forb cover per plot significantly increased (p = 0.023) relative to controls between summer 2013 and summer 2014 while native spray-sensitive species cover significantly decreased (p = 0.021) during the same period. These results suggest that an aerial application of glyphosate can provide an L. maackii control option, but with trade-offs in compositional shifts in the native ground-layer vegetation.