Extended leaf phenology presents an opportunity for herbicidal control of invasive forest shrubs

Abstract

SummaryFor many of the shrub species invading temperate deciduous forests, extended leaf phenology contributes substantially to annual carbon gains, helping to make possible rapid growth and spread. We carried out a pair of proof‐of‐concept studies to evaluate the susceptibility of such shrubs to foliar herbicide treatment during the period of delayed senescence, i.e. well after it is typically attempted. We first evaluated leaf‐level physiology in four species that lose leaves late in autumn; photosynthetic rates were comparable (80–111%) to those reported for the same species in summer. While preliminary, this finding provides a strong indication that diverse shrub taxa remain susceptible to control into late autumn. In addition, we conducted a field trial involving one of these species (Lonicera maackii) to directly evaluate the effectiveness of foliar treatment in November; applications included glyphosate and two concentrations of aminocyclopyrachlor plus metsulfuron methyl. Treatments killed (72%) or severely injured (14%) target plants, inducing greater cambial damage in plants that retained greater fractions of their canopy or had smaller canopy widths; there were no statistically significant differences among application types. This study demonstrated that late autumn can be a viable period in which to treat weedy species that delay senescence strongly, such as the many invasive Lonicera species in North America. Given that climate change and urbanisation are further delaying senescence in invasive plant populations, our study serves as a call for further investigation into what promises to be an increasingly viable opportunity for weed control in deciduous forests.