Pattern of infection by honeysuckle leaf blight, a possible accumulating pathogen, on invasive Amur honeysuckle (Lonicera maackii) shrubs in understory and open habitats

Abstract

Amur honeysuckle (Lonicera maackii) is a widespread invasive species in North America with extensive effects on native ecosystems. Since 2012, there have been extensive outbreaks of the native leaf fungal pathogen, honeysuckle leaf blight (Insolibasidium deformans), on L. maackii. This pathogen infects leaves in the late spring/early summer and eventually kills the leaves. Our objective was to describe patterns of blight occurrence on L. maackii growing in both the forest understory and in the open in northern Kentucky, USA. Smaller shrubs had a larger fraction of blighted leaves, because they allocated more production to long shoots, which are more susceptible to leaf blight. Overall, blight occurrence was as high as 8% on the smallest shrubs, though it was an order of magnitude lower on the largest shrubs sampled. Leaf blight appears to be an emerging pathogen that fits the Pathogen Accumulation Hypothesis. We developed a growth model that suggested small (< 5 cm basal diameter) open shrubs would be most affected by blight. Thus, future work should focus on comparison of the survival and growth of small infected versus uninfected L. maackii plants, as they appear to be most affected by the leaf blight.