Effect of clipping and honeysuckle leaf blight (Insolibasidium deformans, Platygloeaceae) on resprouting of Amur honeysuckle (Lonicera maackii, Caprifoliaceae) shrubs1

Amur honeysuckle (Lonicera maackii) is a highly invasive shrub that spreads rapidly, has many detrimental effects on native species and ecosystems, and is difficult to control. Clipping by itself is usually ineffective unless it is repeated over several years, so herbicides are commonly used, either alone or combined with clipping. Over the past decade, outbreaks of honeysuckle leaf blight have appeared. Previous work shows that long shoots are more susceptible to blight than reproductive short shoots. Clipping induces many long shoot resprouts that are expected to be infected by blight. In this study, I clipped honeysuckle shrubs in forest understory (forested) and open sites in northern and central Kentucky and followed their response through the growing season. Northern Kentucky sites were studied in 2022 and 2023; central Kentucky sites were studied in 2022 only. The total number of shoots, total shoot length, and number of leaves were higher at open sites and declined across the growing season. The fraction of blighted leaves reached maximum levels of 10–30%, higher than levels seen on shoots from intact shrubs. After 1 yr, 62% of all forested shrubs survived clipping, whereas 75% of all open shrubs survived. Survival rates for clipped forested stands were similar to those seen before blight outbreaks occurred, but they declined from the preblight 90% level seen in open stands, so leaf blight mortality effects appear to be largest in open stands. Although this study was not designed to quantify the effect of deer browsing on resprouting shrub mortality, browsing was extensive, with a maximum of 60–80% of all shoots browsed. The current effects of blight combined with a single clipping do not appear to be sufficient to manage honeysuckle; clipping repeated over several years and combined with blight needs to be investigated.