Japanese honeysuckle (Lonicera japonica) is a non-native, invasive perennial vine that colonizes disturbed sites throughout the eastern and southern United States. Surveys for endemic pathogens of honeysuckle exhibiting weed biological control activity were conducted in Maryland in 2021, and an unknown fungal species was recovered from necrotic leaf spots. Based on morphological and DNA sequence evidence, the fungus was identified as Corynespora cassiicola, causal agent of target spot on diverse plant species. Phylogenetic analysis placed three new isolates into two previously described lineages, one containing populations from diverse hosts, including cotton in the southeastern United States, and the other containing isolates collected from hydrangea in Georgia. Isolate pathogenicity was confirmed on honeysuckle and further evaluated on known crop hosts. Tomato, cotton, soybean, and cucumber were inoculated with colonized agar blocks and conidial suspensions. Tomato and cotton developed disease symptoms, while soybean and cucumber were not susceptible to the pathogen. Other weedy hosts of C. cassiicola have been documented, but no isolates collected from honeysuckle in the United States have been assessed previously for crop pathogenicity. Invasive honeysuckle is common in the southeastern United States, and a map-based analysis of cotton and honeysuckle co-occurrence suggested hypothetical opportunities for the movement or persistence of C. cassiicola populations on honeysuckle. Widespread, unmanaged invasive weeds may increase the risk of crop disease epidemics caused by multi-host pathogens or serve as reservoirs for pathogen genetic diversity.
Fulcher et al. (2026) studied this question.