Dissemination and Vectors

Long range

The frequent number of records over the last decades appears to show the great ability of the pathogen to spread (EPPO 2023).  Its aerial spores (conidia) are able to be dispersed with wind over 300 km according to the aerobiological surveillance performed with active traps by Muller et al. (2023). The study of Muller et al. (2023) was the first to prove the efficiency of the conidia to be dispersed over long distances.

Short range

Despite the great mobility of this aerial pathogen, it appears to remain as an endophyte inside its host tree until occurring favorable conditions such as extreme heat and drought during summer. Local dispersion might be facilitated not only by the wind but also by animal vectors. Squirrels are known for their bark-stripping behaviour and by stripping the bark to expose stromata of symptomatic trees, they would carry the spores and transport them to other trees by creating entry wounds (Tanney et al., 2024). Thus, Tanney et al (2024) observed teeth marks in many stromata and strips of bark from symptomatic sycamore trees standing on the ground. Abbott et al., (1977) proved that the C. corticale conidia collected from buccal cavity, claws and hindgut was viable and able to germinate on malt extract agar. Dispersion by birds such as woodpeckers might also be a plausible mode (Kelnarová et al., 2017 Operational activities during the management of the affected trees are also contributing to the dispersion at a local range. Felling and pruning of the trees should be done in winter and early spring and at dump weather as the sporulation rate is the lowest (Bencheva, 2014; Burgdorf et al., 2022) and precipitation wash out the spores preventing the wind dispersion (Bork, 2018). The use of disposable clothing material for the operation prevents also the spread of the fungus.