Control of Hymenoscyphus fraxineus, the causal agent of ash dieback, using composting

Abstract

Viability of Hymenoscyphus fraxineus inocula following temperature treatments for different exposure times was examined in vitro and in aerated flask‐ and large‐scale composting tests using green waste. After an exposure for up to 10 days at 20°C, 97.3% of H. fraxineus mycelium and pseudosclerotia plate cultures remained viable. No viability was detected following a 3‐day exposure to 40°C or a 1‐day exposure to 45°C although pseudosclerotia were more tolerant than mycelium to an exposure to 35°C. Primordial apothecia of H. fraxineus emerged from 62%–100% of infected ash rachises collected from two infected sites and stored at 4°C for 0–5 months; exposure to compost for up to 10 days at 20°C did not affect this emergence. No emergence of H. fraxineus apothecia was observed from ash rachises that were exposed to compost at 45°C for 1 day or at 35°C or 40°C for 3 days in flasks or at 40°C for 1 day or at 30°C for 5 days in a large‐scale composting system. Based on a fitted model, estimates of the survival of H. fraxineus inoculum in infected ash rachises exposed to compost at 50°C for 1 day were 0.081% of that in the untreated H. fraxineus ash rachis inoculum. Increasing loss in viability of H. fraxineus inoculum in infected ash rachises during longer and warmer exposures to compost at 35°C–45°C corresponded with a reduced concentration of pathogen DNA detected in the rachises using real‐time PCR. However, exposure of rachises to compost at >53°C resulted in a smaller reduction in pathogen DNA detected than exposure to compost at lower temperatures, possibly due to the inhibition of enzymatic degradation of DNA at elevated temperatures.

Fungi Detected in the Previous Year’s Leaf Petioles of Fraxinus excelsior and Their Antagonistic Potential against Hymenoscyphus fraxineus

“…Considering the significance of petioles as a necessary substrate for the formation of apothecia and production of H. fraxineus inoculum, there is the possibility of removing (burning or composting) fallen leaves. Such methods may be possible in tree nurseries or town greenery but not, however, in forest stands [22]. In the latter, creating an environment suitable for faster decomposition of ash leaves and debris may be considered [19,20].…”

Fungicolous Fungi on Pseudosclerotial Plates and Apothecia of Hymenoscyphus fraxineus and Their Biocontrol Potential

“…It can be assumed that there would be different applicability of the identified biocontrol fungi against H. fraxineus. In numerous places in forests and in larger ash groups in urban green areas, where leaf removal proposed by Noble et al [13] is impossible, biocontrol fungi could be used to reduce the inoculum reservoir of H. fraxineus in the litter. Basidiomycetous species appear to be particularly promising for this purpose [94][95][96][97].…”

“…Various silvicultural methods are used to reduce the losses caused by the disease, depending on the severity of damage, local climate, age, and stand type [2,6,11]. The possibilities of reduction in the amount of infectious material [12,13] and methods of eliminating the pathogen from seeds and seedlings were indicated [14]. Some fungicides proved to be effective against H. fraxineus.…”

Potential alternative tree species to Fraxinus excelsior in European forests

“…European silvicultural programs are attempting to implement the most current knowledge in their strategies to minimize the impacts of ash dieback. Silvicultural strategies include (1) monitoring, safe elimination of infested plant materials, and alternating fungicides in nurseries (Hrabětová et al, 2017;Noble et al, 2019); (2) identifying and breeding ash dieback-resistant genotypes to H. fraxineus to build immunity in native populations (Plumb et al, 2020); (3) monitoring the health status of ash stands (Chandelier et al, 2011); (4) creating and maintaining mixed stands with vigorous ash individuals (Rosenvald et al, 2015;Short and Hawe, 2019); (5) adapting silvicultural regimes to minimize the impact of ash dieback by adjusting the intensity of thinnings based on dieback level and site conditions (Short and Hawe, 2019); and (6) focusing conservation effort on sites with low infection rates such as dry and warm sites and sites with low ash density (Grosdidier et al, 2020;Klesse et al, 2021). Along with these silvicultural strategies, efforts have been made to identify species that can potentially replace European ash (Broome et al, 2019).…”