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

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 degrees C, 97.3% of H. fraxineus mycelium and pseudosclerotia plate cultures remained viable. No viability was detected following a 3-day exposure to 40 degrees C or a 1-day exposure to 45 degrees C although pseudosclerotia were more tolerant than mycelium to an exposure to 35 degrees C. Primordial apothecia of H. fraxineus emerged from 62%-100% of infected ash rachises collected from two infected sites and stored at 4 degrees C for 0-5 months; exposure to compost for up to 10 days at 20 degrees C did not affect this emergence. No emergence of H. fraxineus apothecia was observed from ash rachises that were exposed to compost at 45 degrees C for 1 day or at 35 degrees C or 40 degrees C for 3 days in flasks or at 40 degrees C for 1 day or at 30 degrees 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 degrees 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 degrees C-45 degrees 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 degrees 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.