Practical management of grapevine trunk diseases

Abstract

Practical strategies for management of the grapevine trunk diseases eutypa and botryosphaeria dieback have been enhanced by new knowledge gained in this project. DNA-based molecular tools were developed to detect inoculum from spore traps, and showed that spore dispersal patterns vary in regions with different climates, highlighting the role of rain and the presence of inoculum over the entire year. Pruning wounds were highly susceptible to infection for the first two weeks, regardless of the pruning time, with susceptibility decreasing thereafter, at various rates, depending on the pathogen. The application of the fungicides Cabrio, Emblem and Folicur to pruning wounds within six days of infection, controlled trunk disease pathogens for a total period of up to three weeks. In the short-term, remedial surgery was successful for control of botryosphaeria dieback on own-rooted vines, with further work required to improve regeneration of scion material on reworked grafted vines. Cultivar susceptibility to dieback varies, with potential for tolerance identified in some germplasm, and preliminary evidence of reduced susceptibility in some clones and rootstocks warrants further investigation. Increased water stress generally decreased the susceptibility of canes to colonisation by trunk disease pathogens, suggesting that drought and deficit irrigation practices are not likely to contribute to an increased prevalence of grapevine trunk disease in Australian vineyards. These outcomes provide new information that is leading to adoption of improved strategies for managing trunk diseases, which will increase vineyard longevity in diverse climates of Australia.

Summary

The grapevine trunk diseases eutypa dieback (ED) and botryosphaeria dieback (BD) contribute to grapevine decline worldwide, reducing vineyard productivity and longevity, threatening the sustainability of the wine industry which contributes $40 billion per annum to the Australian economy. The causal fungi infect vines through pruning wounds and colonise wood, causing dieback and, in the case of ED, stunting and yellowing of shoots and leaves, eventually killing the vine. Research led by the South Australian Research and Development Institute in collaboration with the National Wine and Grape Industry Centre, with funding from Wine Australia and industry, has focused on developing practical management strategies for grapevine trunk diseases.

Burkard spore traps were deployed in four Australian wine regions and protocols for rapid and highly sensitive DNA-based molecular tools were successfully developed and used to detect and quantify ED and BD pathogens on spore tapes. Spores were released at different times of the year, but the seasonal release and number of spores differed between pathogens and regions. ED spores were generally detected in greater numbers than BD spores, possibly due to the size and mode of discharge of these spores. Rainfall was confirmed as the primary factor that triggers the release of spores, which are disseminated throughout the entire year. Therefore, wounds created during sucker removal and shoot trimming may also be at risk of infection, which will require further research. The prevalence of rain varies seasonally between different climatic regions, and therefore influences the timing of spore release. As little as 0.2 mm of rain initiated spore release and, occasionally, spores were continuously trapped for up to two weeks if rain continued. However, not all rain events resulted in spore release and spores were sometimes detected more than a week after any rainfall event, suggesting that spore release may also be attributed to other environmental factors such as relative humidity, dew and wind speed, which requires further investigation. As more data are generated from this and subsequent projects, localised recommendations will be provided for each region to assist growers in making management decisions for grapevine trunk diseases.