Managing grapevine trunk diseases

Abstract

Grapevine trunk diseases cause decline and death of vines, thus severely limiting the sustainability of Australian vineyards. Little was known about the contributory factors of these diseases, how to prevent them, or how to minimise their economic impact when this project began. Petri disease, which causes significant losses during the vineyard establishment phase, was shown to be widespread, whereas esca, currently the most serious grapevine disease in Europe, was shown to be rare in Australia. The causal organism, Phaeomoniella chlamydospora, is spread from infected mother vines into cuttings, and into newly planted vineyards via infected planting material. Long duration (30 minutes) hot water treatment of dormant cuttings was demonstrated to be an effective method of reducing the risk of producing infected planting material. Best practice protocols for the nursery industry were developed and promoted to encourage production of P. chlamydospora-free planting material. Glasshouse studies demonstrated that infected grapevines are more susceptible to water stress. Field trials showed that management practices that reduced stress, such as the use of mulch, reversed the symptoms of decline in infected grapevines. Recently, the number of reports of Petri disease has dropped considerably, suggesting that industry now has the tools both to prevent the spread and to minimise losses attributable to these diseases as a result of this research.

Summary

Grapevine trunk diseases are caused by xylem-inhabiting fungi that cause the slow decline and loss of productivity in vines at all stages of growth. They either infect propagating material and limit the growth of newly planted vines, or they infect established vines through pruning wounds and cause loss of productivity, just as vines are reaching an elite stage of maturity.

Petri disease, formerly known as black goo, is an emerging problem in international grapevine culture. The description of several possible causal organisms, including Phaeomoniella chlamydospora, in 1996 led to the realisation that both the pathogens and the disease are widespread and important. However, there is as yet little understanding of the disease or of its economic effects. The same pathogens are involved in esca, currently the most destructive disease of grapevines in Europe. This project set about to determine which pathogens are the most important, how infection occurs, how it is spread, whether it can be prevented and effective methods of managing infected vineyards.

As a result of this project, it is now known that:

• esca is rare in Australia, whereas Petri disease is widespread.
• the causal pathogen of both diseases is Phaeomoniella chlamydospora.
• Pa. chlamydospora sporulates in cracks on the grapevine trunks associated with machinery damage
• infection is passed from mother vines into cuttings, resulting in symptomless infected planting material
• Pa. chlamydospora spores can be detected in water used during nursery propagation, indicating there is the potential for further infection
• Hot water treatment of dormant cuttings is the most effective method of reducing the incidence of infected planting material
• Best practice nursery protocols were developed and disseminated through Workshops and articles
• Pa. chlamydospora infection in grapevines increases stomatal conductance and reduces xylem function, resulting in reduced capacity to respond to water stress
• Vineyards can recover from Petri disease over time with management practices that reduce stress eg mulch, bunch-thinning.