US trip gives insight into grape pest and diseases
Andrew Taylor, PhD candidate and Plant Pathologist
As part of my PhD studies on grape downy mildew I recently spent two months visiting grape growing regions in America. The aim of the trip was to pick up downy mildew DNA samples to be able to compare with those found in Australia and to see how the disease is managed in its natural environment.
Downy mildew, along with other significant grape pest and diseases in phylloxera, powdery mildew and black rot, originate from North America. The movement of grape material from America has meant that several of these pests and diseases are now found globally.
Despite being an unusually dry summer in north-eastern America, resulting in less than expected downy infections, the trip was an invaluable learning experience. The difference in management styles for America hybrid production versus those of a European origin was of particular interest.
The WA wine industry is based solely on Vitis vinifera production, vines that are highly susceptible to downy and powdery mildew infection. However, native American Vitis species, for example Vitis labrusca and Vitis aestivalis, are tolerant to powdery and downy mildew and therefore canopy management doesn’t need to be open as it is in WA. Imagine not having to worry about spraying for powdery mildew! Several of the universities in America are undertaking breeding and clonal trials to explore this resistance and the ability to produce quality wines from this material.
Some other destructive grape pests were also on show during my travels and highlighted the importance of our stringent quarantine regulations. Japanese beetle (Popollia japonica) was introduced into America and with the hot dry summer was particularly severe on the grapes during the season. These beetles reduce grape leaves to skeletons and are costly to control.
Phylloxera is an ever present threat to growers in north-eastern America and it was interesting to find that phylloxera leaf galls are rarely seen on Vitis vinifera vines but are quite common on the American vines. Given the presence of phylloxera, all European vines need to be on resistant rootstock.
Crown gall is rarely considered an issue in WA but due to the cold winters in America it is a significant issue for the industry there. If temperatures rapidly drop it is not uncommon to lose entire blocks of vines and those that do survive are susceptible to crown gall problems. At present there is no treatment for crown gall so if infection is too damaging then the vines also need to be replaced.
Results from the downy mildew work will be presented at a later date. The PhD is funded via an Australian Postgraduate Award with top up scholarship from Wines Australia.