What World-Leading Research from the 8th International Phylloxera Symposium can teach us about protecting South Australia’s Vineyards.
By Dr Samantha Scarratt, CEO, Vinehealth Australia
Phylloxera (Daktulosphaira vitifoliae) is one of the most destructive pests in viticulture. Feeding on grapevine roots and leaves, root-feeding phylloxera has a substantial impact on vine performance affecting yield and grape quality before killing vines within six years.
While most major winegrowing regions have been impacted by the pest, South Australia remains one of the few places in the world still free from phylloxera thanks to strict quarantine measures and farm-gate hygiene practices.
South Australia’s phylloxera-free status is a national treasure. With approximately 75% of vineyards planted on own roots, the state is home to some of the oldest producing vines in the world. But this legacy is vulnerable.
At the 8th International Phylloxera Symposium held in Geisenheim, Germany, leading scientists shared cutting-edge research and insights into phylloxera’s adaptability, climate-driven behaviour, and control strategies. All of which made it clear that prevention and preparedness is still our best defence in South Australia, reinforcing the need for:
- Strict quarantine and farm-gate hygiene practices to prevent phylloxera incursion.
- Preparedness through rootstock breeding suited to Australian conditions.
- Monitoring and early detection of leaf-feeding phylloxera strains.
- Collaboration with international researchers to stay ahead of emerging threats.
Global Lessons in Rootstock Resistance
One of the strongest themes from the symposium was the importance of plant breeding to mitigate the impacts of phylloxera and the need for researchers to consider the impact of climate change on the plant-insect interactions. Professor Astrid Forneck, a leading phylloxera researcher globally from BOKU University, Vienna, Austria, presented research showing that phylloxera rarely kills vines on its own. It is often the combination of environmental stressors, such as drought as well as phylloxera, that leads to vine decline. Her team is exploring how phylloxera may manipulate nutrient cycles to its advantage, potentially weakening the vine further.
“Phylloxera is a biotroph, it needs a living host to survive” Forneck explained. “Killing the vine is not in its interest, but under stress, the vine becomes more vulnerable.” Her team is also investigating microbiome interactions and how phylloxera may be influencing nutrient uptake to favour its own survival.
Historically, phylloxera was found only on vine roots, but Forneck noted that leaf-feeding strains are becoming more prevalent. “We are seeing phylloxera adapt,” she said. “This could be a response to changing environmental conditions, including climate change.”
This research reinforces the need for resilient rootstocks that can withstand multiple stressors. In South Australia, where the majority of grapevines are planted on own roots, this is a critical consideration for future replanting and vineyard renewal.
Biological Control
Dr Mathilde Ponchon, Geisenheim University, presented research on an entomopathogenic fungus which is naturally occurring in soils worldwide, including Australia. In controlled glasshouse trials, the fungus reduced phylloxera larvae survival, adult development, and root gall formation. “We saw a significant reduction in nodosities on treated vines,” Ponchon reported.
While further work is needed to assess field efficacy and cost implications in terms of application of the fungus, this biological control method could become a valuable tool in the toolkit. For South Australian growers, further research to understand whether the fungi could be used to reduce risk either in a preventative sense, or to help suppress phylloxera populations in existing outbreaks interstate would be valuable.
Rootstock Innovation: Global vs Local Needs
Dr Luis Diaz-Garcia from the University of California, Davis, emphasised the need for greater genetic diversity in rootstocks. With over 90% of vines globally grafted onto fewer than ten rootstocks, expanding the genetic base could improve traits that have become increasingly important including tolerance to salinity, pests, and viruses.
Two new rootstocks Libero and Vinto were registered in 2024 by Geisenheim University. Bred from Börner parentage, they offer strong phylloxera tolerance and adaptability to diverse soils. In Australia, Börner is popular because it is considered tolerant to some prevalent phylloxera strains (such as G38 and G19), and resistantto others (such as G1 and G4).
However, these new Libero and Vinto rootstocks were developed for European conditions, and their performance against Australian phylloxera strains remains uncertain. “Phylloxera strains differ genetically and behaviourally and demands for rootstocks in other countries can differ substantially from Europe in regard to soil types, irrigation requirements, and vineyard management systems” said Dr Kai Voss-Fels, head of the Plant Breeding Department at Geisenheim. This means that what works in Europe may not necessarily perform the same way under Australian conditions.
This highlights the importance of local breeding programs, such as the CSIRO program which led to the development of Merbein rootstocks, which are tailored to Australian soils and climate. Continued screening of genetic resources including Asian Vitis species will be essential to identify stable resistance traits.
Scion Resistance: A Future Possibility
Professor Oliver Trapp from Julius Kühn Institute in Germany posed a slightly controversial question: could we breed phylloxera-resistant scions?
“Scion breeding is faster than rootstock breeding,” Trapp noted. “If we can use genetic markers, we may be able to breed resistance using existing traditional cultivars crossed with a resistant breeding line.” This could be transformative for growers, offering a direct line of defence against phylloxera. However, this will take considerable time to research and develop.
He noted that rootstocks will still play a vital role in managing soil compatibility, nutrient uptake, vigour, and resistance to other pests and diseases. “We need both strategies,” Trapp said. “And we need to intensify research on phylloxera resistance and tolerance.”
With disease-resistant cultivars already in development for powdery and downy mildew, integrating phylloxera resistance could reduce reliance on grafting, lower labour costs, and offer new options for regions like South Australia.
Inside Geisenheim: A Model for Integrated Research
During Vinehealth’s visit to Geisenheim, Professor Kai Voss-Fels provided a tour of the Department of Plant Breeding. The first grapevine breeding activities started at the university in 1872 and one of the most popular examples was the grapevine crossing work in 1882 which later resulted in Müller-Thurgau. The department itself was founded in 1890 in response to Germany’s phylloxera crisis. “Phylloxera is the reason we are here,” he said. With the department being around for over 135 years, it is obvious at every turn, with buildings sustaining bombing in the first world war, to a more than century old underground cellar, it’s history is reminiscent of some of South Australia’s historic old vines.
The department’s approach is holistic, from plant breeding to vineyard to wine. With 11 hectares of research vineyard, where we observed leaf galling phylloxera on the leaves of rootstock , a winery producing up to 300–350 trial wines annually, and a cellar housing thousands of wine samples, the team studies new clones, rootstocks and their influence on wine quality.
“It’s a bit like a museum,” he said, referring to the cellar where wines from different clones, rootstocks, and vintages are stored for long-term study.
Students at the department participate in hands-on viticulture and winemaking projects, learning how clonal selection affects wine outcomes. “We teach from genetic discovery all the way to making wine,” Voss-Fels said.
Key insights from Geisenheim include:
- Over 68 registered Riesling clones bred at the department, with 1,200 more in trial.
- Rootstock breeding is focused on phylloxera resistance, drought tolerance, lime tolerance and moderate vigour.
- Using somatic embryogenesis to accelerate breeding and improve disease resistance.
- A planting of Vitis berlandieri with 4,000 plants grown from 90 mother vines over 20 years.
- A strong connection to Australia, with many researchers having completed PhDs or postdoctoral work in Adelaide.
Voss-Fels is also collaborating with CSIRO on a three-year Wine Australia co-funded ARC Training Centre project focused on Chardonnay clonal development, highlighting the value of international partnerships.
As Hans Schultz, current president of Geisenheim University, aptly stated at the symposium, “We need alliances with institutions, as no one will solve this phylloxera problem alone.”
Virus-Free Vines: A German Perspective
Whilst visiting Geisenheim, Vinehealth was fortunate to meet with Dr Elvira Bleser, who has led Geisenheim’s grapevine virus testing and tissue culture lab for 25 years, and is due to retire in the next year. She shared her work on somatic embryogenesis as a method for producing virus-free vines. Unlike Australia’s more widely used heat therapy approach, in this method immature anthers (developmental stage meiosis) are used to induce somatic embryos. After regeneration to plants under artificial light conditions and adaptation to ex vitro conditions in the glasshouse, the vines grow potted in the vineyard. After several years their virus-free status is checked. “We’ve had some vines growing for over 15 years in the vineyard to ensure they remain virus-free,” she said. This method offers high success rates, in many varieties trueness to type and is the preferred method in Geisenheim, preserving the genetics of old or valuable vines.
She also showed Vinehealth the illuminated tissue culture room where young vines grown from somatic embryos are nurtured under controlled conditions.
Germany’s strict government protocols require regular virus testing of propagation material on certain viral diseases such as Grapevine Leafroll virus 1 and 3, or Grapevine fanleaf virus, with results stored in a national database. “We can routinely test for 10 different viruses if needed,” Bleser explained. She shared with Vinehealth how the government sets the protocols for virus testing and how all results are shared with the government.
This level of rigour highlights the importance of clean planting material in maintaining vineyard health, especially in regions like South Australia, where virus-free vines are essential to preserving quality and yield.
Looking Ahead
A third round of phylloxera research is currently underway in Australia, and a new book on phylloxera, led by Dr Astrid Forneck and Kevin Powell, is planned for release after 2027. This will coincide with the 9th International Phylloxera Symposium, which Vinehealth Australia will assist in hosting in Australia in 2028.
This event will bring leading global phylloxera researchers together in Australia, offering a unique opportunity for knowledge exchange and industry engagement.
Vinehealth would like to thank the organisers of the 8th international phylloxera symposium, with a special thanks to Timo Strack and the International Organisation of Vine and Wine (OIV) for offering patronage to the event.