Authors
Maureen Moroney1,2, Catherine W. Clarke3, Aude A. Watrelot1, Mark L. Gleason2
1 Department of Food Science and Human Nutrition, Iowa State University, USA
2 Department of Plant Pathology and Microbiology, Iowa State University, USA
3 Agriculture Victoria Research, Australia
The Case
You have purchased land in the Yarra Valley in Victoria, Australia, to plant a new vineyard.
You have dreamed of owning your own vineyard and making your own wines for as long as you can remember. After completing your schooling in your homeland of Australia, you spent several years “harvest-hopping" between the world's wine regions, working on seasonal vineyard and winery crews. Now you're ready to settle down with your own vineyard site in the Yarra Valley in Victoria, Australia, and you've taken out a large bank loan in order to do so. However, you have come to learn that your dream of establishing a vineyard is a long-term, high-risk investment. The startup cost of planting and maintaining a vineyard in Australia is about US$18,000 to US$22,000 per hectare (US$7,200 to US$8,800 per acre). Harvestable fruit won't develop for the first couple of years, and it may take close to ten years to see any return on your investment. However, the vines can continue to be productive for decades. In fact, many of the world's most highly desired wines come from vines that are 50 to 100 years old. A successful vineyard can be highly profitable in the long term.
Figure 1. Phylloxera management zones (Vine Health Australia)
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You are aware of the massive devastation of Australian vineyards caused by phylloxera, an aphid-like insect that is the number one pest threat to grapevines. In fact, the topic has come up over and over again in your experience listening to stories from others in the industry in your travels to wine regions across the world. Your available options for grapevine material include phylloxera-resistant hybrid grape varieties, as well as resistant rootstocks for grafting better-known wine grape varieties of
Vitis vinifera. You're aware that choosing between cultivars can mean tradeoffs for vineyard survival, cost and labor inputs, fruit quality, and wine marketability. Even grafting presents its own complications when it comes to the possibilities of graft failure, graft site infection, extra costs, changes to vine growth and grape and wine flavor characteristics, or non-durable resistance against phylloxera. You're worried not only about phylloxera risk, but also about the business of successfully selling your wine, and a failure on either side of that equation would mean losing everything.
Australia has multiple wine-producing regions. Since its introduction to the continent in 1877, phylloxera has spread to some of these regions but not others. To prevent spread from one region to another, Australia uses Area-Wide Pest Management, in which growers in a region coordinate their management actions to restrict the pest's movement from one location to another. Australian vineyards are divided into phylloxera management zones (Figure 1) known as Phylloxera Exclusion Zones (PEZs), Phylloxera Infested Zones (PIZs), and Phylloxera Risk Zones (PRZs):
- PEZs are free from phylloxera.
- PIZs have known phylloxera infestations.
- PRZs have unknown phylloxera status. They have not been fully surveyed and declared phylloxera-free, and they could be at risk from neighboring areas.
Figure 2: Image from Vine Health Australia's awareness campaign warning tourists to avoid letting phylloxera “hitchhike" on them from one vineyard to another.
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Phylloxera is a top biosecurity pest in Australia, and the risk of losing an entire vineyard to phylloxera is real. Vine Health Australia is a national authority dedicated to protecting vineyards from phylloxera. Awareness campaigns designed to discourage human spread of phylloxera (“hitchhiking") are a major part of the prevention efforts (Figure 2). In Victoria where phylloxera has been present for more than 100 years, movement of phylloxera host material or vineyard equipment is regulated by the Plant Biosecurity Act 2010 (the Act) and the Plant Biosecurity Regulations 2012. Conditions for movement require growers to comply and take relevant actions. The Act restricts movement of phylloxera host material and equipment within and out of the state unless certain conditions are met. A 5-kilometer (3.1-mile)-wide buffer is enforced around each phylloxera management zone. Monitoring options include aerial and ground surveys, insect trapping, and identification using DNA-based techniques. You know you'll need to be on the lookout for galls on leaves or roots of the vine, early yellowing, root necrosis, weed undergrowth, and stunted growth. If you suspect a phylloxera infestation, you'll need to report it to the respective state agriculture agencies using the Exotic Plant Pest Hotline so that the pest can be identified, and quarantine zones can be applied if necessary.
 
Figure 3 (Left): Map of Australia (World Atlas).
Figure 4 (Right): Map of Victoria wine regions showing Yarra Valley (wine-pages.com).
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Unlike European wine regions, Australia is considered a “New World" wine region. It has fewer restrictions on which grape varieties can be planted, and phylloxera-resistant hybrid grapevines are allowed. You plan to use innovative winemaking technologies to achieve your own distinctive style rather than trying to mimic more tradition-focused regions such as France, Italy, Germany, and Spain. On the other hand, you know that North American hybrid varieties – which are resistant to phylloxera – may carry some stigma with certain wine consumers, which might make those varieties less profitable.
The possibility of having your entire vineyard wiped out by phylloxera is alarming, and you've been around the industry long enough to hear about management strategies that failed and the massive losses that resulted. Your planned vineyard site is in Victoria, an area that includes management zones belonging to all three phylloxera status zones (infested zone, exclusion zone, and risk zone). The site is located in a “yellow" zone (PRZ), near Monbulk in the Yarra Valley region (Figures 3 and 4). The Yarra Valley has had its management zone boundaries redrawn several times between 2017 and 2020 due to continued phylloxera spread, and the cost of replanting the entire region is estimated at US$750 million. You know that as a grower, you need to balance the risk of phylloxera – along with other pests and diseases – against the need for good-quality grapes, the need to produce a large enough yield to be profitable, and the labor, cost, and down-time involved in having to replant.
You could make a great deal of money if your vineyard and winemaking are successful. However, you could also lose everything you invest in your dream.
It's decision time! You need to decide whether to:
- Graft
V. vinifera varieties (susceptible to phylloxera) onto resistant rootstocks
- Plant non-vinifera varieties that show good phylloxera resistance without grafting
Suggested discussion questions
A few questions can be chosen by the instructor, based on course level and class session length.
- What kind of vines would you plant: phylloxera-resistant hybrid grape varieties, or traditional vinifera varieties grafted onto resistant rootstocks? Why?
- After planting, would you monitor for phylloxera? If so, how?
- What would you do if phylloxera did appear in your new vineyard?
Background
What is phylloxera?
Grape phylloxera (Daktulosphaira vitifoliae) is a small aphid-like insect pest of grapevines (Vitis spp.) (Figure 5). The insect has a complex life cycle with two reproductive stages (sexual and asexual) and two feeding morphs (leaf and root). Eggs are laid in galls (abnormal growths) on roots and leaves (Figure 6).
The root galls cause the most harm; they can lead to root decay, fungal infections, stunting, and vine death. In susceptible grapevines, phylloxera induce the root cells to enlarge and divide, resulting in greater nutrient availability for the insects but a major loss in nutrients for the plant. There is no way to eradicate phylloxera from an infested vineyard, and available foliar pesticides are not effective for prevention or treatment of root infestation. However, some varieties of grape are more susceptible than others. In Australia, phylloxera exists in at least 83 diverse genetic strains with different abilities to feed on rootstocks. Natural predators of phylloxera include lacewing nymphs and some species of millipedes and fly larvae, but their use as biocontrol agents is not well-studied and has never been successfully implemented.
 
Figure 5 (Left): Grape phylloxera insects (Daktulosphaira vitifoliae) (Michigan State University).
Figure 6 (Right): Phylloxera galls on leaves (top, NC State Extension) and roots (bottom, Agriculture Victoria Research).
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History and spread
Phylloxera is best known as the cause of the Great French Wine Blight in the late 19th century. However, phylloxera is native to the Mississippi Valley of the United States. When plants and their pests originate from the same geographic area, they often co-evolve so that the plants develop resistance over thousands of years. In contrast, plant species which are not native to the same area as the pest often remain highly susceptible. North American grapevine material was imported to Europe in large quantities between 1858 and 1862, ending up in France, England, Ireland, Germany, and Portugal – and transporting phylloxera with it. Between 1863 and 1889, nearly 2.5 million hectares (6.2 million acres) of vineyards (Vitis vinifera) in France were destroyed due to phylloxera infestation, with a 72% drop in wine production (Figure 7). In the 1870s, European grape vine material began being imported to Australia. The first outbreak of phylloxera in Australia was observed in 1877. Phylloxera can naturally spread approximately 100 meters per year through a vineyard. Human activity is a major factor in long-distance spread of phylloxera, as the insects can be transported from one location to another on people, vehicles, equipment, and plant material (Figure 2). Over time, phylloxera has spread to most of the world's grape-growing regions, mostly due to human activity. Because of this, vineyard owners in areas at risk for phylloxera spread need to be vigilant about disinfestation practices for their equipment, including inspection, cleaning, and heat treatment.
Figure 7: Historical cartoon published in Punch magazine, 1890, humorously depicting phylloxera's destructive effect on the French wine industry.
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Grapevines fight back
Worldwide, about 1,300 varieties of grapes are used for commercial wine production. Approximately 98% of commercial wines are made from grape varieties belonging to the species
Vitis vinifera, which is native to Eurasia and has no resistance to phylloxera. Some grape species native to North America, such as
Vitis riparia and Vitis rupestris (Figure 8), as well as hybrid cultivars made by crossing North American species with
V. vinifera, show good resistance to root-dwelling phylloxera. These species and hybrids may also exhibit resistance to other pests and diseases, as well as enhanced tolerance of extreme climatic conditions. However, the inter-specific hybrid cultivars are less well-known to consumers than wine grape varieties of
V. vinifera such as Cabernet Sauvignon, Pinot Noir, Chardonnay, and Riesling. They also have different chemical composition and different flavor profiles compared to
V. vinifera, which can make winemaking extra challenging because common practices were developed for
V. vinifera. With so many cultivars available, each with their benefits and drawbacks, growers who carefully select the right cultivars for their location can drastically reduce crop loss, put in less labor for pest and disease management, and greatly improve the quality of the resulting wines.
Figure 8.
The grape species
Vitis vinifera is typically used for commercial winemaking. Species that are native to North America include
Vitis labrusca, Vitis riparia, Vitis aestivalis,
and Vitis rupestris. Names of individual grape cultivars are listed below the species from which they were derived.
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Grafting for resistance
Phylloxera-resistant rootstocks have been developed by crossing different species of
Vitis, and grafted rootstocks are a common defense against phylloxera in many parts of the world. Grafting – a common practice for many high-value specialty crops – joins the root system and lower stem (rootstock) of one variety with the top portion (scion) of another variety (Figure 9). It enables a grower to combine the desirable qualities of two varieties: in this case, a well-known but susceptible grape variety with a phylloxera-resistant rootstock. However, grafting is costly and laborious, and risks include infection by fungus or bacteria at the graft site and changes to the plant's nutrient needs or fruit quality. Additionally, no rootstock is 100% resistant to phylloxera, and new biotypes (genetic variants) of phylloxera continue to emerge with varying levels of ability to overcome resistance. Therefore, continued monitoring is important (Figure 10).
 
Figure 9 (Left): Scion plant material grafted onto rootstock. (Washington State University Extension.)
Figure 10 (Right): Emergence traps used for soil-dwelling pests such as grapevine phylloxera (Agriculture Victoria Research.)
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Glossary
- Biotype: A subdivision within a species based on a specific physiological trait.
- Cultivar: Short for “cultivated variety." Cultivars are selected and cultivated by humans. They may originate as spontaneous mutations or from crossings.
- Durable resistance: Resistance to a pest or disease that remains effective over time in a plant variety, in an environment where both the plant and the pest/disease are common. Durable resistance is not easily overcome by the pest or pathogen.
- Gall: A localized, abnormal swelling on external plant tissue caused by a fungus, bacterium, nematode, insect, or other organism.
- Graft: A joining of the shoot system (scion) from one variety with the root system (rootstock) of another.
- Hybrid: Created by crossing two plant varieties. Often, hybrid grapes refer to inter-species crosses of
Vitis vinifera with a native North American species such as
Vitis labrusca.
- Morphs (noun, plural): Insects belonging to the same species but having differences in form or appearance.
- Own-rooted: A vine that has kept its own roots and has not been grafted.
- Region: Legally designated origin of wine grapes, such as American Viticultural Area, Appellation d'Origine Controlee, or Denominazione di Origine Controllata.
- Rootstock: The root portion of the vine, which is selected for specific characteristics absent in the variety of the shoot material grafted onto it, such as disease and pest resistance.
- Scion: The shoot system of one variety of a plant that is joined to the root system (rootstock) of another variety by grafting.
- Variety: A taxonomic classification within a species based on unique characteristics of a plant. The species
Vitis vinifera includes varieties such as Pinot noir and Chardonnay.
- Viticulture: The cultivation of grapevines.
Further background reading:
Grape phylloxera:
Phylloxera and viticulture in Australia:
Hybrid grape cultivars:
Grape rootstocks and grafting:
Plant health:
Acknowledgments
We thank Lindsay Lifka for early reading and comments on the idea for this case study. We also thank Kephas Mphande, Jose Gonzalez, Sharon Badilla Arias, and Olivia Meyer for a test-run, discussion, and feedback in the Gleason Lab group meeting. Additionally, we thank the undergraduate students in HORT/FSHN 276 in Spring 2021 for their participation in a virtual classroom setting and their valuable comments and evaluations.
