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How phylloxera spread

Phylloxera is an insect that destroyed large areas of European vineyards during the 19th century, almost eliminating some of the most famous wine regions around the world.

We have reported that it is becoming a concern in Washington, Walla Walla. What is phylloxera exactly and what can we do to help?

Grape phylloxera, a small, light yellow, aphid-like bug that is part of the Phylloxeridae, an order of insects that belongs to the Hempitera family. It was first described during the 1860s in France as Phylloxera vastratix (devastator of vines) which was later confirmed to be identical to the previously reported Daktulosphaera vitifoliae or Phylloxera vitifoliae.

The insect is a sap suckers feeding on the roots and leaves of grapevines. It is able to traverse up to 18 stages in its complicated life cycle. They can be divided into four major forms including sexual leaf root, winged, and root.

A single insect could cause sexual form of infestation. First, a Nymph lays male or female eggs on the leaves’ underside. The eggs are then hatched into male and female versions (without the mouth part) that then mate, and die. The female egg laid in winter is placed inside the trunk bark. The egg develops into the leaf form.

The leaf-form nymph, also known as the stem mother or fundatrix climbs onto a leaf of suckers growing from the rootstock at base of the vine. She produces galls with saliva, and into them she puts eggs that are parthenogeneously (without fertilization). There are no clear signs of phylloxera-related attack in the upper vine canopy at this stage. Adults can lay up to 200 eggs in a cycle.

Root form To get nutrients, they cut roots, and secrete a poison which keeps the wounds open. On older roots swellings begin to develop, and hook-shaped galls grow around the root hairs. These latter prevent the growth of feeder roots and eventually cause the vine to end up dying. The root form produces eggs for seven more generations. The form is also able to reproduce parthenogenically every summer. Crawlers may move to other roots of the same plant or through soil cracks or through the canopy. The crawlers that are shaped like roots, but not wingsets, are carried in the breeze for shorter distances.

Winged form nymphs are born in autumn , and then hibernate in the roots until the following spring when they feed on the rising sap. They begin their cycle again by laying fresh eggs on the leaf underneath. In areas with high humidity, these Nymphs grow wings and can then move to vines that are not affected to begin new cycles.

At first, individual vines may be affected. Insects that aren’t flying can spread faster along vine rows than they do across inter-row spacing.

Plants that are damaged at the time they were planted tend to develop signs of damage and then decline in the following seasons. When a mature vineyard gets attacked, it can be 10-15 years before the warning signs are obvious. The only way to get out is to rip the vines.

Climate and soil type have been found to affect the density of phylloxera populations. The bug is attracted to humidity that is between the ground and the air.

More fertile, sandy soils as well as vineyards located in schist-rich areas performed better during the 19th Century worldwide epidemic. The same applies to many of the areas which have best resisted phylloxera throughout the 20th Century. Colares, Portugal, and Santorini, Greece are two examples.

If the human movement of the insects is controlled islands are secure. Similar to that, Chile has been protected by the Andes on one side, the Pacific on the other and the Atacama desert to the north.

Assyrtiko, which is found on Santorini as well as Juan Garcia, which are both on terraces that are made of manmade in the Arribes River Canyon in Spain could be the sole Vitis vinifera cultivars that possess the natural ability to resist phytolloxera. Both have extremely specific growing conditions.

There is a major warning with soils that are extremely dry. If the insect is able to survive, the lack of moisture can increase its impact. This could increase the severity of the current Walla Walla outbreak.

Hard winters are thought to alter the cycle of reproduction in the phylloxera. Climate change may play a role in the emergence of new outbreaks, as many regions experience milder winters. Walla Walla is another example.

For owners of vineyards, the most important thing is that American vine species evolved alongside insects and have evolved resistance to different levels. The sticky sap they produce clogs their mouths. Also in the event that an insect manages to open an opening, they could create a protective layer of tissue to guard against bacterial and fungal infection.

The phylloxera blight of late 19th Century

Phylloxera was not a sudden occurrence in Europe out of the ether. It is paradoxically understood that the first evidence of American vines that brought the insect to Europe by British and European botanists are the ones that brought it to Europe.

The fascination with American grapevines was spurred by the outbreaks of powdery mildew that were ravaging European vineyards in the 1850s. It was believed that American vines were more resistant to disease. These vines were still thriving and alarm bells did not ring.

Technology advances influenced the exact timeframe of the outbreak. These included the development of the Ward Case, a sealed glass container which allowed plants to sit in sunlight on the deck of a ship, while being protected from the elements of spray and winds. Steamships was also a major factor.

Vineyards in Britain were first devastated. The issue was then spread to France as well as other regions of Europe. The first Rhone vineyards started to disappear in 1863. In 1889, the total wine output in France was lower than 28 percent, compared to 1875.

Phylloxera is the culprit

Knowledge spread slowly. A lot of owners of vineyards have lost their vineyards without knowing the reason. To draw out the poison, some French growers buried live toads in the soil beneath their vines.

The intricate life-cycle of phylloxera can make initial detection tricky. Additionally, most growers do not dig up healthier-looking vines. They moved on once the dead ones were removed and examined. Jules-Emile Planchon, along with colleagues, found phylloxera growing on vines in the lower Rhone in 1866. The cause was their mistakenly pulling up the productive plant.

However, this research was not a catalyst for a coordinated response. Some experts, particularly in Paris and Bordeaux, rejected the findings of bumpkins in the south, who were not professional entomologists or plant scientists.

Many believed that the ailment was a symptom and not a cause. This was due to the 19th century’s obsession with the physiological model of disease and focusing on internal imbalances within the plant rather than external forces acting upon it. They continued to search for solutions elsewhere.

Though it would take five more years before the disease would be completely gone in 1869, phylloxera was more well-known as the reason. An infested, dying vine in southern Rhone was impacted by the spring floods that year. Once it dried out the insects had gone, and the vineyards grew.

It was observed that sandy soils provided some degree of protection. In places that are not usually considered suitable, vineyards were planted in the Rhone delta dunes. These plots have been a great success, which also supports the theory of phylloxera.

Some figures, like Planchon, believed that the vines which carried the insect might also trigger a response. Such ideas were supported by now-celebrated American figures such as CV Riley who was the state entomologist for Missouri. His Darwinian convictions allowed him to recognize and pay attention to the resistance to phylloxera in American species.

Hybrids vs . grafted vines

Transatlantic collaboration (led by Planchon and Riley) resulted in 700,000 vine cuttings were imported into France from St Louis over 1872-73. But the knowledge of American vines was lacking in France and extremely limited in the US as well. The stakes were shopped around as to whether rootstocks or direct-producing vines were more effective The initial focus was, at great cost on the most ineffective American species.

Planchon suggested earlier hybrid varieties like Concord and Clinton to Planchon upon his return from the USA in 1873.

These vines contain a high amount of Vitis labrusca, which is a plant that originated in the cooler northern forests of the US. The vines struggled in the French heat and, when used as rootstock material or cultivated as whole plants, proved less phylloxera-resistant in the new conditions.

And, even more importantly, the wines tasted unpleasant, carrying the smoky, sweet odor of labrusca. Many of the producers who believed in these imports from the beginning went out of business for good.

Work on grafted vines was no less challenging. A rootstock that’s productive must be simple to graft, have a long-term affinity with the French wine variety, and be resistant to phylloxera.

The American vines needed to be classified correctly in the course of research, which resulted in new species being discovered, most importantly Vitis Riparia as well as Vitis rupestris. Different species could have distinct preferences and features based on their source. The wild vines that belong to every species function in the same manner.

The 1870s University of Montepellier’s collection of cuttings was carefully selected to permit the propagation and distribution of approximately 12 rootstocks. Riparia Gloire de Montpellier and Rupestris du Lot were among the most effective. Additional work was completed in the 1890s to create an entirely new generation of hybrid rootstocks which were more suited to French conditions.

In the wake of the program of Montpellier the Montpellier program, efforts were made with the help of the University of Bordeaux – to breed new hybrid varieties which would not need a graft (direct producers). The idea of genetic inheritance was the premise of this project. It was suggested that traits from rootstocks of American varieties could be used to create fruit systems derived from French grapevine parents.

The duality was present until the year 1900, and it was less well-known throughout the following century. Although hybrids may not taste as delicious as their vinifera parents, they were more resistant to cold and other diseases. These varieties are generally prohibited in the EU for quality wine, but many of them are strongholds of the North American wine trade outside of California, Oregon, and Washington.

Other efforts to combat phylloxera

The idea of making use of American vine species to fight back was a cause of great conflict in France. They were viewed by many as villains in the tale. But, more powerfully there were many people in the French wine industry did not wish to to compromise the integrity of French vineyards as well as wine through the introduction of foreign plant material. The groups devised a series of non-biological countermeasures known as La Defense, which was based on water and sand.

Flooding methods require a amount of infrastructure, and the federal government was slow to plan the necessary canals. (War between France and Prussia ended in 1871. The conflict and its aftermath limited the efficiency of the French government throughout this period.) Yet, up to 40,000 ha (100,000 acres) were submerged.

The total plantings of sand top at about 20000ha (50,000 acres). Still, there are vineyards throughout the Carmargue Gardoise dunes of Aigues-Mortes. Fertilizers are required for almost all vine nutrition in the sandy soil. The pest was reintroduced when river silt was tried to be pumped onto the plots. Sand was frequently taken away by the winds of the coast which swept across the sandy areas. The wines tasted very different from those made earlier into the interior, but still suitable for drinking.

The Academie Francaise and the government supported insecticide trials during the 1870s. Many were laughable and ineffective and only served to divert attention away from rootstock-based strategies.

The most effective treatments were those that utilized the volatile chemical solvent carbon diulfide as proposed by Baron Paul Thenard. This oily liquid settles in the soil and insulates insects and was particularly effective against phylloxera, however it was not able to eliminate them all. Regular treatments were needed, which slowly weakened the vine. It required skilled laborers and wasn’t available in all areas.

The Champagne region, which lies from the north, escaped the worst effects of the pest up until the early 1890s. The local trade journal recommended that alfalfa, lupins, and Sainfoin be planted in vineyards to prevent the spread of phylloxera.

All the blind alleys eventually ended. La Reconstitution was a greater concentration on the replanting of hybrid rootstocks. By 1900, France had the pest at least under control.

Spread of phylloxera worldwide

Phylloxera was spread through American and French cuttings or both. In the 1870s, we witnessed the eradication of Spain’s wine production, and also Portugal Germany and Switzerland. Phylloxera was discovered in California in 1874 near the city of Sonoma. In 1900 12,000ha (30,000 acres) were devastated across the state.

The Balkans and Greece suffered from around the turn of the century. In the same time, Victoria and New South Wales in Australia were also affected. Other areas were protected by strict quarantines and limitations on the transportation of plant matter, which included South Australia.

French firms were heavily involved in the cultivation of Slovenian and Croatian wine grapes. These vines were ravaged between 1902 and 1905, prompting exodus that would boost the wine industry in North America and Australasia.

In the beginning of the 20th Century, the global industry could draw at the very least conclusions reached the 30 years of debate in France. The situation was stabilized for the majority of the 20th century through careful selection of grafted rootstocks on vinifera varieties (and in some extent and resistant hybrids).

Rootstocks vs phylloxera in the 20th Century

All rootstocks are not equal in their resistance. And the resistance that any rootstock offers can diminish as time passes. The main reason for this is that Phylloxera mutates when faced with vines resistant to it. There are currently several hundred genetic strains of phylloxera identified across the globe.

In the 90s, in California, many vines transplanted to the widely-used AXr1 (Aramon Rupestris Ganzin No.1) were found to be infested. Aramon Vinifera, a varietal of vinifera was believed to be the cause of the problem. However, other hybrids of this type such as 41B continue to show more effectiveness.

Investigative work revealed that phylloxera has mutated into Biotype B that is able to overcome rootstock resistance. About two-thirds (or more) of Napa’s vineyards had to be planted. It was the expense of replanting phylloxera-ravaged vineyards which required the Mondavi family transfer their business to public ownership.

Another crucial point is that only certain rootstocks are resistant to the fact that the insect doesn’t lay eggs. While phylloxera is not as prevalent in vineyards that have been grafted than elsewhere, it can still reproduce and be found in a lot of. The disease can then spread to grapevines that are not grafted, as was the case with transatlantic cuttings in late 19th century.

Sandy soils, however, are not infallible. Bien Nacido Vineyard, Santa Maria Valley AVA is composed of vines with roots that are phylloxera-free to date. Casa Castillo’s Pie Franco (French Foot), red wine made in Jumilla, Spain is made by utilizing roots that are grown by the owner Monastrell vines that were planted in 1942 on soils that had sandy. The pest took root over the course of many years. Every year more vines die and the wine’s volume drops. Bollinger is a Champagne winemaker, has lost one of its non-grafted parcels in the 2004 Vieilles Vignes cuvee. Phylloxera was first discovered in the year before.

A lot of growing regions haven’t considered enough consideration for the selection of rootstocks, despite the benefit of experience. This is not due to trust in the soil type or other mitigating factors. Many of these regions have been developed since the 1960s, and were more focused on expanding. Grafted vines can cost three times as expensive as ungrafted, and sometimes even more.

Since 1910, phylloxera been present in Washington in various forms. The first time it was reported was this year in the Walla Walla area. This region is especially at risk because of the fact that the majority of growers choose to plant their own-rooted vines.

This is because the phylloxera’s growth was slowed by the severe winters. In addition grated vines have been reported to recover faster from frost. There are also lots of sandy soils. Climate change has made it harder to be successful since hard freezes are becoming less frequent.

In 2002 In 2002, the Central Otago wine area in New Zealand’s South Island was hit by the phylloxera. The rapid growth of the area meant that just 55% of the vines on resistant rootstock were discovered at the time. This number was less than that of other parts of the country. This area was not protected by the harsh winters.

Future and present of the Phylloxera

There is no treatment for vines that have been phylloxera-infected. Neither are there biological or chemical methods to prevent it taking hold. The idea of flooding vines isn’t an ideal idea. Currently, the best solution remains to rip out a vineyard and plant on more suitable rootstocks. There is a silver liningto this: the grower may choose the best clone, or even alter the grape variety. But the financial consequences could be quite severe.

Selection of (currently commercially available) rootstock is a challenge. In addition to the suitability for local soils and macroclimates the viticulturists should also be aware of the specific strain(s) of phylloxera are they facing. Vinehealth Australia (formerly the Phylloxera and Grape Industry Board of South Australia) test rootstocks against a minimum of seven strains.

Protocols are being created around the globe to control the movement of people as well as machinery between vineyards. Steam cleaning could be utilized to clean machinery. Employees may also be required to wear shoes specifically designed for each visit.

Allied to this, passes in the vineyard, either mechanized or manual, may be limited to. In a affected vineyard, this would make sense however, other growers (especially biodynamic ones) are required to keep an extremely high level of surveillance. These measures can be voluntary.

Researchers are working to develop new rootstocks that are resistant to the phylloxera. This is in response to the ability of phylloxera to create biotypes that are able to overcome the defenses of specific rootstocks. A 2018 study (Smith et al, BMC Plant Biology) looking at the genetic factors of resistance to phylloxera in rootstocks revealed a single allele (RDV2) which confers this characteristic.

Also in 2018, Vinehealth Australia reported that it had successfully trialled DNA profiling methods to find genetic material of phylloxera in the cores of vineyard soil. Though sample taking is easy however, storage and transport conditions are crucial (as is the availability of laboratory equipment). It will take time before this becomes a common procedure. With the help drones for affordable aerial images, at a minimum Australian winemakers could soon have a viable early warning system toolkit.