Phylloxera is a well-known pest that destroyed huge areas of European wineries in the 19th century nearly destroying some of the most prestigious wine regions.
We’ve reported earlier this month that it’s becoming a concern in Washington, Walla Walla. But what exactly is phylloxera ? And what can we do to help?
Grape phylloxera, a small, light yellow, aphid-like bug is part of Phylloxeridae which is an order of insects belonging to the Hempitera family. It was first mentioned as Phylloxera farratix (devastator vines) in the 1860s French crisis. Later, it was found as being identical to Daktulosphaera vitifoliae and Phylloxera Vitifoliae, previously described.
Sap suckers are insects that feed on grapevine roots and leaves. The complex life cycle of the insect has up to 18 stages. They can be classified into four main forms; sexual, leaf, root and winged.
A single insect could cause sexual form of infestation. The Nymph first lays male or female eggs on the underside of the leaves. They hatch into female and male forms (without mouth parts) that then mate, and die. However, the female first lays a winter egg in the trunk of the vine’s bark. This becomes the leaf shape.
The leaf-form Nymph, commonly called the fundatrix or stem mother can be seen climbing up the suckers-growing leaf of the rootstock. She produces galls with saliva; into these she deposits eggs parthenogenically (without fertilization). At this point there are no visible signs of phylloxera. A mature plant can lay up to 200 eggs in a cycle.
Root form In turn, these new nymphs may move to other leaves, or even to the roots in which they can begin new infections in their root form. To get nutrients, they cut roots and release a poison that keeps the wounds open. There are swellings on the older roots, and characteristic hook-shaped galls develop on root hairs. The latter stop the development of feeder roots, and eventually kill the vine. The root form can also produce eggs for seven generations. The form is also able to reproduce parthenogenically every summer. Crawlers can move to other roots on the same vine, or other vines , via holes in the soil, on the surface, or in the canopy. Although they are not wingsed, root-form crawlers can be carried only a short distance in wind.
The winged form nymphs are born in autumn, then hibernate in roots until spring. They they feed on sap that is rising. They begin the cycle again by laying new eggs on the leaf underneath. Nymphs are able to take on winged forms in areas of high humidity and fly to unaffected vines where they can start new cycles.
At first, only individual vine plants may be affected. Insects that don’t fly can be more prevalent along rows of vine than they do over inter-row spacing.
It is believed that the plants affected at the time of planting tend to show signs of decline after a couple of seasons. It could take up to 10 years for signs to become obvious in an already established vineyard. The only way to get out is to tear the vines.
The soil type and climate are two of the factors that affect the density of phylloxera population. The bug is attracted to humid conditions between the ground and the air.
Vineyards in schist or sandy soils in dry, warm areas fared better during the 19th Century worldwide outbreak. The same applies to many of the areas which have been the most resistant to phylloxera during the 20th century. Colares, Portugal, and Santorini, Greece are two examples.
If human transport of insects is managed islands are safe. 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 on Santorini, and the Juan Garcia variety planted on manmade terraces along the Arribes River Canyon in Spain is possibly the only two Vitis vinifera varieties that have an inherent resistance to phylloxera. But the conditions for growing are very particular in both cases.
Dry soils can pose serious problems. If the bug does manage to survive, its effect is amplified by the absence of water. This could exacerbate the recent outbreak in the Walla Walla region.
It is believed that hard winters alter the cycle of reproduction in phylloxera. Climate change appears to contribute to the appearance of new outbreaks, as many regions experience milder winters. Walla Walla is another example.
Most crucially for vineyard owners, American vine species have evolved along with insects, and have evolved (varying) levels of resistance. The sticky sap that they produce blocks their mouths. Additionally, if an insect does open an opening, they could make a protective layer tissue over it to protect against bacterial and fungal infection.
The phylloxera blight that occurred in the late 19th Century
Phylloxera was not a sudden occurrence in Europe from the ether. In paradox, it is believed that the insect was initially introduced to Europe through specimens of American vines taken by British and European botanists.
The fascination with American grapevines was spurred by the powdery mildew outbreaks in European vineyards in the 1850s. It was hoped that American vines would be more resistant to disease. They were still flourishing, so alarm bells didn’t ring.
Technology advances influenced the time of the outbreak. They included the creation of the Ward Case, a sealed glass container which let plants sit in sunlight on a ship’s deck while protected from the elements of spray and winds. More generally, the advent of the steamship also contributed.
The first time, vineyards in Britain were destroyed. Then the problem spread to France and a large portion of Europe. The first Rhone vineyards started to go out of business in 1863. In France, the total production of wine was just 28 percent as of 1889 compared to 1875.
The cause is Phylloxera.
Knowledge spread slowly. A lot of growers watched their vineyards disappear without knowing why. In France, some decided to put live toads under each vine in order to remove the poison.
The complex life cycle of phylloxera is what makes its initial detection difficult. Growers seldom find healthier looking vines. By the time dead ones were scrubbed up and inspected after which the insects gone on. The discovery in 1866 of phylloxera in vines of the lower Rhone by Jules-Emile Planchon and colleagues is believed to have occurred because they cut down a still productive vine by mistake.
However, this research was not a catalyst for an organized response. Some experts, especially in Paris and Bordeaux, rejected the findings of bumpkins in the south, who were not professional entomologists or plant scientists.
A lot of people believed that the disease was a symptom , and it was not the reason. This was an expression of the 19th-Century obsession with the physiological model disease. It focuses on the internal issues in the plant, not external factors. They continued to look for solutions elsewhere.
Although it would take an additional five years to see the opposition completely dissipate, by 1869, phylloxera was popularly accepted as the reason. An infested, dying vine in the southern part of Rhone was impacted by the spring floods of that year. After it had dried, the insects had gone, and the vines flourished.
It was observed that sandy soils seemed to provide some form of protection. Vineyards were planted in the dunes of the Rhone delta, in places which would otherwise not would have been considered in any way suitable. These plots were a success, which also supports the theory of phylloxera.
People like Planchon believed that the vines that carried the insect might also provide a response. These ideas were supported by prominent American figures like CV Riley the Missouri’s state entomologist. His Darwinian convictions allowed him to recognize and pay attention to the resistance to phylloxera that exists in American species.
Hybrids are different from. the grapes that have been grafted
Transatlantic cooperation, led by Riley and Planchon, resulted in that 700,000.00 vine cuttings were brought to France from St Louis in 1872-73. But the knowledge of American vines was not present in France, and very limited in the US, too. The stakes were shopped around as to between direct-producing or rootstock-based vines that were more effective, and initial efforts focused, at great cost, on the least effective American species.
Planchon suggested earlier hybrid varieties like Concord and Clinton to Planchon following his return from the USA in 1873.
But they also have a significant percentage of Vitis labrusca that originates in the cooler northern forests of the US. The vines struggled with the French heat and, when used as rootstock material or cultivated as whole plants, were less resistant to phylloxera under the new conditions.
The wines tasted awful, bearing the smoky, sweet odor of the labrusca. A lot of the growers who put their trust in these imports from the beginning went out of business forever.
It was not easy to graft vines. A rootstock that’s successful would have to be easy to graft, demonstrate a long-term affinity to the French wine variety, and also be resistant to the phylloxera.
When research discovered new species, Vitis Riparia, Vitis rupestris and others American vines, it became essential to classify them properly. Different species possess distinct traits and preferences based on the circumstances under which they developed. There are not all wild vines of every species function similarly.
The 1870s University of Montepellier’s collection of cuttings was meticulously selected to allow for the propagation and distribution of approximately 12 rootstocks. The most successful were Rupestris de Lot and Riparia Gloire of Montpellier. The work continued in the 1890s to develop a new generation hybrid rootstocks which were better suited to French conditions.
The University of Bordeaux led efforts to create new hybrids that would not require grafts (direct producers) in competition with the Montpellier program. The optimism of inheritance through genetics was the foundation of this project. It was suggested that the traits of rootstocks from American varieties could be used to create fruit systems that are derived from French vine parents.
This duality existed until 1900, and was not as prominent across the globe throughout the following century. While hybrids didn’t taste as delicious than their vinifera counterparts but they were also more resistant to cold and other diseases. Though generally banned for quality wines in the EU, many of these varieties are still a staple of the North American wine industry outside California, Oregon and Washington.
Other strategies to fight phylloxera
The concept of making use of American vines to fight back caused great conflicts in France. Many saw them as the antagonist in the story. However, even more importantly many of the people within the French wine industry did not wish to for the integrity of French vineyards, grape varieties and wine by introducing foreign plants. The groups enacted a series of non-biological countermeasures referred to as La Defense based on sand and water.
Flooding methods require a amount of infrastructure, and the government was not quick to design the necessary canals. (War between France and Prussia ended in 1871. The French government’s effectiveness during this period was limited due to the war and its aftereffects. However, as much as 40,000 acres (100,000 acres) were affected by flooding.
Total plantings in sand topped out at around 20,000ha (50,000 acres). Still, there are vineyards around the Carmargue Gardoise dunes of Aigues-Mortes. Fertilizers are the basis for almost all of the nutrients for the vines that are found in the sand. The pest was reintroduced when silt from rivers was attempted to be dumped onto plots. The winds from the coast on these sandy areas were also problematic as they carried away the sand. These wines differed from those produced further inland, though they were still drinkable.
The Academie Francaise and the government championed insecticide trials in 1870s. They were often laughable, and all proved ineffective and resulted in a shift away from rootstock-based approaches.
The most effective treatment options were those that used the volatile chemical solvent carbon diulfide suggested by Baron Paul Thenard. The oily liquid settles into the soil and asphyxiates bugs It was especially effective against phylloxera, however it didn’t eliminate all. Annual treatments were required and gradually weakened the vine. It required skilled workers and was not available in most areas.
The pest was not as bad in the Champagne region. It was here that the pest was at its most widespread in the 1890s. Even as late as 1890, the local trade magazine was recommending the planting of alfalfa and lupins as well as sainfoin in the vineyards to keep phylloxera out of the area.
In the end, all paths of blindness were discarded. The increased focus on replanting with hybrid rootstocks came to be known as La Reconstitution. France had some control over the pest by 1900.
Spread of phylloxera worldwide
Phylloxera spread via American and French cuttings, or both. In the 1870s, we witnessed the destruction of Spain’s wine industry and also Portugal Germany and Switzerland. Phylloxera was found in California in 1874 in the vicinity of the city of Sonoma. In California, 12,000ha (30,000 acre) had been destroyed in the year 1900.
At the beginning of this century Around the turn of the century, the Balkans as well as Greece were affected. The same time, in Australia, Victoria and New South Wales were also affected. However strict quarantines as well as restrictions on the transport of plant matter were able to protect different regions, such as those of South Australia. South Australia.
French firms were heavily involved in the cultivation of Slovenian and Croatian grapes. These vines were destroyed between 1902 and 2005, causing the exodus of workers in the wine industry from North America and Australasia.
In the early 20th Century the global business could draw at the very least conclusions reached the 30 years of debate in France. The use of carefully selected vinifera scions grafted onto rootstocks (and to a lesser extent resistant hybrid varieties) was able to help stabilize the situation throughout most of the 20th century.
Rootstocks are different from. Phylloxera during the 20th Century
All rootstocks are not equal in their resistance. The degree of resistance provided by any rootstock will decrease with time. The main reason for this is that Phylloxera changes when confronted with vines resistant to it. There are now several hundred genetic strains of phylloxera that have been identified worldwide.
In the 90s, in California many vines that were transplanted to the widely-used AXr1 (Aramon Rupestris Ganzin No.1) were discovered to be infested. Some commentators suggested it was inevitable because Aramon is a vinifera species. However, hybrids that are not as vinifera-like like 41B have proven to be more effective.
The study revealed that phylloxera has mutated into Biotype B, which can overcome rootstock resistance. More than two-thirds (or more) of Napa’s vineyards needed to be replanted. It was the expense of replacing the ruined vineyards caused by phylloxera that forced the Mondavi family to transfer their business to public ownership.
Another crucial point is that only a few rootstocks have this resistance, so the insect doesn’t lay eggs. While phylloxera is not as prevalent in vineyards with grafting than other types, it can still be reproduced and thrive in the majority of these. As happened with transatlantic cuttings during the late 19th Century, this group may spread to non-grafted vines at a later date.
The same goes for sandy soils, which are not guaranteed. The famed Bien Nacido Vineyard located in the AVA Santa Maria Valley is is planted with roots that are owned by the vines and have been phylloxera-free for the time being. Casa Castillo’s Pie Franco (French Foot), red wine from Jumilla, Spain is made with root-based Monastrell vines which were planted in 1942 on sandy soils. The pest took root over the course of many years. Each year, more vines die and the volume of wine drops. Bollinger is one of the Champagne winemaker, lost one of the ungrafted parcels of the 2004 Vieilles Vignes cuvee. Phylloxera was first discovered six years earlier.
In fact, many areas of cultivation have not given enough thought (with the advantage of the benefit of hindsight) to the choice of rootstock. This isn’t due to a lack of confidence in the types of soils or other contributing factors. These regions were first developed in the 1960s, and have been more focused on expanding. Grafted vines can cost three times as expensive as ungrafted, and sometimes even more.
Phylloxera is present in varying forms in the state of Washington since the 1910s. But this year it made its presence known in the Walla Walla region was reported for the first time. This region is vulnerable because many cultivators here have decided to plant own-rooted vines.
This is because the phylloxera’s growth was hindered by the brutal winters. Grated vines appear to be able to recover faster from frost. Additionally, there are plenty of dry sandy soils here. But climate change implies that luck has run out, as the hard freezes are becoming more rare.
In the New Zealand’s South Island, phylloxera was discovered in the Central Otago wine region in 2002. The rapid growth of the region meant that it was estimated at the time that only 55 percent of vines were on resistant rootstock. This figure was much less than that of other regions of the country. Harsh winters were an insufficient security measure for the region.
Future and present of the Phylloxera
There is no cure for vines that have been phylloxera-infected. There are no biological or chemical controls that can keep it from spreading. Flooding the vines is rarely ever a last resort. The best way to save a vineyard is to remove it and plant on better rootstocks. There is a possibility that the farmer can select a more suitable clone, or even change the grape variety, however the financial costs could be huge.
It is still difficult to select the correct rootstock (commercially available). In addition to the suitability for local soils and macroclimates, viticulturalists also have to 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 varieties.
Protocols are being created all over the globe to control the movement of people as well as machines between vineyards. The machinery might be cleaned by steam, and staff may have specific footwear for each vineyard they must visit.
Alongside this, walks through the vineyard, whether mechanized or manual, may be kept to a minimum. This would seem to make sense in a situation where the vineyard is affected However, otherwise, growers (especially biodynamic practitioners) would prefer or need to maintain a high level of vigilance. This can be a voluntary measure.
Researchers are working on creating new rootstocks that are resistant to the phylloxera. This is in response to the ability of phylloxera to create biotypes that are able to defeat the defenses of particular rootstocks. A study from 2018 (Smith et al, BMC Plant Biology) investigating the genetic components of the phylloxera resistance of rootstocks was able to identify one allele (RDV2) which confers this trait.
Vinehealth Australia also reported in 2018 that it had tested successfully methods for DNA profiling to aid in phylloxera detection in cores of soil from the vineyard. While taking samples is straightforward but the storage and transportation conditions are crucial (as are the lab availability). Therefore it may take some time before this practice becomes routine. But, Australian wine producers might soon be able use drones for cost-effective aerial imagery.