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Phylloxera

by David on July 3, 2009

While the glassy-winged sharpshooter has been getting all the attention lately, phylloxera has, so far, had a far bigger impact on the world of wine than any other pest or disease. Once called phylloxera vastatrix – vastatrix meaning “the devastator” – it rivals the Irish potato famine for taking its toll on the economic well-being of those affected by it, especially those first afflicted, the French.

This devastator is a tiny, aphid-like insect, difficult for the human eye to detect at about a millimeter long. It’s native to the east coast of the United States and created a lot of confusion there long ago with the first attempts to bring European wine varieties to America. They never survived and no one knew why. Now we do. In fact, many like to blame phylloxera for Thomas Jefferson’s lack of success with wine grapes at Monticello, but it’s believed that rot was probably the real culprit.

How The Damage Is Done

Here’s how it works: the phylloxera feeds on the roots of the vine and, in the process, injects saliva that causes the roots to swell, become deformed and begin to decay. The injuries impair the vine’s ability to absorb nutrients and water and also make them more vulnerable to molds, fungus and other insects and mites. The vines seem to starve to death. At first the grower might notice a few stunted or dead vines and then the damage moves outward, often down wind. Eventually, there’s no choice but to replant. Otherwise healthy vines growing in fertile soil may produce well for many years after phylloxera first attacks. Those in poor soils or that are struggling from other causes will succumb quickly.

There are several generations of phylloxera produced each summer. When the eggs hatch the young phylloxera begin crawling to other roots, causing a slow spread. They may also climb up the trunk, which can broaden the spread and speed it up. From the trunk and the leaves they can be blown to other vines. They’re knocked around by tractors and other vineyard equipment, eventually reaching other vineyards. Man probably does a better job of spreading them than they do themselves, tracking them around on worker’s boots and carrying them from one vineyard to the next on farm equipment and plant material. They overwinter as small nymphs on the roots, so the spread is still a danger during dormancy if the grower transfers plant material. In the spring, when soil temperatures exceed 60°F, they start feeding and growing.

How It All Started

The 7000-year history of wine hummed happily along without any awareness or concern about phylloxera until the 1800s. In that century, as French varieties were being shipped to America, Native American varieties were also going to Europe and carried phylloxera with them. We believe phylloxera migrated from the east coast to the Southeast, the Mississippi Valley and the gulf coast early on because the native vines there appear to have evolved with strong resistance. But, the French vines, a different species from American, had never been exposed before and it truly was devastating. In the mid-1860s, just as they were recovering from another nasty American import, powdery mildew, they began to notice vines dying off for unknown reasons.

The experts blamed it on over-production, bad weather, not rotating the crops, poor soil and even the wrath of the Gods. A member of a group studying the issue, Jules Planchon, noticed that the dying vines had small, yellow insects on their roots and noted the resemblance to an aphid that lived on oak trees. He was on the right track, but others couldn’t believe that such a small insect could wreak so much havoc. Finally, it was acknowledged that it was, indeed, those little bugs that were the cause. As the total production of French wine fell by the year, the French government became so alarmed that they offered a large prize to anyone who could come up with a cure. Little did they know that, in the meantime, phylloxera was busily spreading to other parts of Europe and the world, reaching California by the late 1880s.

So what to do? The offer of the prize brought in thousands of suggestions from people all over the world, some practical, others rather comical. The scientists tried flooding the vineyard and using the chemicals that were available at the time. Carbon Bisulfide had worked well on other pests and, even though it proved to be ineffective against phylloxera, many persisted in using it. Nothing worked.

American Rootstock to the Rescue

While all this was going on, it was noticed that the Native American varieties were phylloxera resistant, spurring Planchon to visit America. He met with a man named C. V. Riley, the state entomologist of Missouri, who positively identified the unknown French insect as identical to the American one. He was also among the first to suggest grafting European varieties to American rootstock. It was a radical suggestion in the view of the French and took a very long time to become accepted. Concern about the rootstock affecting wine quality was so great that it was illegal to import the American rootstock into the Burgundy region until 1887. To this day there are doubters, but the grafting was eventually responsible for saving the vineyards of Europe and later California. Millions of rootstock cuttings were shipped to France in the mid 1870s. Phylloxera has proved to be a jet-setter and is found all over the world. Some parts of Australia, Chile and Argentina, among others, are phylloxera free and we know that phylloxera doesn’t do well in high altitudes or light, sandy soil.

If only the story ended there. In the 1980s, vineyards In California began, once again, to die off due to phylloxera. It was soon noticed that they all had one rootstock in common: a widely used rootstock called AxR-1. It became popular in California in the 1950s because it had a lot going for it. It was easy to graft and grow, it’s adaptable and a big producer. Everyone thought “What a great rootstock!” That is, until the vines started to die.

AxR-1 is a French-American hybrid, so it’s assumed that the French parent is the weak link. There were a few theories about what was happening. One was that the vines survived for the first few decades because they were young and vigorous and we had good rainfall. 20-30 years later the vines were less vigorous and more susceptible to the damage done by the pest and the trouble began. Then, phylloxera biotype “B” was identified. It seems that phylloxera had mutated in such a way that, if AxR-1 ever had been resistant, it wasn’t any longer. In any case, if a grower’s vineyard was on AxR-1, it wasn’t a question of if, but when it would die. This meant replanting over 60% of the vines in Napa and Sonoma over a period of several years in the 80s and 90s.

The lesson learned from all this is that we should never be complacent. In fact, as recently as 2005, there were reports of grapevines declining in the presence of phylloxera activity, despite being planted on pure-American, theoretically highly-resistant rootstock. It’s still being investigated.

In a more positive light, the major replanting in the 80s and 90s served to accelerate the quality of north-coast wines more quickly than might have otherwise been. Significant advances in our understanding of viticulture had taken place in recent times, but it was much too expensive for a grower to replant just because he wished he’d done things a little differently. By forcing us to replant, phylloxera led us to the use of superior clones, training methods, and ideas about spacing that we enjoy today.

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