Wine Plague: Myth or Reality?
Have you ever heard of the ‘wine plague’? It erupted first in Europe, nearly destroying every single wine grape in the world. In the late 1800s, wineries all over Europe burned and demolished their vineyards in an attempt to stop the spread of this horrible disease. By the 1900s, the wine plague had killed over 70% of the vineyards in France. Its destruction even spread to Australia, New Zealand, South Africa, and even California. So, who is responsible for this periodic devastation of the wine industry?
Characteristics of grapevines when infected by Phylloxera, or known as the ‘wine plague’. This includes galls (abnormal growth and swellings) on the surface of leaves and roots of the grapevines.
Well, the crown belongs to the Phylloxera. Phylloxera (Daktulosphaira vitifoliae) are tiny pale-yellow insects. They are sap-suckers who feed on the roots and leaves of the grapevines. The damage done on the vines, however, depends on where in the life cycle these insects are. Phylloxera has a very complicated life-cycle consisting of 18 stages, but they can be divided into four main forms: sexual, leaf, roof, and winged.
Phylloxera insects. They are tiny, yellow aphid-like insects.
The sexual form infestation can start with one single insect. First, a nymph (immature form of an insect) will lay male and female eggs on the underside of the leaves. These eggs will hatch into a male and female form, but without mouthparts and therefore do not cause damage to the grapevines. These insects will then mate and die. However, the females will first lay their eggs in the bark of the vine’s trunk, usually during winter. These eggs will hatch and develop into the leaf form of the Phylloxera.
The leaf-form nymph, female insects after hatching, will then climb onto a leaf of suckers (vertical growth from the roots or lower main stem of a plant), which grow from the base of the vine. She creates galls (abnormal growth) using her saliva, piercing the leaf’s surface. Into these galls she will lay her eggs parthenogenetically, which means despite these eggs being unfertilized, they will still develop into a new individual. It is a form of asexual reproduction. These nymphs can lay up to 200 eggs per cycle.
From these eggs, new root-form nymphs develop and can move to other leaves or to the roots where they begin new infections. They do this by puncturing the surface of the roots, causing the vines to form galls (abnormal growth) and swellings on the root hair. They pierce the roots to find sap to eat, secreting a poison that keeps the wounds of their piercing open. On the root hair, these galls have a hook-shaped form, stopping the growth of the feeder roots. This ultimately kills the vine, as the roots are unable to supply the rest of the plant with the necessary amount of nutrients and water required for metabolism and growth. Besides, the wounds on the roots can leave them at more risk to develop root rot, where the roots of the vines start to rot and decay. The root form nymphs will lay eggs for seven more generations, and can even reproduce parthenogenetically each summer. These insects will move to other roots on the same vine, or other vines through cracks in the soil or the canopy, spreading the disease to neighboring vines.
Winged-form nymphs hatch in the autumn, and they hibernate in the roots until the following spring. They restart the cycle by laying new eggs on the leaf underside. As they have wings, they can fly to unaffected vines to start the new cycle.
Life Cycle of Phylloxera - can be split into 4 main forms: Sexual, leaf, root, and winged nymphs. The leaf nymphs are responsible for the leaf galls, while the root nymphs are responsible for the root nodosity (galls and swelling in the roots).
So root-form nymphs are mainly responsible for killing the vines, while the other forms of the insects are responsible for the spread of the disease. However, how did these insects travel to the other half of the world to propagate this vine-killing disease? Well, it was actually because of humans. In fact, this pest only ever came to Europe because some American botanists brought their vineyard species with these pests to Europe to set up vineyards. These insects can latch onto our shoes and belongings, and then we essentially bring them to the different vineyards all around the world, without them having to exert any effort. Although these insects originate from the USA, a lot of American vineyards have developed varying degrees of resistance to these pests, as they evolved alongside them. They can exude a sticky sap that clogs the insect’s mouth, prevents them from forming galls or swellings. Also, they can develop a layer of protective tissues if the insects open up a wound, to protect the vines from fungal and bacterial infections.
There is no cure for Phylloxera. Instead, winemakers have developed multiple ways of growing grape-vines that are resistant to this insect. The most common method is that grapevines are grafted to the Phylloxera tolerant rootstocks. Grafting is a technique that joins the tissues of two plants together, so they continue to grow as one plant. Today the majority of the world’s vineyards grow on American rootstock, as most Phylloxera tolerant rootstocks originate in the USA. However, there are still vineyards around the world that have not been affected by the Phylloxera disease. For example, most Chilean wine is Phylloxera free, as their vineyards have been isolated from the world by the Atacama Desert and the Pacific Ocean. In addition, there are some vineyards in Europe, at the center of the plague, that was not affected by the insect. There are a couple of vineyards in Italy that are unaffected, including the vineyard in the Lisini estate in Montalcino, which contains vines that date back to the mid-1800s. Furthermore, there are a lot of vineyards on the slopes of Sicily’s Mount Etna that are Phylloxera-free. This is mainly due to the very low concentration of clay (less than 3%) and high levels of silica sand in the volcanic soils. Phylloxera insects can’t survive in these conditions as the surface water from rain seals these types of soil which imprisons these insects underground, which effectively drowns and kills them. Strangely, the Barossa Valley in Southern Australia also has always been Phylloxera free.
Phylloxera distribution around the world. Chilean vineyards are Phylloxera free due to the geographic location, being guarded by the Atacama Desert and the Pacific Ocean. Although the USA is not Phylloxera-free, most of the vineyards have developed natural resistance towards these insects. There are a couple of vineyards in Europe and Australia that are also Phylloxera free.
So although the wine industry has recuperated, and now has evolved to one of the largest industries in the world, wine-makers have to be extremely careful of any other pests, no matter of tiny they are, that can have as much or more devastating effect as our very own Phylloxera insects. Let us hope that this time vineyards all around the world can thrive under fruitful conditions, under the care of us humans without having to worry about plagues spreading around!
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