Phylloxera Infestations in Grape Vineyards

"Galls" on phylloxera infected grape leaves
"Galls" on phylloxera infected grape leaves

One of the largest impacts to the grape industry throughout history has been the spread of Phylloxera. Since the 1800's, Phylloxera has kept grape growers on edge not only about the health of their grapes, but also about the possibilities of spreading the dangerous bug infestations to other areas of the region. Phylloxera has a long and complex history, and throughout it's history, Phylloxera has been extremely difficult to stop . Thanks to current innovations and technology, many new solutions to Phylloxera infestations have been developed. But often the same preventative measures that were used back in the 1800's are still the most cost efficient and effective today.

Phylloxera is a small, sap eating, insect that can come in a variety of different colors. Phylloxeras feed on leaves and roots, and many species produce galls on the areas where the feeding took place. Their life cycle is complex; one species is known to pass through 21 different stages. All mature Phylloxera are female, and reproduce a-sexually, which means they do not need a mate in order to lay eggs. A single female Phylloxera can lay more than 400, yellow, oval shaped eggs at one time. The males never reproduce and never reach maturity. Color of the adults varies with what the insect is feeding on. On healthy roots they are light green, yellowish green, or light brown. On weakened roots they are brown or even orange. Mature adults become brown or purple in color. The most notorious type of Phylloxera is the grape Phylloxera, "Phylloxera Vitifoliae", native to North America. The species can be winged and wingless, the winged type causes galls on grape leaves and the wingless type generally feeds on the grapes' roots, causing nodules and eventually killing the vine. The grape phylloxeras' spread in (roughly) 1854-1860 was so intense, that it came close to destroying the wine industry of France. Phylloxeras are classified in the phylum "Arthropoda", class "Insecta", order "Homoptera", and the family "Phylloxeridae".

Phylloxera infected roots
Phylloxera infected roots

The spread of Grape Phylloxera throughout France and later, England, was very difficult to stop. At the end of the 19th century, Phylloxera had destroyed roughly two thirds of the existing European vineyards. England and France reportedly became infested with Phylloxera due to a nursery stock. Phylloxera was apparently introduced to California in the 1850s however it is native to the southern and eastern United States. It was identified in the 1800's as Phylloxera. Phylloxera was identified in the Penticton area of British Columbia in 1960 as well as in Washington. Phylloxera was also discovered in Oregon about the same time. However, in 1990, this insect was discovered for the first time in "modern" commercial sized vineyards. Phylloxera is currently found in every major grape producing region in Oregon. In 1988 the Washington State Department of Agriculture (or WSDA) surveyed 129 vineyards to determine if grape Phylloxera was present. The WSDA found grape phylloxera in 8 of the vineyards. All but one of the findings were in Concord grapes.

Because of how easily this pest is spread, and how brutal it is once it has infected a vineyard, Phylloxera has a strong and lasting impact on the grape industry. Some people believe that the nodes that are created by Phylloxera during feeding is do to an injection of poisonous saliva that is injected into the roots (or leaves) during feeding. These nodes often stop root growth completely. This extensive damage to the root systems causes the grape vines to be unable to adequately absorb water and nutrients from the soil. A grapevine that is infected by Phylloxera eventually becomes very weak and consequently, more susceptible to fungal diseases, other insects, and environmental stresses which all have potential to destroy a weak vine. Recently, Phylloxera has become a huge problem, especially in California and New Zealand. Rootstocks that were developed in the 1960s and 1970s, which were planted because they were resistant to many other problems grape vines face, have turned out to be much less resistant to Phylloxera and are being replaced at high cost. This is obviously a huge financial issue for many of today's grape growers. This enormous expense makes the grape industry much more financially unstable. Throughout the 1990s, Phylloxera was a major factor influencing vineyard values in Napa and Sonoma Counties. While replacing Phylloxera infected vineyards is still going on today in Sonoma County, Napa County has limited the number of vines which are not protected against the Phylloxera pest. This means that in Napa County, Phylloxera is now limited to only a few isolated vineyards. The remaining vineyards which are still susceptible to the Phylloxera infestations are currently still able to survive due to careful fertilization and irrigation techniques.

The life cycle of Phylloxera
The life cycle of Phylloxera

There are currently many options to vineyard planters when it comes to preventing the infestation of Phylloxera. Many of the techniques used for generations are still the most effective today. Vine variety, age, soil type and drainage have a direct correlation to the severity of a possible infection. Vigorous vines tolerate phylloxera attack much better than weaker vines. Vines growing in heavy, shallow soils tend to become infested much more easily than grape vines growing on lighter, well drained soil. In California, it was discovered that vines growing on light, sandy soils seem to be nearly immune to Phylloxera. These soils directly affect phylloxera mobility. Heavier and thicker soils crack when drying, creating passageways for phylloxera to easily travel and infect other nearby areas. Therefore, if you were worried about a possible outbreak of Phylloxera in your vineyard, one possible solution worth considering would be to use more water during irrigation and increasing the amount of lighter, sandy soil in your vineyard. One more obvious way of preventing Phylloxera would be to have the healthiest vines possible. A commonly used technique to do this is to increase the number of vines per acre to create a much denser vineyard. This would mean each vine produces less grapes, however, there is also less stress on the vine which would mean a healthier vine that could be in a better position to withstand a Phylloxera outbreak. Another option would be to purchase grafted vines that are grafted with a rootstock resistant to Phylloxera. Although this means a higher initial cost for a vineyard, it helps ensure that a Phylloxera outbreak will not occur (potentially costing much more to recover from). These are all options for vineyard growers who want to stop an outbreak of this pest before it occurs.

Although this is a devastating and destructive pest, and has been since the 1800s, vineyard planters are slowly winning the war against this pest. It's destructive capabilities are clear when looking at how many vineyards were destroyed by Phylloxera in Europe, as well as Phylloxeras‘ effects on local vineyards. Perhaps the most important weapon we have to use against this pest is knowledge. If all vineyard growers were aware of what Phylloxera is, what consequences it can have, and techniques for preventing a Phylloxera outbreak, then there is potentially much less risk when going into the vineyard business. This destructive pest can be prevented from spreading today, in this modern economy, just as it was as long ago as the 1860s.

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