Vidal Blanc grape leaves heavily infested with the foliar form of grape phylloxera at RayLen Vineyards, Mocksville, NC. Photo: Turner Sutton
This Wednesday, I received an email from Steve Shepard, vintner at RayLen Vineyards, describing a large infestation of the foliar form of grape phylloxera in his Vidal Blanc block. Vidal Blanc (or just Vidal) is a French hybrid grape widely planted in the eastern US because of its cold tolerance. I made plans to visit the vineyard next week and was not too concerned about the potential for damage. Then I received an email from Turner Sutton, NC State plant pathologist, who sent me a photo of the damage (above).
Grape phylloxera (Daktulosphaira vitifoliae) is an aphid like insect which can feed on both leaves and roots of grape vines. Foliar infestations of grape phylloxera are fairly common in NC, but they are usually limited to a few galled leaves and do not impact photosynthesis. If only a few galls are present, removing the affected leaves before the galls spread can limit an infestation. In fact, phylloxera was of so little concern last year that we did not address its management in the Southern Region Small Fruit Consortium Bunch Grape IPM Guide. We are meeting to edit this guide in 3 weeks, and adding phylloxera will on the top of my list of changes. The root feeding form of phylloxera has received most of the attention as a pest because of its potential damage to western US grape plantings and its history as an invasive species in France. Native North American grapes are naturally tolerant to root feeding by phylloxera, but native French varieties were not. The use of American root stocks grafted to French varieties (developed by pioneering American entomologist Charles Valentine Riley) is credited with saving the French wine industry.
Foliar phylloxera has become increasingly common in recent years, and infestations as severe as the one at RayLen can reduce photosynthesis therefore decrease fruit quality and vine vigor. French-American hybrid grapes are being planted more frequently in the eastern US because of their tolerance to varying climatic conditions, but many of these varieties appear more susceptible to foliar phylloxera. The grape phylloxera life cycle is very complicated, but the stage most amenable to management are the crawlers, which move on the plant surface to found new galls. Not all the galls on the leaves in Turner's photo necessarily contain live phylloxera, as the galls will remain after the insects have moved on.
Comparatively little work has been done on foliar phylloxera, but Dr. Donn Johnson at the University of Arkansas has put together an excellent fact sheet on phylloxera biology and management. Dr. Johnson also works with Missouri wine growers, who have been dealing with damaging foliar phylloxera infestations for several years.
Biology and management of grape phylloxera - Johnson, Sleezer, and Lewis