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Thursday, July 22, 2010

Grape phylloxera update

Grape phylloxera adults and eggs in foliar galls at RayLen Vineyard. Photo: HJB

Last Thursday I visited RayLen Vineyard to see the grape phylloxera (Daktulosphaira vitifoliae) infestation I posted about previously.  In person, the extent of the damage was even more impressive.  The Vidal Blanc vines were nearly completely infested.  This suggests that several generations have cycled through during this summer.  Vidal is a French-American hybrid grape.  Hybrids (ie. Traminette, Seyval Blanc, Chambourcinare increasing in popularity among eastern grape growers because they are often more tolerant of our weather conditions that European varietals (ie. Merlot, Chardonnay, Cabernet Sauvignon).  However, it appears that some of these hybrids are more susceptible to foliar phylloxera.  Because they are grown on phylloxera tolerant rootstock, it is unlikely that phylloxera are also damaging roots.

Infested Vidal vines. Photo: HJB

Leaves at the base of the canes had no live phylloxera present.  I started to find live phylloxera about half way up the canes, and the youngest leaves had females and eggs in the galls as well as few crawlers.  

Mature grape phylloxera female and eggs (indicated by red arrow) and crawler (blue arrow) on a young grape leaf.  Photo: HJB

Donn Johnson, University of Arkansas small fruit entomologist, has posted several other images of eggs, crawlers and adults here.  The leaves with active infestations were near the end of canes and likely to be removed during hedging (which was planned for the next few days after my visit to RayLen), and because of this, I was reluctant to recommend a pesticide application.  Instead, I suggested removing as many infested leaves as possible during hedging/leaf removal and destroying them.  They could then follow this up with a pesticide treatment if crawlers or open galls (see below) were still present.  

Open galls on young leaves.  The insects in these galls are susceptible to contact insecticides.  Photo: HJB

It seems likely that phylloxera will continue to be a problem in French-American hybird grapes, which I am still a fan of for their many other good qualities.  The strategy at RayLen and other infested vineyards should include early season scouting for first generation phylloxera--likely to be a few galls near the base of cane in spring.  Once crawlers of this first generation appear, foliar treatments should be applied (some of the materials available for phylloxera management are listed in this University of Arkansas fact sheet). Regular scouting for subsequent generations should be conducted throughout the summer followed by treatment as they appear.  Severe phylloxera infestations weaken vines and leave them more susceptible to winter injury.

Phylloxera infested cane.  Photo: HJB

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