Not phylloxera. Phylloxera on the leaf has a more gall like appearance, and no "fuzzy" underside.
As already stated, this is a vine mite. It causes no damage to the grapes. But if you have a large infection it can cause enough leaf damage that it can starve the vine and affect the crop. But that rarely occurs. Sulfur sprays in the spring and a regime of integrated pest management can normally control this mite without much effort.
Some may even think this pest is downy mildew, due to the white "fuzzy" looking underside early in the season (late in the season, they turn brown), but it is not.
It has been cool and raining the past few days. Good conditions for downy mildew. Despite the cooler climate we live in here, and the regular rains we have, this fungal disease is surprisingly unco…
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