Answer: The symptoms you describe could be a result of environmental or cultural conditions, or could indicate some pest has been feeding on the leaves. If the leaves are well formed and do not have swellings, unusual growths or yellowish streaks, I'd chalk it up to environmental conditions and expect that subsequent leaves will be just fine. If, upon closer inspection, you find cast skins, fine webbing or tiny yellow spots, I'd say insects have visited and sucked the fluids from the tissues of the leaves, causing them to curl. The most commonly encountered sucking insects include spider mites, aphids, whitflies and grape leafhoppers. It's possible for these pests to feed and then leave the area which would account for your seeing the damage but not the pest. Why not take a wait and see attitude? If newer leaves look healthy, nothing needs to be done. If they begin curling, too, take a sample to your local Cooperative Extension office (909) 387-2171 for a positive diagnosis. Good luck with your grapevines!
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