Answer: These symptoms are typical of the work of a weevil called the grape cane girdler. Check inside the fallen shoots for tiny white legless larvae. If they are present, you have cane girdlers on your hands. Pick up all of the fallen shoots, and cut off damaged shoots that are still clinging to the vine, as they contain larvae or pupae of the pest. Squash, burn, or bury the shoots to kill the pests. Generally the damage is minimal and doesn't affect your crop because the pests tend to infest shoots beyond the grape clusters. Keep tall weeds cut from the area surrounding the vine. Inspect other shoots for evidence of the pest, and cut these from the vine. These precautions will keep the number of pests well within the tolerance of a vigorous grape vine.
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