Many galls of various shapes occur on grapevines as a result of attack by small flies (gall midges). Galls can occur on leaves, tendrils and blossom buds. Numerous species of gall midges attack grape. Galls are formed by larvae of small cecidomyiid flies, which lay their eggs into the leaf. There may be one to three generations per year. The life cycle begins with eggs laid within the unfolding buds or shoot tips. Orange, maggotlike larvae hatch from these eggs and enter the vine tissue. As the larvae feed, galls form around them.
Infestations are generally spotty, both within vineyards and within infested vines, and they rarely cause significant economic damage.
No practical control for these galls is known, though removing the galls by hand and destroying them would reduce future populations.
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