Seeded grapes, particularly Emperor & Calmeria
Affects Emperor, particularly on resistant rootstocks, and sometimes older, own-rooted vines. Five to 30% of clusters may be discarded. Occasionally so severe that vineyard is removed. Affects own-rooted Calmerias; up to 20% of clusters may be culled. Both varieties are decreasing in importance.
After ripening begins, Emperor berries become flaccid and sunken. Some affected berries develop color; some remain white. The flaccid berries are usually interspersed with normal ones, but occasionally several berries at the tip of a lateral or at the cluster apex are affected.
With Calmeria, whole clusters may be involved. Sometimes the disorder is difficult to recognize. The clusters may be a slightly duller green but the berries must be touched to confirm the flaccid condition. The amount of fruit involved usually increases up to harvest.
The cause is unknown. With Emperor, 16 grams per acre of gibberellin applied about two weeks after fruit set when the berry diameters average 10-15 mm will reduce the shrivel by 50 to 70% compared to the untreated. Similar treatments are not tolerated by the Calmeria variety.