THOMPSON SEEDLESS GRAPES must bethinned to allow production of loose clusters of well-developed berries. In recent years, the usual shatter-stage thinning has become a major labor-consuming operation for the grower. Hand thinning during the prebloom period, while foliage is light, clusters are small, and shoots are 12 to 16 inches long, would be economically desirable but has not been practical because of the increase in berry set, resulting in tight clusters.

Merck and Company and Abbott Laboratories contributed financial assistance for this research.