Seasonal variations in the characteristics of raspberry fruit drop

Several berry characteristics relating to raspberry (Rubus idaeus L. ’Willamette’) fruit drop were measured during the 1971, 1972, and 1973 harvest periods. These characteristics included fruit removal force, peduncle strength, berry weight, berry ripeness, and receptacle and peduncle dimensions. All of the characteristics exhibited large fluctuations during the harvest periods. Fruit removal force and peduncle strength were particularly variable; during the 1972 harvest period each of these characteristics decreased to less than one-fifth of its original value. The only characteristics that showed net increases during the harvest period were peduncle diameter and average berry ripeness. Among the characteristics surveyed, peduncle strength was correlated with berry weight and peduncle length, and was inversely correlated with peduncle diameter. Decreases in fruit removal force were correlated with increased berry ripeness and decreased receptacle dimensions. These results may assist in the improvement of the design or use of mechanical raspberry harvesters.