Foliar B sprays (500 ppm) applied in the fall to ‘Italian’ prune (Prunus domestica L.) trees had no effect on fruit set in a warm spring when set was high (average, 12.2%), but increased fruit set by 32% in a cool spring when set was low (3.2%). Fall B sprays increased flower B levels and decreased pistil length, but had no effect on the rate of pollen tube growth through styles in the cool spring. Calcium sprays (0.5 m) applied in the fall prior to the cool spring did not affect fruit set, pistil length, pollen tube growth or flower Ca or B levels. Flowers on cut branches forced indoors accumulated as much B as those on intact trees, indicating that flowers are supplied B from reserves in nearby branches. Simulated rain did not leach B from flower buds readily. Flowers blooming on excised branches in high relative humidity (86%) contained 13% less B per flower than flowers in low humidity (29%). The amount of set and B concentrations in flowers in a given year may influence the response to fall applied B.
Former Graduate Student. Present address: Dept. of Hort., Michigan State Univ., East Lansing, MI 48824.
Received for publication 19 July 1984. Technical paper No. 7241 of the Oregon Agr. Expt. Sta. Part of the PhD Thesis of the senior author. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper therefore must be hereby marked advertisement solely to indicate this fact.