Pistillate Flower Abscission (pfa)

PFA was not different with shaded vs. exposed limbs of the same trees nor between shaded interior trees and outside ones with high light exposure. Tehama trees expressed lower PFA than adjacent Serre PFA of Tehama was also low at a site where Serr trees (removed 1982) had very high drop the previous three years. Fruitfulness of all monitored limbs in 1982 ranged from 6 to 97% and the earlier conclusion that PFA is not related to degree of fruitfulness was substantiated. In a common planting PFA of Serr was low and only slightly greater than with Sunland. Chandler and Howard. This suggests that PFA for the new U. C. varieties could be high in a location where this problem may be serious. Comparison of the same limbs monitored in 1981 and 1982 did not support the contention that PFA was less severe in 1982. Tree age in itself does not appear related to PFA. All measurements and observations in 1982 support the contention that PFA is related to planting site. OBJECTIVES: To continue monitoring of PFA of walnut to characterize its occurrence. Determination of fruitfulness of spurs was a secondary consideration. To conduct limited experiments to eliminate or discover causal influences or to indicate directions for future investigation.