|Abstract or Summary
- The alternate bearing cycle in the 'Barcelona' cultivar poses a
major problem to the filbert industry. This study was conducted to
alleviate this problem in one of two ways: by (1) increased floral
initiation in the "on" year, and (2) increased cluster set in the "off"
year. Growth regulators were selected on the basis of their
effectiveness when applied to other alternate bearing crops. These
growth regulators were then applied to 'Barcelona' trees at the times
corresponding to floral initiation and cluster set in this cultivar.
During April and May, trees were treated with two concentrations
(15 and 50ppm) of GA₃ to influence cluster set. The GA₃ applications
caused a large number of clusters to abscise in the season applied,
however, female flower production was quadrupled for the following
season. These results suggest that when applied to filbert trees in
the spring, GA₃ may have a hormonal effect on cluster abscission.
The first GA₃ application (April 20) significantly increased catkin
production, indicating that the initiation of the catkins was in progress
during this month. Gibberellic acid's influence on vegetative growth
was minimal, with no substantial increase in shoot length or node
number observed. Increased floral initiation is suggested to be the
outcome of hormonal and carbohydrate level changes rather than through
any dramatic change in vegetative growth. In the year following
treatment, yield increases were due to the greater number of flowers
initiated rather than an increase in percent cluster set.
Gibberellic acid (50ppm), TIBA (25ppm), and ethephon (500ppm)
were also applied to 'Barcelona1 filbert trees during the floral
initiation process (July-August). Hand-thinning of nut clusters was
also done during the initiation process. All of these treatments,
except GA₃, resulted in increased female flower clusters the following
spring. Gibberellic acid did not affect female flower initiation,
however, catkin drop was accelerated. The average number of nuts per
cluster, percent set, and yield were not affected by TIBA, ethephon,
or GA₃ sprays in the year applied. Increased yield in the following
year was attributed to the increased floral initiation brought about by
the TIBA, ethephon, and hand-thinning treatments. Yield was also
increased by GA₃ through greater percent set, and it is suggested the
latter may be linked to the catkin abscission. The carbohydrates that
would have been utilized in catkin production may have been made
available to the developing nut clusters and vegetative structures, and
may account for the resulting increase in yield.