March/April 2024 - 8

the fruit to feed and in this process inoculate the fruit with
conidia that can be carried by them. Infection will start from
one or two fruit, grow through the peduncle, and move into
the cluster rachis to cause cluster blight. After reaching the
base of the rachis, the infection will move into the last year's
shoot to cause a distinct canker.
The blighted rachis and the cankers play a significant role
in the life cycle of the pathogen and the disease because
portions of these tissues are covered with pycnidia of the
pathogen surviving on to the trees. If a late rain in the season
occurs and temperatures are still above 68 °F, flower buds
which were set in June/July can get infected and become
blighted entirely or partially.
In addition to yearly yield losses due to blighted clusters,
blighted buds contribute to losses of the next year's crop.
Once the blighted shoots, clusters, and buds develop, it is
too late to control the disease. However, protecting the green
tissues from latent infections in the spring can control the
disease significantly. Sprays are done starting at bloom and
finish by the end of July; sprays in August and/or later are
not effective. If a grower has low pressure of the disease and
desires to do a fungicide application, the best timing would
be the first part of June.
Botryosphaeria canker and blight of walnut
A second disease that also causes blights and cankers is the
Botryosphaeria canker and blight of walnut. This disease has
many similarities with the pistachio panicle and shoot blight.
The blight phase of the walnut Bot disease results in the
blight of the fruit (it was the fruit cluster in the pistachio).
The disease starts as latent infection of green fruit in
the spring. Symptoms and disease progression will start
developing in the summer as the fruit starts maturing. The
blight from one fruit will move to one to two neighboring
fruit, which will also blight and then from the peduncle the
infection will move into the spur and from that spurinto the
shoot and cause a canker.
The result of this canker, and depending on how far the
canker will move, is the killing of the next season's flower
and vegetative buds. Therefore, the Bot of walnut will
blight part of the season's fruit and at the same time will
reduce yields of the subsequent season by killing the flower
and vegetative buds. Depending on the environmental
conditions and the extent of infection, the pathogen can
also enter from the blighted spur into last year's wood and
cause large cankers.
In walnuts, because the wood is softer than that of
pistachio, the entire surface of the cankered tissues
will be covered with pycnidia, which are the fruiting
structures of the Bot fungi. In walnut but not found
in pistachio, some of these species will also develop
pseudothecia in some areas of the canker along with
areas with numerous pycnidia. Pseudothecia contain sack
(asci) with eight ascospores each, which when there is
Buyers Guide'
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March/April 2024

Table of Contents for the Digital Edition of March/April 2024

Editor's Letter
The blight phase of Botryosphaeria diseases in nut crops of California
Tree nut outlook for 2024
From the top
Water stress
Buzz pollination
Hazelnut crop concerns
Almond Board of California
Ad Index
March/April 2024 - 1
March/April 2024 - 2
March/April 2024 - 3
March/April 2024 - Editor's Letter
March/April 2024 - 5
March/April 2024 - The blight phase of Botryosphaeria diseases in nut crops of California
March/April 2024 - 7
March/April 2024 - 8
March/April 2024 - 9
March/April 2024 - Tree nut outlook for 2024
March/April 2024 - 11
March/April 2024 - 12
March/April 2024 - 13
March/April 2024 - From the top
March/April 2024 - 15
March/April 2024 - 16
March/April 2024 - 17
March/April 2024 - Water stress
March/April 2024 - 19
March/April 2024 - Buzz pollination
March/April 2024 - 21
March/April 2024 - Hazelnut crop concerns
March/April 2024 - 23
March/April 2024 - Business
March/April 2024 - 25
March/April 2024 - Almond Board of California
March/April 2024 - Events
March/April 2024 - 28