March/April 2024 - 23

DISEASE
with the vulnerability of susceptible varieties to strains
prevalent in other regions, accentuates the need for vigilant
control measures.
" Our commercial varieties will die if planted in the MidAtlantic
and are not sprayed with fungicides for EFB because
there are other strains of EFB present there that overcome
the resistance gene that is in nearly all of the OSU resistant
hazelnut varieties, " Wiman said. " That is why we maintain
vigilance against another potential introduction of EFB from
the East and our state Dept of Ag has a control order against
importation of any hazelnut material from the East. "
Symptoms
" There is a 15-month latency period from the time a tree
is infected and when the symptoms can first be noticed, " he
said. " This makes it a very difficult disease to manage. By
the time an infection is noticed, there is a high chance there
is much more infection that is not yet showing symptoms. "
The first symptoms appear in the mid- to late-summer
one year after infection of young shoots in spring, as the
fungal infections in the branches expand and kill plant
tissues, Wiman explained.
He noted that this causes " flagging, " where the leaves of
the infected shoot die and turn brown, which is easy to see
when scouting otherwise green tree canopies.
" Later in the fall and winter after leaf drop, the dead
leaves from infected shoots or strikes may still cling to the
tree, " he said. " The time to really scout for infections is
winter when it is easier to see the symptoms of the disease
on the bark. Infected areas will show rows of stroma, which
are bumps that erupt through the bark and produce the
spores during periods of rainfall. "
Wiman said in the past, when new resistant hazelnut
varieties became infected with the legacy strain of EFB, " the
stroma would rarely form or would be incompletely formed,
and cankers from the disease were small. "
Typically, the tree wound response would appear around
cankers with evident callus tissue and the symptoms would
lessen over time as the resistance mechanism would defeat
the disease.
" Sometimes, if the main trunk became infected, the
tree would not improve and would need to be removed.
However, there was no spread of the disease from the
resistant varieties, " he said.
Wiman noted that the major difference with the
symptoms from the potentially new strain in the resistant
varieties is that the stroma or pustules are fully developed,
and " they fully erupt through the bark, indicating active
sporulation and there is active spread of the disease from
resistant varieties. The cankers are long, and the disease will
actively kill the tree. Essentially, these are the symptoms
of EFB on a susceptible variety, but many of the newer
hazelnut growers may not be familiar. "
He underscored the severity of the new strain, noting
its ability to cause symptoms as severe as strains from the
mid-Atlantic region. Moreover, the spread of the disease
to well-managed orchards downwind from the epicenter
highlighted the urgency of the situation. Despite ongoing
research, the genetic characterization of the new strain
remains elusive, leaving growers grappling with uncertainty.
Disease management
Wiman advised growers to adopt a proactive approach to
scouting and recommended consulting resources provided
by OSU for comprehensive management strategies.
Effective management of EFB involves a combination of
winter pruning and spring fungicide applications. While
chemical treatments have proven efficacy, biological
alternatives have yielded inconsistent results in trials.
Wiman underscored the importance of adhering to a
comprehensive fungicide program to mitigate the spread
of the disease effectively.
With more than 40 years of research, OSU understands
how to manage this disease successfully. But for growers,
Wiman said there is, unfortunately, an increased cost to
managing EFB.
Resources such as the Hazelnut Pest Management Guide and
the Eastern Filbert Blight Help Page maintained by OSU are
available to growers. Wiman noted that these resources have a
lot of information on management supported by research.
" We have no reason to believe that a potentially new
strain would not be manageable using our standard EFB
fungicide program. A lot of growers have asked about that.
Unfortunately, biological treatments have not provided
consistent results in disease management trials but copper
sprays do work as fungicides against the disease so organic
growers have at least one viable option, " he said. " Note
that single applications during the spring infection period
typically do not provide complete control, so the full
program, which can be four or more sprays depending
on the weather is recommended. "
Collaborative call to action
In the face of the evolving threat posed by the new
strain of EFB, collaboration and information sharing
are paramount. Growers are encouraged to report
suspected infections promptly to facilitate research and
containment efforts. Wiman and his colleagues at OSU
are actively soliciting reports of infections on resistant
varieties to gain insights into the behavior and spread of
the new strain.
The emergence of this new strain of EFB presents a
formidable challenge to hazelnut growers. With the stakes
high and uncertainties looming, collaboration between
researchers, growers and industry stakeholders is essential,
and will undoubtedly play a pivotal role in shaping the
industry's response to this emerging threat.
Growers can share information by emailing Nik Wiman
(nik.wiman@oregonstate.edu) or Jay Pscheidt, Extension
plant pathologist (jay.pscheidt@oregonstate.edu).
NATIONALNUTGROWER.COM 23
http://www.NATIONALNUTGROWER.COM

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
Business
Almond Board of California
Ad Index
Events
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
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