Progressive Crop Consultant July/August 2019

Neofabraea leaf and
twig lesions were first
detected in California
super-high-density oil olive
orchards in 2016. Since then the
disease was found in Glenn, San
Joaquin, and Stanislaus Counties.
Causal agents of this new disease of
olive were identified as Neofabraea
kienholzii and Phlyctema vagabunda
(syn: Neofabraea vagabunda).
Phlyctema vagabunda is known in
Spain as the causal agent responsible
for the olive leprosy or lepra
fruit rot, causing fruit malformation
as well as leaf lesion and twig
canker. This disease is of increasing
concern in Spain, Portugal and
Italy. Dr. Trouillas at UC Davis has
outlined the disease epidemiology,
disease cycle, and determined best
spray timings and materials that
will help to control this disease.
Disease Symptoms
Neofabraea leaf and twig lesions
are primarily associated with
wounds, such as those sustained
during mechanical harvest. Leaf
lesions are circular to elongate,
necrotic, approximately 0.5 to 1cm
in diameter and normally do not
number more than one lesion per
leaf (Figure 1, see page 40). Twig
lesions are reddish-brown in color
mainly affecting the bark tissues
(Figure 2, see page 42). The disease
may occasionally cause fruit rot
near the time of harvest. In severely
infected orchards, defoliation and
fruit loss may occur.
Disease Biology
Two fungal pathogens have been
identified using morphological and
molecular techniques: Neofabraea
kienholzii and Phlyctema
vagabunda (syn: Neofabraea
vagabunda). These pathogens have
been associated with bull’s eye rot
and canker of apples and pears in
the Pacific Northwest.
In olive, the disease has been
detected primarily from superhigh-density
oil olive orchards in
Glenn, San Joaquin and Stanislaus
counties. The cultivar ‘Arbosana’
is the most susceptible but the
disease has also been isolated on
occasion from ‘Arbequina’ olives in
the Central Valley. It was not found
in the Koroneiki cultivar. Previous
reports of the disease in California olive
have included fruit spots in ‘Cortina’,
‘Picholine’ and ‘Frantoio’ varieties in
Sonoma county. To date, table olive
varieties (Manzanillo and Sevillano)
in the Central Valley have not tested
positive for Neofabraea leaf and twig
lesions.
Infection occurs at the site of plant
injuries. In super-high-density oil
olives, these wounds are typically
associated with damage caused by
mechanical harvesters but may also
include abrasion sites where leaves or
twigs rub against each other. Following
mechanical harvest, rain events allow
for fungal inoculum to be released in
the air, leading to infection of the fresh
wound sites. Leaf spot symptoms are
most visible in March, with defoliation
occurring in April and May. Infected
leaves and fruits act as inoculum
sources for infection the following year.
Disease Management
Field trials have been conducted for
three consecutive years in the highly
Keep Birds Out
GUARANTEED
“I’ve used Bird Gard
for years to protect my
growers’ crops and keep
birds from damaging
the irrigation.
Bird Gard works, what
more can I say?”
Tim Peltzer
Peltzer Farm Management
Terra Bella, CA
Continued on Page 42
Bird Gard is the ONLY bird control with a
1-YEAR UNCONDITIONAL MONEY-BACK GUARANTEE
888-332-2328 www.BirdGard.com
Guaranteed Bird Control for over 30 Years!
July /August 2019
www.progressivecrop.com
41