University of California Cooperative Extension • Tulare County
Citrus Notes
Vol. 1, Issue 6
September 2004
Fall Citrus Meeting
Wednesday, October 20th
8:30 A.M. - 12:00
Agricultural Auditorium
4437 South Laspina Street, Tulare
8:30
Registration
9:00
IPM Demonstration in Tulare County
Neil O’Connell, UC Cooperative Extension, Tulare County
9:30
Frost Protection Strategy-When to Turn On/Off Wind Machines, Water
Dr. Rick Synder, UC Davis
10:00 What You Do In The Field Influences Fruit Quality
Dr. Mary Lu Arpaia, Kearney Agricultural Research & Extension Center
10:30 Break
10:45 Management of Citrus Nematode
Dr Mike McKenry, Kearney Agricultural Research & Extension Center
11:15 The Efficacy of Insecticides for Various Citrus Pests & The Current Status of Citrus Peelminer
Research
Dr. Beth Grafton Cardwell, Kearney Agricultural Research & Extension Center
Continuing education credit has been requested
4437B Laspina St, Tulare, CA 93274  Phone: 559/685-3303  Fax: 559/685-3319  Web Site: cetulare.ucdavis.edu
US Department of Agriculture, University of California, and Tulare County Cooperating
Dieback
Woolly Whitefly
Shoot dieback was seen throughout the county
beginning in July. Dieback was seen in Cara Cara
navels, Washington navel, Lane Late Navel, and
Valencias. Frequently much of the dieback was
located in the top of the tree or the south and west
quadrants of the tree. Gumming was generally
associated with the dieback. Leaves on affected
shoots dried and remained in place.
Infestations of this insect have been detected in
backyard citrus trees in the city of Bakersfield. This
pest produces copious amounts of honeydew, the
deposits of honeydew later being a site for sooty
mold fungus. Reductions in yield and fruit quality are
likely results of infestations of this insect. Wooly
whitefly was detected in Santa Barbara in 1979 and
in Ventura County in 1980, and then invaded
commercial citrus throughout Southern California,
including orchards in the Escondido, Pauma Valley
and Fallbrook areas. Three species of imported
parasites had significant effect on infestations of the
whitefly and were able to establish biological control
in some locations. How well these same parasites
would do in the climate of the valley and how
effective they would be will have to be established.
No infestations in commercial citrus in Kern County
have been detected at this point.
Sudden wilting and dying back of leaves and small
branches has been reported for many years in
California citrus. Gumming has been reported with
the dieback. It generally occurs in late summer
following hot dry conditions. No pathogen has been
associated with the condition. It might be confused
with citrus blast; however blast is associated with
cool moist conditions and is the result of the activity
of the organism Pseudomonas syringae. Dieback in
the spring in new flush growth with warming air
temperature is known as Tulare County dieback and
is not the result of a pathogen. The dieback in a
shoot following hot dry conditions generally is self
limiting and the dieback stops at the origin of the
shoot; it does not generally progress into larger
branches. The condition is thought to result from a
temporary water deficit in the tree. As weather
conditions moderate the potential for this condition
should decline.
Splitting in Navel Oranges
September is typically the period when reports of
splitting in navel oranges increases. The split begins
at the navel where the tissue is thinner and often a
check or a very small rupture of the tissue has
occurred. The split progresses vertically from this
point. Frequently the earliest of the split fruit will
color prematurely and on close inspection will
exhibit a black discoloration that progresses from
the navel into the core of the fruit. This condition is
referred to as black heart which is the result of a
pathogen, Alternaria citri. Frequently drosophila
fruit flies are attracted to the area. Another insect,
navel orangeworm, may lay its eggs on the affected
tissue, with larvae of the insect found later infesting
the navel end of the fruit.
Texas Citrus Mite
Last fall this mite was detected in high numbers in
some orchards in Kern County, in the Edison,
General Beale and Belridge areas. Reportedly, it had
been in the Belridge area at very low numbers for
two years prior to that. It was first detected in
Coachella Valley citrus in 1990 and in the Filmore
region of Ventura County in 2000 according to David
Haviland, Cooperative Extension entomologist.
Populations often reach peak numbers in the fall
when significant leaf drop may occur as well as
dieback. Warm fall conditions, deficit irrigation and
dust influenced some of the worst outbreaks of the
mite in Kern County. Numbers of mites have been
significantly lower this spring and summer in the
infested properties. Chemical treatments were applied
in a significant number of the infested orchards
where leaf drop was occurring and were effective if
applied before cool weather set in. Infestations of a
new pest sometimes exhibit a rapid increase in
numbers as this mite did, with a subsequent dramatic
decline in numbers. Infested properties will be
closely monitored for a resurgence of the mite this
fall.
Citrus Notes • October • Page 2
Weed Management
Recently enacted regulations regarding use of
certain preemergence herbicides in citrus within a
groundwater protection area (gpa) require certain
cultural procedures for a restricted material permit
for application of the herbicide(s). For most citrus
locations within the county in a gpa this
requirement involves incorporation of the herbicide
by water or mechanical means. A substitute for the
use of the restricted material for weed management
would be the use of a postemergence material such
as glyphosate. In order to minimize weed growth
during the winter, the postemergence material
would have to be applied as late as possible before
sustained rainfall prohibits entry or, if the ground
allows it, application during the winter depending
on weed growth. The amount of fall/winter weed
growth will relate to the resident seed load present
in the orchard which will vary depending upon the
number of years of fall preemergence herbicide
applications. For young orchards the load would be
expected to be considerably greater than for a
mature orchard.
Hypoderma Decline of Lemons
This problem was first observed in April of 2000 in
the Terra Bella area in a mature block of lemons.
Symptoms included shoot dieback with leaves
remaining in place with gum formation. In some
cases cracking of bark with gumming was seen on
large branches even scaffolds, and in worst cases,
cracking and gumming on the trunk down to the
bud union. The organism was identified to be a
wood rotting organism, a species not previously
reported to be a problem in citrus. Additional blocks
of lemons were detected in other parts of the county.
The problem appears to have been restricted to
lemons and to mature trees. The same decline was
detected in Ventura and Riverside counties shortly
after the identification in Tulare County. In some
cases growers had been unsuccessfully treating the
affected trees thinking it was gummosis caused by
the Phytophthora fungus. Screening of potential
chemicals for efficacy in controlling Hypoderma
have been of very limited success to this point.
Management procedures that are thought to be of
value are pruning out affected areas in late spring or
early summer after the period of rain and fog when
moisture is not present for reinfection of cut surfaces.
Prunings should not be left in the orchard but
removed and burned. The organism is capable of
continuing to be active in pruned material left in the
orchard. Pruning cuts should be made beyond the
visibly affected areas into healthy tissue. Infected
branches when cut show a staining of the wood
where the organism has invaded the area. The fungus
is thought to gain entrance through cracks in the bark
perhaps as a result of freeze damage or sunburn but
the means of entry and rate of spread in the tree has
not been determined. Additional research is ongoing
to investigate the biology of the organism and to
further investigate the efficacy of chemicals and the
benefit of cultural operations. Surveying for
additional lemon orchards in Tulare and Ventura
counties that might be affected by the fungus is
continuing.
Citrus Notes • October • Page 3
Neil O’Connell
Farm Advisor
University of California
Cooperative Extension
Tulare County
4437B S Laspina St
Tulare, CA 93274-9537
Nonprofit Org
US Postage Paid
Visalia, CA 93277
Permit No. 240
Citrus Notes
FALL CITRUS MEETING
Wednesday, October 20, 2004
Neil O’Connell
Farm Advisor
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