Title: Citrus industry update
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Title: Citrus industry update
Series Title: Citrus industry update
Physical Description: Serial
Language: English
Creator: Institute of Food and Agricultural Sciences, University of Florida
Publisher: Institute of Food and Agricultural Sciences
Publication Date: June/July 2008
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Bibliographic ID: UF00086519
Volume ID: VID00006
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.

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IWF^ I UNIVERSITY of
UF FLORIDA


I e JU N /J UL Y 0 0 e :


Citrus Industry Update


Working
To Keep You
Informed


Published by the University of Florida, Institute of Food and Agricultural Sciences, with the mission
of keeping the Florida Citrus Industry informed of current research concerning canker and greening.


GREENING TRANSMISSION
AND SPREAD
Effects of Systemic Insecticides on Pathogen
Transmission by HLB Infected Psyllids
Work continues to determine whether psyllids
feeding on an insecticide treated plant will die
before successfully transmitting the greening
pathogen. To date, more than 200 plants, half
treated with soil applied imidacloprid and half
untreated, have been challenged with HLB infected
psyllids in transmission trials. In these
experiments, approximately 10 HLB infected
psyllids are placed onto each plant and left to feed
until death (on imidacloprid treated plants) or for
72 hours on untreated plants. Once the psyllids are
removed from the plants, psyllids are analyzed
individually using PCR to determine how many
psyllids were HLB positive. Plants are then held in a
secure quarantine greenhouse facility for periodic
testing using PCR to determine if imidacloprid was
able to prevent transmission (or at least reduce
infection rates) compared to the untreated plants.
So far, we have observed suspicious symptoms on
some of the plants, but all PCR run thus far have
given negative results. Based on our transmission
studies conducted to date, it takes about eight
months from the time that an infected psyllid
feeds on a plant before that plant tests PCR
positive for HLB. Thus, not enough time has yet
passed since these experiments were initiated for
us to be successful in identifying HLB positive
plants. We expect to be able to detect positive
plants within the next couple of months. (Michael
Rogers, mrgrs@ufl.edu; Ron Brlansky,
rhby@ufl.edu)
Movement of Asian Citrus Psyllid
Within and Between Groves
Studies continue on psyllid movement following
the development of an effective protein marker,
psyllids are now being marked in the field and their
movement is being tracked by recapturing marked
psyllids with sticky traps and analyzing them with
an ELISA method. The initial results suggest that


psyllid movement between adjacent groves
occurs frequently.
We have found that psyllids can move back and
forth between abandoned and managed groves
separated by 50-100 yards within two days.
Although the underlying reasons for this
dispersal are not yet understood, the data
provide direct proof that psyllid-infested groves
(managed or abandoned) likely serve as a
source of infestation for nearby uninfested
groves. (Lukasz Stelinski, stelinski@ufl.edu)
Seasonality of Psyllid Transmission of the Citrus
Greening Pathogen
Work by post-doctoral associate Dr. Tim Ebert
(CREC) continues to assess the seasonal
variation in Asian Citrus Psyllid acquisition rates
of HLB (Greening disease). Ebert is currently
working in five groves in Polk, two groves in
Highlands, and one in Desoto counties.
Collections of wild psyllids are being made to
estimate the HLB infection rates in the psyllid
populations at each location. Healthy (not
infected with HLB) psyllids are also being caged
on healthy and HLB positive citrus shoots and
later tested to determine if those psyllids were
able to acquire the greening pathogen and if the
rate of acquisition changes throughout the year.
Since the beginning of this year, more than
7,900 psyllids have been collected from these
grove sites. An additional 6,384 psyllids have
also been caged on trees. From the results
obtained thus far, we estimate that the
infection rate in the wild psyllid population has
never exceeded 1 percent at these locations.
Acquisition of HLB by psyllids caged on HLB
infected trees has also been lower than the
average 30 percent rate we see under
laboratory conditions. (Michael Rogers,
mrgrs@ufl.edu; Ron Brlansky, rhbv@ufl.edu)

2008 Citrus Research & Education Center, University of Florida,
Institute of Food and Agricultural Sciences, 700 Experiment Station
Road, Lake Alfred, FL, 33850, phone: 863-956-1151.







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HORTICULTURAL PRACTICES FOR DEALING WITH
GREENING
The primary horticultural objective to deal with
greening is to shorten the time required to bring
trees into production and to control summer flush
growth to limit psyllid feeding opportunities. A
number of projects being developed by IFAS
faculty will investigate intensive management/
fertigation practices (open hydroponics, OHS) as
well as plant growth regulators, novel methods to
impose drought stress and modifying hedging
practices to control shoot growth. Specific projects
being developed are: 1. An OHS planting at CREC is
being used to test the response of mature Hamlins
to the introduction of pulse drip irrigation and
intensive hydroponics nutrition (13 nutrient
elements). 2. A block with an established perennial
peanut cover crop at CREC is being converted to
drip irrigation to study the effects of a limited
wetted zone combined with the consumptive
water use of the peanut to reduce vegetative
growth on both existing and newly planted trees.
3. A 15 acre citrus block with Gapway Groves is
being developed for an open hydroponics trial
using two rootstocks, three trees spacings, and
various fertigation comparisons. 3. A $500,000
proposal has been submitted to the USDA-CSREES
National Integrated Water Quality Program
entitled, "Water Conservation Using Intensively
Managed Citrus Fertigation to Maximize Water Use
Efficiency" to study the complete open
hydroponics system under Florida conditions.
4. Greenhouse trials are underway to assess the
response of trees to different timings of pulsed
irrigation to develop preliminary data for use in
setting up field trials. 5. Greenhouse and field
studies are being started to determine the
interactions between drought stress and plant
growth regulators in controlling shoot growth. 6. A
heading trial began in September in cooperation
with Gapway Groves to assess the timing of
hedging on tree growth responses. Plans call for
plant growth regulators to be incorporated into
that trial this season to further evaluate
mechanisms for controlling tree growth. (Arnold
Schumann, schumaw@ufl.edu)


GREENING DIAGNOSTICS
A GLIMPSE OF CHINA HUANGLONGBING IN
SOUTHERN CHINA
(Photos referred to in this article appear on page 4.)
Citrus Huanglongbing (HLB) is widely spread and
extremely devastating in several southern
provinces of China, including Guangdong,
Guangxi, Fujian, and Jiangxi. However, as Todd
Holtsberry said in at the Greening Summit in
Avon Park, "It's (greening) been in China a
thousand years, and they're still producing
citrus." Although that is true, citrus fruit
production in the southern regions still accounts
for a substantial proportion of the total in China.

Last month, collaborating with Dr. Ganjun Yi,
the Director of Guangdong Fruit Research
Institute (GFRI), Guangdong Provincial Academy
of Agricultural Sciences, we visited citrus groves
in the HLB regions in Guangdong and Guangxi
Provinces, and gathered first-hand information
on the seriousness of the problem and practical
management. Additionally, we defined ways to
continue the collaboration in research areas of
our mutual interest.

In Guangdong Province, infected and dead trees
were found in almost every grove, and many
small farms were abandoned. Season-long high
temperature and humidity make it impossible to
prevent HLB spread and infection through killing
the transmission vectors alone. However,
controlling psyllids can greatly reduce the
transmission incidence and help maintain
profitable production. Other practices for
survival that are widely adopted include: 1) Use
of localized citrus varieties; they may have
better adaptability and longer production life.
Two local varieties, called Nianju and Shatangju,
now account for about 90 percent of the total
citrus production in Guangdong Province. High
financial returns for these varieties in the
market allow production to continue, even in
the face of significant tree losses. 2) Use of all
cultural methods to promote early production;
for example, girdling is widely and intensively
used in many groves (Photo 1). Cheaper labor in
the countryside also provides an economic
advantage, though labor is becoming more
difficult to find. 3) Use of dwarfing and high-


Citrus Industry Update
Community Service Bulletin






lJ I UNIVERSITY of
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'11-AS


density plantation; almost all groves are very
dense, with small tree size, particularly in those
small farms where no mechanical equipment is
used. 4) Use of covers to extend the harvest
season (Photo 2); this practice is starting in some
groves, to maintain fruits on trees until next
March-April when the price will be 5-10 times
higher than the normal harvest season. The cover
may also reduce the likelihood of HLB
transmission.
Compared to most groves in Guangdong, Guangxi
Province groves showed something different.
Some poorly managed groves with highly
susceptible sweet orange varieties looked much
worse. Other well-managed groves looked
perfectly healthy (Photo 3); it was hard to believe
that many groves, just 30 miles away, were
completely wiped out by the disease (Photo 4).
These groves were in Fuchuan County, Hezhou
(City) District. The difference in these groves was
strict management from the very beginning! They
have their own pathogen-free foundation and
increase trees in locked greenhouses. All nursery
trees are propagated and maintained in screen
houses (Photo 5). Vector control spray is constant
and coordinated. In the meantime, the vector is
monitored to provide feedback on the
effectiveness of control measures.
Another purpose of the field survey was to find
citrus survivors or escapes in severely infected
or abandoned groves. Some trees were identified
in abandoned groves in Guangdong and Guangxi,
including one in Photo 6. They are now under
investigation in their facility, as a component of
our collaborative agreement with GFRI. (Chunxian
Chen, cxchen@ufl.edu; Fred Gmitter,
fgmitter@ufl.edu)

PSYLLID MANAGEMENT
The Influence of Post-treatment Temperature on
the Toxicity of Insecticides against the Asian Citrus
Psyllid
Effective psyllid and disease management in
Florida requires insecticide applications
throughout the entire season over a range of
temperature and environmental conditions.
Temperature is known to affect the toxicity of
insecticides and thus their efficacy. Quantifying the


Citrus Industry Update
Community Service Bulletin


effect of temperature on the toxicity of
recommended and new insecticides against the
psyllid should allow for informed selection of an
insecticide based on prevailing seasonal
conditions. Dr. Dhana Raj Boina, a trained insect
toxicologist, working with Dr. Salyani and
Dr. Stelinski at CREC, has been investigating the
influence of post-treatment temperature on
toxicity of several insecticides used for psyllid
control. Dr. Boina's investigations show that the
toxicities of organophosphate, carbamate, and
avermectin insecticides against the psyllid
increase with increasing temperature while the
toxicity of synthetic pyrethroids decreases with
increasing temperature. In contrast,
neonicotinoids show a mixed temperature-
dependent response with an initial decrease in
toxicity between 62 to 80F followed by a
subsequent increase in toxicity between 80 and
98F. This data suggests that synthetic
pyrethroids may be more effective during the
cooler winter months in Florida, while
organophosphate, carbamate, and avermectin
insecticides may be more effective during the
warmer spring and summer months. Since the
neonicotinoid imidacloprid was found to be
more toxic at both of the extreme
temperatures, it can be rotated with
pyrethroids at low field temperatures and with
organophosphate, carbamate, or avermectin
insecticides at high field temperatures while still
maintaining optimal temperature-dependent
toxicity. (Lukasz Stelinski, stelinski@ufl.edu)

EVENT UPDATE
GREENING SUMMIT PRESENTATIONS
The Greening Summit, held in Avon Park at the
South Florida Community College on April 8,
was one of the largest citrus programs in years
with more than 350 growers, managers and
allied industry representatives attending the
day-long program. In an effort to allow
individuals to view or review the presentations,
all PowerPoint presentations the speakers
provided are now available on the web at
http:// citrusagents.ifas.ufl.edu The recorded
video presentations are also posted to the same
web site. (Steve Futch, shf@crec.ifas.ufL.edu)


e JU E/ U Y 2 0:






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photo 1


e JU E/J LY 208:


photo 2


photo 4


photo 3


,1


photo 5


photo 6


1. Girdling many times to enhance early and heavy fruiting; 2. Covering the grove to extend the harvest season three to five
months; 3. Aggressive management to maintain the tree health and production in a severe HLB region; 4. A grove, about 30 miles
away from the one in Photo 3, devastated by HLB; 5. Pathogen-free nursery trees propagated inside screen houses with good
irrigation and fertilization system; 6. A healthy-looking survivor standing alone in an abandoned ten-year-old grove where most of
the trees were already dead, and all remaining trees were showing obvious HLB symptoms.
Citrus Industry Update
Community Service Bulletin 4


1. ..,




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