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Angular Leaf Spot and Its Control Jim Mertely and
Xanthomonasfragariae, the bacterium that causes
angular leaf spot, is present in many west central Florida
production fields. This season's El Nino weather pattern has
apparently contributed to its development and spread. X.
fragariae multiplies prolifically in the small angular spots it
produces on diseased leaves. The bacterium oozes out of the
spots on the underside of the leaf as a viscous secretion.
Development of the pathogen is favored by mild humid days
(65-70 F) and cold nights with near-freezing temperatures,
while spread is facilitated by rainfall, overhead irrigation,
and harvest operations. Serious losses may occur during
epidemics when fruit caps calycess) are spotted or dry up in
systemically infected plants.
angular leaf spot
Angular leaf spot is ideally controlled by the use of
healthy transplants to exclude the bacterium from newly -
planted fields. Most epidemics are thought to originate from
infected planting materials because X. fragariae is restricted
to strawberry, and does not persist well in annual strawberry
if crop residues are disposed of properly. Control measures
are limited once the disease appears in the field. Our current
control recommendations are listed below:
A. Avoid harvesting and moving equipment through
the field when the plants are wet.
B. Harvest fields showing the least amount of
symptoms first; move progressively to the field
showing the most symptoms.
C. Monitor weather conditions closely, and use
sprinkler irrigation only when freeze protection is
D. Use copper-based bactericides judiciously. While
these products should suppress the disease, they
may also reduce yields if overused. The best
practice might be to spray only if lesions start to
appear on fruit calyces. Thorough coverage is
necessary since most inoculum is produced and
spread from the underside of the leaf.
More details about angular leaf spot can be found
on our website at http://strawberry.ifas.ufl.edu. Click on
the plant pathology button at the top of the home page, and
see information and photos found under "Plant Pathology
Fact Sheets" and "Digital Library of Diseases". Additional
information is available on the internet from universities in
other strawberry-growing states, e.g.,
Aphids in Strawberry -Jim Price
This season aphids are persisting in west central
Florida strawberries through December and the problem
merits attention. There are usually two aphids that are
commonly found on Florida strawberry, the strawberry
aphid and the melon aphid (also called the cotton aphid).
The two appear similar in the field and usually are
managed alike. Aphids on strawberry are tiny green to
dark blue-green insects that easily can be encircled by an
"o" on a printed page. Only a few aphids have wings, but
all have a pair of cornicles, "exhaust pipes", one on each
side of the rear end, which should be used as a diagnostic
aid in the field.
Almost all of the aphids found in strawberry are
females that can give live birth to females that will bear
young in a few days. That rapid reproduction rate leads to
their pest status on strawberry. The presence of aphids,
their fragile, white, cast skins and sugary excretions on
fruit are objectionable to consumers and reduce quality.
Too many aphids sucking plant juices can devitalize the
plant and may reduce yields. Accordingly, attention needs
to be directed toward aphids and remedial measures
applied as necessary.
In our environment there are several parasites and
predators of aphids that always will eliminate aphids as a
problem, but sometimes not before economic damage has
occurred. Hover (syrphid) fly larvae, lacewing adults and
larvae, several lady beetle adults and larvae, midge larvae,
and some other insects eat many aphids during their
development and contribute greatly to aphid control.
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However, it is the activity of a very tiny,
mosquito-looking wasp that parasitizes aphids and ensures
the end of aphid problems here. Parasitized aphids
become brown and slightly enlarged, reminiscent of a
brown paper sac. Eventually the parasitized, "paper sac"
aphids have a young female parasite cut a round hole in
their upper-rears. The parasites then emerge to parasitize
other aphids. Harsh, broad-spectrum insecticides can kill
these predators and parasites and eliminate this effective
Parasitized, "paper sac" aphid compared to a
Drs. Dan Cantliffe, Silvia Rondon, and Jim Price
of the University of Florida are working to develop plans
to use insectary -reared predators practically and
economically in concert with naturally occurring agents in
strawberry for aphid control. Presently, however, growers
wishing to reduce aphids before naturally occurring
predators and parasites have done so must rely on
insecticides. Fortunately, several exist and some may
require only one application for satisfactory control.
Among the products registered in Florida and practical for
use in a winter annual hill cultural system are: Diazinon,
malathion, methomyl, naled, azadirachtin, Beauveria
bassiana, bifenthrin, endosulfan, oils (read phytotoxicity
precautions on product labels), and soap.
Careful attention to conserving naturally
occurring parasites and predators and applying appropriate
insecticides only as needed can eliminate economic losses
to aphids and enhance the reputation of Florida strawberry.
You may obtain more information regarding this subject at
Causes of Misshapen Fruit in Strawberry Craig
High numbers of misshapen fruit in a field lower harvest
efficiency and marketable yield. There are many potential
causes of misshapen fruit, but those listed below appear to
be the most common:
Cultivar. Differences in fertility (i.e. the viability
of male [pollen] and female flower parts) among
cultivars have been documented. Breeders are
currently striving to develop cultivars that produce
symmetrically shaped fruit under a range of
Fruit position. Primary fruit (king berries)
generally have a greater tendency to be malformed
than secondary and tertiary fruit. This may be due to
lower male fertility in primary flowers, compared to
secondary and tertiary flowers.
* Weather. Pollination may be poor during extended
periods of low light intensity (e.g., when there are
several days of heavy cloud cover during December
or January) or during cool, wet weather. Freezing
weather may also result in misshapen fruit. In west
central Florida, strawberry flowers will be damaged
when the temperature of the flower surface is about
30 F (-1.1 C). A period of very warm weather
followed by a freeze may raise the freeze damage
threshold to near freezing, and, conversely, a period
of cold weather can lower the threshold. The most
likely portion of the flower to be damaged is the tip.
As the fruit develops, the damaged tip becomes a
sunken area surrounded by normal tissue. Large fruit
may split. Cultivars are known to vary in their
susceptibility to this type of damage. Earl Albregts
and Charlie Howard, in a study conducted at the
Dover center in the early 1980s, found that 'Dover',
a cultivar that has a dense canopy which conceals
most of its flowers and many of its fruit, was less
susceptible to freeze damage than 'Tufts', a cultivar
with a more open canopy (Albregts and Howard,
* Pesticides. The application of pesticides to plants
may, under some circumstances, adversely affect the
plant, flowers, and fruit. Captan applied at a high
concentration (2000 ppm) has been shown to inhibit
pollen germination (Eaton and Chen, 1969). The
application of certain insecticides can reduce the
population of insect pollinators, which in turn may
result in more misshapen fruit.
* Nutrient deficiency or excess. Boron deficiency
(leaf concentration less than 25 ppm) can result in
fruit malformation, while excessive nitrogen
applications have been shown to result in an increase
of misshapen fruit (Albregts and Howard, 1982).
Albregts, E.E. and C.M. Howard. 1982. Effect of fertilizer rate
on number of malformed strawberry fruit. Proc. Fla. State
Hort. Soc. 95:323-324.
Albregts, E.E. and C.M. Howard. 1985. Cycling irrigation for
freeze protection during a radiation freeze. Soil and Crop Sci.
Soc. Fla. Proc. 45:125-128.
Eaton, G.W. and L.I. Chen. 1969. The effect of captain on
strawberry pollen germination. J. Amer. Soc. Hort. Sci.
Berry Times 2
Foliar Fertilization of Strawberry John R. Duval
When it has been determined through foliar tissue
analysis that a plant is deficient in a micro-nutrient (iron,
zinc, copper, manganese, magnesium, boron) it is possible
to alleviate symptoms quickly with a foliar spray. This
practice should only be used as an 'emergency' method of
fertilization. Leaves are not designed for nutrient uptake.
The leaf surface is covered with a waxy cuticle which
minimizes the absorption of nutrients. The longer the leaf
stays wet (from the nutrient spray) the more effective the
application is in terms of nutrient uptake. Therefore,
growers should consider applying nutrient sprays late in
the afternoon when the sun is setting and temperatures are
dropping. The addition of a surfactant will also improve
the effectiveness of foliar fertilization. However
organosilicate surfactants should not be used due the
possibility of bur and promotion of bacterial diseases. To
avoid reducing the effectiveness of pesticides, nutrient
sprays should not be tank mixed with other chemicals
unless it is specifically stated on the label that it is safe to
do so. The crops requirement for micro-elements may be
met with only one or two nutrient sprays correctly timed
and applied. Foliar fertilization products are available
from most fertilizer dealers. Purchase a product that
contains only the nutrient you are trying to supply.
Supplying excess amounts of unneeded micro-nutrients
can lead to toxicities in the plant and there is no way to
remove excess nutrients from a plant. After cropping, soil
testing and the addition of micro-nutrients to the soil can
help eliminate future problems and reduce the need for
Strawberry Flavor Kurt Schulbach, Postdoctoral
researcher, Food Science and Human Nutrition
Dept., Univ. of Florida
Consumers are initially drawn to strawberries for
their attractive shape and color, but it is the sweetness and
flavor that keeps them coming back for more. Strawberry
flavor is not a single flavor but a complex blend of many
aromatic compounds. The unique taste and aroma of
strawberries has been widely studied by flavor scientists
since the 1930s. Hundreds of compounds with aroma have
been identified in strawberry, none of which smell much
like a strawberry! For example, strawberries contain a
compound called linalool which smells like lemon
blossoms, another called gamma -decalactone that has an
odor of peaches, one called Furaneol which smells just like
cotton candy, and another compound called ethyl butyrate
which is reminiscent of Juicy Fruit gum. All these
compounds and many others combine together to create
the unique aroma of strawberry.
While we know a lot about the identity of the
compounds in strawberry, there is still a lot more to be
learned about which compounds are the most important, or
which comp ounds make one strawberry variety preferred
over another. Recently, we have conducted taste panels in
order to describe the flavor of some strawberry varieties
Strawberries... one of the world's most popular fruit
and compare these sensory attributes to a chemical
analysis of the fruit. Comparing fruit flavor with chemical
composition provides some interesting information. For
example, we have found that the compound gamma-
decalactone seems to enhance the fruity flavor in Sweet
Charlie, but this important compound is not found in
Camarosa. Another compound, Furaneol (the one that
smells like cotton candy) seems to enhance the sweetness
of the fruit. It may be possible, through a breeding
program, to develop varieties that produce relatively high
quantities of this compound in their fruit, thus improving
Continued research into the complex flavor of
strawberries at the University of Florida should help
maintain the strawberry's position as one of the world's
most popular fruits.
Center Update Christine Manley
Mark your calendars for our Field Day scheduled
for February 13, 2003 starting at 2:30 pm. Meet and talk
with our faculty and staff regarding the strawberry industry
and the research conducted at GCREC. Our Field Day is
opened to the public and will provide valuable information
to the attendees as well as give us a chance to show the
community what goes on behind the scenes of agricultural
For those interested in attend the 2003 Florida
Postharvest Horticulture Industry Tour March 10-13
contact our office as soon as possible for details. The tour
is being cosponsored by the University of Florida,
Cooperative Extension Service, Horticultural Sciences
Department and the Florida Fruit and Vegetable
Association. This tour will provide an opportunity to
experience first-hand the latest technologies for handling
and shipping subtropical and tropical fruits, warm and cool
season vegetables and ornamental crops. The tour will
depart from Gainesville early Monday, March 10.
Enrollment is limited to 35 participants and the deadline
for early registration is February 14. Call Christine
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Manley at (813) 744-6630 for a registration form or visit the Horticultural Sciences website atwww.hos.ufl.edu.
If you are interested in having your group tour our facilities, please contact Christine Manley (813) 744-6630 ext.
60 or cmanlev(Aufl.edu. We encourage educators and schools to contact us for educational tours for students of any age.
We are working on a special PowerPoint presentation that will be available to educators that will give an overview of our
research in both elementary and technical versions. Watch for the release of this presentation on our website
Plans for our relocation to the new regional center in Balm are continuing to progress. Several committees have
been formed to give input as to field layout and building design. These committees, made up of both staff and faculty, have
been traveling to other research centers throughout the state to obtain ideas and inspiration as to how the new center should
be designed. This has provided a lot of excitement and anticipation for our staff and faculty, and we are all looking forward
to working in a state-of-the-art facility. We will keep you updated as information becomes available.
The use of trade names in this publication is solely for the purpose of providing A monthly newsletter of the University of Florida Institute of Food and
specific information. It is not a guarantee or warranty of the products named, and Agricultural Sciences, Gulf Coast Research and Education Center, and
does not signfy that they are approved to the exclusion of others of suitable Florida Cooperative Extension Service
composition. Use pesticides safely. Read andfollow directions on the manufacturer's Gulf Coast Research and Education Center
label. 13138 Lewis Gallagher Road, Dover, FL 33527
(813) 744-6630 SC512-1160
Website http//strawberry ifas ufl edu
The Institute of Food and Agricultural Sciences is an equal Editor Craig Chandler (ckc@ ufl edu), Design, Layout & Distribution
opportunity/affirmative action employer authorized to provide research, Christine Manley (cmanlevrLufledu), Director Jack Rechclgl
educational information and other services only to individuals and institutions
that function without regard to race, color, sex, age, handicap, or national origin.