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EXTENSION Bery Times
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I Volume IIIIse2Fbur 03'
Anthracnose fruit rot: Epidemic looming?
- Jim Mertely
The weather sure is unusual this year, so goes the
old refrain. The unusually wet weather early this season has
undoubtedly contributed to the spread of anthracnose fruit rot
in our strawberry fields. Normally, growers have few
problems with this disease until February or March, but this
year, samples of infected fruit have been seen in the
Strawberry Diagnostic Lab (and in our own field) since late
December. While cool weather in January should slow down
the disease, a serious epidemic could develop this spring if
mild weather is accompanied by showers.
Black spots are produced on green fruit, and sunken brown
lesions develop on ripening fruit.
Anthracnose fruit rot (or black spot) is caused by
the fungus Colletotrichum acutatum. This fungus infects
most plant tissues and all stages of the fruit. Flowers
infected upon opening produce small black fruit. Black spots
are produced on green fruit, and sunken brown lesions
develop on ripening fruit. Where does the fungus come
from? Assuming the previous strawberry crop was properly
destroyed and incorporated into the soil, C. acutatum does
not normally persist in the field over our hot wet summers.
In addition, disease inoculum is not thought to come from
weeds or other crops outside the strawberry field. Wild
strawberry, a potential host, is not native to our state.
Therefore, infected runner plants probably account for the
first disease outbreaks here in Florida. This hypothesis is
supported by the detection of C. acutatum on Canadian
runner plants by our laboratory, and several reports of C.
acutatum on nursery plants from California.
The control of anthracnose fruit rot ultimately
depends on the production of healthy runner plants in the
nursery. But for the moment, the fight must be carried on in
the field. C. acutatum produces enormous numbers of spores
on diseased fruit. This inoculum is spread by splashing
water, wind-driven rain, and people or equipment in the
fields. If possible, harvest healthy fields first, and avoid
picking berries when the plants are wet. Captan is the
foundation of an effective anthracnose control program,
and should be applied regularly when susceptible varieties
such as Aromas, Camarosa, Festival, and Treasure are
grown. Applications should begin immediately after
plants have been "watered in", and continue at weekly
intervals throughout the season. Reduced rates can be
used initially, but full rates should be applied later in the
season when inoculum build-up and mild weather facilitate
the development of epidemics. If the disease is detected
and conditions favor its spread, Quadris or Cabrio can be
mixed with Captan to enhance control. Both products
belong to the strobilurin class of fungicides. To avoid the
development of resistance, avoid more than five
applications of strobilurins per season, as well as more
than two successive applications of either product. Switch
is a possible alternative to the strobilurins, but growers
should be aware of its plant-back restrictions. If
strawberries are to be followed by a second crop, Switch
should not be used.
C. acutatum attacks the plant as well as the fruit,
and is often responsible for establishment problems after
planting. When the fungus is present on the old roots of
runner plants, it causes a root rot of new roots emerging
from the crown. This phase of the disease is called root
necrosis and was first discovered in Israel. Many infected
plants survive, but are slow to establish, and produce a
poor first crop. However, such plants often recover over
the winter, and may produce a sizeable spring crop if the
weather is dry. Unfortunately, such fields are at high risk
for epidemics of anthracnose fruit rot during rainy periods.
Berry Times 1
Spotlight on Diagnosis Teresa Seijo and Jim
Over 60 samples have been submitted to the
Strawberry Diagnostic Lab in December and January.
Colletotrichum acutatum (the cause of anthracnose fruit rot
and Colletotrichum slow decline) continues to plague us,
infecting a third of the samples. In early December the
majority of C. acutatum infected plants showed vegetative
symptoms (i.e., slow establishment, poor growth,
stunting), but since late December, anthracnose fruit rot
and blossom blight have predominated. Nearly a quarter
of the samples consisted of plants collapsing from crown
rot. Another anthracnose fungus (Colletotrichum
gloeosporioides) was isolated from the majority of these
plants; however Colletotrichumfragariae and
Phytophthora spp. were recovered from a few specimens.
Leather rot is caused
eventually engulfs the
Two cases of leather rot on fruit (Phytophthora
cactorum) were received in January. This disease had not
been seen in the UF Strawberry Diagnostic Lab in recent
years. Symptoms of leather rot usually begin with a brown
lesion, which eventually engulfs the entire fruit, giving it a
shrunken, leathery appearance. Sometimes white fungal
growth is visible on the lesion. On ripe fruit, young
lesions are occasionally dark purple, making diseased fruit
more difficult to spot. Infection can occur on fruit at all
stages of development. Fruit with leather rot have an
unpleasant odor and taste.
Examples ofdisease caused by phytoplasmas.
Several growers have brought in plants or fruit
infected with phytoplasmas. Phytoplasmas are an unusual
class of bacteria, which cause asters yellows, green petal,
multiplier, and other strawberry diseases. Some
phytoplasmas may be transmitted locally by leafhoppers,
but others are brought in on infected runner plants. The
symptoms we are currently observing include stunted
plants with small, distorted new leaves yellowing at the
edges (marginal chlorosis), and reddening at the margin of
older leaves. Berry samples showed leafy growths coming
out of the seeds (phyllody) and occasionally, elongation or
malformation. Phytoplasma infection is tentatively
diagnosed by symptoms, and elimination of other possible
causes such cyclamen mites and nematodes. Confirmation
currently requires that samples be sent out for expensive
tests. However, phyllody and green petal symptoms (see
photos) are good diagnostic indicators of phytoplasma
Supplemental calcium as a means to
increase shelf life of strawberry Camille
Esmel and John R. Duval
Post harvest integrity of strawberry is a major
concern to growers because it affects how far and how long a
berry can be shipped and stored. It has been suggested that
calcium plays a major role in post harvest shelf life. Many
growers currently apply supplemental calcium to their
strawberry crop. However, studies to test the effectiveness
of calcium to improve post harvest quality of berries have
been inconclusive. 'Sweet Charlie' tends to produce soft
fruit, which can bruise easily and has a short shelf life;
therefore it makes an ideal test cultivar for study. Two
different methods to apply supplemental calcium are being
studied at GCREC-Dover. They are a pre-plant soil
amendment of calcium sulfate as gypsum and foliar
applications of calcium sulfate or calcium chloride. The
rates of the pre-plant soil applied gypsum are 0 lbs/A, 200
lbs/A, and 4001b/A of calcium. The rates for foliar applied
calcium are a water spray-control, 400 ppm calcium sulfate,
400 ppm calcium chloride, and 800 ppm calcium chloride.
The treatments are being assessed for differences in calcium
concentration within the leaves, fruit and calyx, yield, shelf
life, and fruit firmness. This study could potentially lead to
non-destructive firmness measurements and a
recommendation on supplemental calcium applications to
increase post harvest quality of strawberry.
Early planting important for early yield this
season Craig Chandler and John Duval
A planting date trial at GCREC-Dover has
demonstrated the importance of planting early. 'Sweet
Charlie', 'Earlibrite', 'Strawberry Festival', and 'Carmine'
produced their highest Nov./Dec. yield when planted on Oct.
2nd (Table 1). Significantly lower Nov./Dec. yields were
generally obtained when these cultivars were planted on Oct.
9th, 17th, or 25th. 'Earlibrite', 'Strawberry Festival', and
'Carmine' had greater than a 25% reduction in Nov./Dec.
yield when planted on the 9th, compared to the 2nd. In a
similar trial conducted during the 2001-02 season, a
reduction in Nov./Dec. yield did not occur between plants
sets on the 2nd and 9th, but reductions of 15 to 50% did
occur between plants set on the 9th and 17th. Weather
Berry Times 2
undoubtedly interacts with planting date to affect a cultivar's
performance. Nov./Dec. 2001 was warmer than average,
while Nov./Dec. 2002 was cooler than average. The large
planting date effect in this season's trial is likely due to the
fact that earlier set plants had a longer time to grow
vegetatively (i.e. "make a bush") before the weather cooled
down in Nov.
Based on this season's and last season's trial,
'Earlibrite' appears to be the new UF/IFAS cultivar least
affected by planting date. It has generally had higher
Nov./Dec. yields of marketable fruit than the other cultivars,
regardless of planting date, but has also produced the highest
percentage of cull fruit. 'Carmine's marketable yields were
similar to those of 'Earlibrite' for plants set on Oct. 2nd and
9th (both this season and last), and it generally produced
significantly fewer cull fruit than 'Earlibrite.
'Strawberry Festival' had lower Nov./Dec. yields
than the other UF/IFAS cultivars, especially when planted on
Oct. 17th and Oct. 25th (Table 1). On the positive side, it
produced very uniform fruit, with few culls early in the
Nov./Dec. production has amounted to only 10% of
the total crop yield in Florida over the last 10 seasons (1991-
2001; Florida Agricultural Statistics, www.nass.usda. gov/fl),
but that production is valuable. It returned the highest
average value per flat, $16.25, compared to $12.86, $10.13,
and $7.00 for January, February, and March respectively.
Increasing the supply of Nov./Dec. strawberries by growing
higher yielding cultivars (or planting earlier) may force
prices lower, but it seems to us that this product (fresh
strawberries available during the major holiday season)
should be amenable to marketing campaigns aimed at
increasing its demand. Fresh strawberries help make holiday
parties and meals more colorful and festive.
Nov./Dec. production is also important because it
generally occurs before damaging freezes or pests and
diseases have had a chance to significantly affect fruit
In conclusion, an on-going field trial at GCREC-
Dover has shown the importance of planting early to obtain
high Nov./Dec. yield- at least during a cool El Nino season.
The January, February, and March yields of cultivars in this
trial will be reported in a later issue of the Berry Times.
Table 1. Effect of planting date on Nov./Dec. fruit yield of
strawberry cultivars planted at Dover, Florida in
Marketable fruit yield (pounds per acre)
Oct. 9 Oct. 17
Whitefly in California Strawberry Jim Price
Some of California's strawberry production is
affected by a relatively new pest of strawberry, the
greenhouse whitefly (Trialeurodes vaporariorum). This
insect is not new to California, and it has been a part of
Florida's fauna for many decades. The problem in
California became intense about 3 years ago and is not
restricted to strawberry. Beans and many other annual
crops are attacked too. As a matter-of-fact, control
concerns there are shifting from the silverleaf whitefly
(Bemisia .. ,- ,i i/;) to the greenhouse whitefly.
Greenhouse whitefly pupa (right), empty pupal case /, '
and black pupa parasitized by Encarsiaformosa (center).
Photo by Jack Kelly Clark. Printed with permission from Regents,
University of California.
There are no reports of the greenhouse whitefly
infesting strawberry in Florida, but there is a small but
increased presence of silverleaf whitefly and banded wing
whitefly (Trialeurodes abutiloneus). It is not known if one
or both of these two Florida residents will become
problematic on our strawberry. Certainly, the silverleaf
whitefly has caused more than its share of problems in
Florida's tomato, melon, squash and other horticultural
Also unknown is whether the California problem
with the greenhouse whitefly on vegetables and strawberry
will manifest in Florida. Mechanisms for such a scenario
could be that our resident strain would adapt to our
horticulture or that the California strain would be
transported and established here. Changes in our
horticultural practices (crops, crop rotations, crop growing
periods, pesticides used and their use patterns, etc.) can
drive formerly innocuous resident insects into pest status.
More simply, the California strain could hitchhike on
leafy, host vegetables or ornamentals and find a suitable
home here. Neither scenario is a certainty.
Florida horticultural interests should insist that
only clean produce enter Florida, remain vigilant to detect
a new problem early, practice wise crop culture, and
develop management plans to minimize any new whitefly
zPlants of each cultivar were dug (with leaves on) from a high elevation
nursery in northern California. The plants were shipped to GCREC-Dover
via overnight courier, and planted immediately.
Berry Times 3
Center Update Christine Cooley
Most people might not know that we have a dedicated group of volunteers that come to our farm and harvest strawberries
for area charities. John Gibson helps organize a group called the Gleaners from Lake Magdalene United Methodist Church. This
biblical term refers to groups of people in the Old Testament that would gather by hand any usable parts of a crop that remain after a
harvest. At GCREC-Dover, John brings a group of volunteers to pick strawberries and then delivers them to organizations such as
The Spring, First Baptist Church of College Hill, Angels Unaware, Hope Children's Home and many other charitable organizations
and individuals. We wanted to acknowledge John and his group for all their hard work year after year, and thank them for allowing
us to be part of such an important cause.
The Gleaners (left to right):
Otto Wiesneth, John Pery, Rob
Smucker, John Gibson, and
GCREC-Dover is pleased to welcome Alicia Whidden as the new Hillsborough County Extension Agent. Alicia is a former
GCREC employee who worked with our soil science and plant pathology programs. A long-time resident of Polk County, Alicia is
knowledgeable in the many aspects of the strawberry industry and is well known by many of the local growers. Her experience and
expertise will be a major benefit to the extension program. You can contact her at the Hillsborough County Extension Office (813)
744-5519, Ext. 134.
Committees are continuing to meet regarding our relocation to Balm, which is now slated for September 2005. Several
architects in the Tampa Bay area have already expressed interest in working on the project and proposals should be arriving in the
near future. Our excitement continues to grow as plans and ideas come together for this state-of-the-art research center.
Don't forget to attend our Strawberry Field Day on Thursday, February 13 at 2 pm. The faculty and staff will be
presenting information regarding the field trials for the 2002-2003 growing season and will be available to answer your
questions. Presentations in the field will include disease research, arthropod trials, effects of planting dates on new cultivars,
transplant establishment trials, nitrogen and calcium studies, and nematode research. This will be the last scheduled
Strawberry Field Day at the Dover center, and we will be marking the event by celebrating 40 years of research at this
location. For information call (813) 744-6630 Ext. 60 or visit our website http://strawberrv.ifas.ufl.edu.
See you there.