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Group Title: Research report - Dover, Florida Agricultural Research Center ; DOV-1982-2
Title: Strawberry anthracnose, crown rot, fruit rot and black leaf spot caused by Colletotrichum fragariae
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Title: Strawberry anthracnose, crown rot, fruit rot and black leaf spot caused by Colletotrichum fragariae
Series Title: Research report - Dover, Florida Agricultural Research Center ; DOV-1982-2
Physical Description: Book
Language: English
Creator: Howard, C. M.
Albregts, E. E.
Publisher: Agricultural Research Center, IFAS, University of Florida
Publication Date: 1982
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Bibliographic ID: UF00076469
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 104644190

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D AR

h Dover ARC I


Research Rejort DOV-1982-2


STRAWBERRY Ai





Strawberry anthrac
has been a serious pro
least since the late 1
of runners and petiole
fruit rot. Since the
associated with a blac
spot has now been show
indication that the an




Strawberry anthrac
He named the fungus th
that it caused spottin
it also caused spottin
nursery which resulted
found all the above sy
fruit production field
caused by the anthracn
black leaf spot caused


ANTHRACNOSE Smal
of plants in the nurse
When a lesion girdles
and die. Lesions may
involved. When a peti
often form on the unde
point and the leaf han
position and remain gr

CROWN ROT The cr
grows into the crowns
spores germinate in th
splashed or washed int
with crown rot may die
the fruit production f
wilt suddenly and die.
occures in portions of
most readily by cutting
diagnostic feature of


THRACNOSE, CROWN ROT, FRUIT ROT, iD BLA tL6A SPOT
CAUSED BY COLLETOTRICHUM FRAGARIA i
.F.A.S.- Univ. of Florid
C. M. Howard, and E. E. AlbregtsU -*'"

INTRODUCTION

nose, caused by the fungus Colletotrichum fragariae, Brooks,
blem in summer plant production nurseries in Florida at
920's. The fungus is known to cause spotting and girdling
s, crown rot resulting in wilting and death of plants, and
late 1970's, the anthracnose fungus has been consistently
( leaf spot of strawberry in the summer nursery. Black leaf
i to be caused by this fungus and often is the first
thracnose disease is present.


HISTORY OF ANTHRACNOSE

lose was first described by Brooks in Florida in 1931 (1).
at causes the disease Colletotrichum fragariae and reported
Sand girdling of runners. Brooks (2) later reported that
Sof petioles (leaf stems), and a crown rot in the summer
in wilting and death of plants. Researchers in Louisiana
nptoms and reported that crown rot also occurred in the
(3,5,6). In 1972 Howard (8) described a fruit rot that was
)se pathogen and in 1982 Howard and Albregts (11) reported a
by the pathogen.
DISEASE PHASES AND SYHPTOHS

Sdark lesions appear on runners and petioles (leaf stems)
y. These lesions enlarge, become black, dry, and sunken.
i runner, unrooted daughter plants beyond the lesion wilt
continue to elongate until the entire runner or petiole is
le is girdled, the leaf dies and turns brown. Lesions
side of a petiole. The petiole then bends sharply at this
4s downward. The leaves may continue to live in this
en for an extended period of time.

wns of plants in the nursery become infected when the fungus
rom runner or stem lesions, or when a sufficient number of
central buds (4). The latter occurs when spores are
the central bud from runner and petiole lesions. Plants
in the nursery or after they have been transplanted into
eld. Infected plants grow normally for some time, then
A reddish-brown, firm rot or reddish-brown streaking
the interiors of crowns of wilted plants. This can be seen
lengthwise through the crown. The reddish tint is the
his discoloration. The crown of a plant turns brown


AGRICULTURAL RESEARCH CENTER
IFAS, University of Florida
Dover, Florida





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regardless of what kills the plant, but a darker brown without the reddish tint
usually occurs if death is caused by agents other than the anthracnose pathogen.

Wilt caused by fertilizer burn during the first 2 to 4 weeks after the plants are
established in the fruit production field is sometimes mistaken for crown rot. In
these cases plants wilt suddenly but do not have the marginal leaf burn that is
typical of fertilizer burn. This apparently occurs.because the salt concentrations
in the soil rise so rapidly as the soil dries that the feeder roots are destroyed
before leaf burn can occur. The plants then wilt because they are unable to absorb
water. If crowns of these plants are cut within the first 2 to 3 days after they
have wilted, no internal discoloration is found. These plants recover if irrigation
is resumed within 2 or 3 days after wilting begins. Discoloration is always present
in the crowns of plants that wilt because of crown rot, and no amount of irrigation
will cause the plants to recover..

FRUIT ROT Round, firm, sunken spots develop on ripening fruit. The spots
usually turn black but sometimes remain light tan for a few days, especially during
wet weather. The spots enlarge until the entire fruit is involved. The fruit then
dries and mummifies. This rot is most often found on ripe fruit, but green fruit in
all stages of development can be affected when rot becomes severe in a field.

BLACK LEAF SPOT Spots are round and vary in diameter from about the size of
the period at the end of this sentence to 1/16 inch (occasionally up to 1/8 inch).
They are usually black, but may remain light grey in color. Spots become very
numerous on some leaflets but do not kill them. Black leaf spot is usually present
in areas of nurseries where typical anthracnose of runners and petioles is severe.
However, it is often found before symptoms can be detected on runners or petioles.
In such cases it is usually found on the expanding leaves of the youngest runner
plants Black leaf spot, thus, can serve as an early warning that the anthracnose
)athogen is present in the nursery and has infected some plants. At the first sign
:f black leaf spot,. all possible efforts for control of anthracnose should be
initiated.

DISTRIBUTION OF ANTHRACNOSE

For many years anthracnose was considered to be a problem only in Florida and
.ouisiana. However, in the early to mid 1970's it became severe in North Carolina.
:he crown rot phase of the disease, which results in sudden wilting and death of
plantss during the winter fruit production period in Florida, has since been found in
plantss from Georgia, Tennessee, Arkansas, and Nississippi. In two or three cases
extremelyy small percentages (less than 0.1%) of plants grown in California and
:ransplanted into Florida fruit production fields wilted and died from crown rot.
he anthracnose fungus was isolated from these plants. Although it may be possible
:hat infection of these plants occurred after they were set in Florida, their early
'eath and the lack of infection.in adjacent fields set with plants from Florida
urseries that were anthracnose-free, indicates that the California plants were
infected before they were brought into Florida. Neither anthracnose nor crown rot
.as been found as yet in plants from Ilichigan, Main, or New York, but minor problems
'ith Verticillium wilt (10) and an undiagnosed stunting (perhaps red stele) have
.een encountered with plants from these states.
DISEASE DEVELOPMENT

The origin of inoculum that initiates thefirst infection in a strawberry
,ursery is unknown. It is known that.Colletotrichum fragariae attacks coffeeweed
9) and'might survive from one summer to the next on this.weed. It is probable
;hat it also survives on other weeds. Many of the fungi that cause anthracnose





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diseases of tomato eggplant, cucumber, watermelon, and other crops are closely
related to the str wberry pathogen but will not infect strawberries in the field.
Conversely, the st awberry pathogen will not infect any of the other crops under
) natural conditions The fungus does not survive from season to season in the soil.
Horn and Carver (7 placed soil from a bed in which the plants were severely
diseased into pots and set strawberry plants into this soil. None of the plants
contracted anthracrose. They also grew the pathogen on oat medium and mixed this
into sterilized soil. The infested soil was then placed in a large crock and buried
in the field. Evey three months for a year, portions of this soil were placed in
pots and healthy s rawberry plants were set into it. None of the plants became
diseased. Numerous observations in Florida have shown that in fruit production
fields in which up o 80% of the plants die from crown rot one year, no anthracnose
or crown rot develop s the following year when plants are set in these fields from
nurseries that are definitely anthracnose-free. Also, within two to three weeks
after plants have w Ited and died from crown rot, it is very difficult to isolate
the anthracnose pat ogen from the crowns, whereas it is often the only microorganism
that is isolated fr m the interior parts of the crowns during the first few days
after the plants ha e wilted. Thus, the pathogen apparently does not survive for
extended periods ev n in infected dead crowns. Regardless of where the initial
inoculum arises, af er the aerial parts of one or a few plants are infected,many
spores are produced on the lesions that develop. These spores are blown or
splashed by water t other plants and the pathogen spreads quickly under:conditions
of high temperature and moisture that are favorable for disease development.

The crown rot p ase of anthracnose occurs in the fruit production field when
plants that become i fected in the nursery are transplanted into the fruit
production field in he fall. It is difficult to detect crown rot in batches of
plants by cutting th ough large numbers of the crowns immediately before setting
because nursery grow rs generally avoid digging plants from obviously diseased
areas. Thus, infect ons would be in the initial stages and the red streaking in
the crowns which is typical of crown rot would not yet have developed. However,
the fungus continues to develop in the crowns and the infected plants die sometime
during the winter or spring. The time of death of a particular plant:depends on
the stage of infecti n at transplanting, the temperatures during the fruit production
;eason, and perhaps their factors.: Under low temperatures, the fungus can survive
in infected crowns f r long periods without killing the plants. Horn and Carver
:7) injected spores nto crowns, allowed 4 days at high temperatures for infection
to occur, then place the plants at 41 F with 10 hours of light daily. Every
Weeks for 30 weeks they removed some of the plants from 41oF and placed them
it 82 to 890F. None of the plants wilted or died while being maintained at 41 F
>ut, even after 30 weeks, some of the plants wilted and died from crown rot
afterr they were placed at 82 to 89 F.

There apparently s little or no spread of crown rot in the fruit production
Field. When plants fom an anthracnose-free nursery-are set adjacent to plants
from a diseased nursery (sometimes even on the same bed), plants from the disease-
Free nursery do not die during the year even though high percentages of those
from the diseased nur ery wilt and die. Plants that are fruiting, appear to be
nuch less susceptible to infection by the pathogen than those in the runner
reductionn stage even though the fruits are highly susceptible. Since spores
ire very abundant on ruit infected by this pathogen, it seems that infection
>f petioles and crown rot would follow fruit rot. However, we have not observed
it. Also, when fruit ng plants are inoculated in the greenhouse, very little
Infection of petioles occurs even though temperatures are favorable for anthracnose
development .






CONTROL

Stringent methods must be employed to prevent or control anthracnose, black
leaf spot, and crown rot on susceptible varieties in the summer nursery (12).
Since high soil fertility favors development of the disease, summer nurseries
should be established only on land that has very low residual fertility. After
the plants are set in the nursery, only enough fertilizer should be used to get
them established, and little or no fertilizer should be applied during July and
August. Fertilizer applications may be resumed in early September. Fungicides
should be.applied at least every other day from mid-June through mid-September.
Careful inspections of the nursery should be made frequently. If any signs of
anthracnose or black leaf spot are found, all applications of nitrogen and potash
fertilizer should be stopped and additional fungicide applications should be made
after every rain or period of irrigation. Two fungicide applications per week
should be continued from mid-September until the plants are dug. Resistant
varieties such as 'Dover' and 'Florida Belle' can be grown successfully under
much higher fertility regimes and with two fungicide application per week.

Crown rot and wilt in the fruit production field can be prevented by
preventing anthracnose in the summer nursery.

Fruit rot caused by the anthracnose pathogen is one of the most difficult of
rots to control. It has caused loss of all fruit from particular harvests in
some fields and early abandonment of other fields. Therefore, it is very
important that all possible efforts be made to prevent the occurrence of this rot.
Approved fungicides should be applied twice a week beginning no later than the
early blossom stage in the fall. After harvest begins, the fungicides should be
applied after each harvest. Since this is primarily a rot of ripe fruit, 3 or 4
day picking schedules should be employed to prevent accumulation of overripe
fruit in the field. This is especially important during warm weather because
this pathogen is favored by temperatures above 750F.

If fruit rot becomes moderate to severe on ripe fruit in a field, it may
be most economical to strip all ripe and pink fruit from the plants, then apply
approved fungicides every other day until it is determined that control has been
achieved. If many green fruits also are infected, it may be necessary to strip
all green fruit from the plants before beginning the intensive fungicide
applications. This rot sometimes becomes severe on green fruit, and we have
seen one field in which all green fruits were infected.
LITERATURE CITED

1. Brooks, A. N. 1931. Anthracnose of strawberry caused by Colletotrichum
fragariae, N. sp. Phytopathology 21:739-744.
2. Brooks, A. N. 1935. Anthracnose and wilt of strawberry caused by Colletotrichunn
.fragariae. Phytopathology 25:973 (Abstr.).
3. Carver, R. G. and N. L. Horn. 1960. Summer killing of strawberry plants
caused by Colletotrichum fragariae. Phytopathology 50:575 (Abstr.).

4. Delp, B. R. and R. D. Milholland. 1980. Evaluating strawberry plants for
resistance to Colletotrichum fragariae. Plant Disease 64:1070-1073.

5. Horn, N. L. and R. G. Carver. 1962. Anthracnose and powdery mildew on
strawberry plants in Louisiana. Plant Disease Reporter 46:591-592.







6. Horn, N. L. and
caused by Colle

7. Horn, N. L. and
fragariae in stl


R. G. Carver. 1963.
;otrichum fragariae.


A new crown rot of strawberry plants
Phytopathology 53:768-770.


R. G. Carver. 1968. Overwintering of Colletotrichum
,awberry crowns. Phytopathology 58:540:-541


8. Howard, C. M. 1 72. A strawberry fruit rot caused by Colletotrichum
fragariae. Phy pathology 62:600-602.
9. Howard, C. M. a d E. E. Albregts. 1973. Cassia obtusifolia, a possible
reservoir for i oculum of Colletotrichum fragariae. Phytopathology 63:533-534.
.0. Howard, C. M. and E. E. Albregts. 1981. Verticillium wilt of strawberries in
central Florida. University of Florida, Dover ARC Research Report SV-1981-4.

.1. Howard, C. M. an E. E. Albregts. 1982. Black leaf spot phase of strawberry
anthracnose cause d by Colletotrichum fragariae. Phytopathology 72:994
(Abstr.).
2. Howard, C. M., E E. Albregts, and A. J. Overman. 1978. Strawberry plant
production. Uni ersity of Florida, Dover ARC Research Report SV-1978-2.









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