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 The pathogen and disease cycle
 Disease management






Title: Botrytis blossom blight of southern highbush blueberry
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Permanent Link: http://ufdc.ufl.edu/UF00066810/00001
 Material Information
Title: Botrytis blossom blight of southern highbush blueberry
Alternate Title: EDIS PP198
Physical Description: Book
Language: English
Creator: Harmon, Philip F
Publisher: University of Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, EDIS
Place of Publication: Gainesville Fla.
Publication Date: [2004]-
 Subjects
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Summary: Information contained in this publication is intended to help blueberry growers in Florida identify and manage Botrytis blossom blight. For more information, search the EDIS website or contact your local University of Florida, IFAS extension agent.
System Details: Internet access required.
Statement of Responsibility: Philip F. Harmon.
General Note: Title from Web page viewed on October 20, 2004.
General Note: At head of title: University of Florida, Cooperative Extension Service, Institute of Food and Agricultural Sciences, EDIS.
General Note: "This document is PP198, one of a series of the Plant Pathology Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Original publication date April 2004."--Footnote.
Funding: Florida Historical Agriculture and Rural Life
 Record Information
Bibliographic ID: UF00066810
Volume ID: VID00001
Source Institution: Marston Science Library, George A. Smathers Libraries, University of Florida
Holding Location: Florida Agricultural Experiment Station, Florida Cooperative Extension Service, Florida Department of Agriculture and Consumer Services, and the Engineering and Industrial Experiment Station; Institute for Food and Agricultural Services (IFAS), University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: aleph - 003105048
oclc - 56792847

Table of Contents
    The pathogen and disease cycle
        Page 1
        Page 2
    Disease management
        Page 3
        Page 4
Full Text




UNIVERSITY OF

FLORIDA

EXTENSION
Institute of Food and Agricultural Sciences


Botrytis Blossom Blight of Southern Highbush

Blueberrv1


Philip F. Harmon2


Information contained in this publication is
intended to help blueberry growers in Florida identify
and manage Botrytis blossom blight. For more
information, search the EDIS website or contact your
local University of Florida, IFAS extension agent.

The Pathogen and Disease Cycle

Botrytis blossom blight is an important disease
of blueberries and several flowering ornamental
plants. The fungus, Botrytis cinerea, most commonly
infects and blights wounded or senescent plant
tissues. As a blueberry bush blooms, corollas (the
fused petal of the flowers) senesce and become quite
susceptible to infection. Ideally the corolla should
drop from the flower after pollination but before
senescence occurs. Frost damage on tender new
growth may wound the plant, delay petal drop, and
facilitate infection by the fungus.

The pathogen survives well as a saprophyte on
dead host and non-crop plant material. Spores of the
pathogen are abundant during blueberry bloom most
years. Sanitation efforts to remove diseased and
infested plant materials are good horticultural
practices but would not significantly limit
development of this disease.


Figure 1. Corollas of southern highbush blueberry infected
with Botrytis cinerea and exhibiting typical symptoms of
Botrytis blossom blight. Disease has progressed into the
peduncle of the center flower.

Botrytis blossom blight can spread from the
corolla into the ovary and eventually into the
peduncle (stem of the immature berry) (Fig. 1).
During periods of high relative humidity, conidia
(spores) of the fungus are produced on infected plant
parts (Fig. 2). If the blight continues, an entire
cluster of berries can be aborted (Fig. 3).

When disease is severe, the berry reduction can
become economically important (Fig. 4). After


1. This document is PP198, one of a series of the Plant Pathology Department, Florida Cooperative Extension Service, Institute of Food and Agricultural
Sciences, University of Florida. Original publication date April 2004. Visit the EDIS Web Site at http://edis.ifas.ufl.edu.
2. Philip F. Harmon, assistant professor, Plant Pathology Department, Cooperative Extension Service, Institute of Food and Agricultural Sciences, University
of Florida, Gainesville, 32611.


PP198


The Institute of Food and Agricultural Sciences (IFAS) is an Equal Employment Opportunity Affirmative Action Employer authorized to provide
research, educational information and other services only to individuals and institutions that function without regard to race, creed, color, religion,
age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For information on obtaining other extension
publications, contact your county Cooperative Extension Service office. Florida Cooperative Extension Service / Institute of Food and Agricultural
Sciences / University of Florida / Larry R. Arrington, Interim Dean








Botrytis Blossom Blight of Southern Highbush Blueberry 2


fungus may then cause the gray fuzzy rot commonly
observed on blueberries in grocery stores. Because
of the relatively short interval from harvest to retail
sales in Florida, the fruit rot stage of the disease is
not typically a concern.


Figure 2. Gray sporulation of Botrytis cinerea is observed
on corolla and calyx of southern highbush blueberry
flowers after an extended period of high relative humidity.
Corollas do not typically senesce and turn brown on the
plant but are usually dropped after pollination while still
white. Brown corollas that remain on the bush and gray
sporulation are good diagnostic symptoms of Botrytis
blossom blight.


Figure 4. Many of the blighted flowers on this southern
highbush blueberry will not produce fruit. When extended
periods of disease favorable conditions occur during
bloom, Botrytis blossom blight can reduce yield enough to
impact economic return. A preventative fungicide
application could have protected the blossoms during the
favorable conditions and may have limited disease
development.


Figure 3. Severe symptoms of Botrytis blossom blight
were observed on a cluster of flowers of southern highbush
blueberry. The flowers that produced the immature fruits
(top) developed before the cool wet period and escaped
infection. Some of these fruits could be infected, but they
will likely mature if no further periods of disease-favorable
weather recur.


pollination of a flower and drop of the corolla, the
risk of infection of the developing fruit is reduced. If
progress of the blight is suppressed by environmental
conditions, a fungicide application, or by plant
defenses, disease progress may stop, but the fungus
may lie dormant in the immature fruit. Infected
berries are sometimes deformed and may develop
further rot if environmental conditions later become
favorable for disease (Fig. 5). If the fruit is stored
cool and humid for long periods after harvest, the


Figure 5. Some blueberry fruits rot or develop shriveled
and deformed if the flowers are infected by Botrytis cinerea
at bloom. Diseased berries that remain on the bush
produce inoculum capable of infecting other ripening fruits.

The development of Botrytis blight, like many
other foliar fungal diseases, is highly dependent on
environmental conditions. Infection and disease
development are favored by extended periods of high


Botrvtis Blossom Blight of Southern Highbush Blueberrv


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Botrytis Blossom Blight of Southern Highbush Blueberry 3


relative humidity. Most years, blueberries in Florida
are overhead irrigated for freeze protection during
bloom. While sometimes necessary, frequent
overhead irrigation at this time of year increases the
likelihood of Botrytis blossom blight.

Botrytis blossom blight is unusual, because
disease can occur at a wide range of temperatures
from as low as 320F, where growth of the fungus is
slow, to over 700F. Periods of low temperatures and
extended periods of high relative humidity that occur
during bloom and result in more-than 24 hours of leaf
wetness increase the likelihood of significant disease
development.

According to Florida Automated Weather
Network (FAWN) data from the Alachua location,
hourly temperatures between February 24 and 27
were (on average) 90F lower in 2004 than the
average of the hourly temperatures recorded the
previous four years. In addition to the unusually low
temperatures during this period, the hourly relative
humidity remained above 90% for the entire time.
The extended cool and wet period was favorable for
disease development and likely contributed to the
severe outbreak of Botrytis blossom blight observed
in Gainesville around March 4, 2004.

Disease Management

Blueberry cultivars differ in susceptibility to
Botrytis blossom blight, but no one cultivar is
completely resistant. In an average year in Florida,
the economic loss due to Botrytis can be minimized
by judicious fungicide applications and limited use of
irrigation for freeze protection. Overhead irrigation
extends periods of leaf wetness and favors disease
development. Fungicide applications prior to, during,
or immediately following extended cool wet periods
during bloom can limit early infection. Untreated
infections during bloom can lead to disease problems
throughout the season. If Botrytis does become
established at bloom, fungicide applications later in
the season may be required to manage spread of the
fungus to ripening berries. Applications at this time
are less efficient and less effective for managing this
disease than those at bloom.

Fungicides labeled for Botrytis cinerea control on
blueberries in Florida and their relative efficacies are


listed in Table 1. Captan is familiar to many growers
and a cost-effective fungicide that will prevent
infection and Botrytis blossom blight development if
applied preventatively. Some of the new,
site-specific, systemic fungicides listed in Table 1
have provided excellent control in university trials
when applied preventatively and curatively (soon
after favorable conditions but before symptoms are
apparent) but have not been extensively tested on
blueberries in Florida. Resistance to site-specific
fungicides is a real concern with this pathogen.
Resistance management strategies are included on the
labels of products containing site-specific fungicides.
Each of the different fungicides in Table 1 has a
different mode of action and can be rotated in a
resistance management plan. Always read and follow
each product's specific label instructions carefully as
changes may have occurred since this text was written.
If in doubt, contact your local county agent or
university specialist for up-to-date information.
Products are listed for example only. No
endorsement or criticism of any product listed or
omitted is intended or implied. Relative efficacy data
were taken from results of trials not conducted in
Florida.


Botrvtis Blossom Blight of Southern Highbush Blueberrv


3







Botrvtis Blossom Blight of Southern Highbush Blueberry


Table 1. Fungicides for control of Botrytis cinerea on blueberry.


Common name Trade name Activity Relative efficacy1
prevent control
fenhexamid2 Elevate 50 WDG contact *** **
cyprodinil2, fludioxonil Switch 62.5 WG local systemic *** **
boscalid2, pyraclostrobin2 Pristine local systemic *** **
captain Captan 50 WP contact ** *
pyraclostrobin2 Cabrio EG local systemic *
iprodione2 Rovral local systemic *
*** provides greatest efficacy under disease-favorable conditions
** good management tool under moderate to low disease pressure
provides some control, best used in rotation or tank mix with other chemistries
2 Risk of resistance. Resistance management required for these fungicides.


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