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Copyright 2005, Board of Trustees, University
GULF COAST RESEARCH & EDUCATION CENTER
IFAS, UNIVERSITY OF FLORIDA,
5007 60th Street East
Bradenton, FL 34203
Bradenton GCREC Research Report BRA1988-2
SLIU4 ~-~' 7
Control of Botrytis and the Influence of Moisture and Temperature
on Disease Occurrence
Arthur U. Engelhard1
One of the most common and frequently encountered diseases of herbaceous
plants is Botrytis blight caused by Botrytis cinerea or a related species.
In this paper reference will be made mainly to B. cinerea. Botrytis was
named in 1729 and is one of the oldest known pathogens and one of the most
destructive. The name Botrytis blight commonly is used but symptoms can
be blights, leaf or petal spots, soft rot of leaves and flowers, stem
cankers, basal cankers, bulb rots and even post harvest decays of fruits
and vegetables. Botrytis blight occurs from cool temperate to warm
subtropical areas. Botrytis is cosmopolitan and grows well as a
saprophyte on dead and/or dying herbaceous material or as a pathogen on
living plants. This disease-pathogen has been reviewed extensively by
Coley-Smith et.al. (1980) and Trolinger and Strider (1985).
Examples of Botrytis Disease on Plants
Symptoms on flowers generally start as small, tan colored spots that
appear wet and enlarge rapidly. Infection of leaves occurs but usually
not as prolifically as infection on flowers. However, Botrytis elliptica
causes multiple spotting of leaves, buds and flowers of Asiatic lily. B.
cinerea causes a bud or heart rot of cyclamen, a crown rot, shoot blight
and leaf blight of poinsettia, a stem canker of Exacum, a storage rot of
chrysanthemum cuttings'and occasionally stem cankers and leaf spots. On
flowers of other plants, Botrytis causes a variety of symptoms as follows:
small, wet-appearing spots which enlarge rapidly and
cause the collapse of the flowers.
wet spots that overnight can cause a "melting" and
disintegration of the flowers.
tan, round to elongate spots on petals. The flowers
close and/or decay as spots enlarge in size or
increase in number. On buds, corolla infection can
spread around the unopened bud.
1Professor and Plant Pathologist.
L_ I I
Chrysanthemum- a tan colored, soft, wet decay of petals. Frequently
starts on ray petals on the lower side of spray type
flowers. On the large standard chrysanthemum flowers
a single infection point results in a "nest" of
infected petals with a soft, wet, tan decay. The
petals stick together and the gray mold stage appears
rapidly. Infected cuttings in storage have a soft,
tan colored decay.of.leaves and stems.
King Aster -
A tan colored necrosis of individual petals develops.
Spread to adjacent petals occurs until all petals are
Tan colored, small spots that enlarge rapidly and
cause necrosis of petals.
Life Cycle of BQtrYtis Components
Conidia, mycelia, sclerotia and ascospores are fungous structures involved
in the dissemination of Botrytis blight. The role of each of the above
components is described below.
Conidia. Conidia are 1-celled spores produced in clusters on ends of
conidiophores. When many conidiophores bearing conidia are
produced, the spore mass is gray and called the gray mold
stage. Conidia are dispersed by air currents, water or
insects. They germinate on a susceptible host or on dead
tissue when a suitable nutrient source and water are
Mycelia. Conidia germinate and produce hyphal filaments or strands
which collectively are the mycelia. Mycelia can serve as
sources of inoculum as, for example, when infected geranium
or begonia petals fall on flowers or leaves and the mycelia
grow onto healthy tissue and start new infections.
Sclerotia are produced in the masses of white mycelia. They
are black, composed of fungous cells, round to flat to
elongate, sometimes convoluted and irregular, and 1-15 mm
long. They are formed on plant tissue and may be firmly
attached. The sclerotia may germinate to produce conidia
or apothecia in which the sexual spores ascosporess) are
produced. Sclerotia serve as dispersal propagules for
Botrytis when, for example, diseased plant material is
mixed in trash piles or is left lying around. They thus
serve as overseasoning or overwintering structures for
Botrytis disease and are an important source of biological
Apothecia are produced or grow from sclerotia. An exchange
of nuclear material from sexually compatible strains occurs
before apothecia are produced. The apothecia of Botrytis
cinerea resemble a tiny flat-topped mushroom. Their caps
are about 1.5-7.0 mm in diameter and 3-10 mm in height.
Upright, cigar-shaped asci are produced in the upper
surface. Each ascus contains 8 ascospores which contain
the new genetic combinations. Ascospores and their
dispersal methods have not been studied extensively. They
presumably can be carried by wind currents and water. The
name of this sexual ascospore stage for Botrytis cinerea is
Helminthosporium spp. (some names now changed to Bipolaris, Drechslera and
Exserohilum) and Alternaria spp. may cause symptoms on flowers very
similar to those caused by Botrytis cinerea. Our research in Florida
demonstrated that isolates of Helminthosporium isolated from a petal of a
chrysanthemum and leaves of chrysanthemum, corn and maranta could cause
petal spots on rose, carnation, chrysanthemum and geranium. Alternaria
spp. from aster and chrysanthemum caused petal spots on snapdragon,
chrysanthemum, rose, carnation and petal blight on King Aster.
The importance and frequency of occurrence of the Botrytis-like spots in
Florida and elsewhere is not known. A recent communication from Dr.
Phillip Colbaugh, Texas A&M University, indicated Botrytis blight is
uncommon, except during rainy periods, on rose flowers in Texas and
Helminthsporium is rarely observed. However, Alternaria (A. alternate) is
a dominant pathogen on rose flowers in Texas.
Disease Development as Related to Temperature
Botrytis blight is a disease that develops over a wide range of
temperatures. From a practical view, the temperature range in which
plants are produced is satisfactory for Botrytis disease development.
However, the rate of disease development slows as temperature drops. The
same relationship exists for flower- diseases caused by Helminthosporium
spp. and Alternaria spp.
Floral Infection as related to Wet Periods or Dry-Wet Periods
Botrytis spores require water to germinate. Initially they are
hydrophobic and will float on water but with time they do get wet. They
usually need an external source of nutrients which they get from leaf or
Plant surfaces or from dead or injured tissue.
In our experiments, Botrytis infected rose, snapdragon and King Aster but
usually not chrysanthemum flowers. However, in one experiment we
inoculated White Iceberg chrysanthemum flowers held at 800F, 660F and 40F
and disease developed only at 400F when the flowers were held 17 days
(Table 1). Perhaps this is similar to decay occurring on bulbs and
chrysanthemum cuttings held in cold storage (usually around 400F).
Botrytis blight developed extensively on inoculated King Aster flower.
held at 660F and 800F. However, when the inoculated flowers were allowed<
to dry 18 hours at 780F, 65% R.H., before being rewetted and covered wit
a polyethylene bag for 48 hours to maintain wetness, very little disease
developed. The drying procedure constitutes a non-chemical control methc
and indicates that spores do not survive well after being dry for
period. In separate experiments with fungicides on inoculated King Aster
flowers, disease control with fungicides was less than that provided by
drying the flowers.
If Alternaria is causing disease on flowers a longer dry period is
required to reduce disease. Alternaria spores are large, thick walled and
perhaps are more resistant to desiccation than the small, 1-celled
Botrvtis spores. King Aster flowers inoculated with Alternaria (from King
Aster and chrysanthemum) showed a low rate of disease on King Aster
flowers dried 48 hours before rewetting (Table 3).
Our research in Florida showed that spots develop on rose and snapdragon
petals inoculated with Helminthosnorium (isolated from
chrysanthemum and maranta) and Alternaria (isolated from chrysanthemum and
aster) in the temperature ranges listed below.
*Estimated from literature reports. Our tests were
conduced at 40, 66 and 800F.
Botrytis disease develops at low temperatures on bulbs and cuttings in
'Opening buds of Red American Beauty Rose were inoculated with
Helminthosporium (now called Bipolaris setariae) and incubated at high
humidity for variable periods of time at 760F. A small amount of disease
developed with only 3 hours of continuous moisture and increased
progressively up to about 30 hours (Table 4). It is obvious that if
Helminthosporium (which causes petal spots similar in appearance to those
incited by Botrytis) is involved in disease-on roses, the safe procedure
for disease control would be to have the fungicide on the flowers before a
rain or wet period so spores would be killed when they come in contact
with the fungitoxicant.
Successful disease management on susceptible crops, especially flower
crops, includes using all components (listed below) comprising a disease
i. Control the production of spores (inoculum). The spores produced on
diseased, dying, and dead plant material are a source of biological
contamination for healthy plants. The Botrytis fungus is a prolific
spore producer that grows exceptionally well on dead vegetation.
Therefore, keeping plant trash and debris cleaned up and buried is
tantamount to successful disease control. Spores cause disease and
eliminating or greatly reducing the number of spores helps keep
disease at a lower level.
2. Cultural practices
A. Apply water so foliage and flowers do not get wet. Spaghetti-
type tubes, capillary mats, spitters, and seep hoses are
examples of methods of watering that apply water to the roots
only. Overhead watering, rain and dew encourage disease. Grow
plants under cover.
B. Space plants to insure maximum air movement and drying.
C. Use disease-free propagating material.
D. Do not plant Botrytis susceptible plants, such as geraniums, in
the immediate landscape because Botrytis grows and sporulates
prolifically on the flowers.
E. Adjust greenhouse ventilation and heating so moisture does not
condense on plants when the temperature drops.
F. Do not injure plants. Mechanically damaged plants are very
disease susceptible because nutrients are released at the
damaged site and make an excellent infection site for the growth
of Botrytis and the subsequent production of spores.
G. Plant debris, trash, even individual plants dropped en route to
the packinghouse should be hauled away or buried to prevent the
production of spores.
H. Wash hands before starting to work and handling plants. Wash
stations with soap and water should be close to packinghouses,
seedling transplant areas, entrances to production fields, etc.
Workers may work in their gardens prior to coming to work and
can carry pathogens on their hands. Tomatoes and lettuce on
/ sandwiches can carry pathogens such as Erwinia (soft rot).
I. Scout crops 1-2 times per week to determine if disease problems
are developing. Take immediate corrective action if problems
3. Chemical control Botrytis
Botrytis blight is a very difficult disease to control. Fungicides are a
part of.the overall disease management program. Some excellent fungicides
have been rendered virtually useless because consistent overuse of them
resulted in the increase of nonsusceptible strains of the pathogen.
Specific fungicides are listed below.
Chipco 26019, Rovral (iprodione)
Ornalin, Ronilan (vinclozolin)
These chemically related materials initially were highly effective for the
control of Botrytis blight. However, resistance is a problem so they
should be used as little as possible to not encourage the selection and
increase of resistant strains and to maintain the effectiveness of the
fungicide as long as possible. Tank-mixing with chlorothalonil, mancozeb,
captain or dicloran, with each material at half-rate, is suggested. These
fungicides also are effective against Alternaria and Helminthosporium.
Benlate, Tersan 1991, benomyll)
Topsin H, Fungo, (thiophanate methyl)
Bavistin, MBC, (carbendazim)
These systemic fungicides are substituted benziaidazole fungicides and at
one time were highly effective against Botrytis blight. However, after 15
or more years use, resistance is very common so whether or not these
materials are effective in a given location should be of utmost concern to
the user. Plant losses could increase if they are used. Tank-mixing with
fungicides such as dichlorothalonil, mancozeb, captain or dicloran, with
each material at half-rate, is suggested. Alternaria and Helminthosporium
are not controlled by the benzimidazole-type fungicides.
Daconil 2787, Bravo, Exotherm, (chlorothalonil)
Dithane 1-45, Fore, Manzate 200, (mancozeb)
Chlorothalonil and mancozeb are old non-systemic, chemically unrelated
fungicides effective against Botrytis, Alternaria and Helminthosporium.
Both are good candidates to tank-mix with the systemic fungicides.
Dicloran is a fungicide effective against Botrytis disease but may be
phytotoxic, especially on flowers. The label should be consulted to
determine plant safety and uses. Using tank-mixes, each material at half-
rate, may reduce the risk from phytotoxicity.
Orthocide, Captane, captain )
Thylate, Arasan, Thiosan, (thiram)
Captan and thiram are labelled for control of Botrytis diseases and some
Alternaria diseases. They both may be considered for disease control but
may have reduced effectiveness. They are candidates for tank-mix
combinations with systemic fungicides.
4. Drying flowers prior to packing
When all efforts to control Botrytis blight fail, it is suggested the
flowers be placed in a holding solution in containers and air-dried for at
least 24 hours in a dry storage area (see text for effect of dry periods
on disease development). Heat, infrared lights or other drying methods
may be needed if humidity/moisture is too high for good drying.
Labels, Products and E. P. A. Registrations
All labels and uses are registered with the EPA. Some materials are
labelled nationally and some by states. It is the responsibility of each
user to determine if the intended use and/or tank-mixes are within the law
in the intended location, state or country of use. Mention of a specific
proprietary product does not constitute an endorsement by the authors, the
University of Florida, or the Cooperative Extension Service. Individuals
desiring information regarding currently labeled pesticides for a crop are
encouraged to contact Extension or other knowledgable personnel in their
respective states. The user of information printed in this paper assumes
all risks for injury or damage to self, other persons, animals, plants and
1. Coley-Smith, J. R.,
Biology of Botrytis.
2. Trolinger, J. C. and
17-101 in Diseases
K. Verhoeff and W. R. Jarvis. eds. 1980.
Academic Press, Inc., London. 318 pp.
D. L. Strider. 1985.
of Floral Crops. D.
Greenwood Press, Inc.
Botrytis diseases. Pages
L. Strider, ed. Praeger
Westport, CT. 638 pp.
Table 1. Botrytis blight on White Iceberg flowers held 17 days at 80, 66
Incubation 17 Days
Inoculated Temperatures OF Avg. Spots/Flowera
Yes 80 0
No 80 0
Yes 66 0
Ho 66 0
Yes 40 60
:No 40 2
a3 replications, 3 flowers/replication (9 flowers).
Table 2.' Botrytis cinerea on King Aster: Disease after exposure to wet
and dry-wet periods.
Hours delay (dry period) in
starting wet period after No. of necrotic petals/King Aster flowera
inoculation 660F 80OF
0 42 30
18 Trace 5
42 Trace 1
Control not inoculated 2 6
aHean of 4 replications, 3 flowers/replication (12 flowers/treatment).
Incubation at high humidity 48 hrs in all cases.
Table 3. Alternaria blight on King Aster flowers: Disease after exposure
to wet and dry-wet periods.
Hours delay in
starting wet period Avg. % disease per flower
after inoculation Alternaria (Aster) Alternaria (Gum) Control
0 32 47 1
48 5 1 0
a3 replications, 3 flowers/replication (9 flowers). All flowers wet 48
hrs., rated after 4 days.
Table 4. Helminthosporium (Bipolaris setariae) infection on buds of Red
American Beauty Rose inoculated and incubated for variable
Hours of Avg. %
Wet Incubation 760F Disease/Rosea
0 (control) 0
6 (control) 1
24 (control) 2
48 (control) 5
aAvg. of 3 flowers replicated 3 times (total 9 flowers).