Title: Florida plant disease management guide
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Permanent Link: http://ufdc.ufl.edu/UF00053871/00031
 Material Information
Title: Florida plant disease management guide
Alternate Title: Ornamentals and turf
Fruit and vegetables
General plant pathology, field crops and pasture grasses, fungicides, adjuvants and application techniques
Physical Description: v. : ; 28 cm.
Language: English
Creator: University of Florida -- Dept. of Plant Pathology
Florida Cooperative Extension Service
Publisher: The Extension
Place of Publication: Gainesville Fla
Frequency: annual
regular
 Subjects
Subject: Plant diseases -- Periodicals -- Florida   ( lcsh )
Pesticides -- Periodicals   ( lcsh )
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Statement of Responsibility: Plant Pathology Dept., University of Florida and Institute of Food and Agricultural Sciences, Florida Cooperative Extension, University of Florida.
Numbering Peculiarities: Issued in three volumes: v. 1, General plant pathology, field crops and pasture grasses, fungicides, adjuvants and application techniques; v. 2, Ornamentals and turf; v. 3, Fruit and vegetables.
General Note: Description based on: 1999-2000.
General Note: "SP-52"
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Bibliographic ID: UF00053871
Volume ID: VID00031
Source Institution: University of Florida
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Resource Identifier: oclc - 44549741
lccn - 00229071
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PDMG-V3-05
UF UNIVERSITY of
UFFLORIDA
IFAS Extension



2007 Florida Plant Disease Management Guide: Apple

(Malus sylvestris) 1


Tim Momol, Laura Ritchie, and Hank Dankers 2

APPLE SCAB

Introduction:

Apple scab is an economically important disease
resulting in direct loss from fruit or pedicel
infections. Indirectly, repeated defoliation reduces
tree growth and yield. In the southeastern United
States, however, apple scab severity is inconsistent
due to the necessity of cool, wet weather for
infection.

Symptoms:

Young leaf lesions are olive green with indistinct
margins. As the infected leaf ages, several lesions
may coalesce and tissues adjacent to lesions thicken,
causing the leaf to become curled, dwarfed, or
distorted (Fig. 1).


Figure 1. Apple scab on apple leaf caused by Venturia
inaequalis. Credits: Ohio State University Extension


Fruit lesions are similar to those of leaves;
however, as infected fruit enlarge the lesions become
brown and corky. Early season infection may result
in uneven fruit development, further causing cracks in
the skin and flesh (Fig. 2). Late season infection may
result in pin-point scab where circular lesions are
rough and black.


Figure 2. Apple scab on apple fruit caused by Venturia
inaequalis. Credits: Clemson University USDA
Cooperative Extension Slide Series (IPM Images, The
Bugwood Network)


1. This document is Fact Sheet PDMG-V3-05, one of a series of the Plant Pathology Department, Florida Cooperative Extension Services, Institute of Food
and Agricultural Sciences, University of Florida. Published October 2007. Please visit the EDIS Website at http://edis.ifas.ufl.edu/
2. Tim Momol, associate professor, North Florida Research and Education Center (NFREC), Quincy, FL 32351; Laura Ritchie, Biologist, NFREC; and Hank
Dankers, senior biologist, NFREC, Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL
32611.

The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and
other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex,
sexual orientation, marital status, national origin, political opinions or affiliations. U.S. Department of Agriculture, Cooperative Extension Service,
University of Florida, IFAS, Florida A. & M. University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Larry
Arrington, Dean






2007 Florida Plant Disease Management Guide: Apple (Malus sylvestris) 2


Causal Organism:

Venturia inaequalis is the causal organism of
apple scab. Pseudothecia, produced in overwintered
leaves or fruit, are separate, dark brown to black,
spherical, with a short beak and distinct ostioles with
single-celled bristles at the apex. Asci are fasciculate,
cylindrical, short-stipitate, eight-spored and have
thin, bitunicate walls. Ascospores are yellowish
green to tan and unequally two-celled. Conidia are
olive, have one or two cells, are ovate to lanceolate
and are produced sequentially by a series of
abscission ridges on the conidiophore.

Disease Cycle and Epidemiology

V Inaequalis overwinters in infected fruit and
leaves on the ground. As infected fruit and leaves
become wet asci discharge ascospores which are
disseminated by the wind, initiating primary
infections on new growth. Free moisture is required
for the germination of an ascospore on the new leaf
or fruit. After initiation, germination will continue as
long as the relative humidity is 95% or greater. After
fungal penetration of the cuticle, conidiophores and
conidia are produced in a visible lesion. Conidia are
then disseminated by rain and wind to new leaves and
fruit, initiating a secondary infection cycle.

Management:

Removal of fallen leaves and fruit in the fall can
reduce disease inoculum. Attention to weather
forecasts, particularly those of extended wet periods,
can assist in chemical control. See Table 1.

BITTER ROT

Introduction:

Bitter rot is an important summer disease of
apples grown in the southern United States. During
periods of warm, moist weather bitter rot can destroy
an entire crop within a few weeks.

Symptoms:

Fruit infections begin as small, circular, tan to
light brown spots that expand rapidly under warm,
moist conditions. As the lesion sinks into the fruit
surface it is covered with rings of spore masses which


appear creamy and salmon to pink in color (Fig. 3).
The fruit may become soft and watery, developing a
sour rot odor, then drying to a darker, leathery
appearance.


Figure 3. Bitter rot lesion on apple fruit caused by
Colletotrichum gloeosporiodes. Note creamy spore
massses on lesion surface. Credits: Clemson University -
USDA Cooperative Extension Slide Series (IPM Images,
The Bugwood Network)

The pathogen can form cankers on twigs and
cause leaf spots as well. Although not as common,
lesions on leaves start as small, red flecks which
enlarge to irregular brown spots. Severely infected
leaves often abscise.

Causal Organism:

Colletotrichum gloeosporioides (teleomorph
Glomerella cingulata) is the causal organism of bitter
rot. Acervuli are produced beneath the cuticle, which
is ruptured by the growth of conidiophores and
conidia. Conidia are uninucleate, vary in size and
shape, and are produced in pink to salmon, sticky
masses. Perithecia can be solitary or aggregated,
dark brown to black and vary in size and shape. Asci
vary in size and are clavate to cylindrical; ascospores
vary in size, are slightly curved and unicellular.

Disease Cycle and Epidemiology:

Fruit infection, through direct penetration or
through wounds, is most common from midseason to
late in the growing season. Infected fruit, mummified
apples (from chemical thinning), and newly
colonized dead tissues can serve as additional
inoculum during the growing season. Lesion






2007 Florida Plant Disease Management Guide: Apple (Malus sylvestris) 3


expansion is most rapid in warm weather (around
850F). Prolonged warm, wet weather can lead to
epidemics and extensive losses. A warm, wet early
season can be the most severe as the primary
infection provides abundant secondary inoculum.

Perithecia and acervuli of C. gloeosporioides
survive from one season to the next in mummified
apples, dead wood and cankers. Mummified apples
and stems left on the tree provide over wintering
sites, mummified fruit on the ground can serve as a
source of inoculum.

Management:

Management of bitter rot is based on sanitation
and a fungicide spray program. Removal of
mummified fruit, cankers, dead wood and blighted
branches from the previous season as well as
throughout the current growing season will remove
potential inoculum sources. Removal of fruit
infected with C. gloeosporioides during the growing
season will also help slow the spread of disease.

No commercial cultivar is sufficiently resistant
to bitter rot to negate the need for sprays. Fungicides
should be applied on a 10-14 day schedule from first
cover until harvest. See Table 1.

BLACK ROT

Introduction:

Black rot of apples occurs throughout the eastern
United States but is most severe in the southeast.
Losses from the disease come not only from fruit rot,
but from the weakening of trees due to limb cankers
and leaf spot-induced defoliation

Symptoms:

Leaf lesions begin as small purple flecks which
enlarge and develop a tan to brown center, giving a
frog eye appearance (Fig. 4). Heavily infected leaves
may become chlorotic and abscise. Fruit symptoms
from direct infection begin as minute red flecks
which develop into raised purple spots bordered by a
red ring. Upon maturation of fruit the lesions will
darken and enlarge (Fig. 5), often with alternating
black and brown concentric rings.


Figure 4. 'Frog eye' appearance of Black rot lesions on
appple leaf. Credits: Clemson University USDA
Cooperative Extension Slide Series (IPM Images, The
Bugwood Network)


Figure 5. Black rot fruit decay. Credits: Clemson University
- USDA Cooperative Extension Slide Series (IPM Images,
The Bugwood Network)



Limb cankers begin as slightly sunken reddish
brown areas in the bark and can lead to a superficial
hardening of the bark or the canker may cause the
wood to crack open and die. Fruit may develop
rotting around the core, yet remain on the tree,
ripening 3-6 weeks before harvest and often dropping
before the rot appears on the surface.

Causal Organism:

Botryosphaeria obtusa (anamorph Sphaeropsis
malorum) is the causal organism of black rot.
Pycnidia, commonly found on infected wood and
fruit, are globose, solitary or botryose, and stromatic
with papillate ostioles. At maturity, conidia are
nonsepate, ovoid, melanized, with a rough or faintly
echinulate wall. Asci are bitunicate and eight-spored;
ascospores are fusiform and occasionally one-septate.
Pseudothecia are rare in the southeastern United
States.






2007 Florida Plant Disease Management Guide: Apple (Malus sylvestris) 4


Disease Cycle and Epidemiology:

B. obtusa can survive between seasons in tree
cankers and mummified apples providing an early
season source of inoculum. Mummified apples,
wounded bark, and fire-blighted twigs are rapidly
colonized by B. obtusa and provide inoculum during
the growing season. Conidia and ascospores are
released from fruiting structures during rainfall
throughout the year in the southern United States.
Infection can occur through stomata of leaves or fruit
(early season), and through wounds and cracks in the
fruit cuticles (later season).

Management:

Throughout the season fire-blighted twigs should
be removed to lessen the colonization cites for B.
obtusa. Mummified apples and dead wood should be
pruned and removed from the orchard or burned.
Black rot is best controlled through chemical
applications. See Table 1.

BOTRYOSPHAERIA ROT/WHITE
ROT

BOTRYOSPHAERIA ROT/WHITE ROT

Introduction:

Botryosphaeria rot, also referred to as Bot rot or
white rot, has symptoms similar to black rot. This
disease can have a severe impact in the southeast
United States. Extensive fruit losses (50%) have been
reported and cankers can cause the loss of scaffold
limbs and possible tree death.

Symptoms:

Fruit lesions begin as small, slightly sunken
brown to tan spots, often surrounded by a red halo
(halo may appear purple to black on red cultivars).
The rotted area extends in a cylindrical manner to the
core as the lesions expand in diameter (Fig. 6),
forming a v-shaped lesion in cross section. This
criterion can be used as a distinction between black
rot and Botryosphaeria rot.

Limb and twig infections begin as small, sunken,
oozing lesions, often red in color. The lesions


Figure 6. Botrosphaeria rot/White rot of friut. Credits: The
Bugwood Network, Insect and Disease Indentification
Guide for IPM in the Southeast, The University of Georgia,
Cooperative Extension Service Bulletin 849, September
1981

enlarge, exhibiting rings of black Pycnidia and loss of
bark (Fig. 7).


Figure 7. Botryospaeria canker on apple limb. Credits:
Michael A. Ellis, The Ohio State University

Causal Organism:

Botryosphaeria dothidea (anamorph Fusicoccum
aesculi) is the causal organism of Botryosphaeria rot.
Pycnidia, found on infected wood and fruit, are
typically compound and spherical (153 X 197pm).
Conidia are nonseptate and hyaline. Ascostroma are
solitary and scattered, botryose, ostiolate, and
spherical. Asci are cylindrical, eight-spored, and
bitunicate; ascospores are hyaline, one-celled, and
ovoid.

Disease Cycle and Epidemiology:

Although ascospores and conidia are produced
throughout the growing season in the southeastern
United States, inoculum production is dependent on
temperature (optimum 82-900F) and number of
spores released is dependent upon the amount and
duration of rain. Infection by spores is most common
through wounds in fruit, twigs and limbs, although
twig and limb infection is often associated with the
periods of hot and dry weather.

Mycelium, pycnidia, and pseudothecia of B.
dothidea survive between seasons in cankers,
colonized dead bark, and mummified fruit. B.
dothidea can colonize in current-season mummified






2007 Florida Plant Disease Management Guide: Apple (Malus sylvestris) 5


fruit and fire blight strikes to provide a secondary
source of inoculum.

Management:

Dead limbs, cankers and mummified fruit should
be pruned and removed from the orchard.
Current-season fire blight strikes should be removed
to lessen colonization of B. dothidea. Limb and
branch infections can also be reduced by irrigation
during hot, dry periods. Severity of Botryosphaeria
rot in the area and whether early-season latent
infections are common are the deciding factors for
chemical control timing. See Table 1.

CERCOSPORA LEAF SPOT

Introduction:

Cercospora leaf spot is a minor foliar disease of
apple which may cause early defoliation.

Symptoms:

Lesions on infected leaves are round to oblong,
often with a zonate appearance.

Causal Organism:

Pseudocercopsora mali is the causal organism of
cercospora leaf spot. Produced in clusters,
conidiophores are dark in color, sparingly branched
and septate. Conidia are typically hyaline, long and
slender and septate.

Management:

Fallen infected leaves should be removed from
the area and destroyed. See Table 1 for chemical
control.



CROWN GALL

Introduction:

Crown gall affects woody and herbaceous plants
from over 90 families, including apples grown for
fruit production and ornamental use. Crown gall is
variable in severity but gradually lowers tree vigor
and may lead to tree death.


Symptoms:

Galls, varying in size, form on the crown, roots,
trunk or limbs. The texture of a gall can range from
soft and spongy to hard, depending on the amount of
vascular tissue it contains (Fig. 8). Careful diagnosis
of smaller galls is important, as they may be confused
with excessive callus growth around wound sites, or
with nematode or insect induced galls.



Causal Organism:

Agrobacterium tumefacien bacteria is the causal
organism of crown gall. It lacks endospores, is
rod-shaped, gram-negative, aerobic and motile by one
to six flagella. A large extrachromosomal piece of
DNA, commonly referred to as a tumor-inducing (Ti)
plasmid), is carried by A. tumefaciens.

Disease Cycle and Epidemiology:

Wounds are essential to the infection process and
initiation of the disease cycle. A. tumefaciens enters
through a wound, attaches to a susceptible plant cell
and inserts transfer DNA (T-DNA) from the Ti
plasmid into the plant cell chromosome. Expression
of the T-DNA results in overproduction of plant
hormones, stimulating plant cells to divide, enlarge
and form a gall. The pathogen may move from galls
to surrounding roots and soil, then disseminate to new
plants or planting sites by rain, irrigation water, wind,
insects, tools, and plant parts used for propagation.

Management:

Good cultural and sanitation practices are key
deterrents to crown gall. These include choosing a
rootstock with low susceptibility, budding rather than
grafting, developing management practices that
minimize wounding, removing young infected trees
as well as older galled trees, and dipping shears in
rubbing alcohol for 10-15 seconds between cuts.
Planting sites where galled plants were grown should
be left fallow for several years.

Effectiveness of chemical control through soil
fumigation and rootstock dipping varies.






2007 Florida Plant Disease Management Guide: Apple (Malus sylvestris) 6


ENTOMOSPORIUM LEAF SPOT

Introduction:

Entomosporium leaf spot usually begins in early
summer. In other references, this disease may be
referred to as Fabraea leaf spot.



Symptoms:

Initially, leaf lesions appear as small, purplish,
circular spots. Lesions will become sunken, with a
raised dark purple to black border, and a gray to white
center. Within the center is a small, dark, mound-like
fruiting body (acervulus).

Causal Organism:

Entomosporium mespili is the causal organism of
entomosporium leaf spot. Conidia have a distinct
insect-like appearance, composed of four cells
(lateral cells smaller than central cells) and
bristle-like appendages on all but the basal cells.
Asci, containing eight hyaline, clavate two-celled
ascospores, extend above the leaf cuticle surface
when the ascospores are mature.

Disease Cycle and Epidemiology:

E. mespili overwinters in infected leaves and
twig cankers as ascospores and conidia. Rain and
overhead irrigation spread the spores to susceptible
tissue. Severity increases when wet springs follow
mild winters.

Management:

Infected leaves and twigs should be removed
from the area and destroyed by burial or composting
and burning. Adequate spacing between rows and
avoidance of overhead irrigation will allow good
airflow and rapid drying of the foliage. Chemical
control may be difficult if primary leaf and twig
infections are abundant. See Table 1.


FIRE BLIGHT

Introduction:

Fire blight is one of the most devastating
bacterial diseases affecting apple, pear and other
rosaceous plants. This disease varies in severity from
year to year, dependent upon temperature and
precipitation. Additionally, fire blighted wood can
provide a suitable site for other diseases such as black
rot and white rot.

Symptoms:

Plant parts affected by fire blight appear
scorched by fire. Infected blossoms may exhibit
ooze, and then change color from red to brown to
black as the disease progresses. Infected leaves will
turn brown to black and desiccate, yet remain
attached to the branches. Vegetative shoots often wilt
and take on the shape of a shepherds crook (Fig. 8),
the pith of infected stems exhibiting a dark brown
discoloration. The outer bark of infected branches
and limbs are often sunken and darker than normal,
whereas the inner tissues will be water-soaked with
reddish streaks while the pathogen is active, later
turning brown.


Figure 8. Fire blight on apple branch. Credits: Tim J.
Smith, Washington State University

Fruit infected during the early-season remain
attached to the cluster base, yet remain small and
appear shriveled and dark, whereas fruit infected as
the disease progresses from the branches appear less
shriveled and dark. Fruit infected following injury
often develop red, brown or black lesions, and may
exude an ooze which first appears clear or milky,
later turning red to brown.






2007 Florida Plant Disease Management Guide: Apple (Malus sylvestris) 7


Causal Organism:

Erwinia amylovora is the causal organism of fire
blight. The rod-shaped bacterium is gram-negative
and facultatively anaerobic. Isolation and tentative
identification can be made using several selective or
differential media; rigorous identification requires
additional biochemical and molecular testing.

Disease Cycle and Epidemiology:

E. amylovora overwinters in small twig cankers
and dead wood to provide an initial source of
inoculum early in the next season. Transferred by
rain or insects, the bacterium penetrates host tissue at
wounds or natural openings. Inoculum produced as
ooze from fresh infections can serve as a secondary
source of disease for later-season vegetative shoots,
blossoms and fruits. Lesion extension slows in late
summer to autumn in response to less favorable
conditions.

Severity of fire blight varies from season to
season, dependent upon the interaction of a
susceptible plant, a virulent pathogen, and favorable
weather conditions. Plant susceptibility varies with
plant age, phonological stage and horticultural
practices employed; strains ofE. amylovora vary in
virulence toward plant genotypes. Weather
conditions, particularly temperature and moisture,
affect vector activity (primarily bees) and pathogen
growth.

Management:

Overwintering cankers should be removed
during the dormant season. Active lesions should be
pruned out at least 6-8 inches below obvious
discoloration. Pruning tools must be disinfected
between cuts to reduce spread of the bacterium.

Susceptible cultivars and rootstocks should be
avoided, as should the use of nitrogen fertilizers early
in the season and late-summer cultivation. There are
forecasting models available to time chemical
applications. Properly timed chemical applications
can be highly effective against the blossom phase of
fire blight. See Table 1.


FLY SPECK

Introduction:

Flyspeck is a common disease of apple whereby
fruit quality is lowered by fungal growth on the fruit
surface. Due to the warm, moist weather, fungicide
use is essential in the southeastern United States.

Symptoms:

Flyspeck colonies on fruit surfaces are
well-defined groupings of shiny, black, superficial
pseudothecia (Fig. 9). Colony size varies from 1-3cm
and round to irregular. Conidiophores and conidia
are produced within the colonies of pseudothecia
during warm, moist weather.


Figure 9. Credits: Michael A. Ellis, The Ohio State
University



Causal Organism:

Schizothyrium pomi (formerly Microthyriella
rubi; anamorph Zvgolhialt jamaicensis) is the causal
organism of flyspeck. Pseudothecia vary in size and
have irregular margins. Embedded in a centrum
tissue asci are spherical to oval and bitunicate, each
ascus containing eight hyaline, two-celled ascospores.
The upper cells of ascospores are shorter and wider
than the basal cells. Conidiophores consist of a
subhyaline basal cell; a smooth, thick-walled brown
sector; an angular, subhyaline terminal cell; and two
hyaline conidiogenous cells. Two-celled conidia are
thin-walled and elliptical to obovate.

Disease Cycle and Epidemiology:

S. pomi overwinters as pseudothecia on infected
apple twigs and woody reservoir hosts. Airborne
ascospores are released by the pseudothecia just prior
to bloom and germinate from 60.80F to 82.40F.
Under optimum conditions (63.1 F, relative
humidity above 96%) conidia may be produced in
10-12 days. Airborne conidia are released after






2007 Florida Plant Disease Management Guide: Apple (Malus sylvestris) 8


sunrise as the relative humidity declines and the twigs
dry, providing the secondary inoculum.


Management:


During normal to dry weather, well-pruned trees
will usually have less disease; during wet seasons
well-pruned and poorly pruned trees may be equally
diseased. Proper thinning of fruit can lessen the
microclimate for disease development that tightly
clustered fruit provides and allows for thorough
coverage of fungicide sprays. Primary control of
flyspeck is through fungicide sprays. See Table 1.

MUSHROOM ROOT ROT

Introduction:

Mushroom root rot is also known as Armillaria
root rot, oak root fungus disease, and shoestring root
rot.

Symptoms:

Foliage may turn yellow, then brown and dry
rapidly. Dark brown to black rhizomorphs, or
"shoestrings" appear at the soil line around the
trunk of the tree. A creamy white layer of fungus is
often present between the bark and the wood; a white
to light yellow mycelial growth within the bark of
surface roots. Honey-colored mushrooms may form
in groups around the drip line of the tree or next to
the trunk during moist periods.

Causal Organism:

Armillaria tabescens is the causal organism of
mushroom root rot. Lacking an annulus on the stipe
of the mushroom (basidiocarp), it is easily
distinguished from other Armillaria species.
Blackish, hardened, mycelial extrusions are produced
on the bark of infected roots.

Disease Cycle and Epidemiology:

In recently-cleared woodland (particularly that
which had oak cover), rhizomorphs and mycelial
strands of the fungus can remain on infected roots in
the soil for many years, serving as an initial source of
inoculum for new orchard trees. Rhizomorphs also
spread between trees, attaching to the roots of a new


host and entering through pressure and enzymatic
activity.



Management:

Location of orchard plantings is important. New
trees should not be planted in recently cleared
woodland (particularly that which had oak cover),
near existing stumps or buried debris, nor where trees
have recently died from mushroom root rot, unless
the root system has been removed in its entirety and
several years of fallow have passed. Fumigation of
soil can assist in control of mushroom root rot.

PINK LIMB BLIGHT

Symptoms:

Pink limb blight produces a pale pink mycelium
which often encircles limbs, twigs and trunks of trees.
The foliage distal from the affected area wilts and
dies, eventually killing the limb or twig.

Causal Organism:

Erythricium salmonicolor (anamorph Necator
decretus).

Management:

Infected tissue should be removed immediately;
pruning limbs a minimum of 4-6 inches below the
external appearance of mycelium on twigs. Prunings
should be collected and destroyed.

POWDERY MILDEW

Introduction:

A persistent disease, the severity of powdery
mildew and resulting economic loss varies with
environmental conditions, cultivar susceptibility, and
management practices. Powdery mildew can be
especially damaging in nursery production.

Symptoms:

Infections on leaves first appear on the lower
surface as grayish-white patches of mycelium and
spores, with chlorotic spots on the upper surface.






2007 Florida Plant Disease Management Guide: Apple (Malus sylvestris) 9


Infections may spread to the upper surfaces, covering
the entire leaf and eventually turning brown. Leaves
infected along the margin may curl, while severely
infected leaves may fold longitudinally, become
brittle and abscise.

Infected flower buds will open 5-8 days later
than healthy buds and exhibit reduced fruit set; flower
petals will be distorted and pale yellow or light green.
Apples affected during bloom will be stunted in
growth and covered with a network pattern of cork
cells (russet) that may be so closely woven as to
appear as a solid patch (Fig. 10).


Figure 10. permission needed, sent E-Mail Credits:
Clemson University USDA Cooperative Extension Slide
Series (IPM Images, The Bugwood Network)

Causal Organism:

Podosphaera leucotricha (anamorph Oidium
farinosum) is the causal organism of powdery
mildew on apple. Produced in long chains on thin,
amphigenous mycelium, conidia are ellipsoidal,
truncate, hyaline, and contain fibrosin bodies.
Perithecia are densely gregarious and subglobulose,
with apical and basal appendages. Apical appendages
are three to seven times longer than the diameter of
the perithecium, brown basally and widely spreading
or erect-fasticulate. Rudimentary basal appendages
are pale brown, short-tortuous, and simple or
irregularly branched. Asci are oblong to
subglobulose and contain 8 ovate to elliptical
ascospores.


Disease Cycle and Epidemiology:

P. leucotricha overwinters as mycelium in
dormant buds infected during the previous growing
season. Conidia produced on the mycelium serve as
primary inoculum. Healthy buds often open earlier
than infected buds, thus providing susceptible tissue
upon conidia development. Limited germination
occurs at high temperatures or in free water. High
concentrations of spores are released in the air from
midday to early afternoon. Infection of young or
mechanically damaged leaves, blossoms and fruit
serve as a secondary source of inoculum.

Management:

Dormant season pruning may remove infected
buds and reduce the level of primary inoculum.
During the growing season severely infected shoots
should be pruned and destroyed. Prevention of new
spores and reduction of spores produced on new
lesions may be accomplished through fungicide
sprays. See Table 1.

RUST

Introduction:

Several related rust fungi infect apple in the
southeastern United States, including cedar apple
rust, quince rust, and American hawthorn rust. These
fungi involve two host plants in their life cycle,
usually requiring a Juniperus species as an alternate
host. The various fungi differ in life cycle complexity
and whether they affect fruit, leaves, or both.

Symptoms:

Cedar apple rust affects leaves, petioles and fruit,
beginning as small yellow lesions (upper surface of
leaves) which may be surrounded by chlorotic halo or
red band. Small orange-brown pustules (pycnia)
develop within the lesions, producing watery orange
drops. Later, yellow-brown lesions form on the
undersurface of leaves which produce small, dark
tubular structures (aecia) that fracture to release
red-brown spores (Fig. 11). Fruit lesions are usually
superficial, causing a brown necrosis 1-5mm into the
flesh (Fig. 12). Cedar apple rust on alternate host
juniper often forms a gelatinous homed gall (Fig. 13).







2007 Florida Plant Disease Management Guide: Apple (Malus sylvestris) 10


Figure 11. Credits: Clemson University- USDA
Cooperative Extension Slide Series (IPM Images, The
Bugwood Network)


Figure 12. Cedar/Apple rust on apple fruit Credits: Lorraine
Berkett, University of Vermont


Figure 13. Cedar/Apple rust on alternate host, Juniper.
Credits: Hank Dankers, Uiversity of Florida, IFAS,
NFREC,Quincy

Quince rust does not affect apple leaves but it
does affect fruit. However, obvious rust symptoms
(such as pycnia and aecia) are often not present.
American hawthorn rust infects apple leaves, but
rarely infects fruit.

Causal Organism:

Various Gymnosporangium species are the
causal organisms of rust on apple. Morphologies of
fungal structures vary between species.


Disease Cycle and Epidemiology:

On native cedars Gymnosporangium sp. will
induce a gall, from which telial horns will emerge
under wet conditions. During rains telia swell and
appear jellylike, releasing teliospores which then
germinate to produce basidiospores. Basidiospores
are immediately discharged into the air and can travel
more than 1 mile on air currents; those landing on
susceptible apple tissue may germinate and infect the
host if a film of water is present for a suitable length
of time. Aeciospores are later released from aecia
during dry weather and may germinate and infect
native cedars.

Management:

Removal of infected native cedars within close
proximity may reduce infection pressure, however,
elimination is unlikely as basidiospores can travel
great distances. Rust is best controlled using
fungicides. See Table 1.



SOOTY BLOTCH

Introduction:

Sooty blotch is a late summer disease of apple
whereby fruit quality is lowered by fungal growth on
the fruit surface. Due to the warm, moist weather,
fungicide use is essential in the southeastern United
States.

Symptoms:

Sooty blotch colonies appear as olive green,
soot-like smudges on mature fruit. Large portions of
the fruit surface may be covered by colonies due to
secondary spread on the fruit (Fig. 14).

Causal Organism:

Gloeodes pomigena is the causal organism of
sooty blotch. Produced in the thallus, pycnidia are
dark brown, scattered or aggregate, and dimidiate.
Conidia are variable in length, generally
cigar-shaped, with slight constrictions at the point of
septation. Spores in mass are cream to pinkish in
color.






2007 Florida Plant Disease Management Guide: Apple (Malus sylvestris) 11


Figure 14. Sooty mold on apple. Note Fly speck. Credits:
Clemson University USDA Cooperative Extension Slide
Series (IPM Images, The Bugwood Network)

Disease Cycle and Epidemiology:

Sooty blotch survives between seasons as
mycelium and pycnidia on infected twigs of apple
and reservoir hosts (woody plants common to
hedgerows and woodlots). Spores are released during
spring and early summer rains. Infection can occur
any time, but is most noticeable during late season.
Mycelial growth is possible despite a lack of free
water at relative humidities above 90%.

Management:

During normal to dry weather, well-pruned trees
will usually have less disease. During wet seasons
well-pruned and poorly pruned trees may be equally
diseased. Proper thinning of fruit lessens the
microclimate for disease development that tightly
clustered fruit provides and allows for thorough
coverage of fungicide sprays. Primary control of
sooty blotch is through fungicide sprays. See Table 1.

SOUTHERN BLIGHT

Introduction:

Southern blight occurs in orchards and nurseries
on trees approximately 3 years old and younger. Due,
in part, to the warm, humid weather, tree losses in
some southeastern United States have reached 30%
due to this disease.


Symptoms:

A coarse, white mycelial mat is often found at
the base of an infected tree, progressing upward.
Small, white sclerotia develop within the mycelium,
later turning tan to brown. Leaves of an infected tree
may exhibit a reddish or grayish purple discoloration,
later drying and turning brown as the fungus girdles
the crown and the tree dies.



Causal Organism:

Sclerotium rolfsii is the causal organism of
southern blight. Grown on a wide range of media,
the fungus produces white mycelium and reddish
brown to dark brown or tan, hard, round sclerotia. No
asexual spores are produced.

Disease Cycle and Epidemiology:

Sclerotia are easily dislodged from mycelium
and fall into soil, where they can survive for several
years. Infection occurs directly through both injured
and healthy bark. Warm summer temperatures
(77-950F), high soil moisture, good soil aeration and
plentiful organic debris promote a high incidence of
disease.

Management:

Delay placement of apple trees where legumes or
solanaceous crops have been grown until the area has
been deep-plowed, fallowed for a season, and
fumigated.

INFORMATION SOURCES

American Phytopathological Society. 1990.
Compendium ofApple and Pear Diseases.

Simone, Gary W., Mullin, R.S. 2000. 1999-2000
Florida Plant Disease Management Guide Volume 3:
Fruit and Vegetables.

CDMS Chem Search.
http://premier.cdms.net/webapls







2007 Florida Plant Disease Management Guide: Apple (Malus sylvestris) 12


Table 1. Fungicides approved for disease management of Apple in Florida.


Max rate/acre
Chemical (a.i.) Fungicide Application Season Min. days Disease Remarks 2
Group 1 to harvest

Captan 50WP, Captan M3 4-8 Ib 64 Ib 0 Bitter rot, Black rot,
50W Botryosphaeria rot,
captain ) Flyspeck, Powdery
mildew, Scab,
Sooty blotch

Basic Copper 53, M1 1-5 Ib 32 Ib 0 Bitter rot, See label for use
Cuprofix Disperss Fireblight, with hydrated lime
(basic copper sulfate) Flyspeck, Powdery
mildew, Scab,
Sooty blotch, White

Kocide 101, M1 1-16 Ib 1 Fireblight, Scab Varying rates for
Champion WP, Nu desired fruit finish
Cop 50WP
(copper hydroxide)
Kocide 2000, Kocide M1 0.75-6 Ib 1 Fireblight, Scab Varying rates for
DF, Nu Cop 50DF desired fruit finish
(copper hydroxide)

Kocide 4.5LF, Champ M1 1.3-10.6 pt 1 Fireblight, Scab Varying rates for
Formula 2F, Nu Cop desired fruit finish
3L
(copper hydroxide)

Dithane DF M2 3-6.4 Ib 21-25.6 Ib 77 Entomosporium For Fireblight mix
Rainshield, Manzate leaf spot, with Copper
75DF, Penncozeb Fireblight, Rusts,
(mancozeb) Scab
Dithane F45 M2 2.4-4.8 pt 16.8-19.2 pt 77 Entomosporium For Fireblight mix
Rainshield, Manzate leaf spot, with Copper
Flowable Fireblight, Rusts,
(mancozeb -__ Scab
Dithane M45, Manzate M2 3-6 Ib 21-24 Ib 77 Entomosporium For Fireblight mix
Pro-Stick, Penncozeb leaf spot, with Copper
80WP Fireblight, Rusts,
(mancozeb) Scab
Maneb 75DF, Maneb M2 3-6 Ib 21-25.6 Ib 77 Entomosporium
80WP leaf spot, Flyspeck,
(maneb) Scab, Sooty blotch

Manex M2 2.4-4.8 oz 16.8-19.2 oz 77 Entomosporium
(maneb) leaf spot, Flyspeck,
Scab, Sooty blotch

Nova 40W, Rally 40W, 3 1.25-2.5 5 Ib 14 Powdery mildew,
Rally 40WSP oz/100 gal Rusts, Scab
(myclobutanil)







2007 Florida Plant Disease Management Guide: Apple (Malus sylvestris) 13


Table 1. Fungicides approved for disease management of Apple in Florida.


Agri-Mycin 17, 25 24-48 oz 50 Fireblight
Streptrol
(streptomycin)

Dusting Sulfur, M1 rate varies, see labels Powdery mildew, Do not use within 2
Kumulus DF, Rust, Scab, Sooty weeks of an oil
Micronized Gold, blotch spray treatment
Micrthiol Disperss,
Sulfur 90W
(sulfur)
Thiophanate Methyl 1 0.6-0.8 Ib 3.3 Ib Bitter rot, Black rot,
85WDG Flyspeck, Powdery
(thiophanate methyl) mildew, Scab,
Sooty blotch, White
rot
Topsin M 70WP, 1 1-1.5 Ib 4 Ib Black rot, Flyspeck,
Topsin M WSB Powdery mildew,
(thiophanate methyl) Scab, Sooty
blotch

Ziram 76DF, Ziram M2 6-8 Ib 56 Ib 14 Bitter rot, Flyspeck,
Granuflo Rust, Scab, Sooty
(ziram) blotch


1 Fungicide group (FRAC code): Numbers (1-37) and letters (M, U, P) are used to distinguish the fungicide mode of action
groups. All fungicides within the same group (with same number or letter) indicate same active ingredient or similar mode of
action. This information must be considered for the fungicide resistance management decisions. M = Multi site inhibitors,
fungicide resistance risk is low; U = Recent molecules with unknown mode of action; P = host plant defense inducers. Source:
http://www.frac.info/ (FRAC = Fungicide Resistance Action Committee).
2 Information provided in this table applies only to Florida. Be sure to read a current product label before applying any
chemical. The use of brand names and any mention or listing of commercial products or services in the publication does not
imply endorsement by the University of Florida Cooperative Extension Service nor discrimination against similar products or
services not mentioned




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