Angular leaf spot
 Rhizoctonia aerial blight
 Mushroom root rot
 Rough bark disease
 New disease alert

Title: Diseases of pittosporum in Florida
Full Citation
Permanent Link: http://ufdc.ufl.edu/UF00066893/00001
 Material Information
Title: Diseases of pittosporum in Florida
Series Title: Plant Pathology Fact Sheet PP-29
Physical Description: Book
Language: English
Creator: Chase, A. R.
Simone, Gary W.
Affiliation: University of Florida -- Florida Cooperative Extension Service -- Department of Plant Pathology -- Institute of Food and Agricultural Sciences
Publisher: Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida
Publication Date: 1986
Spatial Coverage: North America -- United States of America -- Florida
 Record Information
Bibliographic ID: UF00066893
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: oclc - 51340960

Table of Contents
    Angular leaf spot
        Page 1
    Rhizoctonia aerial blight
        Page 2
    Mushroom root rot
        Page 3
    Rough bark disease
        Page 4
    New disease alert
        Page 5
        Page 6
        Page 7
Full Text

Plant Pathology Fact Sheet

Diseases of Pittosporum in Florida

A.R. Chase and G.W. Simone, Professor (Retired), University of Florida, ARC,
Apopka; Professor (Retired), Plant Pathology, Department of Plant Pathology;
University of Florida, Gainesville 32611. 1986; Copied January 2001.

Florida Cooperative Extension Service/ Institute of Food and Agricultural Sciences/ University of Florida/ Christine Waddill, Dean

Pittosporum tobira (Thunb.) Ait. (Japanese
Pittosporum), P. tobira Ait. cv. Variegata, and P.
tobtra cv. I \7ccleri are used in Florida as outdoor
landscape plants, as products of woody orna-
mental nurseries and as cut foliage.
Pittosporum tolerates shade to full sun, freez-
ing temperatures and relatively high soluble
salts levels. In many growing situations,
pittosporum are subject to pests and diseases
which attack leaves, stems and roots. The most
common diseases of pittosporum are angular
leaf spot, Rhizoctonia aerial blight, Southern
blight, root rots and dieback.

Angular Leaf Spot

Angular leaf spot, caused by Cercospora
pittospori Plakidas, was first described in 1949
and is common in field and landscape plantings
of pittosporum that are not routinely sprayed
for its control. Symptoms of angular leaf spot
are light-yellow to pale-green and tan angular
spots, developing first on upper leaf surfaces
(Fig. 1). Leaf spots have straight borders (angu-
lar) due to the restriction of fungal growth
through the leaf by veins and veinlets. Leaf le-
sions (Fig. 1) commonly have indistinct mar-
gins, with spot patterns similar on the leaf un-
dersides as well. Severe infections on immature
leaves occasionally result in leaf distortion and
may cause severe drop of lower leaves. The key
to recognition of this leaf spot is the character-
istic angular shape. Loss in production of high

quality foliage is important in the cut foliage
nursery, since cuttings may be unsalable when
infected with C, pittospori.

Warm, wet weather favors leaf spot de-
velopment. Weekly applications of fungicides
may be necessary to control this disease. Since
C. pittospori produces spores solely from the
lower leaf surface, it is extremely important that
all fungicides be applied evenly to both leaf
surfaces for rapid and effective control. Con-
sult your nearest County Extension Office for
the latest fungicide recommendations for the
control of angular leaf spot and other diseases
discussed in this publication;

Alternaria Leaf Spot

Alternaria leaf spot of pittosporuin is
caused by Alternaria tenuissima (Fr.) Wiltsh. This
disease was first noted in the early 1960s in
Florida. Early stages of Alternaria leaf spot may
resemble angular leaf spot; however, as lesions
develop, the diseases become distinctly differ-
ent. With Alternaria leaf spot, irregularly
shaped, chlorotic spots are scattered over the
leaf surface. These spots later develop necrotic
centers which are usually absent in angular leaf
spot disease. Spots caused by A. tenuissima are
typically rounded, have tan to dark-brown cen-
ters and generally are smaller (I to 3 min) than
those caused by C. pittospori. Alternaria lesions
are frequently surrounded by yellow halos and
their centers are slightly depressed. Symptoms


on immature leaves often result in distortion,
giving leaves a crinkled appearance (Fig. 2).

This disease is found less commonly in
cut foliage production facilities, nurseries, and
in the landscape than is angular leaf spot, but it
can be very damaging when it does occur. Some
fungicides for control of leaf spots on
pittosponim are effective for both angular and
Alternaria leaf spot diseases; others are not.
Obtain an accurate disease diagnosis from your
local County Extension Office or a commercial
laboratory prior to choosing a fungicide. Fun-
gicide applications can be extremely important
during the wet, warim portions of the year when
conditions for leaf spot development are opti-
mum. Producers of potted pittosporum may be
able to avoid these foliar diseases by growing
plants under solid structures that eliminate
much of the free water on leaves which is nec-
essary for leaf spot development. Use of day-
time irrigation cycles may also reduce foliar
disease severity by decreasing the amount of
time that leaves stay wet.

Producers of woody ornamentals should
pay particular attention to foliar disease con-
trol on those pittosporum that are destined to
be stock plants. New growth should be free
from leaf spots prior to taking softwood cut-
tings. Both angular and Alternaria leaf spots can
be damaging in the propagation bed and on
newly rooted liners set out in the nursery.

Rhizoctonia Aerial Blight

The most severe leaf spot of pittosporum
is caused by either Rhizoctonia ramicola Weber
& Roberts, reported in 1951, or R. solani Kiiehn,
reported in 1982. In many cases, this disease
may more accurately be referred to as aerial
blight and has been commonly named silky
threadblight (R. ramicola). Aerial blight is ini-
tially characterized by small, tan, irregularly
shaped spots, usually surrounded by purplish
margins. Spots frequently reach one centime-
ter in diameter (Fig. 3) and can encompass the

entire leaf. Rhizoctonia spp. inhabit the soil and
thus cause spots on lower leaves first. The fun-
gus can spread into upper portions of plants
when conditions are favorable. Leaves curl into
a cylinder in severe cases and become matted
by the threadlike mycelium of the fungus (thus
the common name, silky threadblight).

Recently, aerial blight of pittosporum
was shown to be the same as aerial blight of
Rumohra adiantiforints (G. Forst) Ching. The
pathogen spreads easily from one plant genus
to the other, and special care must be taken to
provide control on both pittosporum and leath-
erleaf fern. Aerial blight of pittosporum is most
serious in the summer months when hot, wet
conditions prevail, stimulating the fungus to
grow from the soil and crop debris into the plant
canopy. Trim severely infected tissues prior to
the application of a recommended fungicide.

In cases of severe disease pressure,
steins of pittosporum may also become infected
with R. solani. The most common infection site
is a wound, created during the harvesting of
shoots for cut foliage sale. Unless measures are
taken to protect the open wounds, this fungus
and many other fungi can invade the tissue and
cause dieback.

Galls, Dieback and Stem Blights

The most common genera of organisms
causing stem galls and twig death include
Agrobacterium, Diaporthe, Diplodia, Nectriella,
Phomopsis and Sphaeropsis. Some of the organ-
isms form a black layer of fungal tissue under
the bark, which usually sloughs off (Fig. 4). The
major route of entry of these pathogens is
through pruning wounds. Fungi may be intro-
duced into wounds on cutting instruments and
by spore movement aided by wind or water.
Cold winter seasons and/or the use of thick
mulch layers may cause stem injury typified
by one-sided splits in the bark on limbs or in
forks of branches. Cold temperatures can kill
the cambial layer along these splits, exposing

the internal plant tissues to dieback organisms.

Galls often girdle stems, resulting in
twig death. Pruning infected areas carefully
eliminates spread to adjacent tissues and is a
recommended practice. Excise affected plant
parts several inches below obvious external
symptoms to stop the advancing growth of the
dieback fungus.

Sooty molds and lichens are commonly
mistaken as a cause of diebacks on pittosporum
and other ornamentals in the landscape. Sooty
mold fungi form a brown-to-black sooty film
on leaves and branches of pittosportun, but they
do not cause disease. These fungi subsist on
the honeydew excrement of insect pests (e.g.
aphids, mealy bugs, whitefly, scale, etc.). One
should view sooty molds as indicators of po-
tential insect pest problems rather than dieback-
causing organisms. The lichens are symbiotic
life forms composed of a fungus and an alga in
a complex relationship. These organisms may
grow on branches or stems of pittosportim in
moist, shady locations, but do not cause dis-
ease. Lichens are variable in color and may ap-
pear as leaflike, crustlike, or raised structures
on woody tissues of many plant species in

Mushroom Root Rot

Some organisms cause a severe dieback
problem in the absence of obvious wounds. The
appearance of the bark is blistered and slightly
discolored and may show evidence of fungal
growth of various types. The most common
problem is mushroom root rot. The fungal
pathogen rots not only the roots of infected
pittosporum but also infects the main stem at
the soil level, causing girdling and eventual
plant death. The mycelium of Armillariella
tabescens (Scop. ex Fr.) Singer, the causal fun-
gus, can often be seen underneath the bark at
the base of an infected plant as a white coating
extending from the soil up into the main stem
and also along major roots.

During warm, wet weather, the mushroom
stage of A. tabescens may appear near the stem
of the affected plant. These mushrooms emerge
in groups of clumps and are honey-to-amber
in color, about 1 to 2 inches (2.5 to 5.0 cm) tall,
with a 0. 5 to 1. 5 inch (1.25 to 3.75 cm)-wide
cap. This stage usually does not appear until
after the plant has been killed.

Mushroom root rot is controlled by re-
moval of infected plants, since there are no fun-
gicides which significantly alter development
of this disease once it starts. Avoid planting
amid or above oak debris, since oak species are
native hosts for A. tabescens in Florida. Thor-
oughly excavate planting sites along house
foundations where tree stumps and debris are
often buried during house construction. When
mushroom root rot occurs in a hedge or circle
planting, consider the removal of adjacent
plants as well as the affected one in an effort to
stop lateral spread of the fungus. Since A.
tabescens spreads through root grafts as well as
directly through soil, additional plant loss can
be expected unless all infected plants are re-
moved simultaneously. Remove all root debris
(screening soil if necessary) and follow with a
planting site soil fumigation prior to replant-

Corticium Limb Blight

Another serious dieback disease is
caused by Corticium salmonicolor Berk. & Br., a
basidiomycete fungus. Symptoms are typical
of dieback, with the exception that the bark ap-
pears a pinkish-orange color around the infec-
tion site. These sites occur anywhere on plants.
Removal of the bark reveals a discolored area
in the vascular system which can be confined
to the cambium or spread internally into older
woody tissue (Fig. 5). In severe cases, infected
twigs and branches are characteristically wilted
and the infection may extend completely
through the stem and result in plant death (Fig.
6). As with mushroom root rot, there is very

little which can be advised for control of this
disease. Once symptoms are detected, removal
of infected areas and strict sanitation are neces-
sary. Prime 4 to 6 inches (10 to 15 cm) below
external symptoms of disease and remove all
prunings from the growing site. Check other
susceptible woody species, such as loquat and
fig, that may be in the landscape.

Rough Bark Disease

Rough bark disease of pittosporum be-
lieved to be caused by a virus. Infected plants
typically have a roughened bark, and stems
may be girdled and swollen, causing death of
twigs or branches above that point (Fig. 7). The
entire plant may be stunted in severe infections.
Leaves at tips of infected branches appear dis-
torted and may have chlorotic or yellow areas
of indefinite, shape. Sometimes, these spots re-
semble early stages of angular leaf spot. The
causal agent is transferred between plants on
cutting instruments. Removal of infected plants
and sterilization of cutting tools between plants
is required to control spread of this disease.
Diseased plants should never be used for
propagation, since the causal agent may be
present in cuttings and the problem would be

Southern Blight

Southern blight (stem rot, Southern wilt,
ca serotiun rot) is causedbclerotium roffisii
Sacc. and is a serious disease of pittosporum
and many other ornamentals.

Symptoms of this disease are wilting,
stem rot, and eventual death. Rotted tissue and
white wefts of coarse fungal mycelium Occur
on the plant base at the soil line (Fig. 8). Under
optimum conditions for disease development
(hot and humid), the mycelium may extend
over-a large portion of the infected plant (usu-
ally dead at this point), and muslard seed-sized
brown sclerotia form. These sclerotia allow the
fungus to persist in Florida soils for a number

of years.

Plants grown in the ground or in pots
on the ground are especially susceptible to this
disease. Infected plants may serve as a source
of inoculum for nearby plants and can even re-
sult in contamination of the ground if moved
around a nursery. After removal of the infected
plant, the ground should be sterilized to pre-
vent infection of new plants. Treat soil either
with heat or with various multipurpose chemi-
cal soil fumigants according to recommenda-
tions and label instructions. Few fungicides
have activity against this fungus. Consult your
County Extension Office for additional infor-

Root Rots

Root rot of pittosporum is caused by
Pythium spp. or Rhizoctonia spp. Root rot is most
severe when plants are grown in wet, poorly
drained soil. Declining plants may lose leaves
suddenly or over a period of time, beginning
at the base of the plants (Fig. 9). Leaves may
also be smaller and chlorotic, since roots have
reduced ability to transfer nutrients from the
soil. Roots of infected plants are often black
and/or soggy. Pythium root rot typically
causes a sloughing Of Outer root layers, leav-
ing only the central core intact. In both root rots,
small feeder roots are usually absent from
severely infected areas.

Careful water management in planting
sites is a valuable aid in controlling these rots.
Where soil drainage is a persistent problem, set
plants into raised beds and avoid planting di-
rectly beneath the drip line of the house, or
downslope from a driveway or sidewalk where
excessive water will persist. Always obtain an
accurate diagnosis of a root problem, since the
pesticides used for root rot control may differ.
Root knot nematode also commonly infects
pittosporum, and since the symptoms above
ground are similar to root rot diseases, the roots
must be examined for characteristic nematode

galling. Submit galled roots and a pint of soil
to your local County Extension Office or com-
mercial laboratory for nematode diagnosis.

New Disease Alert

A new leaf spot disease of Pittosporum
tenuifolium has been described in Europe, but it
has not been noted in Florida. Symptoms of this
leaf spot, caused by Phomopsis pittospori Archer,
are small (3 to 6 turn), dark-brown to black, cir-
cular to elliptical spots which often coalesce.

Figure 1. Typical symptoms of angular leaf
spot of variegated pittosporum caused by C.

The disease is most severe on young plants.
Phomopsis leaf spot has riot been found on P.
tobira, but other Phomopsis spp. are commonly
associated with dieback of this plant.

Another leaf disease of P. tobira is
caused by a virus and has only been reported
in Italy. Symptoms caused by this virus are
primarily lightening of leaf veins kind occa-
sional curling and puckering of immature
leaves. Do not propagate from plants show-
ing these symptoms, unless the symptoms are
known to be caused by other factors.

Figure 2. Alternaria leaf spot can result in
high quality loss of shoots due to distortion
of new leaves, and necrotic, reddish-brown
lesions scattered over the leaf surface.

Figure 3. Severe infections of Rhizoctonia Figure 4. Fungal infection of pittosporum
aerial blight can result in defoliation and wood, showing black growth of fungus
matting of infectedleaves well above under bark.
ground level.

Figure 5. Pittosporum branches infected with
Corticium salmonicolor, showing discolored
cambial layer below the bark (middle two).
Advanced infections extend well into the
wood (far left). The far right branch shows
healthy cambium and wood tissue

Figure 6. Corticium limb blight of
pittosporum showing dieback and wilt.

Figure 7. Rough bark disease of pittosporum
is believed to be caused by a virus. Severe
infections result in girdling of stems and

Figure 8. Southern blight of pittosporum
showing the coarse white mycelium advanc-
ing up the stem from the soil line.

Figure 9. Root rot fungi of pittosporum plant
on left, showing chlorosis, wilting and an
overall decline in plant vigor.


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