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SOME DISEASES OF PITTOSPORUM TOBIRA (THUNB;)-A1-T,
A. R. Chase '
IFAS University of Florida
Agricultural Research Center-Apopka .
ARC-A Research Report RH-81-2
.S. Univ. of Flor~;-
Pittosporum tobira (Thunb.) Ait. (Japanese Pittosporum) and P. __FTra-
Ait. cv. Variegata are grown in Florida as outdoor landscape plants as well as
for production in the cut foliage market. Pittosporum tolerate full sun and
freezing temperatures. Plantingsof pittosporum are relatively carefree, although
in some locations they may be subject to pests and diseases attacking roots, stems
and leaves. The following discussion is concerned with three groups of diseases
of pittosporum based on symptomatology: A) leafspots, B) stem galls and diebacks,
and C) root rots.
There are several fungal organisms causing leafspots of pittosporum.
Angular leafspot caused by Cercospora pittospori Plak. was first described in
1940 by Plakidas (4), and is common in field plantings of pittosporum not
routinely sprayed for its control and in the landscape (6). Symptoms of angular
leafspot are light yellow to pale green and tan angular spots developing on
upper leaf surfaces. Leafspots are angular due to expansion between leaf veins
and commonly have an indistinct margin. The spot pattern is similar on leaf
undersides. Severe infections of immature leaves may result in leaf distortion.
The key to recognition of this leafspot is the characteristic angular shape.
Another leafspot of pittosporum is caused by Alternaria tenuissima (Fr.)
Wiltsh. This disease was first noted by Sobers in early 1960's (7,8)'who
established the pathogenic role of A. tenuissima in that leafspot. Early
stages of Alternaria leafspot resemble angular leafspots. However, as lesions
develop, they become distinctly different. Irregular chlorotic spots are
scattered over the leaf surface, later developing necrotic centers absent
in angular leafspot. Spots are typically rounded, have tan to dark brown
centers, and generally are smaller than those caused by Cercospora sp.
Many of the lesions are surrounded by a yellow halo and their centers are
slightly depressed. Symptoms on immature leaves may result again in
distortion giving leaves a crinkled appearance. This disease is not as
commonly found as angular leafspot in the field (although it is common in
nurseries) and is generally less damaging to a planting. Control measures
can be the same for both diseases. Basic copper can be used to control both
leafspots when sprayed two or three times at 7-10 day intervals (2). BenlateD
benomyll) can be used also for control of angular leafspot but not for control'
of Alternaria leafspot since it has no activity against the fungus.
The most severe leafspot of pittosporum is caused by Rhizoctonia ramicola
Weber & Roberts reported in 1951 (10). In many cases this disease may more
accurately be referred to as a blight and has been commonly named silky
threadblight. Silky threadblight is characterized by small, tan, irregularly
shaped spots, generally surrounded by purplish margins, Spots frequently reach
1 cm in diameter and can encompass the entire leaf. R. ramicola inhabits the
soil and thus creates spots on lower leaves initially and extends into upper
portions of plants when conditions are favorable, In severe cases leaves curl
into a cylinder and become matted by the threadlike growth of the fungus, thus
the common name silky threadblight. Recommended control methods include
sanitation and one or more summer applications of Terraclor-(PCNB) at the
rate of 2 g/liter (3).
A new leafspot disease of P. tenuifolium has been described by Archer in
Europe (1) but has not been noted in Florida as yet. Symptoms of this leafspot,
cutting instruments or by passive spore movements. Galls often girdle stems
resulting in twig death. Pruning infected areas carefully can eliminate
spread to adjacent tissues and is a recommended control (2).
C. Root rots
Root rot of pittosporum is caused by Pythium spp. and Rhizoctonia spp.
(2). Although no papers supporting the role of these organisms as pathogens
of pittosporum are available, they are readily isolated from rotting roots.
Root rot is most severe when plants are grown in wet, poorly drained soil.
Declining plants may lose their leaves suddenly or over a long period of time
beginning at the base of the plants. Leaves may also appear chlorotic as the
roots are unable to extract nutrients from the soil. Root examination often
reveals black and/or soggy roots. Pythium root rot generally is typified by
a sloughing off of outer root layers leaving the central core intact. In both
root rots small feeder roots are usually absent from severely infected areas
of the roots. Careful water management in planting sites is a valuable aid in
controlling these rots. Drenches with Benlate@ or LesanO (fenaminosulf)
have been recommended for treatment of young plants as a preventative treatment
1. Archer, S. A. 1973. Phomopsis pittospori sp. nov., associated with
leafspotting of Pittosporum tenuifolium. Trans. Brit. Mycol. Soc.
2. Kucharek, T., G. W. Simone, and R. S. Mullin. 1978. Florida Plant
Disease Control Guide. IFAS, Fla. Coop. Ext. Serv., Univ. of Fla.
3. Martinez, A. P. 1967. Silky threadblight of Pittosporum. Fla. Dept.
of Agric., Div. of P1. Ind., P1. Path. Circ. No. 60.
4. Plakidas, A. B. 1940. Angular leafspot of Pittosporum. Mycologia
5. Rana, G. L., and A. Di Franco. 1980. Isolation of two rhabdoviruses
from Pittosproum and Pelargonium. Acta Horticulturae 110:191-193.
6. Sobers, E. K. 1962. Angular leafspot of Pittosporum Cercospora
pittospori Plak. Fla. Dept. of Agr., Div. of P1. Ind., P1. Path Circ.
7. Sobers, E. K. 1962. Alternaria leafspot of Pittosporum tobira Ait. -
.(Alternaria sp.). Fla. Dept. of Agr., Div. of P1. Ind., P1. Path.
Circ. No. 5.
8. Sobers, E. K. 1964. Alternaria leafspot of Pittosproum. Phytopathology
9. Thomas, H. Earl, and Kenneth F. Baker. 1947. A rough-bark disease of
Pittosporum tobira. Phytopathology 37:192-194.
10. Weber, G. F., and D. A. Roberts. 1951. Silky threadblight of Elaeagnus
pungens caused by Rhizoctonia ramicola n. sp. Phytopathology 41:615-621.