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COMMON DISEASES OF TROPICAL FOLIAGE PLANTS: I FOLIAR FUNGAL DISEASES1
J. F. KnaussE LIBRARY
IFAS, University of Florida
Apopka, Florida AUG 2 7 1976
ARC-Apopka Research Report RH-75-6
The increasing demand for foliage plants as foia f rinl frrOfirtr4g
decoration of homes, offices and shopping malls is certainly news to"eay7,.
especially in Florida. The green plant boom can be witnessed daily in the
Apopka or Miami areas as growers attempt to fill ever-increasing orders.
Florida is the foliage production capital of the world, primarily because
of its subtropical environment that promotes rapid plant growth. One fact that
many persons fail to realize is the same conditions that are optimum for plant
growth are the same conditions that are optimum for plant disease development.
This article and succeeding ones will describe the more important foliage
plant diseases and explain why they develop, what controls are available and
what future research holds. The information in the articles is based upon the
author's research data and field experience obtained during his past six years'
work with Apopka foliage growers and research findings obtained by other
researchers at the University of Florida, research centers in Homestead and
Gainesville and the research group of the Division of Plant Industry, Gainesville.
WHAT IS PLANT DISEASE?
The following diagram illustrates the factors necessary for plant disease
development. Understanding the influence of these factors upon plant disease
will aid the reader in understanding this important problem area.
Originally published as ARC-A Mimeo 71-2. In a revised form published in
Florists' Review, May 17, 1973, 152(3937) and reprinted in Florida Nurseryman,
November 1974, 19(11).
Plant disease, whether it's in Apopka, Florida or in Anchorage,Alaska
can occur only when the above three factors, i.e.: Susceptible plant, disease-
causing pathogen and favorable environment, are present in the same place at
the same time. The susceptible plant needs no explanation. Pathogen is a term
given to an entity that actually causes disease. The most common pathogens are
fungi, bacteria and viruses. Environment is a major factor because pathogens
can only cause disease when temperature, moisture and other conditions are to
their liking. A basic fact to remember is that the absence of any one or more
of the factors will result in NO DISEASE. This is a fundamental truth that,
when understood, can work to the benefit of the grower.
In Florida, a wide variety of plant disease-causing pathogens enjoy year-
round environmental conditions conducive to their rapid growth and multiplication
at the expense of the foliage plants and to the chagrin of the foliage grower.
Cultural controls, when available and used, often are insufficient to control
many pathogens. As a result, foliage plant growers in Florida often rely
heavily upon pesticide application for control of many of the more devastating,
The remainder of this article will cover the most common foliar diseases 0
of foliage plants caused by fungal pathogens. Succeeding articles on ornamental
foliage plant diseases will cover bacterial pathogens, soil-borne pathogens
and general information on disease control. At the end of each article, the
disease control chemicals, found by research to be effective and nonphytotoxic,
will be listed. The control chemical information, however, must not be interpreted
as a formal recommendation. Rather, foliage plant growers are advised to consult
with their state extension agent as to the legality of employing any compound listed.
FOLIAGE PLANT DISEASES CAUSED BY FUNGAL PATHOGENS
In the discussion that follows, numerical reference to original research
articles on the disease in question will follow the common disease name or
may be included in the text where appropriate. These references are listed at
the end of the article, and the reader is advised to consult these sources for
I. "ALTERNARIA BLIGHT" (7,14,15)
Pathogen: Alternaria actinophylla
Susceptible plant: Brassaia actinophylla (schefflera)
This is the most important foliar disease of schefflera and has been
observed to occur year-round. The disease is extremely common, especially in
plants grown out-of-doors in full sun or in structures which afford little or
no control of foliar wetting resulting from rain or overhead sprinkler irrigation.
Leaves attacked by this fungus exhibit brown-black lesions that may be small and
circular to those that are varied in shape and take up most, if not all, of the
Most often, a yellow halo can be noted around the diseased area. Infection
usually results in leaf abscission, and, in severe cases, even petioles and
stems may show the brown black lesions. Because the pathogen needs free water
to spread and cause infection, and because of the extreme susceptibility of
schefflera to spray injury (3,6,9), a method of keeping the foliage dry at all
times definitely should be employed when growing this plant. As with all
foliar pathogens (except the powdery mildew fungi), keeping the foliage dry will
control the pathogen without the need for fungicide application.
II. "CEPHALOSPORIUM LEAF SPOT (SHOTGUN FUNGUS DISEASE)" (2,7,10)
Pathogen: Cephalosporium cinnamomeum
Susceptible plants: Syngonium spp. nephthytiss varieties).
Cephalosporium leaf spot of nephthytis usually occurs in the warm wet
periods. Infection by this pathogen causes minute to small leaf spots that
usually are circular and bright reddish brown with a yellow border. During
periods when environmental conditions are optimum for disease development, leaf
spots may be so numerous on the plant that it appears to have been shot with
a shotgun. Thus, the common name. Infection only occurs on young leaves and
can be prevented by keeping the foliage dry.
III. "CERCOSPORA LEAF SPOT" (1,7,12).
Pathogen: Cercospora spp.
Susceptible plants: Brassaia actinophylla (schefflera), Cordyline spp.,
Ficus spp. (rubber tree), Peperomia spp., Crassula
spp., Pilea spp., palms and many others.
Foliar symptoms caused by this plant pathogen are extremely common and
often diagnosed as resulting from improper plant water relations or as a
plant response to spider mite feeding. This is due primarily to the pinpoint
swellings that are produced on the leaf undersurface, as a result of cercospora
infection. Because of recent research findings in Florida (1,12), these edema-
like symptoms, previously attributed to poor water relations or mite attack,
now may be attributed to infection by Cercospora spp. On several of the host
plants attacked by this pathogen, numerous small red to brown lesions with a
chlorotic border may be produced, the leaf later turning yellow and falling
from the plant. Crowding of plants and.high humidity, condensate formation,
and foliar wetting by poor watering practices assist in the spread of this
IV. "DACTYLARIA LEAF SPOT" (7,8).
Pathogen: Dactylaria humicola
Susceptible plants: Philodendron oxycardium and some other philodendrons.
Because of its unique symptom expression, this disease for many years was
diagnosed mistakenly as resulting from thrips feeding and because of this
insecticides were needlessly applied. The pathogen causing this disease is most
active during warm wet periods. All cultural practices that assist in foliar
wetting encourage development of this disease. Only young leaves are susceptible,
with infection occurring mostly on the undersurface of the leaf and producing
small pinpoint, water-soaked spots that rarely enlarge to greater than 2 millimeters
in diameter. As the infected leaves mature, the lesions turn yellowish green
to yellow, often exhibiting a brown, water-soaked center. The most prominent
feature, however, is the collapse of the infected area giving the lesions a
concave appearance closely resembling thrips injury. The disease may be
distinguished from thrips feeding in that the spots are dispersed throughout
the leaf, whereas thrips feed in definite patterns, leaving trails that indicate
the movement of the insect across the leaf surface.
V. FUSARIUMM LEAF SPOT" (7,16).
Pathogen: Fusarium moniliforme
Susceptible plants: Dracaena marginata, other Dracaena spp. and Pleomele spp.
All growers of Dracaena marginata have probably seen this disease because
it is the one most commonly found on this ornamental foliage plant. Infection
by this fungus only occurs in the young growing point. Under prolonged warm wet
periods, disease development may be severe enough to completely rot out the
infected meristem area. Leaf spots appear initially as small pinpoint, water-
soaked spots that enlarge and become circular to elongate and vary in color from
yellow to red. Under optimum conditions for disease development, the cream-
colored infective spores of the fungus may be seen with the unaided eye within
the infected areas. Because infection only occurs in the young leaf whorl,
keeping this area dry at all times will control this disease.
VI. "BROWN LEAF SPOT" (7,11).
Pathogen: Leptosphaeria spp.
Susceptible plant: Dieffenbachia spp.
This disease can cause considerable damage to the foliage of Dieffenbachia
spp. The spots resulting from infection may be extremely numerous on an affected
leaf, and individual spots may range in size from pinpoint up to that of a
quarter. Lesions range from yellowish to a more common grayish brown and may be
found on the leaf laminae, midveins, petioles and the flower spathe. Severely
affected leaves often become chlorotic and die. In the centers of older lesions
the prominent black fruiting structures of the pathogen may be seen with the
unaided eye. As with all the preceding, keeping the foliage dry is the key to
VII. "RHIZOCTONIA FOLIAR BLIGHT" (5,7)
Pathogen: Rhizoctonia solani
Susceptible plants: Ferns, syngonium seedlings, philodendron seedlings,
schefflera seedlings and other closely spaced plants or seedlings.
Infection by this pathogen may occur any time the temperatures are warm and
the foliage stays wet. Close spacing of seedlings or potted plants will
encourage plants to remain wet for long periods. Ferns are especially
susceptible to this pathogen and should never be allowed to become crowded or
remain wet for long periods.
Symptoms resulting from infection usually appears as a brownish-black wet
rot that will turn tan to brown upon drying. Usually, positive diagnosis can
be made if one looks closely to observe the prominent spiderweb-like reddish-
brown threads of the fungus. These threads are the body of the pathogen and
tend to mat and hold affected leaves together. Wider spacing of seedlings and
potted plants, or any other changes in culture which promote rapid drying and
elimination of wet foliage, will assist greatly in control of this pathogen.
VIII. "PHYTOPHTHORA LEAF SPOT" (4,7,13).
Pathogen: Phytophthora spp.
Susceptible plant: Philodendron oxycardium (cordatum) and Dieffenbachia spp.
In ground beds containing Philodendron oxycardium stock plants, this
disease is commonly seen along the walkways. In warm, excessively wet periods,
during which excessive splashing occurs, disease development may become severe,
even resulting in infection of leaves in the middle of the beds. It is believed
that disease development is severe along the stock bed edges because the walk-
ways of native soil contain high populations of the pathogen. Mulching walkways
with two to three inches of sawdust or wood chips greatly reduce infection by
reducing soil splash to susceptible foliage. Although the disease is somewhat
rare on potted cordatum, it has been observed to be severe when potted plants
are placed close together just above bare soil areas where overhead irrigation
is employed and splashing of soil occurs.
Early symptoms of infection closely resemble those of bacterial infection,
and the disease often is mistaken to be bacterial. Initially, the spot appears
as an almost mushy, shiny water-soaked area. Under warm wet conditions the
lesion enlarges and quickly may encompass a greater part of all of the leaf.
Upon drying, the lesion becomes a light reddish tan and could be mistaken for
a chemical injury.
EFFECTIVE CONTROL FUNGICIDES
Under some growing situations, control of the previously mentioned pathogens
is impossible without the use of preventative fungicidal sprays. The table that
follows is not to be taken as a formal recommendation but rather to give the
reader the latest in research results on the efficacy and potential phytotoxi-
city of the fungicides tested for control of the diseases mentioned.
Table 1. Fungicides for control of foliar fungal pathogens of foliage plants.
Fungicide and conc/100 gal water
Leaf Zineb Zinc Daconil Benlate4 Captan
Disease 75 WP Maneb 75 WP 50 WP 50 WP
Controlled 1 1/2 lb 1 1/2 lb 1 1/2 lb 1/2 lb 1 1/2 Ib
Schefflera A1_-2 A-W S-1 No F-1
Syngonium F-W F-W F-W F-W F-W
Ficus, etc. A-W A-W S-W S-W NT
Philodendron NT A-W A-W A-W A-W
Pleomele NT A-W S-W S-W NT
on Dieffenbachia NT A-W NT NT NT
Ferns and Seedlings NT A-W S-1 S-W F-W
Philodendron NT A-W A-W No F-W
Efficacy of control: S = Superior, A = Adequate, F = Fair, No = No Control,
NT = Not Tested.
2Number of applications without phytotoxicity: 1 = once only, W = may be
repeated on a weekly schedule.
3Dithane M-45, Fore, Manzate 200.
4Must be alternated with other fungicides when employed in a continuing
5Do not tank mix with other chemicals. Do not add spreader-sticker.
1. Alfieri, S. A., Jr. 1968. Cercospora and edema of Peperomia. Proc. Fla.
State Hort. Soc. 81:388-391.
2. Alfieri, S. A., Jr. and C. Wehlburg. 1969. Cephalosporium leaf spot of
Syngonium podophyllum Schott. Proc. Fla. State Hort. Soc. 82:366-368.
3.' Forsyth, John, and Joyce Maynard. 1969. The sensitivity of ornamental
plants to insecticides and acaricides. Hort. Review No. 1, Commonwealth
Bureau of Horticulture and Plantation Crops, East Malling, Maidstone,
Kent, England. 66p.
4. Harkness, Roy W., and J. E. Reynolds. 1964. Effect of nitrogen and
potassium nutrition on the phytophthora leaf spot of Philodendron
oxycardium. Proc. Fla. State Hort. Soc. 77:475-481.
5. Knauss, J. F. 1971. Rhizoctonia blight of 'Florida Ruffle' fern and its
control. Plant Dis. Reptr. 55:614-616.
6, Knauss, J. F. 1971. The phytotoxicity of seventeen miticides applied as
repeated weekly sprays under slat shed conditions to five foliage plant
species. Proc. Fla. State Hort. Soc. 84:428-432.
7, Knauss, J. F. 1971. Suggestions for the control of some common diseases
of foliage plants. Univ. of Florida, Agricultural Research Center-Apopka,
Mimeo 71-2: 20pp.
8. Knauss, J. F., and S. A. Alfieri, Jr. 1970. Dactylaria leaf spot, a new
disease of Philodendron oxycardium Schott. Proc. Fla. State Hort. Soc.
9. Knauss, J. F., D. B. McConnell and Eleanor Hawkins. 1971. The safety of
fungicides and fungicide-insecticide combinations for selected foliage
plants. Florida Foliage Grower 8(1):1-10.
10. Linn, M. B. 1940. Cephalosporium leaf spot of two aroids. Phytopath.
11. Marlatt, Robert B. 1966. Brown leaf spot of Dieffenbachia. Plant Dis.
12. Marlatt, Robert B. 1970. Isolation, inoculation, temperature relations
and culture of a Cercospora pathogenic to Ficus elastica 'Decora'. Plant
Dis. Reptr. 54:199-202.
13. McFadden, L. A. 1963. Florida Agricultural Experiment Station Annual
Report. p344, Gainesville, FL.
14. Miller, H, N. 1957. An Alternaria leaf spot of Schefflera actinophylla.
Phytopath. 47:529. Abstr.
15. Miller, J. W. 1969. Alternaria leaf spot of Schefflera. Fla. Dept. Agr.
Division of Plant Industry, Circular No. 80.
16. Wehlburg, C., and A. P. Martinez. 1967. Leaf spot of Dracaena marginata
Lam. caused by Fusarium moniliforme Sheld. and its control. Proc. Fla. State
Hort. Soc. 80:454-456.
To simplify information, trade names of products have been used.
No endorsement of named products is intended, nor is critism
implied of similar products not mentioned. Mention of a chemical
does not imply guarantee of effectiveness or safety, nor that
the chemicals or uses discussed have been registered by appropriate
state and federal agencies.