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7-- COMMON DISEASES OF TROPICAL FOLIAGE PLANTS: II BACTERIAL DISEASES1
J. F. Knauss
IFAS, University of Florida
Apopka, Florida HUME LIBRARY
ARC-Apopka Research Report RH-75
Bacterial plant pathogens find the warm/hot, moi t environment of Florid
especially fitting for their continued growth and sur A. S of: 8i sa
severe and devastating diseases of tropical foliage pltanisiM, ae' ta' 1-b, ,
bacteria belonging to the genera Erwinia, Xanthomonas and Pseudomonas.
The remainder of this article describes the more important bacterial
diseases of tropical foliage plants. At the end of each individual disease
discussion, the bactericides found by research to be effective and nonphytotoxic
will be stated. The bactericide 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
In the discussion that follows, numerical references to original research
articles, on the disease in question, 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 go to these sources for additional
information, if desired.
I. BACTERIAL LEAF SPOT AND TIPBURN OF CORDATUM (4,5,7,9,12,13,15,16,26)
Pathogen: Xanthomonas dieffenbachiae
Susceptible plants: Philodendron oxycardium (cordatum), Dieffenbachia spp.,
Anthurium spp., others
Just a few short years ago, Xanthomonas dieffenbachiae threatened the
successful production of cordatum, which was then and probably still is the
backbone of the foliage plant industry.
Although the pathogen, X. dieffenbachiae, was first described on Dieffenbachia
picta in 1939 (13), it wasn't until 1963 (16) that it was noted on cordatum and
not until 1968 (26) that it was definitely found to be X. dieffenbachiae. From
1963 to 1971, the pathogen was disseminated throughout most of the foliage
Originally published as ARC-A Mimeo 71-2. In a revised form published in
Florists' Review 153(3958), October 11, 1973 and reprinted in Florida Nurseryman,
December 1974, 19(12).
industry and produced what became the foliage industry's most important disease
problem. It remains yet today a common and important foliar bacterial disease.
Few stock areas of P. oxycardium are free of this pathogen. The pathogen's
ability to move so rapidly within the industry has been facilitated by sales of
X. dieffenbachiae-infected cordatum between growers. Early symptoms of infection
within the lamina of the leaf are small water-soaked dots which turn yellow.
With age, the center of the lesion often turns brown. The most common symptom,
however, occurs as a yellowing along the leaf margin, with the earliest sign
occurring at the pointed leaf tip. During the hot wet summer, the infected leaf
margin becomes nectrotic and turns a reddish-brown, hence the name "red edge",
given to it by the growers. As the disease progresses, the affected leaf turns
yellow and drops from the stem, thus making the node useless as a propagative
unit. Severe leaf drop within stock plantings severely limits the number of
cuttings produced per area. Often diseased leaves appearing free or nearly
free of disease are stuck into propagative beds and turn yellow and die during
the first weeks of propagation. The disease is most active in the summer months
and may be present, but not detected, during the cooler parts of the year.
Once established, the pathogen is difficult and costly to control.
If a new stock area is planned, plant only cuttings known to come from
clean sources. Never establish clean stock in the same structure and preferably
not on the same property with X. dieffenbachiae-infected cordatum or dieffenbachia.
Take steps to prevent any recontamination of clean areas. Because the pathogen
attacks only the leaves and needs wet foliage to gain entrance, any cultural
change that will aid in keeping the foliage dry will assist greatly in controlling
the disease. Where disease is present and chemical control is required, weekly
applications of a combination of Kocide 101 86 WP (one and one-half pounds in
100 gallons of water) and Dithane M-45 (one and one-half pounds in 100 gallons
of water) will give effective control (12). A spreader-sticker such as Plyac
(Allied Chemical, Atlanta, GA), should be added to the preceding combination at
the concentration of two ounces in 100 gallons of water to ensure proper coverage
and retention of the protective bactericide combination. Streptomycin,
recommended in the early attempts to control this pathogen, was found after
repeated sprays to be ineffective because the pathogen developed resistance to
this antibiotic (7). If streptomycin is used it should be employed only on a
schedule alternating with the Kocide-Dithane M-45 combination and then never at a
concentration above 200 parts per million active ingredient.
Another effect influencing control is the possibility of a plant's
nutritional level affecting disease development. In research conducted under
glasshouse conditions, disease severity was found to decrease with increasing
levels of nitrogen (4). To date, however, this effect has not been adequately
studied and shown to occur under field conditions.
II. ERWINIA BLIGHT OF FOLIAGE PLANTS (9,11,14,17,19,20,23)
Pathogen: Erwinia chrysanthemi
Susceptible plants: Aglaonema spp. Dieffenbachia amoena, other Dieffenbachia
spp., Philodendron panduraeforme, Philodendron selloum,
other Philodendron spp., Syngonium spp. and many others.
Without question, Erwinia chrysanthemi is the single most important bacterial
phytopathogen of tropical foliage plants. Although discovered on chrysanthemum
(3), the pathogen is by no means restricted to this ornamental crop and recently
has been found as an important pathogen on poinsettia (6) as well as several
other ornamental crops (1), many of them foliage plants.
The pathogen is by no means meek in its attacks on foliage plants. Symptoms
of attack may result from internal (systemic) invasion, these being a foliar
yellowing of new leaves often with an accompanying wilt followed by a mushy,
foul-smelling stem rot. Infected dieffenbachia, especially Dieffenbachia amoena,
exhibit these symptoms. When aerially disseminated, the pathogen can cause
foliar infection, resulting in a rapid mushy leaf collapse similar to that
produced on Philodendron panduraeforme and Philodendron 'Florida', or definite
leaf spots as seen on Syngonium podophyllum 'Green Gold'. With some foliage such
as Philodendron selloum,the pathogen might produce all the preceding symptoms in
addition to several others. With this latter plant, attack often results in
total and utter destruction.
Aerial spread of the pathogen from diseased to healthy plants occurs most
often in free water that results from rainfall or overhead irrigation. Fresh
wounds in the plant's epidermis facilitate infection, but in many cases they
are not necessary for infection to occur. Another important method of
dissemination of the pathogen may occur during the normal vegetative propagation
of foliage plants. During propagation, workers handling and cutting E. chrysanthemi-
infected canes, cuttings or vines unknowingly contaminate their hands and tools.
These same contaminated hands and tools often are then employed in cutting clean
plant material, which in turn becomes contaminated in the process. Thus, an
important phase of the pathogen's travels through the production cycle is main-
tained in the normal propagative process.
Erwinia chrysanthemi grows best in warm-to-hot, wet and humid environments.
Under these conditions, common in Florida, the short period of time required by
E. chrysanthemi to decimate a crop often is astounding. The pathogen appears
to survive in infested propagative media, in stock bed areas (especially where
overhead irrigation is used) and on and in infected plants, even during times
when temperatures are adverse to its rapid development. Surveys of plant
material for freedom from this pathogen must be made during periods of the year
conducive to the pathogen's development and growth.
Although preventive streptomycin sprays (100 to 200 ppm active ingredient)
to stock and production plants and 5-30 minute streptomycin dips (100 to 200 ppm
active ingredient) to propagative cane units have been shown to have activity
against E. chrysanthemi, this approach alone is far from the answer for control
of this pathogen. Growers are advised to seriously reevaluate any and all
cultural procedures which induce and encourage either foliar wetting or
condensation on the foliage. Whenever possible, changes necessary to keep the
foliage dry at all times should be made.
When new areas for stock production are contemplated, they should be
established under a permanent (glass, fiberglass, rigid plastic) structure.
Plant in raised beds containing sterilized media. Employ a watering system
that does not wet the foliage, and select the best stock available (known
pathogen-free, when possible) for planting.
In established stock areas, maintain a constant vigilance for diseased
plants. Remove and destroy all diseased plants. Keep the foliage dry at all
times. When this is impossible, apply streptomycin sprays on a weekly basis
during the wet warm periods that are particularly conducive to disease develop-
ment. Never use plant material that is exhibiting disease symptoms for
propagation. Lastly, always sterilize propagative media between crops, especially
following a severe case of cutting or cane decay caused by E. chrysanthemi.
III. BACTERIAL LEAF BLIGHT OF SYNGONIUM (9,24,25)
Pathogen: Xanthomonas vitians
Susceptible plants: Syngonium spp., Aglaonema roebellinii, possibly other
The pathogen causing bacterial leaf spot of syngonium was determined in
1969 (25) to be identical to that described in 1918 (2) as a pathogen of
lettuce. Xanthomonas vitians, like its sister species, X. dieffenbachiae,
abounds in warm-to-hot, wet and humid environments. Cultural practices like
crowding of plants and overhead irrigation are particularly conducive to its
The most characteristic symptom of infection on syngonium, which is the
principle host plant, is the presence of water-soaked lesions along the leaf
margin and leaf tip. The lesions may elongate and extend into the midrib
of the leaf. Lesions are initially dark green, then turn yellow and eventually
become brown and necrotic. The diseased area often is surrounded by a bright
yellow zone that separates it from the apparently healthy portion of the leaf.
On the undersurface of leaves with older lesions, white flakes of dried bacterial
exudate (which in reality are billions of bacterial cells) often are visible
to the unaided eye.
Along with attack of the leaves, the pathogen recently has been found to
cause a cutting decay during propagation. Cuttings taken from vines showing
severe leaf infection stand a good chance of rotting during propagation,
especially in the warmer months.
Methods for control of this pathogen are similar to those used for the
preceding pathogens. Clean stock, proper sanitation and production procedures
that ensure dry foliage will aid a great deal in control. To date, bactericide
applications have not been so effective in control of X. vitians as experienced
in control of X. dieffenbachiae. If bactericides must be employed, however, the
combination given earlier for the control of X. dieffenbachiae appears to be the
IV. RAPID DECAY OF POTHOS (9,10,18).
Pathogen: Erwinia carotovora
Susceptible plants: Scindapsus aureus (pothos) and other foliage plants.
Rapid decay of pothos first was noted in 1961 (18). The pathogen working
alone or.often in conjunction with Pythium splendens (8) is a major reason for
the failure of many growers to produce this foliage plant species successfully.
The pathogen E. carotovora, is the same one that often causes a rapid, mushy
foul-smelling rot of vegetables and ornamental tuber crops. It also plays
a role in the propagative decays of foliage plants other than S. aureus and
is widely present in the foliage plant industry.
The pathogen on S. aureus invades the leaves and petioles of potted
plants and the stems, leaves and petioles of unrooted and rooted cuttings.
The most severe disease development occurs under wet, warm-to-hot environments.
Often during periods conducive to optimal disease development, young emerging
shoots of propagative cuttings will be completely blighted, with the rot
eventually progressing into the stems of the cuttings.
Infection can occur through intact plant tissue but is enhanced by
wounds in the plant epidermis. Infected plant tissue appears initially as a
discrete water-soaked grayish-green area which rapidly enlarges, becomes mushy
and turns brown to black, eventually resulting in the complete collapse of the
affected plant unit. If during leaf infection the environmental conditions
become excessively dry, leaf lesions will turn dry brownish-black, often with
a yellow margin. Cuttings taken near the vine apex and those taken from rapidly
growing vines are most susceptible to the pathogen. Infection of unrooted
cuttings usually occurs through cut ends at the area where aerial roots have been
removed, with the decay eventually progressing into the petiole and lamina of
the parent leaf. Complete collapse of the cutting often can occur within two
to four days. Parent leaves of cuttings attacked by E, carotovora often turn
a bright yellow as a result of the stem infection.
Excellent control of this pathogen can be achieved by growing pothos under
conditions which keep the foliage dry. Stock areas should be planted with the
cleanest plants available. If a bactericide must be used in the stock areas,
a weekly streptomycin spray (100 ppm active ingredient) will assist in control.
Recent studies (8,10) show that Dexon applied as a drench (1.0 pound in 100
gallons of water at the rate of one pint to a square foot) to beds prior to
propagation,or as a 10-minute dip,aided in the control of E. carotovora.
It is not suggested as a substitute for streptomycin, however, because the latter
is superior as a bactericide. Rather, Dexon employed as a soil fungicide
where pythium root and cutting decay occur will supply the added benefit of
activity.against E. carotovora. A 10-minute streptomycin dip (200 ppm active
ingredient) of cuttings soon after cutting and prior to sticking will reduce
disease resulting from transfer of the pathogen from diseased to healthy
cuttings during the cutting process.
V. BACTERIAL LEAF SPOT OF DRACAENA SANDERIANA (22)
Pathogen: Pseudomonas sp.
Susceptible plant: Dracaena sanderiana
This pseudomonas species can and has been shown to cause a serious disease
of D. sanderiana. This disease is not, however, so common nor so economically
important as those caused by the preceding members of the genera Erwinia and
Initial symptoms of infection usually are seen as circular to irregular
water-soaked spots which can occur anywhere on the leaf blade. A thin, reddish-
brown margin occasionally forms around the water-soaked centers, with diffuse
chlorotic patterns developing around the lesions. The spots often enlarge,
and the affected area may turn papery and dry. In severe cases, the affected
area becomes brown and necrotic. Infection does not appear to progress into
The pathogen is capable of invading uninjured as well as injured plant
tissue. Excessive moisture during propagation or foliar wetting to potted
plants encourages disease development. Severely affected plants should be
pulled and destroyed. Slightly infected plants can be saved by removing the
affected leaves and spraying on a weekly interval with streptomycin (100 ppm
active ingredient). Select cuttings carefully for propagation, and discard
those showing infection. A 10-minute dip of streptomycin prior to
planting may supply some protection, but its value is as yet undetermined.
The best control of all, however, is employment of clean cuttings carried
through propagation and finishing under the best sanitary and cultural practices
VI. PSEUDOMONAS LEAF SPOT (27).
Pathogen: Pseudomonas cichorii
Susceptible plants: Scindapsus spp., Philodendron panduraeforme,
Aglaonema spp. and Monstera spp.
Little is known of P. cichorii's role in the production of foliage plants.
Its presence first was noted in the middle '60s (27) on Scindapsus aureus. As
recently as 1972 (21) P. cichorii was found causing a serious and new disease
of gerberas at one of the largest foliage nurseries in Apopka, FL. This latter
report further verifies the presence of the pathogen in the Apopka foliage-
Artificial inoculations of foliage plants produce a brownish-black lesion
which takes four to seven days to develop. With Scindapsus aureus, the
formation of lighter and darker zones is quite noticeable. In inoculations
to Monstera deliciosa, a yellow halo around the affected area is particularly
prominent. The author has seen in foliage nurseries symptoms on S. aureus and
monstera similar to those produced by artificial inoculations but cannot say
with assurance that P. cichorii was the cause.
1. Boesewinkel, H. J. 1973. Bacterical wilt of carnation in New Zealand.
Plant Dis. Reptr. 57:136-140.
2. Brown, Nellie A. 1918. Some bacterial diseases of lettuce. J. Agr.
3. Burkholder, W. H., L. A. McFadden, and A. W. Dimock. 1953. A bacterial
blight of chrysanthemums. Phytopath. 43:522-526.
4. Harkness, Roy W., and R. B. Marlatt. 1970. Effect of nitrogen, phosphorus
and potassium on growth and Xanthomonas diseaseof Philodendron oxycardium.
J. Amer. Soc. Hort. Sci. 95:37-41.
5. Hayward, A. C. 1972. A bacterial disease of anthurium in Hawaii. Plant
Dis. Reptr. 56:904-908.
6. Hoitink, H. A. J., and Gilbert C. Daft. 1972. Bacterial stem rot of
poinsettia, a new disease caused by Erwinia carotovora var. chrysanthemi.
Plant Dis. Reptr. 56:480-484.
7. Knauss, J. F. 1972. Resistance of Xanthomonas dieffenbachiaeisolates to
streptomycin. Plant Dis. Reptr. 56:394-397.
8. Knauss, J. F. 1972. Field evaluation of several soil fungicides for
control of Scindapsus aureus cutting decay incited by Pythium splendens.
Plant Dis. Reptr. 56:1074-1077.
9. 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.
10. Knauss, J. F., and J. W. Miller. 1972. Description and control of the
rapid decay of Scindapsus aureus incited by Erwinia carotovora. Proc.
Fla. State Hort. Soc. 85:348-352.
11. Knauss, J. F., and C. Wehlburg. 1969. The distribution and pathogenicity
of Erwinia chrysanthemi Burkholder et al to Syngonium podophyllum Schott.
Proc. Fla. State Hort. Soc. 82:370-373.
12. Knauss, J. F., W. E. Waters, and R. T. Poole. 1971. The evaluation of
bactericides and bactericide combinations for the control of bacterial
leaf spot and tipburn of Philodendron oxycardium incited by Xanthomonas
dieffenbachiae. Proc. Fla. State Hort. Soc. 84:423-428.
13. McCulloch, Lucia, and P. P. Pirone. 1939. Bacterial leaf spot of
Dieffenbachia. Phytopath. 29:956-962.
14. McFadden, L. A. 1969. Algaonema pictum, a new host of Erwinia chrysanthemi.
Plant Dis. Reptr. 53:253-254.
15. McFadden, Lorne A. 1967. A Xanthomonas infection of Philodendron oxycardium.
Phytopath. 57:343 (Abstr.).
16. McFadden, Lorne A. 1963. Nature, cause and control of diseases of
tropical foliage plants. Florida Agr. Exp. Sta. Ann. Rept. p.344.
17. McFadden, Lorne A. 1961. Bacterial stem and leaf rot of Dieffenbachia
in Florida. Phytopath. 51:663-668.
18. McFadden, Lorne A. 1961. Nature, cause and control of diseases of tropical
foliage plants. Florida Agr. Exp. St. Ann. Rept. p.356.
19. Miller, Howard N. 1955. Investigations with antibiotics for control of
bacterial diseases of foliage plants. Proc. Fla. State Hort. Soc. 68:354-358.
20. Miller, H. N., and Lorne A. McFadden. 1961. A bacterial disease of
Philodendron. Phytopath. 51:826-831.
21. Miller, J. W., and J. F. Knauss. 1973. Bacterial blight of Gerbera
jamesonii incited by Pseudomonas cichorii. Plant Dis. Reptr. 57:504-505.
22. Miller, J. W. and C. Wehlburg. 1969. Bacterial leaf spot of Dracaena
sanderiana. Proc. Fla. State Hort. Soc. 82:368-370.
23. Munnecke, Donald E. 1960. Bacterial stem rot of Dieffenbachia.
24. Wehlburg, C. 1970. Bacterial leaf blight of Syngonium. Plant Path.
Circular No. 91, Fla. Dept. Agr. and Cons. Serv., Div. of Plant Ind.,
25. Wehlburg, C. 1969. Bacterial leaf blight of Syngonium podophyllum.
Phytopath. 59:1056 (Abstr.).
26. Wehlburg, C. 1968. Bacterial leaf spot and tipburn of Philodendron
oxycardium caused by Xanthomonas dieffenbachiae. Proc. Fla. State
Hort. Soc. 81:394-397.
27. Wehlburg, C., and C. P. Seymour. Leaf spot of Araceae caused by
Pseudomonas cichorii (Swingle) Stapp. Twenty-Sixth Biennial Report,
1964-1966, Fla. Dept. Agr. and Cons. Serv., Div. of Plant Ind.,
Gainesville, FL. pp154-156.
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