Colletotrichum leaf spot of red ceiling wax palm by nyut545e2

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									Cooperative Extension Service                                                                                                                   Plant Disease
                                                                                                                                                January 1997
                                                                                                                                                        PD-10




           Colletotrichum Leaf Spot of Red Sealing Wax Palm
                                                    Janice Y. Uchida and Chris Y. Kadooka
                                                        Department of Plant Pathology



Introduction                                                                          Symptoms and spread
Red sealing wax palm, Cyrtostachys renda Blume., is                                   Leaf spots on red sealing wax palm begin as small, wa-
an unarmed, monoecious, clumping palm with glossy                                     ter-soaked, dark green areas about 1–2 mm wide. These
green leaves. The petioles and sheaths are yellow on                                  areas expand into circular spots with tan to light brown
young plants and turn distinctively red on mature plants.                             centers, bordered by water-soaked tissue (Figure 1). As
This attractive indoor tropical palm is relatively uncom-                             the spots expand, lesion centers lighten to very light tan
mon and generally commands high prices. In response                                   to cream color, with some spots developing brown mar-
to market demand, production of red sealing wax palm                                  gins around the centers. Most of the circular spots are
grown for export in Hawaii has recently expanded.                                     3–7 mm wide, and the size of the necrotic (dead) areas
     In l994, leaf spots were observed on hundreds of                                 increases as spots coalesce (Figure 2). Large spots de-
red sealing wax palms at a commercial nursery. Fungi                                  velop on young, expanding leaves.
that commonly cause palm leaf spots, such as Bipolaris                                     Young leaves are highly susceptible, while older
and Calonectria, were not found to be associated with                                 leaves are more resistant to the disease. As the leaf ma-
these spots. Instead, a Colletotrichum species was re-                                tures, the rate of lesion expansion slows. However, with
covered from many of the diseased leaves. In the past,                                adequate moisture, new spots continue to form, result-
numerous Colletotrichum isolates were collected from                                  ing in larger, older spots with black edges surrounded
various palm varieties in Hawaii and tested for their abil-                           by numerous small spots and flecks. On mature leaves,
ity to cause disease, but none of them caused disease                                 these flecks do not expand, and large sections of the
when applied to healthy palm leaves. Very little experi-                              leaf become covered by hundreds of flecks. A general
mental work documents Colletotrichum as the cause of                                  yellowing (chlorosis) of the entire leaf surface also oc-
palm diseases, although the association or presence of                                curs (Figures 3 and 4). Yellowing may also occur around
Colletotrichum with leaf spots has been reported from                                 individual spots.
many palm-growing areas in the world. Colletotrichum                                       Leaf petioles and sheaths are also infected. Typical
has been associated with leaf spots on Phoenix roebe-                                 spots are 5–10 mm long and brown to gray with dark
lenii, Caryota mitis, Washingtonia sp., Paurotis sp., and                             brown to black borders.
other palms. Colletotrichum is frequently saprophytic                                      Colletotrichum spores are produced on the surface
(i.e., nonpathogenic) and grows on dead plant tissue.                                 of older diseased leaves and sheaths. These very tiny
Therefore, its isolation from or presence on a leaf spot                              spores spread to healthy leaves when splashed by wa-
may not mean that it caused the leaf spot.                                            ter. When leaves remain wet for at least 12 hours, the
     This fact sheet reports the isolation of a new Colleto-                          spores germinate and form a structure called an appres-
trichum strain in Hawaii, the establishment of its patho-                             sorium. The appressorium firmly attaches the fungus to
genicity and thus its role as the cause of the disease, and                           the leaf. From the appressorium, an infection hypha is
the characterization of this new disease.                                             produced. This fungal hypha (or thread) penetrates the




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PD–10                              Colletotrichum Leaf Spot of Red Sealing Wax Palm            CTAHR — January 1997


Figure 1. Leaf spots caused by Colletotrichum on red seal-    Figure 2. Leaf spots caused by Colletotrichum on red seal-
ing wax palm, 8 days after inoculation. Early symptoms        ing wax palm, 16 days after inoculation.
include circular, tan spots with dark green edges and small
spots with brown centers.




leaf surface, and fungal colonies are eventually formed       pruned. Infected plant debris should be gathered and
in the leaf. This growth appears as brown leaf damage         dumped at county incineration sites or landfills. Potting
or leaf spots. The fungus is also spread by strong wind       soil from infected plants should be discarded. If the pot-
currents that dislodge spores from agitated leaves, by        ting soil is reused, it must be steam-sterilized to elimi-
nursery workers handling diseased plants, and by move-        nate the pathogen. Infected plants and contaminated soil
ment of slugs or other pests. Trays, pots, tags, and other    are sources of spores that can initiate new disease out-
supplies can also be contaminated with spores of the          breaks.
pathogen.                                                          Moisture control is crucial to disease control. Limit
                                                              overhead irrigation or moisture from rain. This will re-
Disease control                                               duce spread of the pathogen, prevent germination of
Efforts to control this and many other fungal diseases        spores, and reduce development of new spots. If mois-
must begin with sanitation. All dead and badly diseased       ture is not controlled, new spots will form continuously,
leaves should be removed from the plant. Any infected         and there will be no breaks in the disease cycle. Dry
sheath that can easily be separated from the stem should      weather will improve crop quality, but the disease will
carefully be removed. For leaves with only a few spots,       return when rain resumes.
affected leaf sections or individual leaflets should be


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PD–10                             Colletotrichum Leaf Spot of Red Sealing Wax Palm            CTAHR — January 1997


Figures 3 and 4. Older spots and small blights on red sealing wax palm caused by Colletotrichum. Note the dark borders
around these spots and the formation of numerous small flecks and spots.




     In areas of Hawaii that are very wet during parts of    of resistant Colletotrichum populations. The highest
the year, solid-covered greenhouses are strongly rec-        level of chemical control of disease is achieved when
ommended. Foliar diseases such as those caused by            combined with sanitation and moisture-control practices.
Colletotrichum, Bipolaris, and Cercospora are greatly             If the palm crop is severely diseased with Colleto-
reduced and can eventually be eliminated on plants trans-    trichum, the following should be implemented:
ferred and grown under solid cover. These fungi do not           • Remove all dead, severely diseased and heavily
survive for long in the soil and are generally easy to             spotted leaves. Trim larger spots from leaves or
manage once the disease cycle is broken.                           remove leaflets on leaves with few spots. Remove
     Traditionally, diseases caused by Colletotrichum              sheaths which are spotted.
have been aggressively controlled by repeated applica-           • Place the crop under solid cover or construct a rect-
tions of fungicides. These chemicals prevent fungal                angular frame to cover the bench with heavy, clear
germination and host penetration, reduce spore produc-             plastic to keep the foliage as dry as possible. The
tion, and interfere with fungal growth within the plant.           frame should be at least 3 feet high. This plastic
Mancozeb fungicides, such as Dithane M45, will re-                 covering should primarily cover the top of the
duce disease levels but are less effective during periods          frame and the sides should be kept open, other-
of continuous rain. Good fungicide coverage of suscep-             wise humidity levels will be too high.
tible young leaves is needed to prevent disease. Cleary          • Increase the spacing between plants to allow good
3336 has been highly effective in preventing new leaf              air circulation.
spots. However, methyl thiophanate fungicides must be            • Apply fungicides to protect new leaves. As new
rotated with other fungicides to prevent development               leaves are produced, remove older leaves that have


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PD–10                                  Colletotrichum Leaf Spot of Red Sealing Wax Palm                       CTAHR — January 1997




      any signs of disease (flecks, small spots, yellow                 ella cingulata are different names for the same fungus.
      areas).                                                           The former name refers to the asexual stage, and the
    • Continually monitor the crop and remove leaves                    latter refers to the sexual stage.
      with spots as soon as they appear.                                     Our studies of several diseases caused by Colleto-
                                                                        trichum have demonstrated that isolates of C. gloeo-
Other palms                                                             sporioides producing the Glomerella sexual stage are
Chrysalidocarpus lutescens (golden palm), Chamae-                       not the causal agents of disease, even if this fungus is
dorea seifrizii (bamboo or reed palm), Howeia forster-                  easily and often isolated from diseased tissue. Thus,
ana (Forster sentry or kentia palm), and Rhapis excelsa                 unless pathogenicity tests are conducted, any Colleto-
(lady palm) were also tested. No disease or a few small                 trichum species isolated from various palm diseases
spots developed following inoculations with the new                     should not be assumed to be the pathogen. Finding the
Colletotrichum.                                                         Glomerella stage in older lesions does not strengthen
                                                                        the assumption that Colletotrichum is the causal agent.
Colletotrichum biology and implications                                      To date, the Glomerella stage for the pathogenic
In laboratory culture, the Colletotrichum species that at-              Colletotrichum isolated from red sealing wax palm has
tacks palms produces spores that are slightly larger than               not been produced in culture or on the host. Spores of
those observed for many isolates of C. gloeosporioides.                 Colletotrichum are readily found on infected palms, but
However, they still fall within the size range given for                dark fruiting bodies have not been observed. If and when
C. gloeosporioides. Further studies are needed to deter-                this stage is found, the type or species of Colletotrichum
mine whether the palm pathogen is a new species.                        it produces needs to be determined. Nonpathogenic
     There are frequent reports of dark fruiting bodies                 strains of C. gloeosporioides could easily grow on tis-
found on older spots or in the center of leaf spots on                  sue killed by the pathogenic Colletotrichum.
palms. These fruiting bodies are identified as those of                      The same situation exists for other diseases caused
Glomerella cingulata, the sexual stage of Colletotrichum                by Colletotrichum. The Glomerella stage of pathogenic
gloeosporioides. However, C. gloeosporioides is an                      Colletotrichum from anthurium, basil, and orchids has
extremely common saprophyte and quickly invades dead                    not been observed on old host tissue or in culture. All
tissue created by other pathogens. Spores produced by                   Colletotrichum isolated from these hosts that produce
Glomerella cingulata are called ascospores and are dis-                 the Glomerella stage have been tested and are not patho-
charged into the air. Thus, the fungus is rapidly distrib-              genic.
uted throughout any greenhouse or field. Glomerella                          The term “anthracnose” is commonly used to de-
ascospores that land on diseased leaves germinate and                   scribe diseases caused by Colletotrichum. In palms, it
produce fungal mycelia (threads) that feed on the dead                  has also been applied to leaf spots on seedlings irre-
leaf tissue. Within a week or two, the fungus will pro-                 spective of the associated fungi, which include Botryodi-
duce Colletotrichum spores on the surface of the dead                   plodia, Leptosphaeria, and Melanconium. To avoid con-
leaf. Later, the dark fruiting bodies of Glomerella are                 fusion, we have not used the term “anthracnose” here.
produced. Colletotrichum gloeosporioides and Glomer-




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This CTAHR Fact Sheet PD–10 (Plant Disease no. 10) is published in continuation of the CTAHR Plant Disease Series, first published in 1975.


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