Colletotrichum Leaf Spot of Red Sealing Wax Palm
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View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by ScholarSpace at University of Hawai'i at Manoa 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 Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture. Charles W. Laughlin, Director and Dean, Cooperative Extension Service, College of Tropical Agriculture and Human Resources, University of Hawaii at Manoa, Honolulu, Hawaii 96822. An Equal Opportunity / Affirmative Action Institution providing programs and services to the people of Hawaii without regard to race, sex, age, religion, color, national origin, ancestry, disability, marital status, arrest and court record, sexual orientation, or veteran status. 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 2 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 3 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.