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False Smut Diagnostic Guide

Graphiola phoenicis

False Smut (Graphiola phoenicis) is an aesthetic fungal leaf disease of several palm species. Small black fruiting bodies erupt through the epidermis of older leaflets creating an unsightly appearance.

Trees at Risk

The primary hosts in Florida are Phoenix species including; Phoenix canariensis (Canary Island date palm) and Phoenix dactylifera (date palm). False smut has also been observed on; Acoelorrhaphe wrightii, Arenga pinnata, Butia odorata, Chamaerops humilis, Coccothrinax argentata, Cocos nucifera, Dypsis lutescens, Livistona alfredii, Livistona chinensis, Phoenix roebelenii, Phoenix sylvestris, Phoenix theophrasti, Prestoea acuminata, Roystonea regia, Sabal minor, Sabal palmetto, Syagrus romanzoffiana, Thrinax morrisii, and Washingtonia robusta.

Affected trees throughout the range of palms where wet humid weather conditions are prevalent.

Phoenix

Signs of False Smut

Fungus on leaf blades Photo: Monica Elliott, University of Florida, Bugwood.org

Signs of False Smut

False Smut Spores on palm leaf

Signs of Damage

  • Initial symptoms of the disease are tiny (1/32 inch or less) yellow, brown, or black spots on both sides of the leaf blade.
  • The fungus will emerge from these spots, breaking through the leaf epidermis.
  • The fruiting structure, or sorus, is a black fruiting body that is less than 1/16 inch in diameter.
  • Yellow spores are produced, short, light-colored filaments will emerge from the black body.
  • These filaments aide in spore dispersal. Once the spores are dispersed, the black fruiting structures deflate and appear like a black, cup-shaped body or black crater.

Physical Appearance

Often found in association with nutrient deficiencies.

Biology

After the fungus infects leaf tissue, it has very limited growth within the leaf tissue, with most growth occurring just below the black fruiting body. It takes 10 to 11 months for new spores to be produced after initial infection. This is atypical of most leaf disease, which life cycles usually take days to weeks.

Treatment Strategy

Field diagnosis of the disease and the host plant are usually sufficient. Take leaf samples and submit them to a local extension for a definite diagnosis.

Other Treatment Practices

Sanitation and water management are the basis for false smut management. Removal and destruction of severely infected leaf fronds would be suggested as a means of reducing inoculum. Increase air movement, reduce leaf wetness, and eliminate overhead irrigation. Fertilize to keep plants healthy.

  • Foliar Spray using T-Bird 85WDG

    Dosage: LOW RATE: 0.3 – 0.8 lbs./100 gal water HIGH RATE: 5-13 oz./ 100 gal water
    Timing: When conditions are conducive to infection
    Re-Treatment: 10-14 day intervals as conditions persist
    T-Bird 85WDG
    T-Bird 85WDG
    $99.50
  • Foliar Spray using T-Bird 4.5L

    Dosage: 20 fl oz/100 gal water
    Timing: When conditions are conducive to infection
    Re-Treatment: 10-14 day intervals as conditions persist
    T-Bird 4.5L
    T-Bird 4.5L
    $176.00
  • Foliar Spray using CuPRO 5000

    Dosage: 1.5lbs/100 gal water
    Timing: When conditions are conducive to infection
    Re-Treatment: 10-14 day intervals as conditions persist
    CuPRO 5000
    CuPRO 5000
    $32.76

A Diagnostic Guide is designed to help you identify a pest issue and management solutions. Always refer to product label for all rates and approved uses. Some images courtesy forestryimages.org. Use of the images does not imply endorsement of treatments by forestryimages.org

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