Some General Recommendations Regarding the Prevention and Management of Anthracnose in Leatherleaf Fern

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Authors: Robert H. Stamps, James O. Strandberg and Gary W. Simone *

A serious anthracnose disease of leatherleaf fern - caused by a species of the fungus Colletotrichum - is present in Florida. This fungal disease is difficult to control once it becomes established and, therefore, every effort should be taken to prevent spreading this pathogen from one fernery to another. In addition, once it is present in a fernery, special steps should be taken to keep it isolated and to bring it under control. Listed below are disease symptoms, information about the fungus, some precautions that can reduce the potential of infection and some guidelines to aid in the control of this disease once it has infected a fernery.

Symptoms:
Anthracnose affects young fern as the fiddleheads (crosiers) are unfurling, so infection is characterized by a lack of production of normal, fully expanded immature fronds. Brown to black-colored areas of dead tissue are typically found on infected fronds. These areas of dead tissue make the fronds look as though they had been singed with a flame.
Fungal ecology:
Growth of Colletotrichum is enhanced by high temperatures and humid/wet conditions. Spores (conidia) are released only when the fruiting bodies (acervuli) are wet. Spores are spread by rainfall, insects, other animals (cats, dogs, humans, etc.), tools (clippers), etc. Water must be present for the spores to germinate. Upon germination, the fungus produces a structure (appressorium) that can penetrate directly into the host. After penetration, threadlike hyphae rapidly grow inside the plant and result in death of plant tissue. Colletotrichum survives in infected plant debris on or in the soil.
Prevention:
  1. Keep equipment, personnel and vehicles from going from one fernery to another without being decontaminated. Decontamination entails the removal of all soil and plant debris from equipment, tires, clothing, clippers, shoes, etc. Washing and drying of clothes, cleaning and drying of shoes and disinfection of equipment and tools should be part of the decontamination process. Disinfection can be done using bleach (1 part household bleach to 9 parts water), quaternary ammonium compounds (see label instructions) or isopropyl (rubbing) alcohol (70% alcohol). This should apply to everyone including weeders, cutters, scouts, delivery personnel, consultants and packers.
  2. Leatherleaf fern and other cut foliages (especially from Central America) should not be brought anywhere near leatherleaf fern production areas. People and equipment coming in contact with such plant materials should be pathogen free prior to moving to leatherleaf fern production areas. Refuse should be disposed of offsite or burned to prevent possible contact and spread of the pathogen.
  3. Use preventative fungicide applications of products that are effective against the anthracnose fungus and, if available, that are systemic. Fungicides labeled for use on leatherleaf fern that have activity against this Colletotrichum include the contact fungicides chloroneb (Terraneb), chlorothalonil (Echo , Daconil, Thalonil), and mancozeb (Dithane T/O), and the (locally) systemic fungicide thiophanate methyl (3336, Domain, Fungo Flo, SysTec 1998 ). Research is underway to determine the relative effectiveness of these and other fungicides for control of the Colletotrichum pathogenic to leatherleaf fern.
  4. Apply fungicides so that coverage of the fern and plant debris is complete, especially to protect the fiddleheads where infection typically occurs.
  5. Use rhizomes only from anthracnose-free ferneries when planting leatherleaf fern.
  6. Schedule irrigation events so that they have the least potential to extend the period of time the foliage is wet. For example, irrigating in the early morning when the foliage is often already wet with dew or the previous evenings rain may not significantly extend the period of time the foliage remains wet.
Suppression:
  1. Quarantine infected parts of ferneries keep cutters and everyone else out of infected areas to reduce the chances of spreading the pathogen.
  2. Spot treat areas that show symptoms of infection as well as a 20 buffer area around them with a thorough spraying of fungicide. Treat as often as permitted by the fungicide label.
  3. Cut out (junk) infected fronds and treat those areas as mentioned above. Dispose of the cut out plant material offsite or by burning. If material cannot be burned or moved offside immediately, keep disposed plant material in garbage bags or otherwise covered. Bags can also be used to reduce the chance of infecting clean fern when cut out fern is removed from infected spots in a fernery.
  4. Apply fungicides throughout the fernery so that coverage of the fern is complete, especially near the soil surface where fiddleheads typically become infected.
  5. Reduce foliar wetting to a minimum by scheduling irrigation events so that they have the least potential to extend the period of time the foliage is wet. Irrigate only when absolutely necessary.
  6. Disinfect clippers frequently when harvesting in affected ferneries.

Note: Mention of a commercial or proprietary product or chemical does not constitute a recommendation or warranty of the product by the authors or the University of Florida, Institute of Food and Agricultural Sciences, nor does it imply its approval to the exclusion of other products that may also be suitable. Products should be used according to label instructions and safety equipment required on the label and by federal or state law should be employed. Users should avoid the use of chemicals under conditions that could lead to ground water contamination. Pesticide registrations may change so it is the responsibility of the user to ascertain if a pesticide is registered by the appropriate state and federal agencies for an intended use.

*Authors: