Anthracnose of Leatherleaf Fern
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Plant Pathology Circular No. 372 July/August
Florida Department of Agriculture and Consumer Services,
Division of Plant Industry
*Authors: Robert Leahze, Tim Schubert, Jim
Strandberg, Bob Stamps, and David Norman.
A species of the fungus Colletotrichum recently found
in Florida ferneries causes a severe anthracnose disease on
leatherleaf fern, Rumohra adiantiformis (G. Forst.) Ching.
First observed in the summer of 1993, the disease began to
attract serious attention in the summer of 1994. By June 1995,
about 11% of the fern acreage was afflicted. By September 1995,
the disease was present on 30-40% of the fern acreage, with
perhaps half or more of all fern growers reporting the disease on
their property. The pathogen apparently spreads easily and the
disease is very difficult to control once it becomes established.
Intensive efforts should be made to prevent the movement of this
pathogen into uninfected ferneries. Yield of marketable fronds
(leaves) from infected areas can drop to essentially nothing. The
pathogen has been tentatively identified as a strain of Colletotrichum
gloeosporioides (Penz.) Penz. & Sacc. or a close
relative. A similar (if not identical) anthracnose disease of
leatherleaf fern has been reported by plant scientists and
growers from Costa Rica and other areas of Central America, and
may be present in the Caribbean.
RECOGNIZING THE DISEASE:
Symptoms of this disease consist of necrosis (death) of the
outermost portions of unfurling croziers (fiddleheads).
Figure 1A: Necrosis of tips of fern
leaflets typical of a light infection of leatherleaf fern
When the infected frond grows and expands, it appears severely
burned or scorched and cannot develop normally. Lesions may
appear at or near the base of petioles. The pathogen appears
incapable of rhizome infection under natural conditions. Also,
mature fern foliage does not appear to be susceptible.
Since the initial symptoms of the disease appear in the
understory of the existing mature fern canopy, early stages can
be overlooked. When infected fronds unfurl and reveal their
damaged condition, the pathogen is already well established in
that locale. Symptoms of anthracnose are easily confused with
fertilizer or other chemical injury. Infection centers are
localized where the disease first appears. These infection
centers are usually a few meters in diameter when first noticed,
but can enlarge to eventually encompass entire fields.
Figure 1B: Severe necrosis of fern
fronds in advanced stages of anthracnose. [48k]
Anthracnose disease development is enhanced by hot, humid,
rainy weather. Colletotrichum spores (conidia) enveloped in a
slimy matrix are produced within acervuli (fungal fruiting
structures). The spores are well-designed for spread by water
splash, but can be transported by wind in the form of dry spore
masses (Bailey et al. 1992). Inoculum can be easily transported
by adhering to hands, tools, clothing, animals, insects, or by
moving infected ferns from place to place.
Once conidia come in contact with susceptible young
leatherleaf fern tissue, germination will occur in the presence
of water. Conidia penetrate host tissue by way of a microscopic
structure called an appressorium. Pathogenicity tests conducted
by UF-IFAS plant pathologists have shown disease symptoms
appearing within 4-5 days after inoculation. These same tests
revealed heavy inoculum production on the infected fronds. Based
on present knowledge of the disease cycle and of other
Colletotrichum diseases, additional inoculum sources are likely
in the soil or at the ground line, but early research does not
suggest additional inoculum is produced there.
Colletotrichum can survive as conidia, hyphae, appressoria,
and possibly sclerotia or hyphal mats (thick-walled, dark masses
of vegetative cells) in infected plant debris on or in the soil
(Agrios 1988, Bailey et al. 1992). So far, no sexual
reproductive stage has been discovered for the causal agent of
leatherleaf fern anthracnose. A probable disease cycle of
leatherleaf fern anthracnose is presented (Fig.
The biology of the leatherleaf fern and its commercial
production present a serious challenge to developing an effective
control strategy. Prevent movement of this pathogen into
uninfected ferneries by limiting access and implementing strict
decontamination procedures to delay or prevent infection,
especially in isolated ferneries. Schedule activities to avoid
the necessity of visiting uninfected areas after visiting
infected areas. Activity in an infected area should be scheduled
for the end of the work day. Infected areas within a femery
should be well marked and avoided by personnel and vehicles
except when applying fungicides or other disease management
Decontamination of personnel, equipment, and vehicles is of
paramount importance when traveling from one fernery to another.
Quaternary ammonium disinfectants are recommended for
decontamination. Products such as Galloway GX 1027(1) hand
soap-disinfectant used according to label directions can be used
for skin decontamination. Quaternary ammonium
detergent-disinfectants such as (listed below) mixed with water
according to label directions can be used to inactivate
anthracnose inoculum on inanimate surfaces such as tools,
vehicles, tires, footwear, clothing, and gloves.
- Galloway Gallex 900(1),
[Galloway Chemical Division, 6414 - 125th Ave. N., Largo,
Phone (813) 531-3375, (800) 445-1143],
[Whitmire Research Labs, 3568 Tree Court, St. Louis, MO
Phone (800) 325-3668],
[R.D. & Associates, Inc., P.O. Box 1616, Pomona, CA
[The Buffalo Co., 6404 Cannel Road, Suite 312, Charlotte,
NC 28226], and
[ZEP Manufacturing, Atlanta. GA 30301]
Rhizomes should be obtained from anthracnose-free sources when
planting new fem beds.
Irrigation should be applied to minimize the dew period.
Prolonged wetting encourages inoculum production and enhances
Leatherleaf fern or cut foliage originating from any outside
source should be kept well away from ferm production areas.
Infected fronds, clippings, cuttings, or debris should be
disposed of far from the femery location, or burned, to destroy
fungal inoculum and prevent disease spread.
Early fungicide trials by UF-IFAS researchers have been
discouraging (Strandberg 1994, 1995a, 1995b). At rates labeled
for foliar spray application, none of the EPA-registered
fungicides were especially effective. Fungicidal treatments with
EPA-registered products at the shortest intervals pemmitted
should be directed at infected fern and plant debris on the
ground. Fungicidal spot treatments of newly diseased areas within
the femery should include a thoroughly treated 20 foot buffer
area around each location. Chemigation (dispensing agricultural
chemicals through an irrigation system) has not been tested. More
fungicide trials and disease management investigations by IFAS
scientists are in progress to determine which compounds and
methods provide the most effective control of this disease.
More drastic cultural methods which may reduce an anthracnose
- 1) complete mowing and debris removal from infected
- 2) destruction of all aboveground fern tissues and
accompanying inoculum with flameweeding equipment;
- 3) application of competitive and antagonistic fungi and
bacteria to suppress the anthracnose pathogen;
- 4) combinations of the above treatments with and without
These drastic treatments can be expected to reduce or
obliterate fern yield for a period of time. The effectiveness of
these measures has yet to be thoroughly evaluated. A fern grower
should employ any of these measures with caution. A regular
monitoring program to detect new outbreaks or follow the progress
of treated areas is strongly encouraged.
To determine if you have anthracnose in your fernery, please
contact one of the following for advice on sampling and sample
- 1. Ms. Linda Landrum, Volusia County Extension Service,
3100 East New York Avenue, DeLand, FL 32724-6497,
- 2. Florida Extension Plant Disease Clinic, P. O. Box
110830, Gainesville, FL 32611-0830, telephone
- 3. Florida Department of Agriculture & Consumer
Services - Division of Plant Industry, Plant Pathology
Section, P. O. Box 147100, Gainesville, FL 32614-7100,
telephone 904/372-3505 x 143.
- 4. Mr. Austin Tilton, Putnam County Extension Service,
111 Yelvington Road, Suite 1, East Palatka, FL
32131-8892, telephone 904/329-0318.
- Agrios, George N. 1988. Plant pathology. Academic Press,
Inc., San Diego, California. pp. 379-390.
- Bailey, J.A., R.J. O'Connell, R.J. Pring, and C. Nash.
1992. Infection strategies of Colletotrichum species. pp. 88-120. In J.A. Bailey and MJ. Jeger (eds.).
Colletotrichum: biology, pathology, and control. CAB
International, Wallingford, Oxford, UK.
- Strandberg, J.O. 1994. Efficacy of selected fungicides
for control of anthracnose in leatherleaf fern - a
preliminary report. Cut Foliage Grower 9(11/12): 1-4.
- Strandberg, J.O. 1995a. Evaluation of foliar fungicide
sprays for control of anthracnose in leatherleaf fern.
Cut Foliage Grower 10(3/4): 1-4.
- Strandberg, J.O. 1995b. Efficacy of selected fungicide
drenches for control of anthracnose in leatherleaf fern.
Cut Foliage Grower 10(7/8): 1-4.
Robert Leahze, Plant pathologist, FDACS, Division of Plant
Indurstry, P.O. Box 147100, Gainesville, FL 32614-7100
Tim Schubert, Plant pathologist, FDACS, Division of Plant
Indurstry, P.O. Box 147100, Gainesville, FL 32614-7100
Jim Strandberg, Professor, Central Florida REC, 2700 E. Celery
Avenue, University of Florida/IFAS, Sanford, FL 32771-9608
Bob Stamps, Professor, University of Florida/IFAS, Central
Florida REC, 2807 Binion Road, Apopka, FL 32703-8504
David Norman, Assistant Professor, University of Florida/IFAS,
Central Florida REC, 2807 Binion Road, Apopka, FL 32703-8504