Disease spread
 Fusarium wilt diagnosis

Title: Fusarium wilt of Canary Island date palms in Florida
Full Citation
Permanent Link: http://ufdc.ufl.edu/UF00066824/00001
 Material Information
Title: Fusarium wilt of Canary Island date palms in Florida
Series Title: Plant Pathology Fact Sheet PP-44
Physical Description: Book
Language: English
Creator: Simone, Gary W.
Cashion, Gerry
Affiliation: University of Florida -- Florida Cooperative Extension Service -- Department of Plant Pathology -- Institute of Food and Agricultural Sciences
Publisher: Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida
Publication Date: 1990?
Spatial Coverage: North America -- United States of America -- Florida
 Record Information
Bibliographic ID: UF00066824
Volume ID: VID00001
Source Institution: Marston Science Library, George A. Smathers Libraries, University of Florida
Holding Location: Florida Agricultural Experiment Station, Florida Cooperative Extension Service, Florida Department of Agriculture and Consumer Services, and the Engineering and Industrial Experiment Station; Institute for Food and Agricultural Services (IFAS), University of Florida
Rights Management: All rights reserved by the source institution and holding location.

Table of Contents
        Page 1
        Page 2
    Disease spread
        Page 3
    Fusarium wilt diagnosis
        Page 4
        Page 5
        Page 6
Full Text

Plant Pathology Fact Sheet

Fusarium Wilt of Canary Island Date Palms

in Florida
Gary W. Simone, and Geri Cashion, Respectively, Extension Plant Pathologist,
Retired, Plant Pathology Department, Gainesville, FL 32611,and Horticultural
Extension Agent II, Manatee County Extension Office, Palmetto, FL 34221.
Florida Cooperative Extension Service/ Institute of Food and Agricultural Sciences/ University of Florida/ Christine Waddill, Dean

The value of ornamental palms in
Florida is virtually impossible to estimate con-
sidering both the nursery and landscape situa-
tions as well as the effect of palms on tourism
each year. In late 1994 and into 1995, a series of
palm disease samples were received in the
Florida Extension Plant Disease Clinic at
Gainesville, from both nursery and landscape
sites where Canary Island date palms (Phoenix
canariensis) had declined to death. Laboratory
isolations resulted in the consistent recovery of
the fungus Fusarium oxysporum. Since that time,
this fungus has been positively identified as F.
oxysporum f.sp. canariensis -a strain of the fun-
gus that is particularly aggressive on the Ca-
nary island date palms. This represents the first
report of this new palm disease in Florida and
only the second report of this wilt disease in
this hemisphere (first report from California).

Fusarium wilt disease is a true wilt dis-
ease. It does not, however, produce the plant
wilt symptoms familiar to most of us from ex-
perience with such common Florida vegetables
as tomatoes, eggplant, and watermelon. Wilt
diseases affecting woody plants do not produce
"droopy" plants but rather cause leaf desicca-
tion to death and irregular dieback of branches
or entire stems. Fusarium wilt of P. canariensis
is just this type of disease and is similar in
symptoms to such diseases as Fusarium wilt
of mimosa or wax myrtle in Florida's land-

scapes. Palm decline symptoms are a direct re-
sult of the loss in function of the water conduct-
ing cells within the plant. In other Fusarium
wilt diseases, there is evidence that the fungus
causes cell dysfunction through physical plug-
ging, enzymatic action, and/or the action of
fungal toxins. The specific mechanism in this
palm wilt disease is not fully known but is
likely to involve one or more of the previously
mentioned mechanisms.


Canary Island date palm wilt is one of
three true wilt diseases that affect specific palm
genera worldwide. The most important of these
diseases is date palm wilt or "Bayoud" disease
of the true date palm (Phoenix dactylifera) that
was described in the late 1800's in north Africa.
This disease is caused by the fungus Fusaium
oxysporum f.sp. albedinis and has caused the
death of >10 million date palms in that region
of the world. The pathogen can infect other Phoe-
nix spp. but is less lethal on these. The second
wilt disease of palms was described in 1946
from African oil palm (Elaeis guineensis) caused
by Fusarium oxysporum f.sp. elaeidis in the west
central African nations of Benin, Congo, Cote
d'Ivoire (Ivory Coast), Nigeria and Zaire. The
oil palm Fusarium is specific to this genus of
palms. Neither the true date palm wilt nor the
oil palm wilt are known to occur in the north-
ern hemisphere. The most recent palm wilt dis-
ease was described by the Italians and French


in 1973. This disease was severe on Canary is-
land date palms and less aggressive toward
true date palms. The fungus involved was
named Fusarium oxysporum f.sp. canariensis. Be-
tween the years 1973-1977, this new disease was
reported from Italy, France, Japan, the Canary
Islands and California. First sightings in Cali-
fornia were from mature 30-50 year old Canary
Island date palms in landscape situations. In
1978, this disease was reported from palm nurs-
eries as well. Present reported distribution of
this disease in California includes: Los Ange-
les, Orange, Riverside, Sacramento, San Bernar-
dino, San Diego, San Mateo, and Santa Barbara
counties. Distribution within Florida to date
includes: Lake, Lee, Manatee, Pinellas and
Sarasota counties in either nurseries or land-
scape sites. Complete survey information for
Florida does not exist.


Palms affected by Fusarium wilt exhibit
general decline symptoms as caused by other
root or stem diseases. Affected palms exhibit
reduced vigor during early disease onset. Pri-
mary symptoms are foliar, with lower, older
fronds desiccating and dying from the lower
trunk toward the bud (Fig. 1). Occasionally, the
first symptomatic leaf may be in the mid-
canopy and the following decline may seem
one-sided on the tree. Affected fronds die in a
one-sided manner, from the lower leaflets (pin-
nae) and spines out to the frond tip. Dieback
continues from the tip to the frond base on the
other side of the rachis (Fig. 2). Some leaves may
die from the frond tip back to the base on both
sides of the rachis simultaneously (Fig. 3). A
linear brown stripe develops on the lower sur-
face of the frond rachis, extending a variable
distance out from the frond base (Fig. 4). Some
pinnae and spines may exhibit necrotic streak-
ing as well. Vascular discoloration is evident
in both cross and longitudinal sections of the
rachis. Discrete pockets of salmon-pink to
brown tissue can be observed in cross sections
(Fig. 5). In longitudinal sections, similarly col-

ored streaks of tissue will be apparent (Fig. 6).

Some variation in symptom appearance
and development is to be expected. Symptoms
will be most pronounced as plants enter a pe-
riod of higher temperature and greater water
demand. There are also several rachis blight
diseases that can cause frond death in a man-
ner similar to Fusarium wilt, but do not lead to
plant death. These other fungi often cause solid
zones of necrotic tissue in the rachis that will
be obvious in cross section. Clear symptoms of
Fusarium wilt can he masked by the occurrence
of two different diseases on the same plant.
Where palm weevils exist in the locality with
Fusarium wilt, these insects can invade the wilt
stressed trees and cause more rapid palm death
and obscure the symptoms of Fusarium wilt.

The Pathogen

The Fusarium genus represents a large
group of related fungi that include both
saprophytes and pathogens. There are more
than 20 species of Fusarium of economic im-
portance in Florida across various crops. One
of these species is Fusarium oxysporum a spe-
cies which has more than two dozen biotypes
or strains that are plant specific. These strains
are called formaa specialist" (f. sp.) or varieties.
They are all morphologically identical in the
laboratory, differing in their ability to infect
particular plant hosts or cultivars of a single
plant species. Clinical recovery of a Fusarium
sp. from a palm frond or root does not mean
that the Fusarium wilt disease is present.
"Fusarium" is a very nonspecific diagnosis.
Similarly, the isolation of a Fusarium oxysporum
from roots, fronds or bud tissues does not con-
firm Fusarium wilt either. Recovery of Fusarium
oxysporum from palms coupled with the key
symptoms mentioned earlier, suggest
Fusarium wilt disease. This fungus still needs
to be clinically identified to the canariensiss'
strain. This verification involves the inoculation
of a healthy plant which may take months to

years to complete, or the nucleic acid finger-
printing of the suspect pathogen compared to
known isolates of the fungus from other areas -
a matter of weeks. The University of Florida at
Gainesville is offering this faster method now.

Based upon available world literature,
the Fusarium wilt pathogen from Canary Island
date palm can infect the following palms: Phoe-
nix canariensis, Phoenix reclinata, and Phoenix
dactylifera. This pathogen does not invade Phoe-
nix roebelenii in California and normally only
damages the offshoots on the true date palm.
Unpublished data from Dr. Howard Ohr of the
University of California Davis, indicates that
this fungus will also invade mature
Washingtonia filifera. In California, neither
I\ashinigtonia robusta nor Archontophoenix
cunninghamiana was susceptible to this patho-
gen. The susceptibility of Phoenix sylvestris or
the many other palm genera and species grown
in Florida is presently unknown.

Disease Spread

Introduction of this disease into new ar-
eas of Florida is primarily dependent upon the
movement of infected trees or infested soil. The
Fusarium pathogen does not have a widely dis-
seminated, airborne spore stage. An infected
plant and/or infested soil must be introduced
into a landscape or nursery for subsequent in-
fection. If a Phoenix planting is disease-free at
present, future development of Fusarium wilt
is highly unlikely without the direct introduc-
tion of the pathogen.

Present scientific literature indicates that
the Fusarium pathogen of oil palm in Africa is
both seed-and pollen-transmitted. This does not
occur in the true date palm pathogen. The abil-
ity of F. oxysporum f.sp. canariensis to infect seed
is unknown at this time.

Local spread in an area where the fun-
gus is known to exist can be directly tied. to
maintenance activities. The Fusarium fungus

is well distributed through the tree especially
through the water conducting cells. Pruning can
introduce the fungus or fungus-infested saw
dust between pruning saw teeth or lopper
blades. Pruning activities can spread the fun-
gus among trees within a landscape or nursery
or between landscapes.

Disease Management

The potential management of Fusarium
wilt on Canary Island date palms is dependent
upon rapid and accurate diagnosis in both the
nursery and landscape. Failure to properly
identify this disease will result in subtle but
effective spread of this fungus in the immedi-
ate environment. Misidentification of a palm
dysfunction such as Fusarium wilt will result
in the unnecessary destruction of an expensive

Management of this disease in the nurs-
ery begins with prevention. In purchasing stock
from other sources, try to inspect stock prior to
purchase. Evaluate palms for key symptoms.
if palms are exhibiting decline symptoms, an
alternative palm supplier would be desirable.
Within the nursery, palms need to be examined
on a bi-weekly basis for frond symptoms as they
appear especially during the warm-to-hot sea-
sons. Properly sample symptomatic palms and
seek lab verification of this pathogen. Infected
palms should be removed and destroyed.
Avoid scattering infested soil within or among
rows of palms. Clean tools used in palm re-
moval with bleach or rubbing alcohol. Leave
the infested site fallow or replant with a non-
palm species. Since the host range of the
Fusarium wilt pathogen is undefined in
Florida, replanting with a palm is a risk situa-
tion where infested soil exists. Restricted use
of soil fumigants like methyl bromide/chlo-
ropicrin or metam sodium (Vapam') can pro-
vide an added measure of fungus control in
infested sites. Use of these fumigants, however,
is not likely to eradicate this fungus from the

The nursery practice of severe lower
frond pruning on P. canariensis to achieve
greater height of cleared trunk can result in ef-
fective, rapid spread of the wilt fungus. Where
this disease is known to exist in the nursery,
limit pruning cycles to once a year and remove
only dead lower fronds. Use several pruning
saws or loppers in the pruning cycle. Use one
tool on each tree. Disinfest this tool in either a
1:1 ratio of bleach in water or undiluted rub-
bing alcohol. Choose the next pruning saw from
the disinfestant solution to prune the next palm.

In landscapes, Fusarium wilt disease can
spread rapidly due to the impact of landscape
maintenance activities across numerous prop-
erties, neighborhoods and communities. Land-
scape maintenance companies should avoid
multiple pruning cycles. Prune only dead
fronds to minimize the risk of fungus move-
ment. Although Canary Island Date palms are
severely pruned in the "hurricane cut" at the
time of installation to enhance establishment,
this severe pruning style should be discontin-
ued once the palm is established. Maintenance
personnel should be alert to the key symptoms
of Fusariurn wilt. Suspect palms should be
sampled and submitted for wilt determination.
Fusarium wilt-affected palms should be care-
fully removed from the landscape. These trees
should be taken to the landfill rather than com-
mitted to a municipality's yard waste recycling
program. It is unlikely that this fungus will be
destroyed by the chipping and piling process
normally used for yard wastes. Infested sites
should be replanted to non-palm species until
further host range information is available.

Fusarium Wilt Diagnosis

Based upon experience with this disease
in Florida thus far, there are four key symptoms
necessary for a field diagnosis of Fusarium wilt

1. Progressive frond death from oldest to new-
est canopy.

2. One-sided leaflet death on a declining frond.

3. A prominent brown stripe on the rachis base
starting at the trunk and extending out a vari-
able distance toward the frond tip.

4. Discolored vascular bundles in the "striped"

If these symptoms are present, a diag-
nosis of Fusarium wilt is likely but not abso-
lute due to the presence of other rachis blights
in Florida. Seek laboratory verification prior to
destruction of a Fusarium wilt-suspect palm.

For proper laboratory verification of
Fusarium wilt of Canary Island date palm, col-
lect 3-4 petiole bases from fronds exhibiting ei-
ther one-sided leaflet death or tip dieback and
the lower brown striping of the rachis. If only
1-2 fronds have clear symptoms, remove a
symptomless lower and upper frond as well.
Remove the lower 12-18 inches of each frond
and remove the spines before packaging. If sev-
eral trees are symptomatic, disinfest loppers or
pruning saws between trees (as discussed ear-
lier). Complete a Plant Disease Diagnostic Form
(#2901) that is available from any county Ex-
tension office in Florida. Submit the completed
form, samples and remittance to the following
address for Fusariurn wilt verification:

Florida Extension Plant Disease Clinic, Bldg.
78 Mowry Rd, University of Florida,
Gainesville, FL 32611; Phone-(352) 392-1795,
Fax-(352) 392-3438.

Verification of Fusarium-wilt suspect
samples is very important. The Gainesville lab
is the only diagnostic facility in Florida and in
the United States that can accurately identify
this pathogen to the strain that kills Canary Is-
land Date palms in a matter of 2-3 weeks. This
new diagnostic method is the result of an on-

going research program directed toward accu-
rate, rapid identification of this new disease in
Florida for best, long-range management of this
problem. Remember that there are several spe-
cies of the fungus Fusarium that can be isolated
from roots, leaves and buds of palms that are
not causing Fusarium wilt disease. Similarly
there are strains of Fusarium oxysporum recov-
ered from palm tissues that do not cause
Fusarium wilt. Do not destroy suspect palms
needlessly. When you can, obtain a precise di-
agnosis on this new plant disease in Florida.

The host range of this new fungus is not de-
fined among all the palm genera used in
Florida. Assist the University of Florida, I.F.A.S.,
in mapping the distribution of this new fungus
to best limit its potential spread in Florida.

Nursery personnel as well as land-
scape maintenance professionals' situations
are urged to proceed with disease diagnosis.
At first symptom appearance, proceed with
proper palm sampling and submission. In
this way, the distribution of this new fungus
can be mapped throughout Florida for most
efficient management. All records relating to
palm wilt incidence in Florida are confiden-

Figure 2. One-sided leaflet death on
Fusarium-infected palm.

Figure 1. Lower frond death caused by
Fusarium wilt.

Figure 3. Fusarium wilt caused frond death
from tip back toward the trunk.

Figure 4. External brown streak on an in-
fected rachis of a Canary Island date palm.

Figure 5. Pockets of vascular browning in
frond cross section.

Figure 6. Vascular streaking and discolora-
tion in longitudinal section of palm frond.



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