Gladiolus Rust : A New Threat
Background
Gladiolus rust (GR), a plant
disease of quarantine
significance, was detected and
confirmed for the first time in
the United States in April 2006
on a gladiolus production farm
in Manatee County, FL. The
disease was later found on
another commercial gladiolus
farm in Hendry County, FL. In
May 2006, GR was detected
at one commercial and three
residential sites in San Diego
County, CA, just north of the
Mexican border. State and
Federal officials destroyed the
infected plants and placed stop
sale notices on the facilities.
The Center for Plant Health
Science and Technology—part
of the U.S. Department of
Agriculture’s (USDA) Animal and
Plant Health Inspection Service
(APHIS )—organized a technical
committee to devise appropriate
eradication techniques specific
to the infested areas of Florida
and California. Although the
Pest Alert
Plant Protection and Quarantine February 2007
specific source of the 2006
infections is not known, in recent
years, GR has been intercepted
many times on cut gladiolus
flowers entering the country
as commercial shipments
and/or in passenger baggage
from Mexico, Brazil, and other
countries.
Causal Agent
The fungus Uromyces
transversalis Thum. causes
GR only in the members of
the family Iridaceae, including
Gladiolus, Tritonia, Crocosmia,
and Watsonia spp. Severely
damaged plants do not flower
and/or their corms do not
ripen. The disease is serious in
nurseries and can completely
destroy commercial gladiolus
crops unless fungicides are used.
Origin
GR is indigenous to southern
Africa, where it was first noted
on leaves of Tritonia securigera in
1876 . U. transversalis remained on the African continent until
it reached the shores of the
Mediterranean and spread
to southern Europe almost a
century later. The fungus was
reported from southern France
and northern Italy in 1966, from
Malta in 1969, and from Morocco
and southern Italy in 1977. U.
transversalis
had also spread to
western France and England by
1996, where it is an aggressive
pathogen of commercial gladioli.
Transmission
Plants and cut flowers are the
primary pathways for the intro-
duction of GR. Its local
spread occurs mainly by
airborne spores, which are
produced in prolific quantities
on aboveground portions of
the plant, especially on leaves,
and disperse easily by wind
or by lightly brushing the
plants. Spores can travel long
distances by wind or through
the movement of cut flowers.
GR spores can also be spread
Figure 1—Healthy gladiolus leaves. Figure 2—Gladiolus leaves severely infected with gladiolus rust.
by surface-contaminated
corms, rhizomes, and flowers.
Interceptions from commercial
shipments and passenger
baggage at ports-of-entry in
Arizona, California, and Texas
confirm that cut flowers are the
major pathway bringing GR into
the country from Mexico and
other countries.
Symptoms and
Identification
The presence of GR is
determined by inspecting the
leaves and stem of a plant.
Symptoms are easily recognized
as “typical rust” with orange sori
(small blisterlike elevations of
epidermis formed when spores
have emerged) or pustules on
both sides of the leaves. In U.
transversalis, pustules tend to
be elongated across the width of
veins of a leaf and contain many
spores.
The first symptoms of GR are
small, yellowish spots. Later,
the epidermis breaks down,
exposing the pustules full of
yellowish-orange spores and
measuring 1 mm x 1 cm. Event-
ually, the pustules coalesce and
form larger patches of damaged
tissue.
Disease Management
Fungicides can control GR, and
for severe infections, weekly
applications of bitertanol or
triadimefon may be necessary
to achieve a marketable yield of
flowers. Systemic fungicides
such as benodanil and
oxycarboxin, sprayed weekly
starting soon after emergence,
provide good control.
Mexican government officials
who recommend technical
procedures for GR management
stress that prevention is key.
A recommended preventative
control strategy is to combine a
contact product (e.g., mancozeb)
with a systemic fungicide (e.g.,
tebuconazole), thus providing
the host plant with external and
internal protection against rust.
For More Information
To learn more about gladiolus
rust (GR), and/or if you see this
disease, please contact USDA–
APHIS at (301) 851–2104.
The U.S. Department of
Agriculture is an equal
opportunity provider and
employer.
This publication reports research
involving pesticides. All uses of
pesticides must be registered by
appropriate State and/or Federal
agencies before they can be
recommended.
CAUTION: Pesticides can be
injurious to humans, domestic
animals, desirable plants, and
fish or other wildlife—if they are
not handled or applied properly.
Use all pesticides selectively and
carefully. Follow recommended
practices for the disposal of
surplus pesticides and pesticide
containers.
Photo credits: All images were
taken by APHIS plant pathologist
Kimberly A. Schwartzburg.
United States
Department of Agriculture
Animal and Plant Health
Inspection Service
APHIS 81–35– 011
Figure 4—Gladiolus plants ready for cutting. Figure 3—Inspecting young gladiolus plants for GR.
