AGRICULTURAL EXTENSION SERVICE
FUSARIUM WILT OF
JOHN H. OWEN
Formerly Professor of Plant Pathology, University of Florida
The Fusarium wilt disease of cucumber was first observed
in Florida as early as 1925, but it was not common. Growers in
Sumter County reported the disease in the fall of 1948 and in
the spring of 1949. It was found to be caused by a soil-borne
fungus, Fusarium oxysporum f. cucumerinum Owen. In the 1949
spring crop losses were severe in several fields, killing from 25
to 75 percent of the plants. Since 1949, the disease has become
progressively worse on infested soil, forcing growers to move
to newly cleared land or to rotate with other crops.
Since 1950 the wilt disease has been observed in the cucum-
ber areas of the lower east and west coasts of Florida. The wide-
spread damage caused by this disease in Sumter County and its
appearance in other parts of Florida indicate it to be a disease
of much concern to cucumber growers in this state.
The wilt fungus is soil-borne and attacks the cucumber plant
at all stages of development.
Seedlings.-Damping-off or killing of young seedlings is com-
mon and often very severe on heavily infested soil. Cucumber
seeds planted in soil infested with the wilt fungus may be at-
tacked as soon as they germinate and killed before the young
seedling reaches the surface. This type of infection is of com-
mon occurrence during periods of cool weather when the seeds
take longer than normal to sprout and emerge. Three to 5 days
after emergence, young infected seedlings become dull green
Fig. 1.-Top: Vertical rows 1, 2 and 3 from left to right are cucumber
varieties; rows 4, 5 and 6 are watermelon varieties. Horizontal rows: Top,
control; center, soil inoculated with the watermelon Fusarium; bottom, soil
inoculated with the cucumber Fusarium. Bottom: Longitudinal sections of
diseased cucumber roots, showing browning of vascular bundles extending
out into stems.
and damp-off. The disease in this stage is similar to that pro-
duced by many of the damping-off fungi. Infected roots become
tan-colored and the young seedlings topple over and die.
Infection of Older Plants.-Infection of plants which have
not yet developed runners usually results in the wilting of the
entire plant. On more mature plants with runners, a single
running branch occasionally wilts, and the other runners follow
and the wilting of the entire plant takes place. Wilting occurs
over a period of 3-5 days with the infected plant often partially
reviving at night in the early stages and wilting again in the
middle of the day. Finally the runners and the entire plant
collapse and die.
Fig. 2.-Fusarium wilt of naturally infected (Marketer) cucumber plants.
This fungus invades the vascular bundles of the roots and
stems producing an internal tan to light brown discoloration of
these structures which may normally extend for 6 to 8 nodes
up the stem. If a wilted plant is removed from the soil so as to
leave the roots attached, and the stem is cut longitudinally with
a knife just above the crown into the tap root, one can easily
observe the brown vascular bundles. The wilting of the plant
and the browning of these bundles are the diagnostic symptoms
of this disease.
In Sumter County in 1949, when the disease hit its highest
epidemic proportions, some fields were so badly affected that
growers plowed under their first plantings and replanted. Other
fields suffered losses ranging from 1 to 40 percent of the stand.
Damage has not been as extensive since then, but the disease
has been present and remains a constant threat.
While it has occurred in fields on East and West Coasts,
the disease has not been as serious a threat there as in Sumter
County, where trough culture is practiced and rotation necessi-
tates moving the troughs.
Cucumbers grown on infested soil for the second or third
consecutive season often exhibited 25 to 70 percent infection by
the time of first picking. Plants in large sections of these fields
became infected and died. It became unprofitable to grow cu-
cumbers on land showing infection of this amount.
SOURCE OF THE DISEASE
The fungus causing Fusarium wilt is soil-borne. When the
fungus is present in the soil it remains there for several years,
growing as a saprophyte on dead organic matter. It is capable
of infecting cucumbers planted in this soil 5 years later. If cu-
cumbers are grown year after year in infested soil the pathogen
increases and after three or more consecutive seasons it is no
longer profitable to raise cucumbers on that soil.
The wilt fungus remains from one season until the next in
the soil, and is readily spread from an infested field to new loca-
tions. In the Sumter County area, cucumbers are covered for
protection under wooden troughs during cold periods. These
troughs are left stacked in the infested fields between seasons.
If moved to a new location the following season there is good
possibility that particles of infested soil are carried along on
these troughs. Cultivating implements, spray rigs, trucks, ir-
rigation pipes, etc., could easily spread small quantities of in-
fested soil from one field to another. Laborers such as pickers,
moving from an infested field to a non-infested area, carry the
pathogen on equipment and even on their shoes. It is also pos-
sible that the fungus could be spread to a nearby field by rain
water or soil blown by hard winds.
The cucumber Fusarium wilt fungus appears to be specific to
cucumber and does not infect other cucurbits such as water-
melon, squash, and cataloupe. In greenhouse experiments the
fungus was shown to cause some infection to cantaloupe seed-
lings on heavily infested soil but caused no infection of older
plants. Cantaloupes were observed in the Ft. Myers area in
1958 growing on soil which was infested with the cucumber wilt
organism. This 50-acre field had been planted to cucumbers the
previous year and resulted in 25 to 50 percent loss of cucumber
plants due to Fusarium wilt. None of the cantaloupe plants
showed wilting symptoms. Cucumbers growing in a field ad-
joining the cantaloupe field were diseased.
In the Sumter County area, watermelons were grown on soil
previously infested with the cucumber Fusarium without any
noticeable wilting. Greenhouse experiments also have shown
that the cucumber wilt fungus would not attack watermelon and
likewise the watermelon Fusarium wilt fungus was specific only
Fusarium wilt is a difficult disease to control since the organ-
ism is soil-borne and the soil remains infested for several years.
All varieties of cucumbers commonly grown in the Southeastern
states have been found to be highly susceptible in the seedling
stage. Attempts should be made to control the disease through
long rotation with other crops and by field sanitation.
Crop Rotation.-If Fusarium wilt disease occurs it is recom-
mended that cucumbers not be grown on this land for several
following seasons. Continuous cropping of cucumbers will only
increase the disease development and destructiveness. After the
second or third consecutive season there might be from 50 to 70
percent loss of cucumber plants before the first picking. It has
been observed that a rotation period of 5 years or more should
be practiced before planting another crop of cucumbers on in-
fested soil. Such crops as pepper, tomato, cabbage, beans, and
eggplant could be worked into this rotation program between
crops of cucumber.
Field Sanitation.-Attempt should be made to prevent as
much as possible the movement of soil from infested fields to
non-infested areas on cultivating implements and by laborers.
Posts used to support overhead irrigation pipe should not be
transferred from infested soil to a new field where cucumbers
are to be grown. Wooden troughs should be removed from the
field, cleaned, and stacked off the ground between seasons if
they are to be used for cucumbers in another field.
COOPERATIVE EXTENSION WORK IN AGRICULTURE AND HOME ECONOMICS
(Acts of May 8 and June 30, 1914)
Agricultural Extension Service, University of Florida,
Florida Stte University and United States Department of Agriculture, Cooperating
M. O. Watkins, Director