Fusarium Wilt
Beginner
Scientific Name
Fusarium oxysporum
Identification
- Early season Fusarium wilt infections result in the damping-off
of seedlings and transplants
- Later infections cause the foliage to turn a dull grey-green
and wilt, followed by a general yellowing and defoliation
- Fusarium infection causes the vascular tissue to turn reddish-brown
- A gummy exudate may form on the underside of infected vines
- Muskmelons from infected fields may develop raspberry-pink fungal growths on the underside of the fruit
Often Confused With
Water stress
Bacterial wilt
Gummy stem blight
Period of Activity
Fusarium wilt may attack the plant at any stage. Outbreaks often
follow periods of crop stress, including hot, dry weather conditions.
Soil temperatures of 18- 25°C (64- 77°F) support rapid disease
progression.
Scouting Notes
While monitoring for other diseases, take note of any wilted
plants. Record the number and location of any infected plants.
Thresholds
None established. Foliar fungicides will not control this disease.
Advanced
Scientific
Name
Fusarium oxysporum
Fusarium wilt is a serious problem in muskmelons. It may also occasionally occur on watermelons and cucumbers. Most other cucurbits have good tolerance to this disease. All cucurbits can be symptom-less carriers.
Identification
Early-season Fusarium wilt infections result in the damping-off
of seedlings and transplants. Later infections cause the foliage
to turn grey-green and wilt, followed by a generalized yellowing
and defoliation. Initial stages are often mistaken for water
stress and the disease remains unidentified until large portions
of the field collapse and die.
Symptoms usually first appear on the crown leaves, progressing
outwards along the vines. The leaf symptoms occasionally appear
only on one side of the vine, while the other leaves remain green
and healthy.
The vascular tissue of infected crowns turns reddish-brown.
Long, linear-shaped, brown stem lesions may form on one side
of the vine, near the crown. Under certain conditions a gummy
red exudate will ooze from these stem lesions.
Muskmelons from infected fields may develop raspberry-pink fungal growths on the underside of the fruit. This mould may also enter the fruit through the blossom scar, developing inside the melon cavity.
Often Confused With
Water
stress
Bacterial
wilt
Gummy
stem blight
Biology
Fusarium wilt is primarily spread via infested soil. While there
may be limited seed transmission, it is quite rare. Fusarium
spores may survive in the soil for several years. There are
several different races of Fusarium known to infect muskmelon.
Race 2 is considered to be the most prevalent race in Canada.
Muskmelon
crops grown in slightly acidic soils (pH 5.0- 5.5) may be more
prone to Fusarium wilt. A heavy fruit load, or excess soil
nitrogen levels (particularly Ammonium-N) may further aggravate
Fusarium infections.
The initial infection occurs through the root. Fusarium may
penetrate through the growing root tip, or though wounds caused
by cucumber beetle larva or other root insects.
Period of Activity
This disease may attack the plant at any stage, although outbreaks
often follow periods of crop stress, including hot, dry weather
conditions. Soil temperatures of 18- 25°C (64- 77°F) and 50-
65% relative humidity support rapid disease progression.
Scouting
Notes.
While monitoring for other diseases, take note of any wilted
plants. Record the number and location of any infected plants.
Thresholds
There are no thresholds for this disease. Since the infection
occurs on the roots, foliar fungicide applications will not prevent
the spread of Fusarium wilt in the field.
Management Notes
- Fusarium-resistant vine crop cultivars are available. As several
different races of Fusarium exist, look for varieties with multiple
resistance genes.
- Fusarium wilt may survive in the soil on infected crop residue
for several years following a melon crop. Follow a 3–4-year rotation
away from all cucurbits and use only sterile, soil-less mix for
cucurbit transplants.
- Fusarium is a stress disease. Any condition that causes stress
to the crop may result in increased levels of Fusarium.
- Lime soil to a target pH of 6.0-6.5 and avoid over-fertilization,
especially with fertilizers containing ammonium.
Maintain adequate soil moisture levels, especially during fruit-set and sizing.