| If your tomato plants yellow and wilt on one side of
the plant or one side of a leaf, they may have
Fusarium wilt. Fusarium wilt on tomatoes is caused
by Fusarium oxysporumsp. lycopersici. It is a soilborn
fungus that is found throughout the United
States, especially in warm regions of the country.
The organism is specific for tomato and is very longlived
in all regions of the United States. The disease
develops more quickly in soils that are high in
nitrogen and low in potassium. In addition, plants
grown in sandy soils tend to contract this disease
more often.
Symptoms and Diagnosis
Fusarium often causes yellowing on one side of the
plant or leaf. Yellowing begins with the older,
bottom leaves, followed by wilting, browning, and
defoliation. Growth is typically stunted, and little or
no fruit develops. Brown, vascular tissue can be
found when the infected stem is cut at its base.
Infected plants often die before maturing.
Life Cycle
Fusarium fungi survive in the soil or associated with
plant debris for up to ten years. Disease development
is favored by warm soil temperatures, and symptoms
are most prevalent when temperatures range from
80–90 degrees F. The fungi enter the plants through
their roots and are then spread throughout the plant
by the plant's water-conducting vessels.
Integrated Pest Management Strategies
1. Plant resistant varieties. These varieties are
labeled VF and include cultivars such as ‘Spring
Giant’, ‘Burpee VF’, ‘Supersonic’, ‘Celebrity’,
‘Manalucie’, ‘Better Boy’, and ‘Small Fry’.
2. Remove infected plants from the garden.
Removal of infected plants will help limit the
disease's spread. Soil sterilization or fumigation
will eliminate wilt fungi from the soil but are
impractical for home gardeners. Soil replacement
should be considered.
3. Avoid over-application of high nitrogen fertilizers.
High soil nitrogen levels accompanied by low
potassium levels can increase susceptibility to the
fungus. Use a soil test to determine potassium
levels and other nutrient deficiencies.
4. Avoid activity in wet plantings. Movement of wet
soil from place to place via shoes or tools will
spread the disease.
5. Sanitize stakes and tomato cages at the end of
the season. Avoid using soil-encrusted tools and
supports season after season. A thorough cleaning
with water will reduce most risk of transmitting
the disease.
6. For four years, do not plant solanaceous plants in
the area where infection occurred. Tomato,
potato, pepper, and eggplant are all susceptible to
the disease and may allow its survival year after
year in the same planting area. | 
