Fusarium Wilt
Beginner
Scientific Name
Fusarium oxysporum
Identification
- Seedlings infected with Fusarium wilt, turn yellow and die within 2– 4 weeks
- Lower leaves are affected first
- Yellowing is often more intense on one side of the plant
Often Confused With
Black rot
Water stress
Period of Activity
Plants may be affected at any time during growth. Outbreaks often follow periods of crop stress, including hot, dry weather conditions. Fusarium wilt will not develop below 16ºC (61°F) or above 32ºC (90°F), with rapid disease progression occurring in soil temperatures between 18 and 25°C (64- 77°F).
Scouting Notes
While monitoring for other diseases, take note of any wilted leaves. 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 disease of the mustard family. While cabbage is most severely affected, other members of this family may also be infected. It is less important now than in the past as most modern varieties are resistant to Fusarium. Where the disease is present in the soil, a high degree of crop loss can be expected in susceptible varieties.
It is caused by a soil-borne fungus. There are a number of races of this fungus which attack different members of the crucifer family. For instance, the race that attacks cabbage will not attack radish.
Identification
Symptoms on all susceptible plants are similar. Plants may be affected at any time during growth. Infected seedlings will turn yellow and die within 2– 4 weeks after transplanting in warm soil. Affected plants are stunted, lopsided, yellowed, lose most of their lower leaves, and have a brown to black discoloration in the veins. The lower leaves are affected first. The yellowing is often more intense on one side of the leaf, which will curl and twist, often leaving only one side of a plant stunted. As the disease progresses, the older leaves drop off the plant.
If the crown is cut lengthwise at the soil level, a brown stain can be seen in the vasculature of the stem.
Often Confused With
Black rot
Water stress
Biology
Fusarium is present in many soils. It enters the plant through young rootlets or through wounds in older roots. Once in the plant, it moves to the water conducting vessels or vasculature, and remains confined until the death of individual leaves or the entire plant. The brown stain in these vessels can be found ahead of the actual fungus and is caused by a toxin that Fusarium produces.
Spores are produced on dead plant tissue and spread on soil particles, wind-blown soil, farm implements and surface water. There are two kinds of spores: a short-lived spore and a long-lived spore. The long-lived spore is thick walled and can survive for years in the soil.
Period of Activity
Plants may be affected at any time during growth. Outbreaks often follow periods of crop stress, including hot, dry weather conditions. Fusarium wilt will not develop below 16ºC (61°F) or above 32ºC (90°F), with rapid disease progression occurring in soil temperatures between 18 and 25°C (64- 77°F).
Scouting Notes
While monitoring for other diseases, take note of any wilted leaves. Record the number and location of any infected plants.
Thresholds
None established. Since the infection occurs on the roots, foliar fungicide applications will not prevent the spread of Fusarium wilt in the field.
Management Notes
- Soil moisture and pH have little or no influence on the development of wilt.
- The disease can be avoided by planting resistant varieties. Monogenic dominant resistance has been incorporated into many varieties of cabbage and some radish and Brussels’ sprouts, but none is currently available in cauliflower and broccoli.
- Due to its persistence in soil without host plants, this fungus is very difficult to control by crop rotation and other methods.
- Avoid contamination by equipment by washing thoroughly before moving from an infested to a non-infested field.
- Avoid planting transplants in areas where there will be surface water run-off from soil known to be contaminated.
- Potassium deficiency can make the disease worse.
