Symptoms and Signs
In California, this pathogen affects primarily cabbage. Symptoms consist of yellowing of the lower leaves, often on one side of the plant. These leaves later turn brown and drop off. A brown discoloration of the water-conducting tissues (xylem) is characteristic of this disease. With time the entire plant may yellow, wilt, and collapse.
Comments on the Disease
Once present, this fungus survives indefinitely in the soil. The pathogen may be introduced to noninfested locations by the movement of infected plant residues and infested soil adhering to farm equipment. This disease causes more severe symptoms on summer crops due to warmer soil temperatures; Fusarium develops most rapidly at temperatures ranging from 75° to 85°F (24° to 29°C); little development occurs below 60°F (16°C).
Avoid introducing the pathogen to clean fields. In areas where the fungus is known to occur, plant cabbage in spring or winter. Some resistant cabbage cultivars are available. However, there are several races of the pathogen, some of which may render these cultivars susceptible and generally, resistance diminishes with increases in soil temperature. For Fusarium-infested fields, consider rotating cabbage with crops that use preplant fumigation, such as strawberry; risk of Fusarium yellows should be significantly reduced in such situations.