Symptoms and Signs
Fusarium wilt symptoms resemble those of Verticillium wilt. Lower leaves of infected plants turn yellow and wilt. Leaf tissue between veins turns yellow then brown. Wilting and yellowing of foliage progresses up the stems of affected plants. Vascular tissue in stems and tubers often develops a brown discoloration; typically there is a stem end rot of the tubers. Wilt symptoms are more severe when temperatures are high and plants are stressed for water. Laboratory analysis of diseased plant tissue usually is necessary to determine whether Fusarium or Verticillium is the causal agent. In most areas Verticillium wilt is more common than Fusarium wilt.
Comments on the Disease
Fusarium wilt is a minor problem of potatoes grown in the San Joaquin Delta. It occurs rarely in other potato-growing areas of California. The fungus that causes Fusarium wilt can survive in the soil for several years in the absence of hosts. The roots of susceptible host plants are infected, and the pathogen moves up in the vascular tissue to infect stems, stolons, and tubers. The pathogen can be introduced to clean ground in infected seed tubers.
Plant disease-free seed tubers. Avoid growing seed potatoes in ground known to be infested with the Fusarium wilt pathogen. Rotation out of potatoes or other solanaceous crops for 4 to 6 years is necessary to reduce soil inoculum levels.