Verticillium Wilt

Verticillium Wilt in Lettuce Field (Gerald Holmes, California Polytechnic State University at San Luis Obispo, Bugwood.org.)
Verticillium Wilt in Lettuce Field (Gerald Holmes, California Polytechnic State University at San Luis Obispo, Bugwood.org.)
Verticillium Wilt Infected Lettuce Head
Verticillium Wilt Infected Lettuce Head (University of California)

Causal Agent

Verticillium wilt is caused by Verticillium dahliae which affects both lettuce and spinach.

Symptoms

Foliar symptoms include necrotic lesion that can be angular. In head lettuce, outer leaves die by remaining folded on the head. Vascular tissue discoloration can be seen by cutting through the main stem. As the lettuce matures the fungus colonizes the center of the head and kills the plant.

Disease Cycle

Verticillium dahliae is a soilborne pathogen that infects many plant species, including several vegetables and alfalfa. Infection occurs through the roots and grows through the vascular tissue up into the plant. The first symptoms usually occur 6-8 weeks after infection. Wilting is caused in part by the fungal growth clogging the phloem and xylem and by the plant trying to stop the movement of the fungus by blocking the colonized vascular tissue. Survival structures of this disease (microsclerotia) can survive many years in the soil.    

Management

Managing Verticillium is difficult. The best option is avoiding its introduction into fields by only using certified, disease-free seed and cleaning equipment after use in other fields. Crop rotation is ineffective due to the pathogen’s large host range. No chemical treatment options are available for this disease.

  • Use disease-free seed to avoid introduction into fields. Some lettuce varieties have resistance to Verticillium race 1 but not to race 2.
  • Use disease-free seeds for other rotating vegetables. Verticillium may colonize seeds of other vegetables..