Verticillium wilt
Verticillium wilt of cotton is caused by Verticillium dahliae, a soil borne fungus that enters the roots and grows into the vascular system of the plant. Symptoms of infection appear as necrotic areas on leaves (photo 1), wilting (photo 2), and usually discoloration of the vascular tissue (photo 3). Plants may lose their leaves if infected with a defoliating strain of the fungus. V. dahliae survives in the soil for long periods of time as microsclerotia, tiny structures produced in the plant tissue. The varieties of both upland (G. hirsutum) and Pima cotton (Gossypium barbadense) planted in Arizona at this time are susceptible, and there are no chemical controls for the disease. Rotation to alfalfa and grains may reduce the number of microsclerotia in the soil.
