Diseases of Pima cotton(
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). Symptoms usually appear in late August and September, and may be more pronounced in years when early season temperatures (May to early June) are lower than usual. Plants may lose their leaves if infected with a defoliating strain of the fungus. If plants wilt and die, foliar symptoms may be confused with those of cotton (Texas) root, but plants infected with Verticillium only have no rotten roots.
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, but varieties differ in the intensity of infection and amount of defoliation. Rotation to alfalfa and grains may reduce the number of microsclerotia in the soil. There are no chemical control measures available.
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October 13, 2008