The density of Verticillium dahliae (causal agent of Verticillium wilt of cotton) microsclerotia was monitored over a 7-yr period in fields located in the Southern High Plains of Texas. Included in the project were eight sites that were essentially in continuous cotton (short to no rotation from cotton); six sites that were planted with hosts for V. dahliae approximately 50 to 71% of the time (intermediate rotation from cotton); and 12 sites that were primarily planted to grain crops (< 2 cotton crops) (long rotation from cotton). There was a decline in the density of microsclerotia at a rate of 1.4 microsclerotia (MS)/cm3 soil per year in fields that were in a long rotation from cotton, but no consistency in microsclerotia dynamics in the intermediate and short rotations from cotton over time. There was an average of 6.7, 6.9, and 26.1 MS/cm3 soil, for the long, intermediate, and short/no rotation from cotton, respectively, in the tested sites. Irrigation rate was associated positively with microsclerotia density for both continuous cotton and in a cotton/cotton/sorghum rotation. Microsclerotia density was correlated (R2 = 0.23) with the incidence of wilt when combined across 26 sites. In sites that have a high density of microsclerotia, it might be necessary to manage irrigation to create a less conducive environment for wilt development, rather than using crop rotation to reduce microsclerotia density.
