Based on systems analyses, the phenology and the growth and development of healthy cotton plants (G. hirsutum ''Acala SJ-2'') were compared with those of cotton plants showing foliar symptoms of Verticillium wilt. A submodel for Verticillium wilt was developed and coupled to an existing simulation model for the growth and development of a population of cotton plants. In the Verticillium wilt submodel, the effects of inoculum density, pathotypes of Verticillium dahliae (defoliating and nondefoliating), and the timing of foliar symptom appearance in relation to physiological time (degree days) were the main variables considered in respect to cotton phenology, dry matter accumulation in plant parts and lint yields. The model also simulates the influence of shading and canopy compensation on photosynthate production in cohorts of diseased and healthy plants. Simulations of cotton crops grown in soils containing 0, 5, 30 and 60 propagules/g of soil (nondefoliating pathotype) indicated decreasing trends in yields of lint with increasing inoculum density. With an increasing incidence of wilt, the fraction of total yield contributed by diseased plants increased; however, the earliness of foliar symptom development and the percentage of plants with foliar symptoms were the most significant factors associated with reductions in lint yields.