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Disease progress of sudden death syndrome (SDS) of soyabean, caused by Fusarium solani, was determined in a standard susceptible cultivar, Lee 74, sown uniformly throughout the test site at Colt, Arkansas, USA and in 42 soyabean cultivars representing maturity groups (MG) IV-VIII, during 1986-89. Disease severity was assessed weekly from the middle of July until 1 Oct. using a visual rating scale of percentage leaf area exhibiting foliar symptoms of SDS. The disease ratings were used to calculate the absolute infection rate (dy/dt) for each cultivar at each rating time and the area under the disease progress curve (AUDPC). In Lee 74, SDS progressed in 2 phases; an initial rapid increase in disease to about 35% leaf area affected and a slower increase after that point. This two-phase disease progress curve was fitted by a segmented model using 2 exponential equations. The fits of these equations were …