The changes of disease progression curves of apple scab disease using of fungicides in North Khorasan province

Scab disease caused by Venturia inaequalis is the most important diseases of apple in the world which causes serious damage, especially in areas with wet and moderate weather. In order to investigate the effect of fungicides on the time progression curve of apple scab disease in North Khorasan province, the experiment was conducted in the form of Randomized Complete Block Design with eight treatments and eight replications in Bojnord city. With the appearance of disease symptoms, samples were taken in a regular schedule every week until the disease progression was reduced in the control.  Disease Incidence and severity percentage of the disease in each tree were determined and statically analyzed. Using linear regression, disease progression curves were fitted with six growth models as conventional models including linear, exponential, monomolecular, logistic, log-logistic and Gompertz linearized. The results showed that the progression curves changes from the Gompertz model in the control samples by using of fungicides according to the efficiency of each treatment to the log-logistic model and finally to the monomolecular model.