effect of previous crop and extra nitrogen application on incidence of leaf and crown wart (urophlyctis leproides) disease of sugar beet

in this research, the effect of crops such as corn, wheat, sugar beet and clover as previous crop on incidence of leaf and crown wart disease of sugar beet was studied. in the first year, corn, wheat, clover and sugar beet were planted as previous crop in a randomized complete block design with four replications. the amounts of turnover of nitrogen to the soil due to crop residue and their effects on soil c/n ratio were measured. in the second year, sugar beet was planted on the previous year’s experiment site and two treatments of 35 kg additional nitrogen and no nitrogen application, in addition to previous crop treatments, were added to the experiment. therefore, in the second year, the intensity of leaf and crown wart disease infection after different crops and applying additional nitrogen was studied as a split plot design in four replications. the second year results showed that intensity of the disease, the quantitative wart characteristics and wart weights neither was affected significantly by the previous crop nor by additional nitrogen application. however, planting sugar beet after sugar beet and corn showed the highest and lowest incidences of infection, respectively. also, the highest and lowest wart weights resulted from planting sugar beet after clover and wheat with 770 and 349 kg/ha, respectively. it was, therefore, concluded that the previous crop had no effect on the intensity of infection to leaf and crown wart disease.