The disease occurs on foliage and sometimes also on tubers. Yield reductions caused by foliage attack reach more than 50%. The effect of early blight may sometimes be obscured by server incidence of other disease, such as verticillium wilt. There is often a discrepancy between damage to foliage and yield loss, which is due to the increase in disease spread at the end of the season, when most of the yield has been produced. When tomato fruit or potato tubers become infected, the quantity and quality of marketable produce is decreased and the number of secondary pathogens increases. Control of early blight has been shown to increase yield.