Leaf scorch, leaf spot, and leaf blight are foliar diseases of strawberry encountered commonly in perennial plantings in New York. The extent of direct losses attributable to these diseases is not known, but high levels of disease reduce the area of photosynthetically active foliage, weakening the plant and affecting winter hardiness and yield in subsequent seasons. Many growers do not manage foliar disease after harvest because the economic benefits of doing so are unclear. To begin to assess the value of foliar disease management, we measured the impact of disease on photosynthesis on individual leaves. For leaf scorch and leaf spot, photosynthesis decreased linearly with increasing disease severity beginning with very low levels of incidence. Mutisya and Sullivan (1994) showed that appreciable yield reductions occurred when leaf scorch severity reached approximately 45% by seasons end. In our study, leaflets with 45% leaf scorch suffered approximately a 50% reduction in photosynthesis; our preliminary analysis suggests that this reduction is achieved with 30% leaf spot. This could indicate that when photosynthesis is reduced by 50%, whether it is by leaf scorch, leaf spot, leaf blight, or any other foliar pathogen, yield is affected. We are currently conducting field studies to validate these laboratory results.