Yield loss due to gray leaf spot may be direct or indirect. Direct yield losses
occur as a result of the reduction of the photosynthetic area of the plant. The upper
eight or nine leaves of the plant contribute 75 to 90% of the photosynthate for
grainfill (1). Severe blighting substantially reduces the green leaf area of the plant,
and consequently, the amount of photosynthate produced and distributed to the
ears. To compensate for the loss of healthy leaf area, photosynthate is redistributed
from the stalk and used for grainfill. This may predispose the plant to stalk rot and
indirect yield losses due to lodging. Other components of yield affected by gray leaf
spot are the size and number of kernels per ear (66).