Corn (Zea mays L.) plants were studied at normal field spacing, and at wide spacing, to determine the effects of removal of leaves from various positions on the plant on stalk rot and yield. Four groups of leaves, two above and two below the ear, were removed or left on the plants in 10 combinations. Defoliations were carried out 2 or 3 weeks after midsilk on a stalk-rot-resistant and a susceptible hybrid. Defoliation increased stalk rot and decreased yield. In normal populations of both resistant and susceptible hybrids, removing or retaining leaves above the ear contributed 70–90% of the differences in stalk rot and in yield found between normal and completely defoliated plants. When shaded by the upper leaves, the two leaves below the ear accounted for about 14% of these differences. In susceptible plants, the lowermost group of leaves contributed 20% and 8% of these differences in disease and yield, respectively. In resistant plants this group of leaves appeared to increase disease and reduce yield slightly. Under wide spacing where shading was minimized, leaves below the ear had similar effects on stalk rot and yield. Resistant plants yielded more and developed less stalk rot than susceptible ones when either of the top two groups of leaves was removed. They also had greater leaf areas initially and after some of the defoliations. In plants normally spaced, the upper leaves of the two genotypes contributed similarly per unit leaf area to yield, but in resistant plants they contributed more in relation to their area to stalk rot reduction than those of susceptible plants. Lower leaves of resistant plants, when shaded by the upper leaves, contributed less to yield and stalk rot resistance than those of susceptible plants.