Years ago, almost all corn grown in the U.S. had wide, droopy leaves. Upright leaves became fashionable for corn along with narrower rows, higher plant densities, better herbicides, and more nitrogen use. Upright leaves cause less self-shading. When sunlight is limiting yield in cool, moist, higher-yielding years, upright leaves may increase yield (more photosynthesis). When water is limiting yield in hot, dry, lower yielding years, upright leaves may decrease yield (more heat and drought stress). However, some upright leaves (strong midrib) are more likely to leaf roll (self-shade) during drought and reduce transpiration. In the future, restrictions on herbicides for environmental protection may bring back droopy, lax leaves to better shade the ground, thus reducing weed growth.