Corn yields are affected by a number of things, so it should be no surprise that they are affected by both maximum (daytime) and minimum (nighttime) temperatures. Heat stress on the hottest days causes the corn plant to shut down, reducing their ability to fill the kernels. Overnight, the science is less clear, with some research indicating warm nights may increase respiration and others saying that warm nights reduce the time for grain fill, reducing yield. Southeast Farm Press describes some of the science behind these studies here.
