Is leaf rolling of corn early in the season a good thing? In the beginning, it can be good, says Bob Nielsen, Purdue University Extension corn agronomist. If leaves are rolled up, they're catching less sunlight, and that helps keep leaves cooler.
If it goes too long, however, because the stressor continues and doesn't let up, it can hurt plants and yield, sometimes in a big way. That's what happened to some fields in 2012.
With leaves rolled up, there is less evapotranspiration. That is what actually cools leaf temperature. More sunlight hits the soil, and if that continues day after day, the soil gets hot creating hotter stalk and leaf tissue.
Before long, reduced evapotranspiration, lower light capture and lower capture of C02 all combine to result in lower photosynthesis. In the final analysis, the more photosynthesis that occurs the more starch it forms.
The point is, when things go from bad to worse and from a week to months as they did in 2012, nothing can stand up to that kind of punishment.
Nielsen and others captured temperatures in the canopy on both irrigated and non-irrigated crops. When it was 102 degrees outside, using a gun that detects actual temperature, the reading inside the canopy of the irrigated field was 94 degrees. Meanwhile, the reading in the corners where water didn't hit, reached 110 degrees F.
He carried that experiment a little farther. On the black top surface of the road near the field, in a day with 100 plus air temperatures, the temperature hit 140 degrees. On bare soil where plants were short, leaves were shriveled, and there was no doubt yields were being affected, the temperature of the soil surface was almost like that of the black top road! Those conditions aren't exactly conducive for growing corn.
The best conclusion about 2012, Nielsen believes, is that it's over. Hope for a cooler season with more moisture this year.