Some hybrids may roll up leaves quicker than others. Should you shy away from a hybrid, even send it back if it's already in your shed, if it rolled a lot and rolled early last summer? Most agronomists would probably say no.
Bob Nielsen, Purdue University Extension corn specialist, says when conditions first turn off a bit hot and dry, leaf rolling can be a good thing. It's a natural defense mechanism of the plant. By rolling leaves in the hottest part of the day, the plant uses less water. It's also possible that since less transpiration occurs, the plant is cooler.
If relief comes in the form of rains or reduced temperatures within a reasonable period, which happens most years, the plant will have weathered the storm in good shape and will revert to unrolled leaves during the afternoon. It will capture sunlight and build the photosynthetic factory that it takes to produce high yields.
What happens if the stress continues and doesn't let up, or even intensifies, is that a good thing becomes a bad thing, Nielsen says. That was evident last year. In fact the 2012 season was probably a classic for showing how plants react to extended stress.
Even if pollination had occurred normally, there would have been some lost yield potential because of decisions made earlier at key points before pollination. Those key points would have been when plants were under stress, says Dave Nanda, a consultant and director of genetics and technology for Seed Consultants, Inc.
What happens with leaf rolling as stress continues is that the leaves roll up longer, roll up tighter, and more sunlight hits the ground instead of being captured by the leaves. The ground temperature rises. Temperatures as high as 140 degrees at the soil surface were reported last year at the peak of the hottest week.
The net result is more water loss instead of water savings. The bottom line is that at some point all bets are off for all hybrids. Last year demonstrated this.