When Heat Really Matters

August 30, 2011 08:41 PM
When Heat Really Matters

2011 heat wave makes a powerful correlation with 1995 and 2010

Since Pro Farmer started the Midwest Crop Tour in 1993, there have been only three years that featured hot temperatures. We’re not talking about a couple days of 90°F. We’re talking about a heat wave: a stretch of days in the upper 90s and even 100s. This year will go down as one of the hottest, along with 1995 and 2010.

Heat kills.
String together a few days of heat—specifically, high nighttime tempera-tures—and it will eat away at corn yield potential. But it’s the timing of heat that determines just how much damage it will do.

High nighttime temps are a concern because that’s when the plant relaxes and transfers the energy it collected during the day into sugars (starch) in the kernel. Without a chance to relax, the energy-to-sugar transfer is limited.

That’s exactly what happened in 1995 and 2010. There were short periods of heat ahead of pollination, but most of the heat came during the critical kernel-filling stage for corn. Days of nighttime temps above 70°F during kernel fill caused even more stress on the corn plants.
In 1995, widespread gray leaf spot made some crop watchers question the impact of heat on final yields. In 2010, Goss’s wilt, a bacterial disease, did trim yields in some locations, but it was the widespread heat after pollination that linked 2010 to 1995.

This year, heat moved into the Corn Belt a few days ahead of pollination and stuck around for at least 10 days after pollination, again causing stress during the critical yield development period. Time will tell what that means for yield.

A Key Difference in Years Past

When Pro Farmer started the Midwest Crop Tour in 1993, it was not unusual for the corn crop to start turning brown the week we trekked across the Midwest, or shortly after. That was the case in 1995. The combination of hot temperatures and widespread gray leaf spot started to turn the Midwest corn crop brown by the end of August. It wasn’t always gray leaf spot that shut down the crop, though. At that time, bug damage opened up plant tissues, making the crop susceptible to late-season diseases.

With the introduction of the Bt trait, corn crops started staying greener deeper into the growing season. Now it’s not unusual for a green cornstalk to hold a white-husked ear. That certainly testifies to an improvement in plant health characteristics even from just 15 years ago.

Then came 2010. Yes, the bacterial disease Goss’s wilt did trim yields, but the corn crop maintained a healthy, green appearance deep into September. That’s because today’s GMO varieties typically remain a "closed environment." Without any bug damage, diseases typically don’t have an easy entrance into the plant. In 2010, the healthy, green appearance of the crop hid the impact that hot temperatures had on the national average yield.

That might be the case again in 2011. Another year of hot temperatures during the kernel-filling
period tells us to go lean with yield expectations.

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