CHARLESTON, Ill. — Heat and drought stress on corn is not just a function of temperature, but also depends on the duration and timing of high temperatures, as well as the rate of temperature change.
As of May 30, the U.S. Department of Agriculture’s Illinois crop progress and condition report noted the state on average is 1.08 inches below normal of rainfall, with the highest being in western Illinois at 1.21 inches below normal and the southeast crop reporting district at 1.20 inches below normal.
The report note Indiana’s average precipitation was 1.14 inches below normal.
Paul Yoder, Pioneer field agronomist, recently discussed the impacts of those weather stresses and how it can impact the corn crop.
The first sign of heat and drought stress is recognized when the corn leaves begin to curl or twist up.
“The reason why a corn plant does that is a good thing in the fact that it knows that it has to close the stomates on the leaf surface in order to reduce the amount of transpiration that’s occurring during the day,” Yoder said.
“Transpiration is very similar to a human sweating. It’s going to basically transpire moisture to help reduce the amount of temperature on that leaf surface.”
The curling keeps the leaf surface a couple of degrees cooler than the air temperature.
“When there’s not enough moisture in the ground for it to keep those leaves flat and open, a corn plant will naturally begin to curl, tighten, close those stomates which is a good thing,” Yoder noted.
The potential for yield loss begins after several days.
“When it’s closing those stomates, you’re not going to get as much carbon dioxide taken in and the photosynthesis of that leaf is reduced. Because of the reduction of carbon dioxide and basically the energy that’s it’s acquiring from the sunlight and photosynthesis in order to keep that whole engine going is reduced, and a lot of times you’ll see a corn crop slow down in its growth,” Yoder continued.
“So, from that standpoint, that does have an effect on yield once you start seeing this effect four to five days in a row.
“After that fourth or fifth day, that’s when you’re going to start to see a reduction in yield. Prior to that, a corn plant just naturally will adapt and one to four or five days of this and then we get a rain, your yield is probably not going to be affected.
“From VE to V12 you’re probably going to see a 1% to 3% yield loss per day if drought stress persists for four or more consecutive days.
“From V12 to VT, there could be a 2% to 5% yield loss per day, depending on some other factors, the severity of the heat, the severity of the drought, and whether or not you have a compaction layer that’s going to reduce root development. All of those will trend towards the higher percentages if you have all of those factors.
“Once the corn plants get into the reproductive stages, those percentages of loss are going to continue to climb due to the amount of consumption of water that plant would need to meet those needs and you’re going to start to see ear tip-back, especially if that trend continues.”
From pollination to blister, R2, the yield loss could be 3% to 9% per day, and a 3% to 6% loss during the milk stage, R3.
There are proactive management practices growers can take to help make the crop more resilient to early season drought stress:
• Ensure adequate potassium fertility.
• Reduce or eliminate spring tillage to help preserve soil moisture.
• Avoid planting too shallow.
• Ensure good seed-to-soil contact at planting.
• Manage soils to improve structure and water-holding capacity and minimize compaction.