Expert: Excessive heat and humidity not ideal for corn
WEST LAFAYETTE, Ind. —Excessive heat and humidity in Indiana this week may take a toll on potential corn yields, said Purdue Extension agronomist Tony Vyn.
With corn development well ahead of normal, high temperatures will mean an early maturity and harvest. Had drought occurred, yield losses would have been more severe, but just because there's been no drought in 2010, above trend-line yields are not guaranteed.
Daytime temperatures up to 86 F are beneficial for corn plant photosynthesis. Anything above 86 F for a sustained amount of time can foster disease development, cause stress during grainfill and exacerbate ear rots.
"Leaf diseases are more likely to spread in high humidity situations," Vyn said. "On susceptible hybrids and in fields not sprayed with effective fungicides, the leaf area available for photosynthesis during the critical grain filling period can decline too rapidly. Corn plants also are more susceptible to stalk rot infection with high humidity and wet surface soils."
High daytime temperatures can result in corn plants having lower net photosynthetic energy and fewer sugars available for corn kernel development. When nighttime temperatures also are high, corn plants expend more sugars gained during daylight hours on nighttime maintenance respiration. Ideal nighttime temperatures during grainfill range between 60-65 F.
Recent observations of diplodia ear rot in corn ears that are only halfway through the grain filling period are a direct consequence of excessive and prolonged humidity. Problems with ear rot will limit corn yields most on susceptible hybrids already under stress, Vyn said.
Heavy rains and high humidity also have contributed to prolonged wet soil conditions -- especially in fields with inadequate drainage. Those wet conditions have resulted in shallow root systems leaving fields susceptible to stalk lodging. Excessive rainfall can result in nitrogen losses as well.
"Excessive rain in many parts of Indiana in June already compromised nitrogen availability to corn plants, and heavy rains in July and early August have further limited the plant availability of mineral nitrogen," Vyn said. "The expectation of corn being able to take up 40 percent of the total season nitrogen during grain fill is less likely this year than last. That means there will be more mobilization of leaf nitrogen and stalk nitrogen to the ear during grain fill. Too much nitrogen mobilization will impair late season photosynthesis rates."
As the season progresses, each additional stress builds upon earlier season stresses and can have an increasingly more detrimental affect on yield potential.
"I am more concerned about the negative consequences of excessive heat and humidity this season than I would normally be because of the other stress factors corn has experienced in 2010," Vyn said. "Overall, corn hybrids are much more stress tolerant today than those of 30 years ago, but compounding stresses, especially during the grain fill period, can impose significant restrictions to final grain yield."
To read Vyn's full report on the affects of excessive heat and humidity on corn, check out the Purdue Pest and Crop Newsletter, Issue 19 at http://extension.entm.purdue.edu/pestcrop/2010/index.html
Writer: Jennifer Stewart, 765-494-6682, email@example.com
Sources: Tony Vyn, 765-496-3757. firstname.lastname@example.org