HARDIN COUNTY — The following article was written by Dr. Peter Thomison, OSU corn specialist (C.O.R.N. Newsletter, 2016-22).
northern Ohio, there are corn fields exhibiting drought and temperature
stress. Leaf rolling is common and uneven, stunted corn growth is
widespread. Most of these stressed corn fields are at a stage of
development that is especially susceptible to drought and high
temperature injury – pollination.
High temperature stress is
usually associated with drought. Heat stress and drought intensify
damage to corn and soybean but either may cause major crop injury alone.
The recent high temperatures have generated questions about the impact
of high temperatures on corn. How much heat stress can these crops
withstand without incurring major yield losses even when adequate soil
moisture is available? Corn originated as a tropical grass and can
tolerate exposures to adverse temperatures as high as 112 degrees F for
brief periods. Optimal daytime temperatures for corn typically range
between 77 degrees F and 91 degrees. Growth decreases when temperatures
exceed 95 degrees F.
University of Illinois agronomist Dr. Emerson
Nafziger notes that “afternoon temperatures in the mid-90s are not a
problem for corn….. if they have enough soil water available. …. plant
temperatures have been raised to 110 or higher without doing direct
damage to photosynthetic capacity. The level required to damage leaves
depends on the temperature the leaf has experienced before, but it
generally takes temperatures above 100 in field-grown plants”.
to Iowa State University agronomists, high temperatures may have a
double impact on corn “The first is the increase in rolling of corn
leaves in response to moisture deficiency. By rule-of-thumb, the yield
is diminished by 1 percent for every 12 hours of leaf rolling - except
during the week of silking when the yield is cut 1 percent per 4 hours
of leaf rolling. ….The second impact is less obvious initially. When
soil moisture is sufficient, as it is for the most part this July, the
crop does not have a measurable yield response to one day of
temperatures between 93F to 98 F. However, the fourth consecutive day
with a maximum temperature of 93F or above results in a 1 percent yield
loss in addition to that computed from the leaf rolling. The fifth day
there is an additional 2 percent loss; the sixth day an additional 4
percent loss. Data are not sufficient to make generalizations for a heat
wave of more than six days, however firing of leaves then becomes
likely and very large yield losses are incurred. Generally a six-day
heat wave at silking time is sufficient to assure a yield not to exceed
trend.” Some corn agronomists believe newer corn hybrids may have more
tolerance to heat and drought than the hybrids did when this rule of
thumb was originated.
Are corn hybrids that show greater leaf
rolling more susceptible to drought injury than other less affected
hybrids? Not necessarily. In a recent OSU evaluation comparing two
drought tolerant and two drought sensitive hybrids, differences in leaf
rolling were not readily evident. However, they were observed at
Hoytville, in 2012, a site-year that experienced severe drought stress.
Leaf rolling ratings for the drought tolerant hybrids were lower or
about the same as the drought sensitive hybrids. However, other types of
drought tolerant hybrids may express different leaf rolling responses.
Putnam County Ag Tour is going to be hosted by the Putnam County Soil
& Water Conservation District on Saturday, August 13 starting at
7:30 a.m. with breakfast at the OSU Extension office. At 8:30 a.m., the
tour will start at the Soil Health Agricultural Research Plot (SHARP)
site across from the landfill with Jim Hoorman talking about the Soil
Health site and John Bormuth from Legacy talking about the Nutrient
Toolbar. At 10 a.m., participants will be taken to see a Two-Stage Ditch
at Bill Oedy’s farm and Albert Maag, PSWCD and Kayla Miller, OSU will
discuss water monitoring results. At 11 a.m., Vennekotter’s Swine
operation will be visited with presentations by Curt Tobe, PSWCD on
Senate Bill 1, Brian Schroeder, Cooper Farms, and Glen Arnold, OSU on
Manure Management equipment. The final stop will be at the Ellerbrock
and Welch Hops site to discuss the Ohio HOPS Union. Speakers will be
Scott Welch and Brad Ellerbrock, owners and operators. The Hops will be
harvested in late July and early August. The tour will return to the Ag
Center at 12:30. Participants will also see the I-9 bridge and flood
mitigation and Blanchard River logjam removal. To reserve your seat,
register online at https://www.surveymonkey.com/PCAgTour2016 .