MarketForum expert Agromomy Question
Upon exiting church this morning, I inquired of a farmer friend if this weather poses any threat to crops, especially corn. His answer: Potentially very harmful, especially IF corn near/at tasseling stage as pollen could be damaged (not the word he used) and crop fails to pollenate.
Agronomy experts? What area corn crop might be affected? Number acres?
Hi tjc,
I’ll have more shortly But several days of heat with ample moisture shouldn’t be a huge problem. a Week+ and dry soils a big problem.
I'm a corn grower not the end all agronomist
Stress weather heat, lack of moisture, insects clipping off the silks at pollination can lower yields and even be devastating to the crop. aside from that it is believed that <140 stress degree days will cause yield loss
https://mrcc.purdue.edu/VIP/indexSDD
"Water Stress Begins at 86F" according to 10- year-old research on corn in the Midwest. This is better stated: "At temperatures of 86F (30C) corn plants reach incipient water stress more than 50 percent of the time." Naturally, this does not apply to irrigated crops and specifically it applies to non-irrigated corn in the Midwest. In a year with ideal moisture, a perfectly healthy corn plant in prime soil does not begin to experience water stress until temperatures exceed 92F and perhaps not then if humidity is high. Still, 86F is the average and because the government tends to work with the average. the average was set as the upper bound for the U.S. Corn Growing Degree Day and as the lower bound for water stress. The number is rarely the exact switch-over point, but it is "good enough for government work." Because we have the government's critical point numbers, we can make use of them (while remaining keenly aware of the limitations).
Looking at averaged Midwest corn yields over the past 30 years, I (Elwynn Taylor, Department of Agronomy) note that when the SDD (Stress Degree Day based on temperature exceeding 86F) total exceeds 140 it is tough to find corn yields above trend.
Eric Snodgrass shows a map of stress degree days expected over the next7 days, at about 10:20 minuits
Great points, cutworm!
A guy that grows corn for a living might know a thing or 10 about this topic
My understanding as the scientist and corn commodities trader is similar.
Specifically, lets apply that to the impact of current conditions like we have right now.
Let's first look at soil moisture. If soil moisture is high, heat is not going to have as much of an impact.
The drought monitor below actually has the vast majority of the Cornbelt with great moisture. Shortfalls are mainly NE/SD then a narrow band from there to far northern IL/IN and even there, not much MAJOR drought. This will help minimize any damage.
DROUGHT MONITOR
https://droughtmonitor.unl.edu/
Let's look at the heat:
These were yesterday's highs. There were some dry spots that hit close to or over 100 degrees. This likely did some damage/hurt yield potential of X%.
Areas with good moisture and mid 90's or lower likely had minimal damage but we should consider the stress degree days that cutworm mentioned. This is the vegetative state still in many places and heat will not hurt as much as during or after pollination when it will DEFINITELY REDUCE YIELDS from HEAT FILL of corn kernels.
Dew points were/are also pretty high which LESSENS the negative impact.
Also, plants can pollinate in the late morning BEFORE the intense heat hits and the temp is 10+ degrees cooler than the max temp but again, most of this crop will be pollinating in July.
It was planted in timely fashion but progress was slow from our long stretch of cool weather with low GDDs.
This was or will be a brief intense heat wave for most places in the Upper Midwest.
Temps the rest of this week will still be hot in the SCB and ECB but not extreme and with high dew points AND high soil moisture.
Again, consider the stress degree days point that cutworm made:
Highs for upcoming week:
https://www.wpc.ncep.noaa.gov/medr/medr_max.shtml
Re: Re: Re: USDA June 12, 2025
By cutworm - June 20, 2025, 8:03 p.m.
Eric Snodgrass Stress degree days discussion at about 10 min mark
Over 140 stress degree days can cause yield loss.( Iowa research ) Stress degree day is the high temp minus 86 degrees F
https://www.youtube.com/watch?v=-u8Juz8wSlA
Re: Re: Re: Re: USDA June 12, 2025
By metmike - June 20, 2025, 10:41 p.m.
WOW!
Thanks cutworm. I never thought about this before.
https://mrcc.purdue.edu/VIP/indexSDD
This is with regards to heat AFTER pollination!
By metmike - Aug. 13, 2024, 8:21 p.m.
It's too late for the weather to hurt corn much, with the crop pretty much made. However, temperatures can be very important in finishing the crop off.
The filling period can be EXTENDED by an extra couple of weeks with very cool temps(adding yield) or shortened with HEAT FILL.
Here's our best thread for explaining and illustrating this principle:
HeatFill for Corn
Started by metmike - July 14, 2023, 2:47 p.m.
We'll be watching the July weather forecast with high expectations for the heat to return to the Western Cornbelt and Upper Midwest.
This time, it will be during pollination which is more critical. Following that, continuous heat would cause "heat fill" for the kernels and lower yields.
The brief spat of intense heat this time, during the vegetative state likely only reduced yields by a very small amount.