Corn is already in reproductive stages in many parts of the state, particularly in eastern Kansas. One of the main challenges presented in the last month, besides the lack of precipitation, was the high night temperatures.
Nighttime temperatures started increasing as June progressed. During the first half of the month, for even the warmest locations, lows were greater than 70 degrees F only half of the time. However, during the last part of June and the beginning of July (June 16- July 5), the total number of days with temperatures above 70 degrees F increased in the eastern part of the state to almost three-quarters of the time in the warmest regions (Figure 1).
Figure 1. Total days with minimum temperatures greater than 70 degrees F for the period June 1 – June 15 (upper panel) and June 16 - July 5 (lower panel). Map by the K-State Weather Data Library.
High nighttime temperatures during the reproductive growth (at or after flowering) can reduce kernel number, and if later in the season, kernel weight. This effect can be explained as an increase in the rate of respiration, increasing the demand for sugar for energy and diminishing its availability for supplying the growing kernels.
In addition, as experienced in many parts of our state, high night temperatures tend to accelerate plant phenology, running more quickly but with overall lower plant efficiency in using available resources. This situation has been documented in many parts of the state as an earlier-than-usual (close to 2 weeks) flowering time. For example, a corn planted during the first week of May was flowering around the first or second week of July in 2017 (depending on the maturity) and a similar corn hybrid this year was reaching the same stage around the last week of June.
The effect of high night temperatures will be exacerbated as corn is entering into the most critical growth period (a few days before flowering to grain filling). The consequence of high night temperatures will be reflected in reductions in kernel number (if timing of the stress was around flowering) and/or kernel weight (if timing of stress was coincided with the grain filling period).
In summary, high night temperatures will be impacting corn yields primarily in the eastern part of the state, but the final yield reduction is yet to be determined, clearly depending on the timing of the stress (duration) and the area of the state affected.
Scout your corn fields and stay tuned for more information in upcoming eUpdate issues!
(by Ignacio A. Ciampitti, crop production and cropping systems specialist, and Mary Knapp, Weather Data Library. K-State’s Agronomy eUpdate is available online at www.agronomy.k-state.edu.)