The heat continues in Kansas, particularly with the warm minimum temperatures. The Southeast and East Central Divisions had average minimum temperatures for the week ending on June 20th above 70 degrees F. Moving the 7-day period to include the lows through the 22nd has all of the eastern divisions, as well as the Central Division with average low temperatures greater than 70 degrees F. In the East Central Division, the average low for the 7-day period ending on the 22nd was 72.1 degrees F. Night time temperatures in excess of 70 degrees F for more than two consecutive days will increase the risk of stress to livestock (see references). As with people, the stress is cumulative.
Below is a map showing the distribution of 70+ lows for the week ending June 20th:
The heat this June can also cause problems for corn in Kansas. The effect of combined heat and drought stresses can reduce plant size, primarily when the plant is entering the stem elongation process. When the crop reaches the V10 (tenth-leaf) stage, nutrient and water demand (0.25 inch/day) are high. At this specific point, a combination of heat + drought stresses will affect potential number of kernels and ear size. Overall mean temperatures above 90 degrees F, and more importantly lower fluctuations between day and night temperatures, will produce a critical impact on plant size and the yield components of corn.
Heat stress will have more of an impact on corn at this stage of growth when combined with drought stress. But even in the absence of drought stress, heat stress alone can still accelerate vegetative phases and tasseling, potentially increasing the asynchrony between pollen shed and silk extrusion when corn reaches flowering time. The potential for yield reductions from stress at this stage of growth is small, however, compared with severe stress occurring right around pollination.
The K-State Mesonet web site has a special page that tracks the current heat index at:
The data updates every five minutes when you refresh the page, and is available for all 55 stations.
Christopher Redmond, Mesonet Network Manager
Mary Knapp, Weather Data Library
Ignacio Ciampitti, Crop Production and Cropping Systems Specialist
Busby, D., and Loy, D. 1996. Heat Stress in Feedlot Cattle: Producer Survey Results. Ames, IA: Iowa State University. A.S. Leaflet R1348
Hungerford, L. L., Buhman, M. J., Dewell, R. D., Mader, T. L., Griffin, D., Smith, D. R., and Nienaber, J. A. 2000. Investigation of heat stress mortality in four midwest feedlots. 430-433: ISVEE.
Mader, T. L., Hungerford, L. L., Nienaber, J. A., Buhman, M. J., Davis, M. S., Hahn, G. L., Cerkoney, W. M., and Holt, S. M. 2001. Heat stress mortality in Midwest feedlots. J. Anim. Sci. 79: Suppl. 2:2.