The Climate Prediction Center and the National Weather Service have issued heat outlooks for the weekend and continuing through the end of July (Figure 1). With the recent rain, even western portions of the state can expect elevated dew points and increased low temperatures. Nighttime temperatures in excess of 70° F for more than two consecutive days will increase the risk of stress to livestock. As with people, the stress is cumulative.
Figure 1. Risk of Hazardous Temperatures. Source: Climate Prediction Center
The heat can also cause problems for corn in Kansas (Figure 2). 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 is approaching flowering and reproductive stages, nutrient and water demands (0.3-0.2 inch/day) are high. At these stages, a combination of heat plus drought stresses will affect final number of kernels and kernel size. Overall mean temperatures above 90 degrees F, and more importantly, lower variations between day and night temperatures, will produce critical impacts on plant productivity, affecting number of kernels (via changes in kernel abortion rate) and kernel size (final grain weight).
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 hasten tasseling, potentially increasing the asynchrony between pollen shed and silk extrusion when corn reaches flowering time, and during reproductive stages hastening maturity. The potential for yield reductions from stress is high as it is occurring right around pollination or right after (2-weeks after flowering).
Figure 2. Leaf rolling in corn from the combined effect of heat and drought. Photo by Ignacio Ciampitti, K-State Research and Extension.
The K-State Mesonet web site has a special page that tracks the current heat index at: http://mesonet.k-state.edu/weather/heat/ and for animal comfort at http://mesonet.k-state.edu/agriculture/animal/
There is also a page that tracks growing degree accumulation for multiple crops. With this tool, you can pick the planting/emergence date for the start of the interval. Selecting the graph will illustrate the growing degree accumulation for this season versus normal and plant stage. You can access the page at: http://mesonet.k-state.edu/agriculture/degreedays/
The data updates every five minutes when you refresh the page and is available for all 65 stations.
Christopher Redmond, Mesonet Network Manager
Mary Knapp, Weather Data Library
Ignacio Ciampitti, Crop Production and Cropping Systems Specialist