August2015RainGraph WEB

It’s the worst-case scenario for crop yields—a wet spring and a dry August.

After abundant rains in spring and summer, late-planted crops now face droughtlike conditions, says University of Missouri Extension agronomist Bill Wiebold.

Typically, July weather affects corn yield and early to mid-August weather affects soybean yield, Wiebold says. Not so this year.

“With delayed planting in 2015, the most influential periods have shifted two to four weeks later than normal,” he says.

Precipitation in August will influence corn and soybean yields this year.

“The wet spring weather is the gift that keeps on giving,” Wiebold says. Wet weather during and after planting increases the possibility of soil compaction and root diseases. This leads to smaller and less healthy root systems on corn and soybean plants. Smaller root systems make plants more vulnerable to dry weather during grain fill.

Bright sun, warm weather, low relative humidity and wind increase water demand by plants.  Stress to plants during grain filling reduces yield.

Wiebold looked at August precipitation in five Missouri counties distributed among corn and soybean production areas. Mississippi County had only 0.21 inch of rain in the last half of August, half of Audrain County’s 0.44 inch. Knox County fields received 1.07 inches of rain in the last half of the month and Gentry County received 1.81 inches, slightly behind Barton County’s 1.86 inches.

In its August 31 weekly crop report, USDA reported statewide precipitation at 0.19 inches, 0.61 inches below normal.

For good to excellent grain yields, about 1.2 inches of rain are required each week during grain fill. Only two of the locations Wiebold studied received more than 2.4 inches in early August. None of the five locations received adequate precipitation in the last half of August.

Northeastern Missouri, including Audrain County, has been especially dry. “This region is more vulnerable to drought stress because soils in a large portion of the region contain a claypan that restricts water drainage in spring and reduces root depth throughout the growing season,” Wiebold says.

For more information about 2015 weather challenges to Missouri agriculture, go to