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Corn development and yield: Stress now reduces kernel number

Stress to corn during the blister and milk stages from dry or hot conditions can reduce grain yield.

By Jeff Coulter, Extension corn agronomist

Much of the corn in Minnesota has finished pollinating and the kernels are in the blister stage. Kernels enter the blister stage at about 12 days after tasseling and the milk stage at about 20 days after tasseling. In much of the upper Midwest, air temperature and soil moisture were favorable for successful pollination and are expected to remain favorable in the near term. 

Stress to corn during the blister and milk stages from dry or hot conditions can reduce grain yield by causing kernels to dry out, especially at the tips of ears. Some loss of kernels at the tips of ears is expected. Little or no kernel loss at the tips of ears after the milk stage indicate that the plant population for the given hybrid, site, and growing environment may not be high enough to maximize net return. Once kernels enter the dough stage, about four weeks after tasseling, kernel number is set and yield reductions from stress are due to lighter kernels.

Corn yield forecasts

To evaluate the impact of this season’s weather on corn development and yield potential, researchers from the University of Nebraska ran a crop simulation model on July 31 for several locations across the Corn Belt, including three from Minnesota. Results are available at: July 31 Corn Yield Forecasts. Updated forecasts will be available in later August. 

As of July 31, most corn in the Corn Belt was in the early reproductive stages and its development continued to be behind normal and that of last year. Overall, yield potential remains variable and somewhat uncertain, as the critical period for yield determination lasts for about two weeks after pollination. Yield forecasts will become more certain in later August. 

Source: University of Minnesota Extension

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