Assess Frost Risk

As threats of frost continue, you may want to evaluate the probability of a killing frost. You can assess the
risk of a killing frost by using the Corn GDD decision
tool on the Useful
to Useable
 website. The tool uses a combination of factors,
such as customizable planting dates, location, and maturity, to establish
growing degree accumulation.

“This decision tool
allows you to select a county and customize planting date, hybrid maturity, and
comparison year,” says
Mark Licht, Iowa State University
Extension cropping systems agronomist. “The tool then outputs growing degree
accumulation and predicted date of black layer as well as fall frost frequency
and date of 50% probability of first freeze.”

“The last USDA crop progress report indicates
72% of corn in or past the dent stage with 5% of the corn acres mature and
soybean with 26% leaves turning color,” says
Licht. “Heat unit accumulation has been and
continues to be slower than normal resulting in a crop that is not maturing as
early as planned. With the 50% probability of a 28°F frost generally being mid-
to late-October, there is some concern with a fall frost killing the crop
before maturity is reached, especially for corn.”

This decision tool
was used to calculate 2014 risk of frost for four different scenarios in Iowa;
planting a 102- day and 114-day hybrid on April 27, 2014 (Fig. 1) and planting
a 102-day and 114-day hybrid on May 25, 2014 (Fig. 2). April 27 and May 25 were
used because they represent when approximately 10% and 90%, respectively, of
the Iowa corn acres were planted.

img_541b04cdc5c0c_45182.png

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Figure 1. Useful
to Useable Corn GDD decision tool scenarios for April 27 planting date with 102
day and 114 day hybrids. Green, yellow and red colors indicate low, moderate
and high frost risk prior to reaching maturity.

img_541b0538864d5_45185.png

img_541b054e90ed0_45186.png


Figure 2. Useful
to Useable Corn GDD decision tool scenarios for May 25 planting date with 102
day and 114 day hybrids. Green, yellow and red colors indicate low, moderate
and high frost risk prior to reaching maturity.

“These four scenarios
were run for select counties representing each of Iowa’s nine crop reporting
district,” says Licht. “These figures suggest that corn planted in April of
well adapted maturities have little to no risk of a killing freeze before
maturity. The figures also indicate that later planted corn, even at shorter
maturities may be at moderate risk of a killing freeze in the northern two
thirds of Iowa.”

Assess your own risk at mygeohub.org/groups/u2u.

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