By Roger Elmore and Lori Abendroth
11 Sep 2007 -
The National Weather Service reports that tonight may be the “…coldest night of the season so far… with high pressure drifting overhead during the night and dewpoints expected to be in the 30’s… good radiational cooling conditions should set up and areas across the northwest portions of central Iowa could see some patchy frost toward morning.”
It is imperative to note that temperatures in the 30’s may have little to no impact on nearly mature crops. But if temperatures actually drop lower than this, here are a few things to keep in mind.
Not all of Iowa’s corn is ready for a frost, especially in NW Iowa. Based on yesterday’s “Iowa Crops & Weather” report released by the USDA-NASS (vol 07-28), 41% of the crop is mature and will therefore not be injured from frost. Yet 59% of the Iowa’s corn is vulnerable. Corn in the northwest and west central regions of the state is most behind; only 29% and 30% of the crop was rated as mature on 9 Sept 07. Immature corn in low lying fields could experience damage which may reduce yields. The national NASS report may be accessed at: http://usda.mannlib.cornell.edu/MannUsda/viewDocumentInfo.do?documentID=1048.
If significant freezing occurs the greatest yield reduction will occur in fields where the milk line is still progressing downward, toward the cob. Corn with a milk line at ¾ on the kernel could experience up to 3% yield loss. Less mature corn, with the milk line at ½, could lose up to 8% of its yield. In addition to these potential yield losses, drying is more difficult for grain from frost damaged fields.
Although we do not expect significant injury to the state’s corn crop, it is something to be aware of and take note that low lying areas may be affected.