Frosty Temperatures Threaten Crops

September 15, 2011 07:28 PM

A record-early frost could be in store for parts of the Corn Belt.

Some fields across the Midwest were covered with a thick icy coating this week, as temperatures dipped down into the frosting and freezing levels.
In northeast Nebraska, a farmer reported to AgWeb Crop Comments that everything had frost on Thursday morning. “Beans were still grass green where they were irrigated. Dry land had been dead and drying up for the last week,” the farmer reports. “Not a good end to the year.”
A Nobles County, Minn., farmer also says they had enough frost to have to scrape windshields. “Our growing season has come to an end this morning,” the farmer reports. “I’m guessing that 75% of the crops were mature enough to handle it, even though we are two weeks early for an average killing frost.”
A frost in mid-September is early for many areas of the Midwest. See the map below to see the average fall freeze dates from the National Climatic Data Center.
Fall Freeze Occurrence 
(click to enlarge)
Harry Hillaker, state climatologist for Iowa Department of Agriculture, says there is certainly a threat of frost for areas in his state.
If temperatures do drop enough to frost or freeze, he says it could be a record. “This is very, very early to see a freeze at this point.” In northwest Iowa, the area of the state which tends to freeze first, the average freeze date is Sept. 27. A freeze now would be more than 10 days early.

Hillaker says, on the probability, only one time in four years does a freeze come just a week earlier than normal. “The fact that things have been so dry recently will help things cool a little more because of low humidity, which will allow temperatures to drop a little more than normal.”
Luckily, he says, much of the Iowa corn crop is far advanced so these cool temperatures shouldn’t cause much damage. “The bigger issue would be for soybeans, if there are some green beans out there still.”

When Frost Kills

When temperatures reach around 30 F, the corn growing season halts, reports Joe Lauer, University of Wisconsin Extension corn agronomist, in his recent article “Handling Immature Corn After an Early Frost.”
“Corn is killed when temperatures are near 32 F for a few hours, and when temperatures are near 28 F for a few minutes. A damaging frost can occur when temperatures are slightly above 32 F and conditions are optimum for rapid heat loss from the leaves to the atmosphere, such as clear skies, low humidity, no wind.”
Lauer says symptoms of frost damage will start to show up about one to two days after a frost, and frost symptoms are water-soaked leaves that eventually turn brown. He says that because it is difficult to distinguish living from dead tissue immediately after a frost, the assessment should be delayed 5 to 7 days.

The Weather Ahead

In its most-recent 30- and 90-day weather outlooks, the National Weather Service Climate Prediction Center says the October temperature outlook indicates enhanced chances for above normal temperatures from the Rocky Mountains across the southwest U.S. to Texas and northeastward across the southern and central Great Plains to the central Great Lakes.
Oct 2011 Temperatures NOAA
Below-median seasonal total precipitation is forecast for much of the southern portion of the country with enhanced chances for above-median precipitation indicated across parts of the Pacific Northwest. 
Oct 2011 Precipitation NOAA
For More Information
Have your crops seen frost conditions? Share your report with AgWeb Crop Comments.
Stay up-to-date with the National Weather Service’s most-recent warnings and forecasts.  


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