The freezing temperatures recorded last week have put an end to the corn-growing season in most of North Dakota.

"Though we typically think that corn can tolerate some subfreezing temperatures, we can see by looking at this year's crop that corn can be killed when temperatures are at or even approaching 32 degrees," says Joel Ransom,

North Dakota State Univ. Extension Service agronomist for cereal crops.

"Leaves that were damaged by this frost are no longer green and are crisp and dried. Stalks that were killed also are devoid of any green color."

Ransom calculates that the losses to corn growers caused by this frost could exceed $180 million.

A killing frost after the corn matures usually is a welcomed event because it can help speed up the drying process. However, this year, most of the corn crop was not mature, and farmers will experience yield and quality losses. Only 20% of the corn crop has matured, according to the most recent USDA crop condition report.

About 65% of the crop was reported to be in the dent stage, but not mature, which leaves about 15% percent that had not reached the dent stage.

Research indicates that if the leaves and stems of the corn crop are killed by frost in the dent stage, the yield loss will be 23%. There will be greater losses if the crop is in the earliest stage of denting but fewer losses as it approaches the half milk line stage of denting.

Along with the yield loss, farmers also need to be concerned about the impact on test weight. Light test weight corn is discounted at the elevator because it has less energy and therefore is of less value as animal feed or when used in the ethanol industry. Corn that is killed before the dent stage likely will have test weights below 45 pounds per bushel.

In 2011, the crop insurance policy for corn was changed so that the test weight chart of adjustment factors extends down to 40 pounds per bushel. The test weight must fall below 40 pounds before a 0.500 discount factor is applied to unsold production. Previously, the 0.500 factor applied to test weights below 46 pounds per bushel.

"With the early frost this year, this could potentially impact the indemnity paid on many acres," says Dwight Aakre, NDSU Extension agricultural economist.

"Farmers should contact their insurance agent immediately to indicate a potential claim because this will document a potential qualifying loss for the SURE program. The SURE program ends on September 30, 2011, and is not funded for 2012. If the cause of loss, such as frost damage, occurred before September

30, it will be covered as long as it has been documented."

To safely harvest and store corn, field dry down is a concern, regardless of growth stage.

"Farmers should expect the best rate of field dry down through the remainder of

September and October," Ransom says. "In November, because of cool temperatures, field dry down usually is only 2 or 3 percentage points for the whole month.

Dry-down rates have been found to be similar for mature and immature grain.

However, immature grain starts at a higher moisture content than mature grain and will take longer to dry before it can be harvested."