Frost brought the 2011 corn growing season to an end this week for many North Dakota producers.
"Corn in many areas had not reached physiological maturity, which could lead to storage problems if it isn't dried and ensiled properly," cautions J.W. Schroeder, North Dakota State University Extension Service dairy specialist.
Corn is killed when temperatures are near 32 F for a few hours and near 28 F for a few minutes. Corn can be damaged when temperatures are slightly above 32 F and conditions are optimum (clear skies, low humidity, no wind) for rapid heat loss from the leaves.
At temperatures between 32 to 40 F, damage may be quite variable and strongly influenced by small variations in slope or terrain that affect air drainage and thermal radiation, creating small frost pockets. Corn at the edges of fields and in low-lying areas, and the top leaves on the plant, are at greatest risk.
Greener corn has more frost resistance than yellowing corn.
Symptoms of frost damage will start to appear about one to two days after a frost. Frost symptoms are water-soaked leaves that eventually turn brown.
Because distinguishing living from dead tissue immediately after a frost is difficult, delay your assessment five to seven days.
Here are some characteristics of frost-damaged corn grain:
* Small, misshapen, soft kernels
* Undeveloped starch structure, pithy kernels
* Test weights progressively below 52 pounds per bushel, depending on maturity
* Average protein (7.5 to 8 percent) in corn heavier than 45 pounds per bushel, lower protein in corn lighter than 45 pounds per bushel
* High breakage susceptibility; many fines generated in handling
* Lower digestibility compared with normal corn, especially for test weights below 45 pounds per bushel
* Little or no increase in test weight after drying
* Variable amino acid levels
* Moisture meters generally read low in immature corn; surface drying of kernels leads to deceptively low (by 1 to 2 percent) moisture readings on dried corn
These effects are progressive and have the least impact on corn closer to maturity.
"Farmers will need to manage frost-damaged corn silage and grain in fields that were harder hit by frost," Schroeder says.
Corn silage should be harvested at the appropriate moisture content for the type of silo in which it will be stored. In general, more moisture is required for good packing in storage structures that allow easy diffusion of air, such as bunkers.
If corn is frosted prior to 50 percent kernel milk, the corn's moisture content may be too high to be ensiled properly. However, during the dry-down period, dry-matter yield will decrease due to leaf loss, plant lodging and ear droppage.