Frost damage is one issue growers will be concerned about with fall approaching. Corn that hasn't reached physiological maturity can be killed prematurely by frost.

Corn is killed when temperatures are near 32 degrees F for a few hours, and when temperatures are near 28 degrees F for a few minutes. A damaging frost can occur when temperatures are slightly above 32 degrees F and conditions are optimum for rapid heat loss from the leaves to the atmosphere, i.e. clear skies, low humidity, no wind.

At temperatures between 32 to 40 degrees 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. Field edges, 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 show up about 1 to 2 days after a frost. Frost symptoms are water soaked leaves that eventually turn brown. Because it is difficult to distinguish living from dead tissue immediately after a frost event, the assessment should be delayed 5 to 7 days.
 
For fields that only had light frost damage, it is too early to harvest. Growing conditions may improve during September allowing the crop to mature and produce reasonable grain and silage yields.
 
For fields that were harder hit by frost, farmers will need to manage frost damaged corn silage and grain. For some useful guidelines see: http://corn.agronomy.wisc.edu/Management/L041.aspx.