"Will my corn make grain this year?"
Many farmers in the Upper Midwest are asking that question. After planting delays due to wet springtime conditions and a relatively cool summer many cornfields are significantly behind their normal development. Some fields may not even begin grain fill before the first frost hits. Below is a table showing approximate days to maturity from various growth stages, as well as an estimate of yield potential.
These predictions are only an estimate of maturity, based on an average accumulation of 20 Growing Degree Units (GDU) per day (a high of 80 degrees, low of 60 degrees). If the weather is warmer the crop will mature quicker; if it remains cool development will be slower. Also, shorter-season hybrids will tend to mature quicker than full-season hybrids.
"What do I do if my corn gets frosted before it matures?"
The natural tendency after a frost is to start chopping as soon as possible. However, it is always best to chop according to the whole-plant moisture level, not based on the visual appearance. Here are a few key points about frosted corn.
The plant is always wetter than it looks (note the moisture levels in the chart). Most of the moisture is in the stalk and ear; just because the leaves are dry doesn't mean that the silage will be dry as well.
The grain/starch content will be lower, but less grain doesn't necessarily mean lower energy. The energy will be in the form of sugars present in the stalk instead of starch in the ear.
Fiber in the silage will be higher, but it should be more digestible. It will probably feed better than the high fiber/low starch levels would indicate.
Normally the whole-plant moisture level drops 0.5 to 1.0 percentage point per day as the plant matures; these figures still hold true for corn killed by frost. You need to wait for the plant to dry down to an acceptable moisture level based on your storage structure: 66 to 70% for a bunker, bag or pile; slightly drier for an upright or oxygen-limiting silo. In a Canadian study in which corn was frosted prior to reaching ½ milk line, dry matter intake and milk production was maximized by delaying harvest for 12 days after the frost (the day after a second frost), chopping it at 66% moisture, vs. 77% moisture a week before the frost, or 75% moisture 4 days after the frost (St. Pierre et al., 1987, J Dairy Sci. 70:108-115). Remember the old saying, "Haste makes waste!"
It will definitely pay to use a proven silage additive on immature, frosted corn. There will be an abundance of soluble sugars present which provides an environment favorable to the growth of spoilage organisms as well as for normal silage acid-producing bacteria. The frost also would tend to reduce the number of naturally-occurring bacteria on the crop, so choose a silage treatment which contains beneficial lactic-acid producing bacteria to quickly lower the pH and prevent the spoilage organisms from growing.
Postponing harvest until the proper moisture level is reached, treating the silage with a proven inoculant, and rapidly filling, packing and covering will help you make the best silage possible under the circumstances.