Before 1998 becomes too foggy in our memory, what lessons can we learn from the corn forage drydown during September 1998? In most years farmers would most often use the calendar, and typically would begin thinking about cutting corn forage around 15 Sep. Last year most farmers would have been ensiling corn that would probably have turned moldy in the silo because it would have been too dry. Corn drydown started earlier than normal. Fig. 1 describes corn forage drydown for 4 counties in Wisconsin. For a concrete stave silo, the optimum moisture to begin filling the silo is at 65% whole plant moisture. Last year the average date that these counties would be at 65% moisture was 9 Sep. Nearly a week earlier than normally expected.

What is interesting though is the rate of drydown that occurred across the counties. In the past, we have typically seen an average drydown rate of 0.5% per day. Depending on county, the maximum and minimum drydown rate during 1998 was 0.40 to 0.87 % per day with the average being 0.65% per day.

Since 1996, the slowest corn forage drydown rate reported in various Wisconsin counties was 0.36 % per day, while the fastest drydown rate was 0.87 % per day (Table 1). Predicted dates when corn forage in the field would be at 65% moisture range from 11 days in 1997 and 6 days in 1998. The average predicted date at 65% moisture was 15 Sep in 1997 and 6 Sep in 1998.

Table 1. Summary of corn forage drydown rate and predicted dates for 65% moisture in Wisconsin counties during 1996 to 1998.
Year	County	Drydown rate	Predicted date @ 65% moisture
		% per day
1996	Manitowoc	0.36	3 Oct

1997	Chippewa	0.43	15 Sep
	Jefferson	0.55	26 Sep
	Manitowoc	0.60	20 Sep
	Sheboygan	0.78	30 Sep
	Waukesha	0.61	26 Sep

1998	Dodge	0.67	6 Sep
	Jefferson	0.67	9 Sep
	Manitowoc	0.40	12 Sep
	Marathon	0.67	6 Sep
	Waukesha	0.87	10 Sep

Some summary points for determining when to harvest corn forage for ensiling:

Watch for kernel milkline movement in the cornfields you plan to ensile.
Use kernel milkline as a guide to begin checking forage moisture. For a bunker or bag silo, begin measuring forage moisture when kernels on ears are around 80% kernel milk; for concrete stave silos, begin measuring moisture when fields are around 60% kernel milk; and for oxygen limiting silos, begin monitoring moisture when fields are around 40% kernel milk. Usually about 95% of the time forage moisture will be too wet at these kernel stages. But, you will know where that field is at for moisture.
Once the kernel milkline has begun to move and forage moisture is known, then use 0.5% per day forage drydown rate to predict the date you should recheck and/or chop the field to store at the proper moisture for the storage structure.