The optimum date for planting corn for grain is between May 1 and May 7 in Wisconsin. In many years, farmers are still wanting to plant corn after June 1. Later planting dates mean lower grain yields and higher grain moistures. At some date the best use of corn becomes either as high moisture corn or corn silage.

What happens to silage yield and quality with later planting dates? Many people feel that corn silage can be planted at later dates because silage does not have to be harvested at grain maturity. The advantages of early planting of corn may not be as great for silage as it is for grain.

During 1998, research was conducted at Lancaster, Arlington, Hancock, Marshfield, Spooner and Ashland. The objective was to describe the relationship between planting date and corn silage yield and quality.

Highest dry matter yield occurred when corn was planted in early May. Approximately 95% of the expected yield was still seen at the late-May planting (Table 1). Yield decreased at the rate of 0.04 tons of dry matter per day between May 16 and May 30. The decline in silage dry matter yield accelerated to 0.09 tons of dry matter per day between June 15 and June 26. Late June planting dates produced only 65% of the dry matter yield produced on the optimum date in early May.

Milk per ton is a measure of silage quality. It was highest for early planting dates and declined at the rate of 6.5 lbs of milk per ton per day. There was an overall decline of 20% in milk per ton between April 23 and June 26.

Milk per acre is a measure of dry matter yield and quality. It showed a steady decline between May 2 and June 26. Milk per acre decreased at the rate of 83 lbs of milk per acre per day when planting was delayed in late May, and 211 lbs of milk per acre per day when planting was delayed in late June.

Table 1. Relationship between dry matter yield, milk per ton, milk per acre and planting date at six locations in Wisconsin during 1998.
Average planting date	Dry matter yield	Milk per Ton	Milk per Acre
	T/A	lb milk / T	lb milk / A

April 24	8.31	2101	17945
May 2	8.92	2049	18437
May 16	8.41	1742	15079
May 30	7.85	1708	13920
June 15	6.89	1780	12671
June 26	5.86	1685	10347

R²	0.98	0.93	0.96