The economics of corn grain production make June planting in Wisconsin marginal due to lower yield and high grain moisture. Over the last five years it has typically cost $242/A to produce corn in Wisconsin (PEPS, 2000). It costs the same to plant early as it does to plant late (more when considering drying costs). In most years the latest economical planting date for corn grain production in northern Wisconsin is June 1, while for southern Wisconsin corn should not be planted for grain production after June 10.

Maturity switch dates for corn in southern Wisconsin are May 20 and June 1 where on each date hybrid maturity should be 5 to 10 RM units shorter-season than the "full-season" hybrid used for the field. The decision depends upon drying cost and grain price. When grain prices are low and drying costs are high switch dates are earlier. For northern Wisconsin there is only one maturity switch date on May 20. Yield is not different between full- and shorter-season hybrids when planted in June, but shorter-season hybrids should be used to better manage risk from fall frost.

Corn can still be planted in June, but in most years it should be intended for corn silage use. Table 1 describes the relationship between corn silage dry matter yield and planting date for various locations. In general silage yield decreases 31 to 41% as planting date is delayed from the optimum date to June 20.

The economic trade-offs are difficult to establish for late planted corn silage. Milk per acre is more affected than silage yield due to the low grain content of the silage. Most of the silage yield reduction is due to grain yield reduction thereby decreasing the energy content of the silage. This is reflected in Table 2 where delayed planting decreases Milk per acre 40 to 55%.

In most years, planting date and maturity switches for corn silage use should be the same or slightly later than those for grain use. Although there may be more flexibility in years where grain prices are low when it may be possible to add grain to corn silage for later planting dates thereby raising quality. The economics of this management decision must be carefully considered.

Table 1. Corn silage yield response to planting date at various locations in Wisconsin.
Planting date	Arlington 1994, 1997-2000	Hancock 1998-1999	Marshfield 1998-1999	Spooner 1998-1999	Ashland 1998-1999
	Tons of Dry Mater / Acre
April 20	9.2	10.8	9.6	9.0	7.7
April 30	9.2	10.3	9.1	8.6	7.4
May 10	9.1	9.7	8.5	8.2	7.0
May 20	8.7	9.0	7.9	7.7	6.6
May 30	8.1	8.3	7.3	7.2	6.2
June 10	7.1	7.5	6.6	6.6	5.7
June 20	6.1	6.7	5.9	6.0	5.3

R²	0.49	0.62	0.60	0.68	0.39

Table 2. Corn milk per acre (Milk95) response to planting date at various locations in Wisconsin.
Planting date	Arlington 1994, 1997-2000	Hancock 1998-1999	Marshfield 1998-1999	Spooner 1998-1999	Ashland 1998-1999
	Pounds of Milk / Acre
April 20	17153	20789	18133	19098	13601
April 30	17527	19306	16898	17688	12873
May 10	17299	17824	15556	16155	12082
May 20	16472	16341	14107	14500	11227
May 30	15043	14858	12550	12723	10309
June 10	12778	13227	10713	10625	9226
June 20	10089	11744	8931	8590	8175

R²	0.46	0.41	0.61	0.78	0.30

June Planting Options: How late should we plant corn for silage?

June Planting Options:
How late should we plant corn for silage?