Due to late corn planting dates, some farmers are considering leaving their corn in the field through winter and harvesting in the spring. Delayed planting combined with below normal heat units for the 2004 growing season has resulted in a crop that is behind normal development. As of September 19, only 43% of the corn in Wisconsin was dented making the corn crop more vulnerable to early frost damage before it reaches physiological maturity. Even if it's not damaged by frost, immature corn will exhibit higher moisture which will increase drying costs and lower test weight (weight per bushel at 15.5% moisture), a key indicator of quality in corn.

Every year some fields in Wisconsin are harvested in the spring. If the stalks stay standing and there isn't much ear drop, snow cover or wildlife damage; the crop can get through the winter without much yield loss. Ear drop will vary by hybrid and environmental conditions as well as the amount of grain on the ear (smaller ears should stay attached better than larger ears). If winter conditions are cool without snow then corn will continue to dry and can be harvested throughout the winter without too much yield loss. Stalks will become brittle and broken corn parts may decrease the grade causing discounts at the elevator.

Since we cannot predict the weather, the most prudent decision would be to harvest after a reasonable period of drydown. In some years with heavy snow cover, grain yield can decrease significantly (Table 1). For example, during 2000 grain yield decreased 65% by March and by spring yield decreased 37% from an October harvest date. This is contrasted with the winter following 2001 (little snow cover) when yield only decreased 18% by February and by spring was 10% lower than October harvest.

Greatest grain moisture loss occurs during October and November (Table 2). Drying continues through the winter, but at a slower rate than October and November. This is especially true for later planting dates. By the following spring there is little difference in grain moisture for early versus later planted fields. Grain test weight changes are minimal regardless of planting date (Table 3). Since grain moisture changes are minimal past December and grain yield losses can be significantly affected by environment, the best decision is to complete harvest by December (or the typical first heavy snowfall, if you are good at predicting such things).

Table 1. Grain yield (bu/A) change of corn left standing in the field through winter at Arlington, WI.
	Harvest month
Year	Oct	Nov	Dec	Jan	Feb	Mar	Apr
2000	204	206	113	86	83	72	127
2001	220	208	208	200	181	205	199
Mean	212	206	165	145	134	145	162

Table 2. Grain moisture (%) change of corn left standing in the field through winter. Data are summarized for the 1992, 1993, 1994, 2000, and 2001 production seasons at Arlington, WI.
Planting	Harvest month
dates	Oct	Nov	Dec	Jan	Feb	Mar	Apr
before May 11	31	21	20	19	18	15	12
May 11 to May 31	37	27	22	22	18	16	10
after May 31	46	37	28	27	23	20	15

Table 3. Grain test weight (lb/bu) change of corn left standing in the field through winter. Data are summarized for the 1992, 1993, and 1994 production seasons at Arlington, WI.
Planting	Harvest month
dates	Oct	Nov	Dec	Jan	Feb	Mar	Apr
before May 11	58	55	54	55	54	55	56
May 11 to May 31	57	50	52	51	53	50	52
after May 31	51	44	46	46	46	47	48