This year we have had to deal with cool wet planting conditions and make predictions about the effect of late planting date on corn yield. In Wisconsin, corn yields from early June planting dates decrease at the rate of 3% per day delay. On later planting dates, corn hybrid maturity should be switched to shorter-season maturities because of yield and grain moisture effects. How long can we keep switching corn hybrid maturities and still produce corn economically? Do ultra-short-season hybrids pay? What is the last date I can plant corn and still produce profitable corn?

Deciding when to quit planting corn is not an easy decision. In 1995 at Arlington, WI, four corn hybrids were planted on different dates and yield, moisture and grower return was measured (Table 1). The production year of 1995 had a normal fall first frost date and high fall temperatures which hastened fall dry-down, i.e. drying costs were somewhat lower than typically found in a >normal= year. Grower return is the amount of money left over after subtracting treatment costs. For example, the 100 d hybrid planted on May 1 yielded 172 bushels per acre at 16.6 % moisture: Grower return = (2.75 - (0.04 + 0.017 + 0.015 x (16.6 - 15.5)) x 172 = $460 per acre

Greatest grower return was observed when corn was planted on April 20 and May 1 with the full-season 110 d hybrid. In this example, the 100 d hybrid had greatest grower return on May 15 and on all subsequent planting dates. Performance of the 110 d hybrid was affected by later planting dates as well as high grain moisture. When the 110 d hybrid was planted on June 9, no grain yield was produced by this hybrid.

In south and south central Wisconsin, corn production costs range from $275 to $325 per acre. All corn hybrids planted in April and May returned enough to compensate for production costs at a corn price of $2.75 per bushel. In this year, the 100 d hybrid had high enough yields when planted in June to break-even with production costs. The short- and ultra-short-season corn hybrids had yields too low to break-even with production costs.

A number of factors should be considered when deciding whether or not corn should be planted in June.

Corn production costs (Drying costs): Shorter-season hybrids reduce the risk of immature and wet grain in the fall. But, ultra-short- and short-season corn hybrids must have adequate yield potential to recover production costs.
Corn price: Higher corn prices make planting later into June with shorter-season hybrids more attractive.
Other uses: Corn used for other purposes such as high moisture grain or corn silage can be planted later into June than corn harvested for grain. High moisture grain and silage allow the use of longer season hybrids with greater yield potential.
Other cropping alternatives: Compare the relative yield potential of an alternative crop for a given date with that of late planted corn. For example, corn yield potential declines at a faster rate than the yield potential of soybeans. Other crops to consider include sunflowers, buckwheat, and sorghum-sudan grass.
Environment: First fall frost date and fall drying conditions influence your decision. Years that are longer and warmer than average favor full-season hybrids while shorter cooler than average years favor shorter-season hybrids.

Table 1. Performance of corn hybrids differing in maturity and grown during 1995 at Arlington, WI.
	80 d hybrid	90 d hybrid	100 d hybrid	110 d hybrid
Planting date	ultra-short-season	short-season	mid-season	full-season
Grain yield (bushels per acre)
April 20	107	160	173	184
May 1	115	147	172	177
May 15	115	152	170	170
May 30	115	153	166	148
June 9	92	98	126	0
Grain moisture (%)
April 20	14.3	16.4	16.0	21.9
May 1	14.1	17.0	16.6	20.8
May 15	14.7	16.5	17.4	22.2
May 30	14.6	17.2	18.5	28.5
June 9	15.4	23.0	29.9	---
Grower return (dollars per acre)
April 20	288	429	465	478
May 1	310	393	460	463
May 15	310	407	453	441
May 30	310	408	440	312
June 9	248	253	312	0
Grower return = (Corn price - Treatment costs) x grain yield Corn price = $2.75 per bushel; Treatment costs = Hauling + Handling + Drying = $0.04 per bushel + $0.017 per bushel + ($0.015 per % bushel x (grain moisture % - 15.5 %)) when grain moisture > 15.5 %

Published in Wisconsin Crop Manager 3(12):76-77

Corrected in Wisconsin Crop Manager 3(13):84