Due to the weather delays in corn planting, there is a growing concern about when to switch from full- to shorter-season hybrids. Generally, May 20 is considered the "magic" date to begin switching hybrid maturities in Wisconsin. In general, the date to switch maturities becomes later as one moves south in the Corn Belt.

The decision of when to switch hybrids maturities depends mostly on the intended use of the crop. For dry grain the switch date is earlier than for high moisture corn or silage. Increasing drying costs mean earlier switch dates.

In trials conducted at Lancaster, Arlington, Hancock, Marshfield, Spooner, and Ashland both full- and shorter-season hybrids were planted. The shorter-season hybrid differed from the full-season hybrid by 5 to 7 relative maturity units (days). Corn price ($2.00, 2.75, and 3.50 per bushel) and drying ($0.00, 0.015 and 0.03 per bushel), hauling ($0.04 per bushel), and handling ($0.017 per bushel) costs were all factored into the economic model used to determine switch dates between the full- and shorter-season hybrids.

Corn grain yield was found to decrease about 0.3-0.5% per day during early May (Figure 1). The rate of grain yield decrease accelerated to 1.5-2.3% per day when corn was planted later in May. Drying cost was the most important factor in determining switch date between full - and shorter- season hybrids (Table 1). If corn drying costs are relatively expensive (i.e. drying at a commercial elevator), then switch dates were 7 to 11 days earlier than corn used as high moisture corn in a livestock system or in years when there are no drying costs.

Table 1. Date to switch corn hybrids from full- to shorter- season relative maturity in three corn production systems.
Corn production system	Drying cost per bushel	Average for Marshfield, Spooner, Ashland	Average for Lancaster, Arlington, Hancock
Commercial elevator drying	$0.03	May 18	May 2
On-Farm drying	$0.015	May 23	May 6
Livestock (high moisture corn)	$0.00	May 25	May 13

Corn price had no influence on switch date in a livestock system. In an on-farm drying system low corn prices required switch dates 1 to 3 days earlier at $2.00 corn compared to $3.50 corn. Corn price became increasingly important in the commercial elevator drying system. Depending upon location, switch dates needed to occur 2 to 9 days earlier with $2.00 corn than with $3.50 corn.

Your decision to switch hybrid maturity depends upon:

1. Desire to accept risk: Full-season hybrids offer the highest yield potentials, but may also increase drying costs and/or delay harvest.

2. Potential use of the corn produced

3. Field conditions: Although the penalty for late planting is important, growers also need to be careful to avoid tillage when soil is too wet. Yields may be reduced somewhat this year, but effects of soil compaction can reduce yields for several years to come.

4. Hybrid dry-down and grain quality characteristics: Longer-season hybrids within the latest acceptable planting dates should have fast grain dry-down and high test weight characteristics. Growing season, site and management influence a particular hybrid's actual days to maturity.

5. Ease of trading original hybrids for superior shorter-season alternatives.

Another aspect to consider when switching hybrid maturity is the risk associated with the decision. In some years there are planting dates after May 20 that produce grain yields as high as earlier planting dates (Figure 1). The growing season of 2003 could be one of those years, but the averages are that yields and economic returns of full-season hybrids will be decreasing at a faster rate than shorter-season hybrids. The difference full- and shorter-season hybrids can range up to about $50 per acre after May 20.