The rainy, cold weather and wet, cool soil temperatures we have experienced during April has delayed Wisconsin fieldwork. Most corn was not planted by the optimum May 1 planting date. Due to delayed planting, it is likely that some growers will need to modify their hybrid selections and switch corn hybrid maturities from full-season to shorter -season maturities. Table 1 describes some guidelines for switching corn hybrid maturities in various Wisconsin production zones when the end-use is dry grain. The chances of obtaining dry grain when planting in mid- to late-June are low.

When using these guidelines, please remember that growing season, site and management influence a particular hybrid's actual days to maturity. Also, there is no industry standard for calculating hybrid maturity ratings. Therefore, use the values in Table 1 only as a general guide.

Table 1. Latest acceptable planting date and hybrid maturity for dry corn grain in several Wisconsin production zones.
Hybrid maturity	Southern		South Central		North central		Northern
Hybrid maturity	Latest planting	Relative maturity	Latest planting	Relative maturity	Latest planting	Relative maturity	Latest planting	Relative maturity
	date	days	date	days	date	days	date	days
Full-season	5 May	105-110	8 May	100-105	11 May	95-100	14 May	85-90
Mid-season	15 May	100-105	18 May	95-100	21 May	85-95	24 May	75-85
Short-season	25 May	95-100	28 May	90-95	31 May	75-85	4 June	65-75

Based upon a four year trial conducted at six locations in Wisconsin between 1991 and 1994, corn grain yield was found to decrease about 0.3-0.5% per day during early May. The rate of grain yield decrease accelerated to 1.5-2.3% per day when corn was planted later in May. 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.

Your decision to switch hybrid maturity depends upon:

Desire to accept risk: Longer season hybrids offer the highest yield potentials, but may also increase drying costs and/or delay harvest.
Potential use: For dry grain, relative maturities should be shorter-season within the maturity range for the latest acceptable planting date. For high moisture corn and silage, relative maturities should be longer-season within the maturity range for the latest acceptable planting date.
Field conditions: Shorter season hybrids within the maturity range for the latest acceptable planting date should be selected when field conditions include heavy crop residue, reduced tillage, and heavy soil textures.
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.
Ease of trading original hybrids for superior shorter-season alternatives.