Like last year, significant areas of Wisconsin are encountering corn planting delays. A common question is "When should corn hybrid maturity be switched?" If there were one date to switch hybrid maturity in Wisconsin it would be May 20. But like most answers it depends upon many things such as corn price, drying costs, intended use and location in the state.

For an individual farm the range for a hybrid maturity switch date is about seven days on either side of May 20. Switch dates should be earlier than May 20 if corn is grown for dry grain, is commercially dried at higher drying costs, the corn price is low, or the farm is in the southern part of the state. Switch dates should be later than May 20 if corn is grown for high moisture corn or silage, drying costs are low, corn price is high, or the farm is located in the northern part of the state. Hybrids maturity should be switched from full-season to 5-10 days shorter-season maturity.

Corn grain yield decreases about 0.3-0.5% per day during early May. The rate of grain yield decrease accelerates to 1.5-2.3% per day when corn is planted later in May. In most years the latest date to plant corn economically is June 1 for northern and June 10 for southern Wisconsin. If planting delays continue to occur farmers may want to consider another crop.

Yield potential and drying cost (or the type of corn production system - i.e. dry grain, high moisture corn or silage) are the most important factors in determining switch date between full - and shorter-season hybrids. 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.

For further information on late-planting corn see Corn Replanting or Late-Planting Decisions (UWEX Bulletin A3353).