Considerations for late-planted corn in Minnesota
By Jeff Coulter, Extension Corn Agronomist
As of May 10, approximately 81% of Minnesota's corn had been planted and 11% had emerged. However, corn planting in many parts of the Red River Valley has been limited due to wet soil conditions, leading to questions about agronomic decisions for late-planted corn that are addressed below.
What is the yield penalty for late-planted corn?
Long-term data indicate that corn in Minnesota generally needs to be planted by mid-May to avoid yield losses greater than 9% (Figure 1). On average, yield is reduced by 0.5% for each one-day delay in planting from April 25 to May 30. After May 30, yield reductions due to delayed planting average about 1.2% per day.
Figure 1. Corn response to planting date in Minnesota. Adapted from Hicks et al. (1999).
What are the latest recommended planting dates for corn?
June 5 in central and northern Minnesota if corn is to be harvested for grain.
June 15 in southern Minnesota if corn is to be harvested for grain.
June 25 in southern Minnesota if corn is to be harvested for silage.
What corn maturities should be used when planting late?
Growers should stick with their planned seed corn choices until the last week in May. When planting is delayed until May 25 or later, it will be a good risk management strategy to reduce the relative maturity of the corn hybrids that will be planted. Use the information in Table 1 to guide your decisions regarding corn maturity for late planting.
Table 1. Corn maturity guidelines for late planting in Minnesota.
|Planting date||Relative maturity units earlier than full-season for the region|
|Prior to May 25||Plant normal seed choices|
|May 25 to 31||Plant hybrids that are 5 to 7 relative maturity units earlier than full season|
|June 1 to 10||Plant hybrids that are 8 to 15 relative maturity units earlier than full season|
|June 11 to 15||Plant hybrids that are 15 or more relative maturity unites earlier than full season|
|Source: Hicks et al. (1999).|
Should seeding rate change when planting corn late?
If soil conditions with late planting are better for emergence than those with earlier planting dates, slightly fewer seeds may be needed to obtain a given final plant population. We do not have a lot of information from Minnesota on whether the optimum final plant population differs with planting date. In 2008, with support from the Minnesota Corn Growers Association, we were able to conduct research at two locations in southern Minnesota to address this question (Figure 2). These trials are being repeated this year. In 2008, our results show that the economically optimum final plant population varied by 2,400 plants per acre among planting dates. However, there is not enough evidence from these trials to indicate that the optimum plant population is higher or lower with late planting. This supports previous findings from trials conducted over four years at two locations in Illinois (Nafziger, 2002).
Figure 2. Corn (DKC52-59) response to final plant population for three planting dates. Data are averages from Lamberton and Waseca, MN in 2008. Red triangles indicate the optimum plant population based on a corn price of $4.00 per bushel and a seed cost of $250 per 80,000 seeds.
Should planting depth change when planting corn late?
If very dry conditions are present when planting late, growers may consider planting deeper (as deep as 2.5 inches) to ensure that adequate soil moisture is present in the seed zone for germination. It is more common, however, for delayed planting to be the result of wet field conditions. In general, a planting depth of 1.75 to 2 inches is considered optimal for most planting dates. While a planting depth of 1.5 inches often works, it increases the risk for poor establishment of the nodal roots that develop between the seed and the soil surface. Poor nodal root establishment is commonly associated with both shallow planting and a very dry and fluffy soil surface. It can also be associated with shallow planting followed by heavy rains that settle the soil surface, resulting in seed placement that is shallower than originally desired.
Excellent information and photos on corn emergence and seedling establishment from Purdue University in Indiana are available at: http://www.agry.purdue.edu/ext/corn/cafe/.
Hicks, D.R., S.L. Naeve, and J.M. Bennett. 1999. The corn growers field guide for evaluating crop damage and replant options. Available at http://www.extension.umn.edu/agriculture/corn/planting/docs/corn-field-guide-evaluating-crop-damage-replant-options.pdf. University of Minnesota, St. Paul.
Nafziger, E.D. 2002. Corn. University of Illinois, Urbana.