Corn planting in central Illinois has been delayed due to cold temperatures and wet soils. With those delays comes the thoughts of switching corn products to an earlier maturity to offset late planting. Yield potential can decrease with delayed planting because of a shorter growing season, insect and disease pressure, and potential moisture stress during pollination.
Switching to an earlier corn product because of delayed planting should not be automatic. Full-season corn products for a given area typically have the highest yield potential, which may help offset the cost of drying higher moisture corn. As planting is delayed, corn product maturities come closer together. Corn generally requires 1.6 growing degree units (GDUs) less each day to reach flowering and 6.8 GDUs less each day to reach physiological maturity (black layer) as planting is delayed beyond about May 1.1 Therefore, corn planted in late May compared to an optimum date could actually take 110 to 210 fewer GDUs to reach black layer.
The yield for late-planted corn can vary greatly depending on the remainder of the growing season. The decision to switch maturities can be a difficult one because of variations in the growing season relative to available GDUs, first frost date, and fall drying conditions. Table 1 provides average available growing season GDU accumulations for various planting dates to average frost (32 F). For example, if planting is delayed until the week of May 7 in the Springfield area, a seed product with a GDU to black layer rating of 2910 can still be planted because its GDU to black layer rating is below the 3167 potential. Additionally, a product with a GDU to black layer rating of 2910 planted on May 28, should only require 2726 GDUs to black layer (2910 GDU requirement - (6.8 GDUs less/day X 27 days).
The numbers provided are based on averages and should only be used as a reference. The main reason for switching to an earlier maturity corn product is to reduce the risk of immature and wet grain in the fall. Quite often, the increased yield potential of full-season seed products can outweigh the increased cost of drying in the fall. Based on GDU ratings,full-season products for an area can usually be safely planted until late May. Through the years, products with high yield potential remain products with high yield potential regardless of the planting date. Therefore, the decision to switch to an earlier product should be well thought out and based on science rather than emotion.
Even with delayed planting, it is important to try to minimize the potential effects of adverse weather by planting a package of seed products that fit GDU requirements to flowering and have the potential to mature before a killing frost. Insect protection and crop safety becomes more important with later planting; therefore, corn products with biotech insect trait protection and herbicide tolerance should be considered. Insects such as corn borer and earworm can be drawn to later-maturing plants and rapidly growing plants can be sensitive to certain herbicides. Additionally, the longevity of certain herbicides should be considered if another crop is planned after harvest.
1Brouder, S., Camberato, J., and Casteel, S. 2008. Corn & Soybean Field Guide. ID-179. Purdue University. West Lafayette, Indiana. High Plains Regional Climate Center (https:// hprdd.unl.edu/) Websites verified on 5/1/19. 050119LGM