Conditions throughout the growing season are more important than the planting date when it comes to realizing yield potential in our full season hybrids. This is true, but realizing yield potential would require us actually getting planted. This is usually the time of year when we want to advise producers not to rush to get in the fields when soils are too wet, but this year those warnings almost seem unnecessary considering that rain is falling more often than not. When planting gets delayed this far, one of the questions that comes up is whether farmers should consider switching from their normal full-season hybrids to shorter-season hybrids. The question is based on concerns that a full season crop may not reach physiological maturity before a killing fall freeze, reducing yield. In most other years, even when planting is delayed into early June, you would most likely be better off sticking with your initial plan and planting full season hybrids. 2019 is a different story, particularly in Northern Illinois. Let's examine this further. The tradeoff in altering maturity ratings is that shorter season hybrids can mature quicker so they are often dryer at harvest, but you are probably going to give up a lot of yield to make that happen.

The traditional "days to maturity" rating system for hybrids does not literally refer to calendar time, making it tricky to use when making decisions about switching to earlier maturing hybrids with delayed planting. Let's back up for a moment. Using growing degree day (GDD) accumulation instead of relative maturity (RM) to make hybrid selections may be more useful as it considers heat units throughout the growing season. This is important because how fast a corn plant moves through developmental growth stages is very dependent on temperature, not number of days; warmer temperatures accelerate growth and development. The Midwest Cover Crop Council (MCCC) Corn Growing Degree Day Support Tool can be a helpful tool for making decisions on changing up hybrid maturities. The tool allows producers to generate a graph illustrating projected corn growth and development based on county, hybrid maturity, and planting date. Producers can use this tool to compare hybrids in an effort to determine which hybrids will likely reach physiological maturity prior to the first killing frost. There are many factors to consider when making these decisions, but Extension Agronomist Dr. Emerson Nafziger runs through an scenario in his recent Bulletin article "Dealing with Very Late Planting." Keep in mind this tool is not as precise as we would like it to be and we can't predict growing conditions throughout the season.

The University of Illinois Extension Commercial Agriculture team has come up with a Late Planting Checklist to answer some common questions producers may be asking. Producers should be prepared to switch maturity ratings if rainfall continues into mid-June, if they have not already. North of the I-80 corridor, if planting is extended into mid-June hybrids that are 105 RM or less will be recommended. If planting opportunities extend later into June, even earlier maturities might be in order; importantly early-maturing corn varieties are not bred for Illinois' environments, so be aware of the disease resistance packages (Gray Leaf Spot and Northern Corn Leaf Blight, for example) of hybrids with 105 RM or less. Many producers in Northern Illinois have already begun to switch maturity ratings, or have the means to do so quickly because the rain keeps coming.

In the world of soybeans, flowering is determined by photoperiod so earlier planted soybeans will flower around the same time as soybeans planted in mid-June. Therefore, there is little need to change soybeans to earlier maturing varieties except for producers north of I-80, varieties no later than MG 2.8 or 2.9 should be used if planting is delayed past mid-June. If you would like more information about delayed planting, visit the Illinois Extension website at https://web.extension.illinois.edu/jsw/lpplanting/. For additional questions, contact Phillip Alberti, Crop Science Educator with University of Illinois Extension in the College of Agricultural, Consumer, and Environmental Sciences at palberti@illinois.edu, 815-599-3644 or on Twitter (@NorthernILCrops).