When to Switch Corn Relative Maturity?

If you are in the same boat as many other producers and haven't planted all, or any, of your corn, you may be thinking about options for switching some of your longer 105 to 115-day RM to something a little shorter. However, you may not know when to make this decision or how much shorter to go. There are some resources and estimates that we can use to help us make these decisions.

Understanding Options

1. Start by looking at the growing degree day possibilities for your area. There are many options for tools, apps, and calculators, but for this article, we will use the Climate Smart Farming Growing Degree Calculator from Cornell University. Growing degree days, or GDD, are measurements of heat used to estimate how crops move through their physiological cycles. For more on GDDs, read Understanding Growing Degree Days.

   

   This is a screen capture of the Climate Smart GDD Calculator interface. First, begin by selecting the earliest possible planting date and GDD base for your area. I have selected April 15 and base 50. Notice the plateau of the accumulations. In Masontown, PA, historically, GDD accumulation slows around October 15, which will be important to know for grain drying. Working backwards, corn hybrids typically need about 300-400 GDDs to transition from maturity, or black layer, to a harvestable moisture. If accumulation slows on October 15, at 3,037 GDD, our maturity date should be around September 13, or 2,682 GDDs.

2. Next, determine how many GDDs have been missed this year. As of June 1, 423 GDDs. By subtracting the current accumulated GDDs from the 2,682 GDDs from our estimated black layer date, we have an estimated 2,259 units remaining for the season.

   

3. Before deciding, always know your production costs before planting any crops outside the normal planting times. Understanding your inputs, insurance options, current and projected market, and estimated yield should all be considered. Agronomy Guide Table 1.4-8 Part A, B, and C provide estimated yields for various planting dates.
4. Comparing the calculated remaining GDDs of 2,259 to the table below, we can determine what remaining maturities are appropriate for our areas. For this example, hybrids in the range of 110-day are still an option (see things to consider).

Things to Consider:

• Later planting corn will reduce GGD needs. A study by Neilson et. In 2002, in Indiana and Ohio, researchers found that needs can reduce as much as 4.5 and 3.2 GDD per day for late and early maturities, respectively. This does not mean that you can plant 120-day corn in the northern tier of Pennsylvania on June 15 and make grain, but it does mean that there is some flexibility. Other studies have also found that in Pennsylvania, most corn hybrids mature approximately 200 GDDs shorter than what is reported from midwestern trials.
• If going to the trouble to swap out your longer maturity corn with something shorter, and you aren't fully sure when your planter will return to the field, mid-Atlantic seedsmen are recommending seeking corn that is 7 to 10 days shorter relative maturity than what you wish to exchange. Be careful not to make too drastic changes in your RM. Although a drastic reduction will lead to drier grain and reduced drying costs, it will not be more profitable than a fuller season corn that may need a little drying.
• Seed companies in Pennsylvania try to have a surplus of shorter RM corn available when changing is necessary, often having an extra 20% of each maturity group in reserve. This means that it is usually possible to change your maturity, but you should consult your seed company for availability. An informal poll of several seed corn dealers in central PA indicates that there is a fair amount of shorter-maturity corn yet available for 2025.
• After June 15, for most of PA, especially if the corn is intended for grain harvest, consider changing to alternative crops. If you are already growing soybeans, increasing your soybean acres may be a good option as they provide more planting flexibility. If you are raising your corn for feed, and sub-90-day corn is unavailable, consider an alternative forage option like sorghum/sudangrass. With any change to species, you need to consider fertilizer and herbicide practices.