Minimizing frost risk in corn hybrid selection

By Zachary Fore
University of minnesota Extension cropping Systems Specialist

Home

E-Mail

Back

Prairie Grains is the official publication of
the Minnesota
Association of
Wheat Growers,
North Dakota Grain Growers Association,
South Dakota Wheat, Inc., and the Minnesota Barley Growers Association

don’t suppose I would be the first person to have noticed that the weather varies from year to year in our northern climate. Some years are hotter than other years. Some years the frost comes earlier.

The goal is to select a hybrid that maximizes the use of the growing season without getting frozen before maturity. Fortunately, using available weather data, we can select hybrids that have a minimal chance of being frozen before they mature.

Weather data that is important when selecting relative maturities are: growing degree day accumulation (GDD) and frost dates. Here is an example of how to use this data to help select the relative maturity of a corn hybrid for Crookston, MN.

The average GDD accumulation in Crookston over a 108 year period is 2,442, as shown in Table 1 (using the standard growing degree day formula for corn, with a 50° F. base and an 86° F. ceiling). However, some of these GDD’s occur before planting, and some occur after a killing frost is likely. Let’s assume that I want to grow a corn hybrid that will reach physiological maturity (PM) if it is planted on May 15. I would not count any GDD’s that accumulate before May 15. Thus, I subtract an average of 7 for March, 100 for April, and 117 for May. (I have estimated that 40% of May’s GDD’s accumulate by May 15, which would be 117).

Table 1. Corn Growing Degree Days (GDD's)
and Adjustments for Crookston Minnesota.

Let’s also assume that I want a 90% chance of that hybrid reaching PM before a 30-degree frost event. This means the hybrid must reach PM before Sept. 15 (Table 2). Therefore, I can’t use the GDD’s that accumulate after Sept. 15 (126 for the last half of September, 131 for October, and 9 for November). I have estimated that 40% of September’s GDD’s accumulate after Sept. 15. After making the necessary GDD adjustments, there are 1,952 GDD’s remaining. There are approximately 24 GDD per relative maturity day, so 1,952 GDD’s divided by 24 results in 81 relative maturity days. A hybrid that matures in 81 days or less will have a very high likelihood of reaching PM in Crookston when planted by May 15.

Table 2. Fall Temperature Summary For Crookston, MN
(108 Years of Data)

However, there is a 10% chance that a 300F temperature event will occur before Sept. 15. And, the average GDD accumulation between May 15 and Sept. 15 is 1,952. In any given year more or less GDD’s may accumulate. Planting a hybrid that matures in 81 or less days does not guarantee frost-free weather until the hybrid reaches PM – it just gives us better odds it will reach PM. What if GDD accumulation is less than average, and/or there is an unusually early fall frost? The yield effects of frost before PM are given in Table 3.

Table 3 shows that even if frost occurs 10 to 15 days before PM due to an unusually early fall frost or a lower than average GDD accumulation for the year, expected yield would be 90 to 95% of maximum yield. Therefore, there is minimal risk of significant yield loss when planting a hybrid that matures in 81 days or less in Crookston.

Table 3. Relationship between kernel growth
stage and development.

* Kernel milk-line moved 1/2 to 3/4 the distance between crown and base.

**Black layer formation and/or milk disappearance from kernel under normal development.
Premature frost or extended cold temperatures may cause black layer formation at earlier stages and wetter moisture.

Not only can GDD’s aid in seed selection, but also for more precise treatment of crop pests. Your county extension office is a good place to start for more information on GDD’s. The nearest experiment station and other local sources have historical weather data. One source for ag-related weather data on the web is the North Dakota Agricultural Weather Network (NDAWN), www.ext.nodak.edu/weather/ndawn.html.

Growing Degree Day 101

Plants only grow within a certain temperature range. If temperatures are too high or too low, growth stops. That temperature range for corn is above 50F and below 86F. Corn will grow faster as the temperature nears 86F. Understanding this allows us to estimate the growth stage of corn by monitoring temperature during the growing season. A formula is used to determine heat accumulation over time. This accumulation of heat is called Growing Degree Days (GDD), or some call it heat units. The formula for corn is as follows:

Growing Degree Days = Maximum Temp (no greater than 86F) + Minimum Temp (no less than 50F/2) - 50.

Using this formula, you can see that the maximum accumulation of GDD’s in one day is 36: (86+86/2)-50=36.

GDD’s can be calculated each day and added up over the growing season. The total GDD’s accumulated over the growing season can be used to predict which corn hybrids are likely to mature in a given location. Corn hybrid maturities are often given in relative maturity days — a 90 day hybrid, for example. There are approximately 24 GDD’s per one relative maturity day. Therefore, for a 90 day hybrid there will need to be 90X24=2160 GDD’s accumulated after planting, for that hybrid to mature before a killing frost.

Temperatures and frost dates vary from year to year. However, long term weather data and GDD information can provide an excellent basis for selecting corn hybrids that have a very high likelihood of reaching maturity in a given location.

Prairie Grains welcomes Fore’s "Foresight for Successful Cropping Systems" as a regular feature. If you have questions or topics you’d like to see addressed, contact Fore at 218-253-4401 or by e-mail: zfore@extension.umn.edu.