Choosing the right hybrid is essential for maximizing yield, as there can be a significant difference of 30-50 bushels per acre (or more) between different hybrids when tested under field conditions. The most important factors to consider are maturity, yield for that maturity, standability, and disease and pest resistance.

Because the environment changes from year to year, look for hybrids that perform well across multiple locations and years in your area. While seed companies remain the primary source of information about the varieties they commercialize, the University of Illinois Variety Testing trials provide neutral, third-party information on current public and private varieties as well as comparisons that might not be available from other sources. Other sources of information include tests conducted by grower associations, seed companies, and on-farm trials.

When selecting corn hybrids for grain production, consider the following key factors:

Determine the acceptable maturity range: Maturity is one of the most important characteristics used in choosing a hybrid. Choose hybrids that mature 10-14 days before the first average date of the killing freeze (32ºF) to allow for grain dry-down and to provide a buffer in case of a cool year or delayed planting – see Figure 1.
Diversity hybrid maturity: Consider planting hybrids with varying maturities to help spread the harvest schedule and reduce the risk of the entire crop being exposed to adverse weather conditions (such as drought and heat) during pollination.
Medium maturity hybrids: Generally, hybrids that use most of the growing season to mature should produce higher yields than those that mature much earlier. However, we have seen that full-season hybrids do not always yield better than mid-season hybrids. Grain yield variability is often greater within a given maturity group than between different maturity groups.
Select hybrids according to agronomic traits:
Suitability for Crop Rotation: Ensure the hybrid fits well with your crop rotation plan.
Emergence and Early Growth: Look for strong emergence, especially in cooler conditions.
Root Strength and Standability: Choose hybrids with good root strength and stalk quality to prevent lodging.
Tolerance to Diseases and Pests: Consider hybrids with resistance or tolerance to local disease pressures. For instance, corn rootworms – including the western and northern corn rootworm species – are the most economically important corn insect pests in Illinois.

Maturity and Growing Degree Days

The GDD concept has been very useful in predicting how the crop will respond to temperatures and in helping fit hybrids into situations where expected GDD accumulations are known from weather records. The daily GDD accumulation is the average of the low and high temperatures minus 50ºF. The subtraction of 50 degrees is done because corn plants don’t grow much at or below 50ºF. The high temperature cutoff is 86ºF, which is done because growth rates do not continue to increase as temperature increases above a certain point. For instance, a day with low and high temperatures of 60 and 80 would produce [(60 + 80) / 2] – 50 = 70 – 50 = 20 GDD. For a day with temperatures of 44 and 66, substitute 50 for the actual low: [(50 + 66) / 2] – 50 = 58 – 50 = 8 GDD. And for a warm day with temperatures of 74 and 93, substitute 86 for the actual high: [(74 + 86) / 2] – 50 = 80 – 50 = 30 GDD.

Corn hybrids in Illinois have planting-to-harvest GDD requirements that range from 2,300 to 2,500 for early-maturing hybrids in the northern part of the state to 2,800 to 2,900 for late-maturing hybrids in the southernmost areas. A full-season hybrid in a specific region typically matures in several hundred fewer GDD than the maximum values listed in Figure 2. For example, a full-season hybrid in northern Illinois would mature at around 2,600 GDD, while in southern Illinois, a hybrid would be considered full-season if it matures at 2,900 GDD or more. Medium-maturity hybrids need 100 to 200 fewer GDD than full-season hybrids. This “cushion” in GDD helps reduce the risk of frost damage and provides some flexibility in planting time.

Yield, Grain Moisture, and Relative Maturity

Hybrids that use most of the growing season to mature generally should produce higher yields than those that mature much earlier. However, we have seen limited benefits from using a very long-maturing hybrid than medium-maturing hybrids. Figure 3 shows the yield response to RM in the University of Illinois Variety Testing trials over the past ten years (2014-2023). The planting date in all trials fell between the end of April and mid-May. On average, grain yield increased by 0.5‒1.7 bushels with each one-day increase in RM.

Another key factor to consider is that grain moisture at harvest consistently rises with increasing RM (Figure 10). On average, each one-day increase in RM results in a 0.27‒0.70 percent increase in grain moisture at harvest (Figure 4). Choosing hybrids with the right maturity level is essential to balance maximizing yield potential and managing grain moisture at harvest.

Summary

Selecting a genetically diverse range of locally adapted hybrids with varying maturities and agronomic strengths can help growers reduce the risk of crop loss. By diversifying maturities, farmers can better manage weather-related risks and stagger the harvest period, preventing the entire crop from being either too dry or too wet at harvest time.

When choosing hybrids, consider the following key traits: yield, maturity, drought tolerance, standability, pest resistance, dry-down time, grain quality, and ease of harvest. Consulting with local seed experts to understand the agronomic characteristics of hybrids suited to your area is a valuable first step.

Giovani Preza Fontes, Extension Agronomist

Reviewed in 2024