Every year, Corteva Agriscience conducts extensive corn emergence trials under a wide range of stressful environments and soil types, including early planted and reduced-tillage fields. Using data from stressful locations, as well as lab assays that mimic extreme cold stress, Pioneer brand corn products are assigned a stress emergence rating, which is based on the genetic potential for a hybrid to establish stand under stress conditions (e.g., cold, wet soils or environments with short periods of severe low temperatures). Stress emergence ratings range from 1 to 9. Ratings of 7 to 9 indicate very good potential to establish normal stands under such conditions; a rating of 5 or 6 indicates average potential to establish normal stands under moderate stress conditions; and ratings of 1 to 4 indicate the product has below-average potential to establish normal stands under stress and should not be used if severe cold conditions are expected immediately after planting. In emergence trials conducted in high stress environments, hybrids with higher ratings typically have greater stand establishment than lower rated hybrids (Figure 1).
Pioneer brand corn products are also assigned high-residue suitability (HRS) ratings of highly suitable (HS), suitable (S) or poorly suited (X) for hybrid performance in reduced-tillage systems. Disease and stress emergence traits are key in high-residue fields. The HRS rating is calculated from the following five trait scores: stress emergence, northern corn leaf blight, anthracnose stalk rot, gray leaf spot, and Diplodia ear rot. The relative importance of each trait can vary by region. Therefore, the HRS rating is adjusted for each market region in North America.

Figure 1. Relationship between early stand and stress emergence rating in stressful, high-residue Corteva Agriscience research locations in 2018.
Error bars represent +/- the standard error of the mean where n = the number of hybrids tested in each SE score category.

In Corteva Agriscience high-residue emergence trials, Pioneer® brand corn products with an HRS rating of poorly suited (X) produced lower stands on average than ones with a rating of suitable (S) or highly suitable (HS), regardless of temperature stress level (Figure 2).

Figure 2. Relationship between early stand and high-residue suitability (HRS) rating in high-residue Corteva Agriscience research locations in 2018.
Error bars represent +/- the standard error of the mean where n = the number of hybrids tested in each HRS rating category.
Reduced-tillage systems can also lead to uneven stands and runts. In Corteva Agriscience trials, hybrids with a highly suitable (HS) rating tend to produce fewer runt plants (those at least one leaf stage behind) than suitable (S) and poorly suited (X) hybrids (Figure 3).

Figure 3. Relationship between early runts and high-residue suitability (HRS) rating in high-residue Corteva Agriscience research locations in 2018.
Error bars represent +/- the standard error of the mean where n = the number of hybrids tested in each HRS rating category.