Understanding Corn Product Ratings

September 21, 2022


Product ratings help seed companies position products under the right conditions to meet the farmer’s needs, field conditions, and management practices to promote the most successful outcome.

Product rating categories include agronomic and seed characteristics, maturity, placement recommendations, growing degree unit (GDU) requirements, planting rate recommendations, and stress tolerance.

Overview of Product Ratings

All Channel® brand corn products use the same rating scales. The general product characteristic rating scale runs from 1-9; 1-2 excellent, 3-4 good, 5-6 average, 7-8 fair, and 9 poor. (Table 1). Other characteristics have individualized ratings. Product ratings are relevant within comparisons of other Channel® brand corn products only; comparisons to ratings for competitors' products could be inaccurate since the rating scale between companies is not calibrated.

Table 1: Rating scale for agronomic and seed characteristics
Table 1: Rating scale for agronomic and seed characteristics

Corn product rating categories include agronomic and seed characteristics, maturity, placement recommendations, growing degree unit (GDU) requirements, recommended planting rates, herbicide sensitivity, disease tolerance, and tolerance to abiotic stresses.

Agronomic characteristics, adaptation, and planting rate information is based on observations made during pre-commercial product testing, as well as knowledge of the background of related products used during breeding. These ratings provide essential information to farmers for on-farm positioning.

Herbicide sensitivity ratings provide the anticipated product response to the respective herbicide family. These ratings are based on observations using herbicides at and above labeled rates to simulate extreme environmental conditions, misapplication, and adverse soil pH or organic matter content. Under labeled herbicide use rates and normal environmental conditions, most products do not have sensitivity issues with most herbicide families.

Disease ratings are more difficult to generate because it is difficult to simulate a disease with consistent presence and severity across multiple locations for comparable evaluations. Plant pathologists artificially inoculate products with disease pathogens for evaluation. However, if conditions are not favorable for disease development each year, the incidence of disease may not be adequate for evaluation. Therefore, ratings for specific diseases are not always available for all products.

It is not common for a product to be rated excellent or good for every agronomic factor and disease tolerance rating. Farmers need to evaluate what diseases or agronomic risk factors that have been important in their fields in the past as well as what factors are common to their geography and select products that tend to have stronger ratings for those factors. Not all ratings are important to every geography. For example, if Goss’s wilt tolerance were used as a selection criteria for a farmer in the eastern Corn Belt, the best product adapted for that region may not be selected.

Corn Product Ratings

Relative maturity (RM). A relative measure of the time it takes from planting for the corn product to reach maturity. This is an estimate and actual maturity can vary based on environmental conditions and geographic location.

Greensnap tolerance. Rated on a scale of 1-9; products rated from 1-3 are the best choice for managing fields with greensnap issues.

Root strength and Stalk strength. Rated on a scale of 1-9, with 1 being the highest strength or standability

Drought tolerance. Rated on a scale of 1-9, with 1 being the highest level of drought tolerance.

Harvest appearance. Rated on a scale of 1-9. This is calculated based on the plant's ability to maintain the intactness of leaves and tassels as it approaches maturity, as well as the overall appearance of the plant at maturity.

Drydown. Differences in ear and husk characteristics between corn germplasm can affect the rate of drydown, including the number, thickness, coverage, and tightness of the husk leaves along with how compact the kernels are positioned on the cob. Drydown is rated on a scale of 1-9; products with a rating of 1 have the fastest drydown

Staygreen. Staygreen means that the plant can maintain transpiration and photosynthesis longer into the season, when other corn products may begin to mature naturally, near the end of grain fill period, the plant’s metabolism slowly deteriorates, and the plant starts to dry down (senesce). Staygreen may lengthen the duration of the grain-fill period, thereby improving kernel set and test weight. Staygreen can also help promote improved late season standability. Staygreen can also be an important trait if the corn product is taken for silage as the better the staygreen the longer the product can stay in the correct whole plant moisture content for the improved ensiling of that product. Staygreen potential is rated on a scale of 1-9, with 1 being the best.

Test weight. Rated on a scale of 1-9; products with a rating of 1 have the highest average test weight. Corn products with higher vitreous (hard or flinty) endosperm tend to have higher test weights than products with floury (soft or dent) endosperm due to vitreous kernels having higher densities.

Plant height. Rated as short (S), medium short (MS), medium (M), medium tall (MT), and tall (T). This can vary with environmental conditions. Taller plants have often been considered more desirable for silage production whereas shorter plants are generally more desirable for grain production in fields prone to lodging or in fields where harvest stover needs to be minimized. Plant height can also be influenced by planting date. Later planted dates can influence a product to have a taller plant height.

Ear height. Rated as low (L), medium low (ML), medium (M), medium high (MH), and high (H). The optimum ear height depends on preferences, growing environment, and management practices.

Ear Flex. Ear Flex is rated as F = Flex, SF = Semi Flex, SD = Semi-Determinate, D = Determinate. Products that have a more flex type often do well at lower populations and under moisture stress environments while more determinate ear products often do well at higher plant populations and in higher yield environments.

Seedling vigor. As corn products come through the breeding program each product is evaluated for seedling vigor. Some corn products have demonstrated that they can grow faster under less than ideal growing conditions and these products have been rated at a lower number which indicates a faster seedling vigor characteristic. Seedling growth is rated on a scale of 1-9, with 1 being the best.

Disease tolerances. There are currently 12 corn diseases that have ratings in the National Channel Corn Rating key. Not all products have a rating for all the diseases listed. When listed the product’s level of tolerance to diseases of concern is rated on a 1-9 scale, with 1-2 = excellent tolerance and 9 = poor or very susceptible

Focus Area. Focus areas have been divided into three areas. W = western area, C= Central area, E= Eastern area, and – indicates that no zone has been identified as a focus area.

Herbicide tolerances. The product’s response to different herbicide families is rated as acceptable (A): crop injury from a labeled application is unlikely, caution (C): crop injury is possible from a labeled application if the application occurs with adverse environmental conditions, and warning (W): crop injury is likely from a labeled application even with good environmental conditions. There are currently three herbicide families listed in the Channel National Corn Guide.

Growing Degree Units (GDUs). The estimated number of GDUs needed to reach black layer (maturity) and to mid-pollination (flowering). This rating can vary based on environmental conditions. This rating is especially useful when selecting a product for late planting and when GDUs remaining in the growing season may be limited.

Relative Maturity (“Days to maturity”). It is important to recognize that this value does not refer to actual calendar time between planting and harvest maturity but is based on comparisons among hybrids near the time of harvest maturity. Late-planted corn appears to require less than expected GDUs to reach mid-pollination, so this also effects the expected RM. What contributes to confusion in the industry is there are no agreed upon standards within the seed industry for the application of assigned relative hybrid maturities.1

Emergence. The ability of the crop to emerge quickly and uniformly under stressful conditions is rated on a scale of 1-9, with 1 being the best. Emergence ratings are especially important with early planting and with adverse environmental conditions during and immediately after planting.

Kernel rows. Higher kernel row products are often considered to be flex-ear corn products which can adjust ear size depending on growing conditions and tend to yield well at lower populations, but yields generally plateau at higher populations, whereas fixed-ear products (low kernel row products) generally show increased yield as seeding rate increases. These ratings range from an average of 14 to 18 kernel rows per ear. Individual ears can be found outside of this range if a plant in in an extremely high population (low kernel row count) or an extremely low population (high kernel row count) which is also influenced by the genetic makeup of the product.

Planting rates. To optimize management recommendations, the Product Characterization Team at Bayer evaluates the effects of planting population on yield potential across multiple environments. Population recommendations can be found in the Local Product Recommendation Tool. The producer will need to enter the zip code for the area where the corn will be planted when using this tool.

Channel® agronomists provide corn product recommendations based on local conditions. Local seed guides are linked to your zip code and may provide additional information for your area.

To obtain a complete listing of ratings, contact your local Channel® agronomist. For additional agronomic information, please contact your local seed representative


1 Nielsen, R. L. 2012. Interpreting Corn Hybrid Maturity Ratings. Purdue University. Corny News Network Articles. https://www.agry.purdue.edu/ext/corn/news/timeless/hybridmaturity.html.

Web sources verified 06/23/22.