Understanding Corn Product Ratings

  • Product ratings help seed companies position their 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 DEKALB® brand corn products use the same rating scales. The general product characteristic rating scale runs from 1- 1 is best, 5 is average, and greater than 5 is below average (Table 1). Other characteristics have individualized ratings. Product ratings are relevant within comparisons of other DEKALB 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

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 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 breeders artificially inoculate products with disease pathogens for evaluation. However, if conditions are not favorable for disease development in a given 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 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. 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.

GDUs. The estimated number of GDUs needed to reach mid-pollination (flowering) and black layer (maturity). 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.

Placement recommendation. A recommendation of where the product will perform best and/or regions that should be avoided. This may be in reference to soil type, productivity level, or management practices common to a region. Placement recommendations are typically developed locally based on local testing.

Planting rates. The recommended planting population for each product is based on planting rate trials conducted over a wide range of environments. The general range is listed as high (H), medium-high (MH), medium (M), medium low (ML), or low (L). More precise population recommendations can be obtained from the plant population optimization tool, Optimize My Seed Planting Rate at www.aganytime.com/dekalb/tools/Pages/My-Seed-Rate.aspx.

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 plantings and with adverse environmental conditions during and immediately after planting.

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 are 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.

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.

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

Staygreen. Staygreen means that the plant can maintain transpiration and photosynthesis longer into the season, when other corn products may begin to senesce, which 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 potential is rated on a scale of 1-9, with 1 being the best.

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

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 tassel 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. Drydown is rated on a scale of 1- products with a rating of 1 have the fastest drydown.

Ear rot. The product’s level of tolerance to ear rots is dependent on husk characteristics and genetic resistance. Rated as above average tolerance (AA), average (A), or below average tolerance (BA).

Test weight. Rated on a scale of 1- 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.

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.

Disease tolerances. The product’s level of tolerance to diseases of concern is rated, where possible, on a 1-9 scale, with 1-2 = excellent tolerance and 9 = poor or very susceptible.

For More Information

DEKALB® agronomists provide corn product recommendations based on local conditions. To find the best product for your field, go to www.aganytime.com/Pages/default.aspx and select My Seed to compare up to five products and add your choices to your seed list for easy reference. While this website includes a wealth of information, due to space limitations it does not include every characteristic rating for every product. To obtain a complete listing of ratings, contact your local DEKALB agronomist.

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