Understanding Germination and Vigor Scores

What Information is on a Corn Seed Bag Tag?

State seed laws require a corn seed bag tag to include the state where the seed was produced. Additionally, the Federal Seed Act requires a corn seed bag tag to include:

• The lot number which defines where and when the seed was produced
• The corn seed variety name, often times a number
• The kind of seed (which would be field corn on a corn seed bag)
• Percent warm germination
• Date the warm germination test was conducted
• The percentage of any variety/hybrid in excess of 5% of the whole
• The percentage of other crop seed
• The percentage of noxious weed seed/lb
• The percentage of inert matter
• The percentage of weed seed

Are Other Germination Related Tests Required or Conducted?

The warm germination test (WGT) is a federal requirement. Many seed companies conduct their own tests to help determine germination when seed is subjected to a cold environment and to determine how the seedlings may respond to that environment (vigor). However, there are no federal standards for the cold germination and vigor tests, so there is no requirement to provide the results on a seed tag.

Understanding Warm Germination Percentage

The Warm Germination Test (WGT) is a key component in providing quality seed to the grower, providing assurances that the product is of good quality. A germination test is an indication of the seed’s maximum ability to produce a normal plant under ideal conditions. Understanding this germination information can help the grower determine the seeding rate needed to help achieve a desired seedling population.

Is there a difference between germination and seed vigor?

Viable seeds should germinate if placed under the proper conditions of moisture, temperature, and oxygen. Seed vigor is defined by the International Seed Testing Association (ISTA) as the “sum of those properties that determine the activity and performance of seed lots of acceptable germination in a wide range of environments”.¹ Seed vigor is not a single property, but rather a combination of variables such as the rate, uniformity of germination, and growth of seeds under suboptimal growing conditions. It can also measure performance after storage, particularly the seed’s retention of the ability to germinate. Any test that applies a stress is a vigor test. The type of stress and the number of stresses applied can vary by test method. Due to the lack of regulation, vigor tests can also vary by laboratory. In the case of the “cold test”, there are many different methods using the same name.

How are germination and vigor assessed?

The two major types of tests that Bayer Crop Science uses are:

Warm Germination Test (WGT): The WGT is a standardized test using the protocols approved by the Association of Official Seed Analysts (AOSA) and is required by the Federal Seed Act and state seed laws. The WGT determines the seed’s ability to germinate in ideal conditions (Figure 1, left). The result of this test is required to be included on seed labeling and is only valid for a prescribed period. WGT results are comparable across seed providers because the test methods are standardized as prescribed by law.

Cold Test: A cold test is not required by law and is not standardized across the agriculture industry. It determines the seed’s ability to germinate and grow under less-than-ideal conditions (Figure 1, right). Because test methods can differ among seed providers and seed testing laboratories, the results of these tests should not be compared against one another, unlike the standardized WGT results. Since the cold test induces stress, it is also a test for vigor.

The emergence of seedlings in my field is lower than the WGT indicated. Was the test wrong?

The WGT determines the ability of seed to produce a stand under favorable environmental conditions and actual field performance may differ. The WGT usually provides the maximum germination for the seed and actual field emergence will be impacted by grower-specific field and environmental conditions. This is why the standard recommendation is to increase seeding rates by 5 to 10% above the desired stand when seeding under less-than-ideal conditions.^2,3 As an example, if the desired final population for a seed product is 32,000 plants/acre and the historical emergence is 95% for the farming operation, the seeding rate would be 32,000 divided by 0.95 or 33,684 seeds/acre.^2,3

The cold test is more similar to the conditions under which seeds germinate in the field in less-than-ideal conditions. As planting dates become earlier, germination and emergence conditions become harsher because of cooler soils.

Does seed vigor affect later plant growth?

When plant height, stem diameter, and leaf area at V4 and V8 growth stages were compared among different lots of seed with varying vigor scores, all three factors increased in value when the percentage of seeds with higher vigor was increased.⁴ However, this response can be influenced by the post emergence environmental conditions.

The WGT and vigor tests are only two components of Bayer Crop Science’s robust quality management system used to provide the highest quality seed available to our customers worldwide. The seed production division of Bayer Crop Science has developed a proprietary vigor test that we believe more consistently predicts emergence across the varied environments in which a crop may be planted. Based on the timing requirements for the WGT, you can be assured that the germination score on your seed (which includes the date the test was performed) is relevant to help make planting decisions.

Bayer Crop Science stands behind the quality of our products and growers should have confidence in each bag of seed purchased.

Sources

¹1995. Understanding seed vigor. In, Handbook for Vigour Test Methods, 3rd Edition.

²Nielsen, R.L. (Bob), Camberato, J., and Lee, J. 2019. Yield response of corn to plant population in Indiana. Purdue University Department of Agronomy. https://www.agry.purdue.edu/ext/corn/news/timeless/CornPopulations.pdf

³Nielsen, R.L. (Bob), Quinn, D., and Camberato, J. 2022. Optimum plant populations for corn in Indiana. Purdue University Extension, Corny News Network. https://www.agry.purdue.edu/ext/corn/news/timeless/PlantPopulations.html

⁴Vaz MondoI, V.H., CiceroI, S.M., Dourado-NetoI, D., Pupim, T., Neves Dias, M.A. 2013. Seed vigor and initial growth of corn crop. Journal Seed Science. 35(1): 64–69. https://www.scielo.br/scielo.php?script=sci_arttext&pid=S2317-15372013000100009

Additional Resources

Federal Seed Act. United States Department of Agriculture (USDA). Agricultural Marketing Service. https://www.ams.usda.gov/rules-regulations/fsa

International rules for seed testing. International Seed Testing Association. https://www.seedtest.org/en/publications/international-rules-seed-testing.html

Title 7 – Agriculture. Chapter 37. Seeds. United States Code. Office of the Law Revision Counsel. https://uscode.house.gov/view.xhtml?path=/prelim@title7/chapter37&edition=prelim

Web sources verified 2/25/25.

1216_105974