The “Chlorosis Report Card”
Last year, we introduced the concept of the chlorosis “report card.” We received many favorable comments about this system. We still
report the numerical results (2.2, 3.1, etc.), but a disadvantage of this method is that chlorosis scores, like yields, go up and down from year to year. Thus, a score of ‘2.5’ in one year may not mean the same
thing as a rating of ‘2.5’ in another year. Thus, we are experimenting with a second way of interpreting the data, “The Chlorosis Report Card.”
The Chlorosis Report Card gives a variety a letter grade, from A to D-, representing how a variety did compared to the other
offerings in the marketplace. The range in the scores of commercial varieties is divided into eleven categories (A, A-, B+, B, B-, C+, C, C-, D+, D, D-), and the varieties placed into these eleven categories. In
other words, the most resistant commercial variety defined the top end of the “A” range, and the most susceptible commercial variety defined the bottom of the ‘D-‘ range. We did not give a variety an ‘A+’ grade,
because we have never seen a variety immune to chlorosis. We did not give out any ‘F’ grades either, as no commercial variety has proven to be as susceptible as the two most susceptible varieties identified (T203
and Pride B216).
For chlorosis-prone land, a good interpretation of this system would be:
1. Flee the D’s! These varieties are not adapted for chlorosis-prone land.
2. You can do better than a C! Many varieties exist with better chlorosis resistance.
3. A grade of B or B- is a good grade, especially for fields that tend to have slight to moderate chlorosis for a couple weeks and recover, or where chlorosis is present some years and not others. By going with a B, B-, or
stronger, you are selecting from the top 25% of the varieties on the market with regards to chlorosis resistance.
4. For the fields with significant chlorosis problems, consider a variety with a grade
of A, A-, or B+, consistent with your other objectives, such as maturity. This represents about the top 5-10% of the
varieties with regards to chlorosis resistance.
5. Taking on new land? Be careful. If a farmer is buying or renting new land, the soil test shows calcium carbonate in the topsoil, pH values above 7.6, and the farmer is not sure of the chlorosis history of the field, the
farmer should probably be conservative, and go with a variety with higher levels of resistance.
6. Chlorosis ratings are not perfect. Chlorosis is a variable problem within a field, and chlorosis ratings are affected by experimental error. Ratings do vary from year to year. Consistency of performance is important for
selecting varieties for fields with severe chlorosis problems. A variety with a proven performance across more than one year’s trials is a safer bet for chlorosis-prone land than a new variety with a limited track
7. No chlorosis? Then these charts aren’t for you! Not every production area, not every field, has chlorosis. Chlorosis is generally only seen on poorly-drained fields, or fields with lime
in the topsoil. The letter grades listed here deal only with chlorosis. It is often observed that a variety may have a chlorosis grade of C or D but be an excellent choice for a field with no chlorosis problems.
Soybean Cyst Nematode
The soybean cyst nematode (SCN), Heterodera glycines, is a small parasitic roundworm that
attacks the roots of soybeans. SCN is found and verified in Cass and Richland counties of North Dakota. There are unverified reports that SCN is also found in fields in adjacent counties.
SCN causes yield losses in infested fields. Crop rotation and resistance are the most important management practices growers must use
to control the disease. Growers may want to consider testing their soils for SCN. If a nematode problem is in the field, only resistant soybean varieties should be planted. For performance of adapted SCN-resistant
soybean varieties, see page 28 in this magazine.
General information about the tables
Variety trial data from all NDSU Research Extension Centers for all crops can be found at www.ag.ndsu.edu/varietytrials. The agronomic data presented in this publication are from replicated research plots using experimental designs that enable the use of statistical analysis.
The LSD (least significant difference) numbers beneath the columns in tables are derived from the statistical analyses and only apply
to the numbers in the column in which they appear. If the difference between two varieties exceeds the LSD value, it means that with 95 percent probability, the higher-yielding variety has a significant yield
advantage. If the difference between two varieties is less than the LSD