U of M extension

Soybean Variety Selection I: SCN Resistance

Naeve

Seth Naeve, University of Minnesota Extension Agronomist

Although I think that it’s an absolute disservice to producers, seed sales will soon be in full swing. It’s not that I have anything against seed companies and aggressive sales – it’s simply too early.

Companies don’t really know much about how their products will perform this year, but they do know what products they have to sell. This creates a bit of a division between what’s best for the producer and what’s best for the seed company.

But enough from the soapbox …

Right now is a good time to be thinking about strategies for dealing with Soybean Cyst Nematode (SCN) for next year. This pest likely reduces soybean production in Minnesota by 10 to 20-plus million bushels annually, and can impact individual farmers by reducing yields by 10 to 20-plus percent across the farm. SCN is the most important pest of soybean and it provides the greatest opportunity to increase farm revenues if attacked appropriately.

Most producers are aware that SCN can be found in almost all Minnesota counties where soybeans are grown. They are also likely aware that they have SCN on their farm. Many of them may even feel that they are effectively managing this pest by planting resistant varieties. But, is this enough? Likely not.

For some unknown reason, SCN appeared to have a larger impact on soybean growth this year. Many of the more obvious trouble spots were associated with chlorotic areas in fields that may have shown Iron Deficiency Chlorosis (IDC) symptoms in the past. Soybean cyst nematode does appear to have an association with soil pH. Nematode numbers tend to be much higher in areas with naturally higher pH soils.

Some astute producers took a second look at fields with uneven or stunted growth, or areas of fields where the rows closed later than others. In some cases these farmers dug roots and looked for

nematodes on the roots. Many were surprised to find females present – on varieties marketed as resistant to SCN. How can this be?

There are a couple of possible explanations. First, not all soybean varieties marketed as “resistant” carry enough of the original resistance genes to be effectively resistant for producers. Second, nematode populations have reacted to seeing the same form of resistance year after year. Many fields in Minnesota now carry SCN populations that are virulent on soybeans carrying the most common form of SCN resistance, that from PI88788.

So, what can a producer do?

Understand that it is no longer good enough to manage SCN simply by choosing varieties labeled ‘resistant.’ Farmers should resample fields for SCN to get a new baseline on SCN pressure across their farm.

Farmers must select varieties with proven history of SCN resistance, by using alternate forms of validation other than seed company literature, such as the Minnesota Soybean Variety Trials. Producers should select a number of varieties and monitor their effectiveness to yield well across fields and levels of SCN pressure. Farmers should also consider using varieties with the “Peking” form of resistance. Farmers might even consider using a seed treatment with activity on SCN.

Lastly, farmers should consider extending rotations to reduce the number of soybean crops in fields or portions of fields with very high SCN counts or where soybeans simply do not ever produce well.

None of these strategies alone will change your SCN situation, but increased attention to the pest and increased effort to manage it will pay off in increased yield or the ability to continue to raise this valuable crop.

If you would like to learn more, plan to attend the upcoming SCN Field Day at the Southwestern Research and Outreach Center near Lamberton on Sept. 9.

Seth L. Naeve is a University of Minnesota Extension Soybean Agronomist and Associate Professor of Agronomy and Plant Genetics. Reach Seth at 612-625-4298 or email him at naeve002@umn.edu.