With soybean cyst nematode (SCN) commanding so much attention in agricultural circles lately, soybean growers need to be sure they take appropriate steps to test for the presence of soybean cyst nematode and consider all factors before making any management decisions, says an industry agronomist.

"While production problems and issues relating to soybean cyst nematode (SCN) are nothing new, media attention this past year seems to have brought SCN to the forefront," says Dan Bjorklund, an agronomist with Stine Seed Company. "As a result, we have noticed quite a few more questions concerning SCN management at our fall and winter meetings."

Among the questions Bjorklund has been hearing, one of the most common is, "What level of infestation is needed before switching from a conventional to a resistant variety?" He says answering this question is difficult, especially since some agronomists are recommending farmers plant a resistant variety when SCN is detected at any level, and even universities differ in their assessment of what constitutes a 'significant level' of SCN.

"In one individual case, one producer confided that he was going to plant a resistant variety 'just to be safe,' even though he had not actually tested for SCN," Bjorklund says. "In other words, so much discussion had occurred about the potential problem that this producer thought he'd save himself the trouble of a soil sample and skip to the treatment, without realizing that resistant varieties will not yield with high-yielding susceptible varieties in the absence of SCN. The simple fact is, planting a resistant variety without first testing your soil is like taking pills without ever going to the doctor or knowing whether or not you are ill."

Bjorklund says that the first thing every producer should do before switching to a SCN resistant variety is test suspected problem areas. Only after it is determined what level of infestation exists and how much area in a particular field is affected can an accurate assessment be made. In some cases, he says, planting a high yielding susceptible variety may return higher yields in a field where a low level of SCN is found. Even a high level of infestation in five acres out of an 80-acre field may not justify planting a resistant variety throughout the entire field.

Bjorklund says that it is also important to note that, in addition to resistant varieties, SCN-tolerant varieties offer another possible management tool.

"A few years ago, Stine Seed Company was one of the first seed companies to release SCN-tolerant varieties, named because although they would allow SCN to infect the root, the overall yield would not be affected like a susceptible variety," he says. "At the time, conventional wisdom said that a soybean was either susceptible or resistant, not in between, and companies that were developing tolerant varieties met with considerable resistance. Now, several years later, we are seeing SCN-tolerant varieties becoming more widely recognized as an effective management option."

In summary, Bjorklund says that, when trying to make management decisions concerning SCN, the most important consideration should always be yield. The goal of the latest SCN initiative is to get producers to test their soils for the presence of SCN, not just to plant resistant soybeans exclusively. He says that, if a soil test reveals the presence of SCN, there are numerous factors to consider when selecting seed, including SCN pressures, sources of resistance, soil type and features, and the effects of a crop rotation on profitability. If a grower decides to plant a SCN resistant variety, he or she should choose the one with the highest yield potential, the same way one would select a conventional soybean variety.

Stine Seed Company, located near Adel, Iowa, is an industry-leading seed company marketing soybeans, corn and soft red winter wheat, and is a leading supplier of soybean genetics to the seed industry. For additional information on this topic, visit the Agronomy section of Stine's website at http://www.stine.com.

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