Soybean Cyst Nematode Management Reconsidered.

Abstract

A well-known nematologist once said (in public) that soybean cyst nematode (SCN, Heterodera glycines Ichinohe) was easy to control: “Don’t grow soybeans.” Shortly thereafter, following a barrage of good-natured criticism for this bit of unhelpful advice, he amended the statement to: “Don’t grow soybeans more than once every 5 years or so.” (He made a similar statement in print [22]). From a nematological standpoint, he was quite right in that rotation to a nonhost is the most effective way to reduce SCN population densities and thereby avoid the soybean yield losses associated with moderate to heavy infestations. However, reality often trumps theory, and the reality is that most soybean producers in the U.S. Soybean Belt states (Illinois, Indiana, Iowa, Minnesota, Ohio, Missouri, Wisconsin, and adjacent states) have been unwilling to intersperse their soybean crops with more than a year or two of a nonhost, usually corn. In the South, soybean production has declined dramatically (9). For this reason, most of what follows will emphasize SCN in the Midwestern and North Central states, identified in the preceding sentence as the Soybean Belt. Information on a wide range of issues related to SCN management may be found in the recently published Biology and Management of the Soybean Cyst Nematode, Second Edition (29). As the bulk of soybean production in the United States has shifted northward and westward, so has the known distribution of SCN (Figs. 1 and 2). The most recent discovery of SCN was in North Dakota in 2004 (3). For about the past decade, SCN has been considered the most economically important pathogen of soybean in the United States (7,37,38). Since the last time a feature article appeared in Plant Disease about SCN (36), some changes have occurred in our thinking about this pathogen and in approaches to managing soybean in infested fields. These changes include recommendations for scouting, the meaning and use of damage thresholds, and the means of classifying field populations according to virulence phenotypes (“races”). Some of what is included in this article is still very much a matter of debate, and readers are invited to check with their favorite nematologists regarding varying opinions, or with recent reviews (21,29).