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Resistant varieties aren't a cure-all for soybean cyst nematode

Agriculture.com Staff 03/14/2008 @ 8:55am

The soybean cyst nematode (SCN) can be managed effectively by growing SCN-resistant soybean varieties. There currently are more that 700 SCN-resistant soybean varieties available in maturity groups 1, 2, and 3 for Iowa growers. Click here for more information on the varieties.

Although not 100% effective at preventing reproduction of the nematode, SCN-resistant soybean varieties usually prevent increases in SCN population densities and can even decrease the nematode numbers throughout a growing season. But since some nematode reproduction occurs on resistant varieties, there is the potential for an SCN population to become resistant to the resistance as resistant varieties are repeatedly grown.

SCN-resistant varieties possess resistance genes from one of four sources of resistance (which are breeding lines). To reduce the chance of a SCN population bring selected for that can readily reproduce on resistant varieties, Iowa State University recommends growers use varieties with different sources of resistance in different years. However, almost all SCN-resistant varieties available for Iowa growers have the PI 88788 source of resistance (PI stands for plant introduction). So rotating varieties with different sources of SCN resistance is difficult, if not impossible.

Another tactic that Iowa State University recommends to consider using to slow the development of an SCN population that reproduces well on resistant varieties is growing a susceptible (non-resistant) variety periodically after resistant varieties have been grown a few times. Iowa State University cautions that SCN population densities must be low (1,000 eggs per 100 cubic centimeters of soil or less) before a susceptible variety should be grown in an SCN-infested field. And a good, representative soil sample should be taken from a field prior to determine the SCN population density before considering growing a susceptible variety.

SCN causes much greater damage and seems to reproduce at a greater rate in hot, dry growing seasons than in years of adequate or excess rainfall. So if a severe drought is anticipated, growers might opt not to grow a SCN-susceptible variety in an SCN-infested field, even if SCN population densities are low. Growing SCN-resistant soybeans three or four times in a row should not result in complete breakdown of the effectiveness of the resistance.

The soybean cyst nematode (SCN) can be managed effectively by growing SCN-resistant soybean varieties. There currently are more that 700 SCN-resistant soybean varieties available in maturity groups 1, 2, and 3 for Iowa growers. Click here for more information on the varieties.

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