Rotation Crop Evaluation for Management of the Soybean Cyst Nematode in Minnesota D. R. Miller, S. Y. Chen,* P. M. Porter, G. A. Johnson, D. L. Wyse, S. R. Stetina, L. D. Klossner, and G. A. Nelson ABSTRACT Crop rotation is an effective tactic for soybean cyst nematode (SCN) management. In the North Central region of the USA, corn is almost exclusively used as a nonhost rotation crop with soybean. This study was conducted to determine the effectiveness of crops common to or having potential use in the North Central region as rotation crops for managing SCN. Sixteen potential rotation crops and SCN-resistant and susceptible soybeans were grown along with six fallow controls in three commercial field sites near Waseca, Lamberton, and Morris, MN, in 2001, and SCN-susceptible soybean was grown on all plots in 2002. Nematode populations at planting, midseason, and harvest were measured both years; soybean yield was measured in 2002. There was large variability in SCN populations and soybean yields at the three sites. Nevertheless, significant treatment effects were detected at all sites. While all of the rotation crops lowered SCN populations com- pared with SCN-susceptible soybean, there were only subtle differ- ences among the individual rotation crops and among different groups of the crops. Leguminous nonhosts or poor hosts were best in reduc- ing SCN population density. Corn, the most common rotation crop in Minnesota, was among the least effective in reducing nematode populations. There was an undetectable yield benefit from SCN management, although differences in yield were observed among the rotation crop treatments—probably due to agronomic factors. The data suggest that a single year of rotation of soybean with any of these crops before planting a susceptible soybean may not be sufficient in managing SCN. T HE soybean cyst nematode, Heterodera glycines Ichinohe, was first detected in Minnesota in 1978 (MacDonald et al., 1980). Since then, the SCN has been detected in most (55) counties in southern and central Minnesota where soybean [Glycine max (L.) Merr.] is grown. The nematode has become a major yield-limiting factor in the state (Chen et al., 2001a). Management of the nematode has been dependent on planting resistant cultivars and the use of crop rotations (Schmitt, 1991; Niblack and Chen, 2004). A number of studies have reported on the effect of rotation crops on SCN populations and soybean yields (Ross, 1962; Weaver et al., 1988; Edwards et al., 1988; Rodriguez-Kabana et al., 1991; Weaver et al., 1993; Koenning et al., 1993; Hershman and Bachi, 1995; Koenning et al., 1995; Howard et al., 1998; Long and Todd, 2001; Chen et al., 2001c; Noel and Wax, 2003). In these studies, however, only one or a few nonhost (mainly corn [Zea mays L.], wheat [Triticum aestivum L.], and sorghum [Sorghum bicolor (L.) Moench] or poor-host crops were compared with soybean. In general, SCN population densities following a nonhost or poor host were lower than following soybean. The effectiveness of crop rotation depends on the host status of crop species, the number of years of rotation crops, and geographical location. For example, in North Caro- lina, 1 to 2 yr of a nonhost in a rotation was generally sufficient to lower SCN population density to below damaging levels (Schmitt, 1991; Koenning et al., 1993). In contrast, 5 yr of nonhost and SCN-resistant soybean may be needed in Minnesota to reduce the SCN popu- lation density to a low level where a susceptible cultivar can be grown without significant yield loss (Chen et al., 2001c). Although most nonhost species tested in fields had similar influence on mortality (Niblack and Chen, 2004), variations in effects of crop species on the SCN have been reported from greenhouse (Riga et al., 2001) and field (Rodriguez-Kabana et al., 1991) studies. An- nual ryegrass (Lolium multiflorum Lam.) was more ef- fective than other nonhosts in reducing infectivity of soybean by SCN (Riga et al., 2001). In a field study, corn appeared to be more effective than sorghum in lower- ing SCN second-stage juvenile population densities at the end of the following soybean season (Rodriguez- Kabana et al., 1991). The mechanisms through which rotation crops affect SCN populations are not fully understood. Some non- host and poor-host crops may be effective in lowering nematode population densities by producing root exu- dates or decomposition products toxic to the nematodes. For example, Brassica spp., such as cabbage, rapeseed, and mustard, produce chemicals as they decompose that are toxic to nematodes (Ellenby, 1945; Mojtahedi et al., 1993; Donkin et al., 1995). Also, phenolic acids from some cereal crops such as wheat can be involved in re- ducing SCN population densities (Hershman and Bachi, 1995; Blum, 1996). A poor-host crop such as pea (Pisum sativum L.) may stimulate SCN to hatch, but the nema- todes may not be able to reproduce well (Sortland and MacDonald, 1987; Schmitt and Riggs, 1991). Therefore, growing a poor-host crop may reduce SCN population D.R. Miller, S.Y. Chen, and G.A. Johnson, Univ. of Minnesota Southern Research and Outreach Center, 35838 120th St., Waseca, MN 59093; P.M. Porter and D.L. Wyse, Dep. of Agronomy and Plant Genetics, Univ. of Minnesota, St. Paul, MN 55108; S.R. Stetina and L.D. Klossner, Univ. of Minnesota Southwest Research and Outreach Center, Lamberton, MN 56152; and G.A. Nelson, Univ. of Minnesota West Central Research and Outreach Center, Morris, MN 56267; S.R. Stetina, current address: USDA-ARS-MSA Crop Genetics and Pro- duction Research Unit, Stoneville, MS 38776. Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the USDA and the Univ. of Minnesota. Received 20 June 2005. *Corresponding author (chenx099@umn.edu). Published in Agron. J. 98:569–578 (2006). Integrated Pest Management doi:10.2134/agronj2005.0185 ª American Society of Agronomy 677 S. Segoe Rd., Madison, WI 53711 USA Abbreviations: PCF, population change factor; Pi01, Pm01, Pf01, Pi02, Pm02, and Pf02, soybean cyst nematode egg population density (eggs per 100 cm 3 ) at planting, midseason, and harvest in 2001, and at planting, midseason, and harvest in 2002, respectively; SCN, soybean cyst nematode. Reproduced from Agronomy Journal. Published by American Society of Agronomy. All copyrights reserved. 569 Published online April 11, 2006