Effect of Cover Crops Alfalfa, Red Clover, and Perennial Ryegrass on Soybean Cyst Nematode Population and Soybean and Corn Yields in Minnesota Senyu Chen,* Donald L. Wyse, Gregg A. Johnson, Paul M. Porter, Salliana R. Stetina, Daniel R. Miller, Kevin J. Betts, Lee D. Klossner, and Milton J. Haar ABSTRACT The effects of alfalfa, red clover, and perennial ryegrass as cover crops on soybean cyst nematode (SCN) and soybean and corn yields were evaluated in Waseca, Lamberton, and Rosemount, MN. The cover crops were interseeded in soybean at 0 or 2 wks after planting soybean in 2002 and killed with herbicide before planting corn in 2003. As expected, SCN-susceptible soybean supported higher SCN popula- tion density than SCN-resistant soybean. Reduction of SCN popula- tion density by red clover (up to 40%) and alfalfa (up to 55%) was observed in some sampling occasions at Lamberton and Rosemount, probably due to reduced soybean growth, but the effect was in- consistent. No significant reduction of SCN population by the two crops was detected at Waseca. While perennial ryegrass did not affect SCN population density in most cases, up to 46% higher egg popula- tion densities were observed in the perennial ryegrass treatment as compared to the control at Waseca. SCN-resistant soybean produced higher yield than susceptible soybean at all sites. While alfalfa reduced soybean yield at Lamberton (up to 50%) and Rosemount (up to 11%), red clover and perennial ryegrass reduced soybean yield only at Lamberton (up to 38%) and Waseca (up to 34%), respectively. No difference in corn yield was observed at Waseca. At Lamberton, alfalfa and red clover planted at the time of planting soybean reduced corn yield in the following year 17 and 13%, respectively, and perennial ryegrass planted 2 wks after planting soybean reduced corn yield 13%. At Rosemount, significant reduction of corn yield was observed with red clover (15–21%) interseeded in SCN-susceptible soybean and with alfalfa (12%) and red clover (12%) interseeded in SCN-resistant soy- bean at the time of planting soybean. The results suggest that an even later planting date of cover crops in soybean may reduce yield loss due to competition and make these cover crops more appropriate for use in the soybean-corn rotation in Minnesota. T HE corn (Zea mays L.)-soybean (Glycine max (L.) Merr.) rotation has become a predominant produc- tion system that is currently practiced on over 20 million hectares in the North Central region in the United States. During the past three decades, soybean cyst nematode (SCN), Heterodera glycines Ichinohe, has be- come the major pest problem in the corn-soybean pro- duction system in the region (Wrather et al., 2001; Monson and Schmitt, 2004). Management of the nema- tode has been dependent on planting resistant cultivars and the use of crop rotations (Schmitt, 1991; Niblack and Chen, 2004). In spite of the widespread availability of resistant cultivars, management of SCN has proven dif- ficult. The distribution of SCN is expanding and severity of SCN damage continues to increase in the North Cen- tral region. There are several reasons why SCN remains as the most economically important pest of soybeans. Perhaps the most significant biological factor is the high genetic variability of SCN with regard to parasitism of soybean cultivars which makes it difficult to select resis- tant cultivars. In addition, resistant cultivars impose se- lection pressure on the nematode resulting in shifts from one HG Type (race) to another (Young, 1995, 1998). Although resistant cultivars generally produce higher yields in SCN-infested fields, high SCN population den- sities can cause significant yield loss even to a resistant cultivar (MacGuidwin et al., 1995; Tylka, 1997). Further- more, there is a yield penalty for using a resistant cul- tivar in noninfested fields or those with low levels of infestation when compared with high-yielding suscep- tible cultivars (S. Chen et al., unpublished). This is probably due to the genetic linkage of low yield with SCN-resistance (Mudge et al., 1996). The corn–soybean rotation is conducive to SCN population development. After only one season the SCN population density can increase to a level so high that several years of growing non-host crops are needed to reduce the population density to below the yield-loss threshold (Chen et al., 2001). The SCN survival rate in the North Central re- gion is higher compared with that in the southern re- gions (Riggs et al., 2001). For these reasons, alternative tactics are needed for long-term effective management of SCN and a diversified corn-soybean cropping system in which more crops are included may be useful in man- aging the nematode in the North Central region. Introduction of cover crops into the system is one way to add diversity. Depending on geographic locations and cropping systems, benefits of growing cover crops may include improvement of overall soil and ground- water quality, reduction of soil erosion, suppression of weeds, pathogens and pests, increase of cash crop productivity, and enhancements of environment quality Senyu Chen, Gregg A. Johnson, and Daniel R. Miller, University of Minnesota Southern Research and Outreach Center, 35838 120th Street, Waseca, MN 59093; Donald L. Wyse, Paul M. Porter, and Kevin J. Betts, Department of Agronomy and Plant Genetics, Univer- sity of Minnesota, St. Paul, MN 55108; and Salliana R. Stetina, Lee D. Klossner, and Milton J. Haar, University of Minnesota Southwest Research and Outreach Center, Lamberton, MN 56152. (Salliana R. Stetina’s current address is USDA ARS Crop Genetics and Produc- tion Research Unit, PO Box 345, Stoneville, MS 38776.). This re- search was supported by Cooperative State Research, Education, and Extension Service, USDA, under Agreement Number 2002-34103- 11990. Mention of trade names or commercial products in this article is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture and University of Minnesota. Received 1 Sept. 2005. *Corresponding author (chenx099@umn.edu). Published in Crop Sci. 46:1890–1897 (2006). Crop Ecology, Management & Quality doi:10.2135/cropsci2005.09-0296 ª Crop Science Society of America 677 S. Segoe Rd., Madison, WI 53711 USA Abbreviations: PCF, population change factor 5 egg population den- sity at harvest/egg population density at planting in the same year; SCN, soybean cyst nematode; WAP, weeks after planting soybean. Reproduced from Crop Science. Published by Crop Science Society of America. All copyrights reserved. 1890 Published online July 25, 2006