3.1.2
SOYBEAN CYST NEMATODE MANAGEMENT IN MINNESOTA BY TILLAGE, ROTATION AND RESISTANT VARIETIES IN A SOYBEAN/CORN PRODUCTION SYSTEM

WC STIENSTRA1, S CHEN2, WE LUESCHEN1 and T HOVERSTAD2

University of Minnesota, 1Department of Plant Pathology, St Paul, MN 55108, USA; 2Southern Experiment Station, Waseca, MN USA 56093

Background and objectives
The soybean cyst nematode (SCN), discovered in 1978, has spread and is expected to develop in most MN soils when soybeans are planted every other year. Loss occurs even when above-ground symptoms are minor, and most soybean producers do not discover the cause until nematode populations are large and more difficult to reduce. Management practices are limited. Conservation tillage has increased in the USA and in Minnesota to reduce soil erosion, increase soil moisture holding, and reduce labor and fuel costs associated with conventional tillage. Since there are reports that zero tillage reduced SCN populations and increased soybean yields compared to conventional tillage, a study was proposed to evaluate several primary tillage options and resistance under Minnesota conditions. Our objective was to determine the effects of tillage and soybean yields in a two crop production system.

Materials and methods
The test site had a fairly uniform SCN population. Five tillage treatments: MP-annual moldboard plow, MP/CP-moldboard plow corn and chisel plow soybeans, CP-annual chisel plow, RT-annual ridge tillage, and NT-no tillage and four crop rotations were included. Two sites were set up so rotations could begin with both crops. The SCN susceptible soybean variety Sturdy was planted every year. The resistant variety Bell was planted in 1993, '94, '95 and Freeborn in '96. The soybeans and a locally adapted corn hybrid were planted in 76.2 cm rows. The soybean varieties were susceptible to SCN-Sturdy and resistant in 1993, '94 and '95 Bell with Freeborn in 1996. Soybeans were planted in 76.2 cm rows. Soybean was also planted in narrow rows, 25.4 cm. Seed planted were as follows: S=susceptible soybean, R=resistant soybean, C=corn and Rn=resistant soybean in narrow rows. The four crop sequences at site one are: S/C/S/C, R/C/R/C, R/C/S/C and Rn/C/S/C and at site two: C/S/C/S, C/R/C/R, C/R/C/S and C/Rn/C/S. Soil samples, eight 2.54 cm cores, 20 cm deep in the center two rows of the four-row plots were taken yearly following harvest except that 1995 corn was sampled in April of 1996.

Results and conclusions
SCN egg populations were not affected by tillage except in year one, site two. Sites not uniformly infested with SCN may respond differently to tillage movement/spread, but tillage practices after SCN infestation is present had no consistent positive or negative influence on egg populations. Crop rotation, however, planting corn or resistant soybeans, did reduce egg populations. The reduction was greatest when egg numbers were high and less if egg numbers were near the level of detection. Susceptible soybeans increased egg number from 200 to 2750%, while resistant soybeans reduced egg counts 34 to 57%. Soybean yields were highest in plots with resistant soybeans.

References
1. Hershman DE, Bachi PR, 1995. Plant Dis. 79, 631-633.
2. Wrather JA, Anand S, Koenning SR, 1992. Biology and Management of SCN, pp. 125-131.