Cropping System and Winter Weed Management Effects On Soybean Cyst Nematode: A Five Year Summary.

Soybean cyst nematode (SCN) is a threat to profitable soybean production in Indiana and throughout the soybean growing regions of the U.S.  Research has shown that a number of winter annual weed species can serve as alternative hosts for SCN in the greenhouse.  However, the importance of winter weed management in managing SCN in the field has not been documented.  The objective of this research was to evaluate the impact of winter annual weed management and crop rotation on SCN population densities, winter annual weed populations, and crop yield.  Field trials were established in the fall of 2003and continued through fall 2008 at the Agronomy Center for Research and Education in West Lafayette, IN and at the Southwest Purdue Agricultural Center in Vincennes, IN.  The experimental design was a randomized complete block split-plot with six replications.  The main plots consisted of two crop rotations: continuous soybean and a 2-yr rotation of soybean-corn.  The subplot treatments were comprised of various herbicide application timings and cover crops.  Cover crops included fall-seeded annual ryegrass (Lolium multiflorum) and winter wheat (Triticum aestivum).  Winter weed control timings were 1) a non-treated control, 2) fall and spring control, 3) spring control, and 4) fall control.  After establishment, the plots to which the main- and sub-plot factors were applied remained fixed throughout the entire experiment to determine the cumulative treatment effects over time.  Winter annual weed management did not influence SCN but crop rotation and SCN resistant cultivars were effective at reducing SCN egg density.  Herbicides, applied in either fall or spring, were more effective than cover crops at reducing the amount of weed seed in the soil seedbank.