Cover crops are a valuable management tool to reduce soil and nutrient losses while retaining moisture, improving soil organic matter content, and stabilizing soil N during the winter months when the ground is normally left fallow. Cereal rye (Secale cereale L.) is commonly used as a winter cover crop in the Midwest due to its ability to withstand cold temperatures, reduce soil erosion, and scavenge soil N. However, it has been found that a cereal rye cover crop can sometimes reduce performance and yields in the following corn (Zea mays) crop. Past studies have suggested that reduced corn growth and yield are caused by allelopathic effects of cereal rye without considering the possibility that cover crops may be providing soil fungal pathogens with a living host, allowing greater populations to overwinter, and then infecting the following corn crop.

The objectives of this study were to determine the effect of cover crop treatment, cover crop species, planting date, and corn fungicide seed coatings on corn growth, yield, and fungal infection rates through controlled environment and field experiments. In controlled environment experiments, corn following a cereal rye cover crop exhibited greater reductions in radicle length, extended leaf height, and corn shoot dry weight than corn following no cover crop. Additionally, corn following a cereal rye cover crop exhibited greater reductions in radicle length and greater fungal infection rates in roots than corn following hairy vetch (Vicia villosa Roth) or canola (Brassica napus L.) cover crops. The fungicide seed coating did not appear to prevent fungal root infection in corn following a rye cover crop. Field experiments examined the effect of planting date and cover crop treatment on corn performance. Corn planted later had greater corn leaf development, extended leaf height, corn shoot dry weight, and radicle length than early planted corn, but had greater fungal infections in the radicle and mesocotyl. The effect of the cereal rye cover crop treatment was variable in the field experiments. Corn following a cereal rye cover crop did show reductions in corn development, population, and yields, but these data were often not consistent for both years. In general, a cereal rye cover crop has the ability to reduce corn growth and yields, but other factors may be impacting corn performance as well.