What causes smaller yields in corn planted after a cereal rye cover crop? Dr. Alison Robertson, Iowa State University | Apr 05, 2021 Occasionally, corn planted after a cereal rye cover crop may have reduced yields. Proposed reasons for this yield decline include allelopathy, seedling disease, nitrogen immobilization and poor planter performance. In our lab, we are interested in understanding how seedling disease and allelopathy contribute to corn yield decline to develop best management practices for growing corn after a cereal rye cover crop. We will save the allelopathy story for another blog, and focus on seedling disease in this blog. Corn seedling disease pathogens survive in the roots of cereal rye. We wondered if planting corn at a distance from a cereal rye crop, in other words “social distancing” the two crops, might reduce seedling disease and mitigate yield loss.