On August 14, ICCON was thrilled to be joined by Dr. Alison Robertson, Professor and Extension Field Crops Pathologist with the Iowa State University. Dr. Robertson was invited to share findings and management recommendations based on her research regarding disease in cover crop systems, primarily cereal rye before corn. Dr. Robertson was inspired by Tom Kaspar’s work at USDA-ARS, which focused on cover crops and their effects on corn yield. In Tom Kaspar’s research, he noticed a consistent issue of corn yield reduction when grown after a cereal rye cover crop. Many hypotheses such as planting issues, lower soil temperature, allelopathy, and nitrogen immobilization were suggested as to why the yield reduction persisted.
These planting issues often led to uneven corn stands, yellow seedlings, small or no ears, and overall reduced yields. These symptoms shared striking similarities to the effects of seedling diseases that Dr. Robertson was researching. This collaboration opened the opportunity for further investigation.
The primary focus of Dr. Robertson’s research is to identify whether cereal rye could act as a “green bridge” for seedling pathogens in corn. Initial studies revealed that cereal rye roots contained pathogens, including Fusarium and Pythium, which are generally present in small amounts in Iowa’s soil.
The researchers hypothesized that when cereal rye was terminated with glyphosate, the dying roots would release pathogens into the soil, temporarily raising their population. If corn was planted while these pathogen populations were still high, the risk of seedling disease increased. Field trials confirmed this hypothesis, particularly when cereal rye was terminated less than ten days before planting corn.
Dr. Robertson highlights how her research led to a suggested management practice.
The findings of this initial research led to the suggested recommendation that farmers should wait at least ten days after terminating a cereal rye cover crop before planting corn. This delay allows the pathogen populations to decrease, thus reducing the risk of seedling disease. However, in cold, wet springs, it can be difficult to access the fields to terminate the cover crop in a timely manner. This leaves farmers with the challenge of delaying planting or practicing “planting green.”
Dr. Robertson’s team conducted another study to determine if planting green increased seedling disease and contributed to yield drag. The results showed that planting green led to more severe seedling diseases, primarily Pythium. This result reinforced the recommendation to wait at least ten days.
Dr. Robertson shows the research process between different trial plots.
In a third study, inspired by the concept of “social distancing,” the team took the approach of physically separating corn from cereal rye to see if this could reduce seedling disease. Corn was planted at varying distances from the rye at 0 inches, 7.5 inches, and 15 inches. The rye was terminated three days before planting corn, so the team expected high levels of seedling disease.
The results showed that when corn was planted 15 inches away from the cereal rye, the severity of seedling disease was significantly reduced indicating a possible solution to separate rye and corn while planting.
“Socially distancing” corn and rye at 0″, 15″, 7.5″.
Dr. Robertson mentioned this method comes with its own drawbacks. Distancing the crops may significantly reduce the percentage of land covered by the rye. This is a drawback because cover crops are primarily grown for their agroecosystem benefits.
Dr. Robertson’s research brings forth an important challenge about the balance between utilizing cover crops like cereal rye for their many benefits and managing the potential risks they pose. By understanding the relationship between cover crops and seedling diseases, farmers can make more informed decisions about when to terminate cover crops and how to reduce disease risks.
Dr. Robertson’s full presentation can be viewed on ISAP’s YouTube channel. The ICCON Summer series will continue in September with insect and pest management in cover crop systems. Register for upcoming ICCON call here. If you are interested in joining the Illinois Cover Crop On-Farm Network to learn about new research and hear from cover crop specialists across the Midwest, please join our google group by sending an email to hvanbeck@farmland.org.
