Mitigating Reduced Yields of Corn Following a Winter Rye Cover Crop: What Role Does Allelopathy Play?

Aug 2019


In Iowa, winter rye is the most extensively used cover crop because of its easy adaptability in corn-soybean rotations, establishment success even with late fall planting, superior winter hardiness and growth at cold temperatures. In some years and fields, however, corn yield decreases have been reported following winter rye cover crops, which discourages adoption. A previous project supported by the INRC demonstrated that winter rye can serve as a green bridge for soil-borne pathogens of corn, specifically Clade B Pythium species. However, seedling disease cannot solely be blamed for this yield decline. Allelopathy may also play a role in corn yield losses in the winter rye-corn production system. Winter rye produces numerous allelopathic compounds that suppress growth of numerous small grains and other plants. Some of these compounds affect the soil microbial community, including Fusarium species that are plant pathogens which can cause seedling disease. How do allelopathic compounds affect corn growth and development? How do allelopathic compounds affect seedling disease pathogens, specifically Pythium species? Do allelopathic compounds influence seedling disease development? In addition, since the persistence, availability and activity of allelochemicals is influenced by a range of biotic and abiotic factors, researchers will seek to understand if allelopathy can explain why corn yield decreases in some fields but not others.


This project will:

  • Assess the effect of rye allelochemicals on corn seedling growth.
  • Assess the effect of rye allelochemicals on the growth of Pythium species.
  • Study the interaction between the Pythium species and rye allelochemicals on corn seedling growth and disease development.


Corn growth and eight Pythium species will be evaluated in the laboratory on media amended with the allelopathic compounds at various concentrations and at three temperatures, including two representative of soil temperatures in Iowa at corn planting. Each treatment (Pythium sp. alone, corn alone, Pythium sp. + corn) will be replicated six times and each experiment repeated twice. Germination and growth characteristics will be measured for 10-28 days, depending on the temperature. Root rot severity will be scored at the final assessment date. The growth of Pythium will be measured daily for 3-5 days. 

Finding from this project will be presented at professional meetings and conferences, field days and other extension and outreach activities and publications.

Project Updates

Note: Project reports published on the INRC website are often revised from researchers' original reports to increase consistency.

June 2021


In general, MBOA reduced corn coleoptile length and radicle length and did not cause root rot across all temperatures tested (13°C, 16°C, or room temperature/20-22°C). In general, all Pythium spp. that were tested were tolerant to MBOA at 0.0625 and 0.125 mg/ml across all temperatures. Greater root rot severity in corn was observed on corn seedlings grown in the presence of Pythium lutarium and P. oopapillum on media amended with MBOA compared to the check at all temperatures. Similarly, more root rot caused by P. torulosum, and P. spinosum was observed when MBOA was present at 16 °C compared to the check with no MBOA.

These data suggest that corn seedling disease caused by Pythium species could be more severe when corn is planted following a cover crop of winter cereal rye due to the presence of allelochemicals that are released from the cover crop.

Activities included providing a presentation for an Iowa Learning Farm Webinar at: Iowa Learning Farms: July 1, 2020 on Vimeo

August 2020

Research delayed due to ongoing Covid pandemic.