Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/3/2025
Publication Date: N/A
Citation: N/A

Interpretive Summary: Rapid and uniform seed germination and plant establishment is critical for a productive and long lasting alfalfa stand. However, several soilborne pathogens often cause seed rot, seedling death, and root rot of seedlings leading to thin stands with poor persistence. The current seed treatments to inhibit damage from these pathogens is often ineffective or only partially effective. Alternative seed treatments were tested for inhibiting growth of nine pathogens in agar culture assays. Those with the widest spectrum of activity were used to treat seeds and tested with individual pathogens, in infested soil, in field soil, and in field experiments. EverGol Energy had broad activity, provided protection in single pathogen assays, and augmented genetic disease resistance. However, none of the products tested, including those currently in use on alfalfa seed, improved seedling health in field soil with multiple pathogens under disease conducive conditions. This study highlights the need for enhanced disease resistance in alfalfa cultivars against seedling diseases, which is more effective and economical.

Technical Abstract: Seed rot and damping-off of alfalfa (Medicago sativa L.) is a soilborne disease caused by multiple pathogens. Damage to seeds and plant roots results in thin initial stands of plants and continued damage by pathogens during wet soil conditions decreases forage yield and winter survival. Although several oomycides and fungicides are labeled for use on alfalfa seeds, alternatives with broad activity may aid in establishing alfalfa stands where pathogen complexes are present. In this study, 14 products were tested for mycelial growth inhibition of nine alfalfa pathogens. EverGol Energy, a combination of prothioconazole, penflufen, and metalaxyl, was active against all alfalfa seed rot and damping-off pathogens tested: four species of Pythium, four strains of Aphanomyces euteiches, three strains of Phytophthora medicaginis, and three species of Fusarium. Intego Solo (ethanboxam) was active against all pathogens except Fusarium species. In agar plate and infested soil assays, protection against Pythium species by EverGol Energy was similar to that of ApronXL (mefanoxam). Evergol Energy seed treatment provided modest protection in growth chamber tests with A. euteiches and P. medicaginis indicating that it could provide early season protection against multiple pathogens. Several seed treatments augmented genetic resistance to root rot pathogens. In field soils with a history of poor alfalfa establishment, none of the treatments improved seedling health and had only modest improvements in stand counts and biomass yield in field trials. These results suggest that there are alternative seed treatments to combine with host resistance to improve disease management in alfalfa.