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Seedling diseases - alfalfa

Strong seedling establishment in alfalfa is important to achieve the plant density needed to outcompete weeds and produce high biomass yields. However, establishing alfalfa can be challenging because alfalfa seeds and seedlings are vulnerable to several pathogens present in soil.

Wet soil conditions favor the development of diseases caused by water molds, namely Phytophthora root rot (PRR), Aphanomyces root rot (ARR) and damping off (rotting). The pathogens causing these diseases produce mobile swimming spores called zoospores that require water to develop and infect alfalfa.

When rain is excessive after sowing, stand establishment may fail due to seed and seedling rot caused by these pathogens. Both ARR and PRR can also attack adult plants under wet soil conditions.

Yellow alfalfa and Aphanomyces root rot


Phytophthora root rot


Deborah Samac, plant pathologist, U.S. Department of Agriculture and M. Scott Wells, Extension agronomist

Reviewed in 2021

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