Phytophthora Root and Stem Rot – Diminishes Soybean Yields

by Gary Klopfenstein

“How wonderful was heaven to give man a plant that provides milk, meat and medicine.” – Chinese Proverb

Soybeans. Incorporated in our daily lives from snacks, cooking oils, soap, milk replacer, paints, waterproof cement to cosmetics, soybeans are a vital part in our lives.  I love learning about soybeans and how the plant grows, how to increase yield, and how the plant can be affected by disease.

Phytophthora root and stem rot is one of the most destructive diseases in Ohio.  This disease is an oomycete and survives in the soil, plant debris as oospores and sometimes mycelia.  This root and stem rot can infect the soybean plant at any growth stage, but predominantly infects the plant early in the growing season. It will attack the roots first and can infect leaves when infected soil particles are splashed or blown onto the leaves in a storm.

How do you know if you have this disease in your field?  The disease characteristics are visible during the stem rot phase, where the plant has brown discoloration on the low stem and branches.  The entire root system will appear rotten and the taproot will be dark brown.  The plant won’t lose its leaves but will be chlorotic at first then turn necrotic.

What can you do?  Start with knowing your fields and the soil condition.  Wet soils are a prime location for phytophthora to reside in. Ask you seed company for resistant cultivars. Planting resistant plants for diseased fields will improve your farms production.  There are different physiological races of the disease, so diversifying your seed will help with finding which race is in your field. Seed treatments and fungicides are also practical methods to preventing yield loss.

More information
Phythophthora Damping Off and Root Rot of Soybean, By AE Dorrance and D Mills
> Ohioline fact sheet

This blog post was an assignment for Societal Issues: Pesticides, Alternatives and the Environment (PLNTPTH 4597). The views expressed are those of the author and do not necessarily reflect the views of the class, Department of Plant Pathology or the instructor.

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