Managing Late-Season Soybean Diseases

• Facebook
• Twitter
• LinkedIn
• Email

Article by Jayden Mallette
Crop Sales Specialist
AGRIS Co-operative - LEAMINGTON

Key Symptoms and Control Strategies for White Mould, Sudden Death Syndrome (SDS), and Phytophthora

As the growing season progresses, it's a critical time for field scouting, particularly for soybean crops. Late-season diseases such as white mould, sudden death syndrome (SDS), and Phytophthora leaf and stem rot can significantly impact yield and crop health. Understanding these diseases, their symptoms, and management strategies can help mitigate their effects on your soybeans.

White Mould (Sclerotinia sclerotiorum)

White mould is caused by the fungus Sclerotinia sclerotiorum, which produces sclerotia – hardened structures capable of surviving in the soil for extended periods. During soybean development, the fungus releases spores that infect flowers, leading to a characteristic white, cotton-like fungal growth on and within the stems. Symptoms include pale stems and wilting leaves.

To manage white mould, consider reducing planting population, increasing row spacing, and applying fungicide at flowering to lower disease pressure.

Sudden Death Syndrome (SDS) (Fusarium virguliforme)

SDS is caused by the soilborne fungus Fusarium virguliforme. Infection first occurs early in the season, just after germination. As the plant approaches reproductive stages, the fungus will then start to produce toxins, which are sent up the plant and into the leaves. Heavy rainfall and cool conditions will increase the chances of infection. Symptoms start as interveinal leaf chlorosis, followed by leaf necrosis. Symptoms may appear worse or develop earlier in fields that also have high soybean cyst nematode (SCN) pressure as SCN feeding creates entry points for the fungus.

Using seed treatments containing fluopyram as the active ingredient and selecting SDS resistant varieties will help decrease the chance of sudden death syndrome in your soybeans.

Phytophthora Leaf and Stem Rot (Phytophthora sojae)

Phytophthora leaf and stem rot is caused by the fungus Phytophthora sojae. It can overwinter in crop residues or in the soil as spores. Phytophthora can then infect plant roots at any point in the growing season with cool, wet conditions being the favourable environment. Late-season symptoms include dark brown lesions on the lower stem, which can spread several nodes up the plant, eventually restricting nutrient flow and leading to plant death.

Scouting and Management

Regular field scouting and prompt identification of these diseases are crucial for effective management. Implementing integrated pest management (IPM) strategies, such as selecting resistant varieties, using appropriate seed treatments, and applying fungicides, can help reduce the impact of these diseases on your soybean crops.