Brown spot of soybean, also known as Septoria brown spot, is caused by the fungus Septoria glycines. It is a common foliar disease of soybean that can develop soon after planting and remain present throughout the growing season. Symptoms generally begin in the lower canopy and can progress upwards during grain fill. Severe yield losses are rare, but largely depend on how far the disease progresses into the upper canopy during reproductive growth.
Typical symptoms of brown spot include:
Septoria glycines overwinters on infected soybean leaf and stem residues. This infected plant material provides a source of inoculum for subsequent soybean crops.
Brown spot can develop soon after planting. Initial symptoms generally occur on lower leaves, where the disease establishes in the lower canopy.
Warm, wet weather favours disease development. When favourable conditions persist, brown spot can progress upwards through the canopy, particularly during grain fill.
Disease development usually slows or stops during hot, dry weather. It can become active again towards crop maturity or when environmental conditions become favourable.
Effective control of brown spot in soybean requires an integrated approach combining cultural practices, monitoring and biological control.
Reducing the amount of infected crop residue, through tillage, can help lower the amount of Septoria glycines inoculum available for subsequent soybean crops.
Regular crop monitoring helps detect early symptoms and determine whether the disease is progressing through the canopy.
Inspect crops for:
Weather conditions play an important role in disease development. Pay particular attention during warm, wet periods, especially during grain fill.
Macan is a biological foliar fungicide that can be used to prevent and control brown spot caused by Septoria glycines. It contains the beneficial bacterium Bacillus velezensis CECT 8237. Following application, the bacteria colonise the leaf surface, compete with pathogens for space and nutrients, and produce metabolites that disrupt fungal development.
For brown spot, preventive applications or applications at the beginning of the first symptoms help integrate biological disease control into the soybean crop protection programme.
