Target spot of soybean is caused by the fungus Corynespora cassiicola. Symptoms generally first appear on leaves in the lower canopy. Under favourable conditions (high humidity and temperatures, with extended period of leaf wetness), it can spread upwards through the crop and severe infections can result in defoliation.
Typical symptoms include:
Corynespora cassiicola survives in soil and infected plant debris. The fungus can persist in soil for several years.
Conidia are dispersed by air and water to susceptible soybean tissue. After reaching the leaf surface, spores germinate and infect the tissue.
As the pathogen develops within infected tissue, cells die resulting in the characteristic lesions. Fungal structures known as stroma develop within the lesions.
New spores are produced on the stroma and released. Under favourable conditions, these conidia can spread to other leaves and into the upper canopy, continuing the disease cycle.
Effective control of target spot requires an integrated approach combining cultural practices, monitoring and biological control.
Reducing pathogen survival and avoiding conditions that favour disease build-up can help limit target spot pressure.
Regularly inspect the lower canopy, where target spot generally first develops.
Inspect crops for:
Macan can be used to prevent and control target spot caused by Corynespora cassiicola. Its beneficial bacterium, Bacillus velezensis CECT 8237, colonises the leaf surface and competes with fungal pathogens for space and nutrients. It also produces metabolites that disrupt fungal development.
For target spot, Macan is recommended preventively or at the beginning of the first disease symptoms.
