Robigalia Roundup LXX

Stemphylium vesicarium an ascomycete fungus belonging to the family Pleosporaceae . The sexual stage is Pleospora allii. It produces multicelled, darkly pigmented conidia with characteristic transverse and longitudinal septa, which aid in wind and rain dispersal.

The pathogen has a broad host range, primarily affecting onion, garlic, asparagus, lucerne, pear, and a variety of vegetable and forage crops. Within Allium, it is responsible for significant yield losses and post-harvest quality decline. Non-Allium hosts, such as pear, can serve as alternative inoculum sources.

On Allium species, symptoms typically appear as small, water-soaked lesions on leaves and scapes that expand into elongated necrotic spots with a grey to dark brown centre and chlorotic margins. Severe infection causes rapid leaf senescence, bulb underdevelopment, and premature plant death. In pear, the pathogen causes brown spot disease characterised by necrotic lesions on leaves and fruit. Sporulation occurs on senescing tissue under humid conditions, facilitating secondary infection cycles.

Stemphylium vesicarium is globally distributed, affecting Allium and fruit crops across temperate and subtropical regions. It is widely reported in Europe, North America, Asia, and Australasia. The pathogen favours warm, humid environments, and outbreaks are typically associated with extended leaf wetness periods and dense crop canopies that restrict airflow.

Control relies on integrated disease management. Cultural practices include crop rotation with non-host species, residue removal, optimised irrigation to minimise leaf wetness, and improved canopy ventilation. The use of resistant or tolerant onion cultivars, where available, provides partial disease suppression. Chemical control relies on protective fungicides such as dithiocarbamates, strobulurins, and SDHI fungicides. Disease forecasting models based on weather parameters are increasingly used to refine spray timing and reduce unnecessary applications.

Read on to meet a PhD researchers investigating S. vesicarium in the United States 👇

This week, we meet Matthew John, a PhD researcher from Michigan State researching investigating Stemphylium leaf blight in onions.

Matthew grew up on his family farm in Aponmu-Akure, Nigeria. Growing up, he witnessed how Phytophthora palmivora, the causal agent of Black pod disease of cocoa, could wipe out years of work. When he began his undergraduate studies in Plant Science at Ambrose Alli University, Ekpoma, Nigeria, he met a small community of farmers who depended entirely on their cash crops to survive yet lost a devastating portion of their harvest to plant pathogens every season. These combines experiences drove Matthew to pursue further research in plant pathology.

During his Master’s at North Dakota State University, Matthew focused on identifying effective cover crops for managing root lesion nematode in potato and evaluating how fungal and nematode pathogen interactions affect field pea health and yield.

Now completing a PhD at Michigan State University in Dr. Mary Hausbeck's Vegetable Pathology Lab, his research centers on the epidemiology and management of Stemphylium vesicarium, the causal agent of Stemphylium leaf blight in onions.

He studies the pathogen’s seasonal dynamics by monitoring airborne spores and examining how weather patterns and inoculum presence drive epidemic development. His work also investigates how cover crops, especially barley, can serve as alternative inoculum sources. He is also developing molecular tools and forecasting approaches that support better fungicide timing and integrated management for growers.

Matthew is incredibly proud of his research milestones to date, including showing showing S. vesicarium spores are present in Michigan onion fields well before crop emergence, and demonstrating that barley cover crops can serve as an overlooked inoculum source. He is also proud to have received a conference award for the best research poster during his master’s program!

Be sure to connect with Matthew on LinkedIn and follow him on ResearchGate to keep up to date with his work.

Have a job, scholarship or event to advertise? List a scholarship, job, or event in Robigalia. I help you promote your opportunity or event to a global network of plant pathologists for free.

See you next Monday!

P.S. Why Robigalia? The name originates from the Ancient Roman festival dedicated to crop protection. You can read all about the history here: