Horsetail asteromelliosis

Horsetail asteromelliosis is a plant disease caused by the fungal pathogen Asteromella equiseti. This fungus acts as an obligate or facultative parasite specifically adapted to species of the genus Equisetum. It belongs to the group of coelomycetes, which are characterized by the production of spores within specialized fruit bodies known as pycnidia.

The primary host for this pathogen is the field horsetail (Equisetum arvense). The fungus infects the green photosynthetic shoots of the plant. In agricultural settings, the infection of horsetail is often studied in the context of biological control, as the pathogen reduces the vigor of this difficult-to-control perennial weed.

Symptoms are identified by the appearance of discolored spots on the horsetail stems. Within these spots, small black pycnidia develop, which are clearly visible to the naked eye. As the infection progresses, the tissues surrounding these spots undergo necrosis, leading to the yellowing, browning, and eventually premature dieback of the stem sections affected by the fungus.

Environmental conditions favoring the development and spread of Asteromella equiseti include high relative humidity and moderate temperatures. The fungus requires moisture to release its spores from the pycnidia. Transmission typically occurs through water splash during rainfall, irrigation, or direct contact, allowing the fungus to spread rapidly within dense patches of horsetail.

The economic impact of this disease is primarily associated with the biological suppression of horsetail infestations in fields. Preventive measures, if desired to suppress the fungus, involve standard agronomic practices such as improving field drainage and deep plowing to reduce the population of the host plant. There are currently no fungicides specifically registered for the control of this disease on weeds.