Acrocalymma blight

Acrocalymma blight is a fungal plant disease caused by pathogens of the genus Acrocalymma. This genus belongs to the ascomycetes and includes several species, most notably Acrocalymma medicaginis, which primarily affects alfalfa. The disease is characterized by infection of stems and leaves, leading to significant losses in green mass yield and reduced forage quality.

The primary causal agent is the fungus Acrocalymma medicaginis. The disease type is an infectious fungal necrosis. The pathogen can survive in crop debris, soil, and seeds, making it difficult to eliminate without strict adherence to crop rotation, quarantine measures, and deep incorporation of post-harvest residues into the soil.

The primary host is alfalfa, though research indicates potential susceptibility in other legume forage crops. The infection affects the aerial parts of the plant, developing most aggressively on stems, where characteristic lesions form, disrupting normal nutrient transport and stunting the growth of vegetative mass.

Symptoms manifest as dark, sunken spots or ulcers on the stems, which can coalesce over time, causing lodging and necrosis of affected tissues. Chlorosis of the surrounding tissue is often observed. Under conditions of high humidity, the fungus may produce fruiting bodies (pycnidia) on the surface of the lesions, which are visible upon close inspection.

• High air and soil humidity during the growing season.
• Temperature range between 18 and 25 degrees Celsius.
• Presence of untreated infected plant debris in the field.
• Stem damage caused by insect pests, facilitating spore entry.

The harmfulness of Acrocalymma blight lies in the reduction of crop productivity, the degradation of hay nutritional value, and premature plant death, leading to sparse plant stands. Management strategies include the use of resistant cultivars, crop rotation with a 3-4 year break, deep plowing to suppress inoculum levels, and the application of fungicides during periods of high disease pressure.