Phoma leaf spot of sugar beet

Neocamarosporium betae is a pathogenic fungus belonging to the kingdom Fungi, phylum Ascomycota. Widely recognized in older texts as Phoma betae, this fungus is the causal agent of Phoma leaf spot and root rot in sugar beets, mangels, and table beets. It is a significant pathogen that affects both seedlings and mature plants.

The disease manifests as yellowish-brown necrotic spots on older leaves, characterized by a distinct dark margin. Within these spots, the fungus produces small black fruiting bodies known as pycnidia. When infection occurs during the seedling stage, it causes "damping-off," while in mature beets, the fungus can progress into the root, leading to storage rot and reduced sugar content.

The biological cycle of this pathogen is primarily sustained by infected crop debris left in the field and contaminated seed lots. Neocamarosporium betae survives the winter as mycelium or pycnidia. During the growing season, spores (conidia) are dispersed by wind, rain splashes, and movement of machinery, facilitating rapid spread throughout the field under favorable weather conditions.

Optimal development of the fungus occurs in humid conditions and temperate temperatures, typically between 18°C and 25°C. Excessive soil moisture and high canopy humidity accelerate the infection process. Crops suffering from nutrient deficiencies, particularly low potassium levels, or physical stress are significantly more susceptible to severe outbreaks.

Effective management and control strategies rely on a combination of cultural and chemical practices:

• Using certified, fungicide-treated seeds to eliminate seedborne inoculum.
• Implementing a sound crop rotation plan with a 3–4 year interval between host crops.
• Deep plowing to bury infested plant debris and accelerate decomposition.
• Providing balanced fertilization to improve plant vigor and natural resistance.
• Applying systemic fungicides at the onset of symptoms during the vegetative period.