The disease manifests as the appearance of light brown to dark brown spots on leaves and stems, which can spread and infect the entire plant. Black dots, representing fungal pycnidia, form on the affected tissue areas, while depressed ulcers with a crumbling internal structure form upon infection of root crops and tubers.
The development of the pathogen depends on temperature conditions in the range of +10…+25°C and high air humidity exceeding 70–80%. The infection persists in the soil on plant debris for up to 3–6 years and is also transmitted through infected seeds, tubers, and root crops, which determines a high risk of spread in various climatic zones.
The assessment of variety resistance is carried out within the state variety testing system on specialized plots over several years. In field conditions, specialists conduct a visual scoring of plant infestation, which allows determining varietal responsiveness to the pathogen as an important economic and biological trait.
Varietal resistance to Phoma rot rarely constitutes full immunity and is considered an element of an integrated approach to crop protection. The selection of a resistant variety must be combined with adherence to crop rotation, returning the crop to the same field no earlier than after 3–4 years, and the use of healthy seed material.