Phoma leaf spot

Phoma herbarum is a ubiquitous fungal pathogen responsible for causing a variety of diseases known as phoma leaf spots and stem rots. As a versatile polyphage, it infects a vast range of plant species, making it a significant concern for both commercial agriculture and horticultural operations worldwide.

The pathogen can attack various plant organs, including roots, stems, leaves, and pods. In many crops, the disease manifests initially as small, water-soaked spots that expand into necrotic lesions. These spots often feature concentric rings, and under moist conditions, the center of the lesion becomes dotted with small, black pycnidia.

Symptoms are highly dependent on the host plant, but common indicators include stem lesions that cause lodging, root rot leading to plant wilting, and reduced seed quality. In some cases, the fungal infection can remain latent, only showing symptoms when the host plant is stressed by environmental factors or insect damage.

The development of Phoma herbarum is strongly favored by cool to moderate temperatures and high humidity or prolonged leaf wetness. The pathogen is primarily soil-borne and survives on infected crop debris. It can also be seed-borne, allowing for the introduction of the fungus into previously uninfected areas through contaminated agricultural inputs.

Control strategies should be integrated to be truly effective. Key management practices include:

• implementing long-term crop rotation cycles;
• removing and destroying infected plant debris after harvest;
• selecting resistant or tolerant cultivars when available;
• using certified disease-free seeds;
• applying appropriate fungicidal treatments during high-risk periods of development.