Verticillium wilt of alfalfa

The disease is caused by the fungus Verticillium alfalfae, a soil-borne pathogen that specifically targets the vascular tissue of the host plant. This infection leads to systemic wilting, which drastically restricts the plant's ability to transport water and nutrients, eventually resulting in the decline of the stand.

Alfalfa is the primary host for this pathogen, and it is a major concern for forage producers worldwide. The fungus infects the plant through the root system or through wounds sustained during harvesting operations, establishing a long-term presence within the vascular bundle.

Common symptoms include chlorosis and V-shaped yellowing of the leaf margins, which progress to wilting and necrosis of the entire plant. As the disease advances, the stems become stunted, and the internal tissues show characteristic brown discoloration when cross-sectioned, indicating severe colonization by the fungal mycelium.

The development and spread of Verticillium alfalfae are favored by cool, moist environmental conditions. The fungus produces survival structures known as microsclerotia, which can persist in the soil for several years, making it extremely difficult to eradicate once the field is contaminated.

Management strategies are focused on long-term prevention due to the lack of curative treatments. Effective practices include:

• planting resistant alfalfa varieties;
• following strict crop rotation cycles;
• cleaning harvesting machinery to prevent mechanical spread;
• maintaining good soil fertility to enhance plant vigor.