Crown wart

Crown wart is a significant plant disease caused by the soil-borne pathogen Physoderma alfalfae. As an obligate parasite, this organism primarily targets alfalfa (Medicago sativa), focusing its attack on the crown area of the plant, which is vital for regrowth and overwintering survival.

The disease is most commonly found in regions with high rainfall or in fields that suffer from poor drainage. The pathogen produces resting spores that remain viable in the soil for several years, waiting for favorable moisture conditions to germinate and infect the sensitive crown tissue of the alfalfa host.

Symptoms typically manifest as large, white, fleshy galls appearing on the crown and lower stem sections. As the disease progresses, these galls darken in color, become brittle, and eventually decay, which causes the alfalfa stems to become stunted, chlorotic, and prone to breaking off at the base.

The economic impact of crown wart is significant, as it leads to reduced stand density, poor forage quality, and increased susceptibility to winter injury. Because the infection damages the crown, the plant's ability to store energy and produce new shoots in subsequent seasons is severely compromised.

Management of crown wart relies heavily on cultural control practices. Since there are no effective curative chemical treatments, producers should focus on:

• Improving soil drainage to prevent stagnant water.
• Implementing long-term crop rotations to reduce soil-borne pathogen inoculum.
• Avoiding over-irrigation during the periods when new growth emerges.
• Selecting resistant or tolerant alfalfa cultivars where available.