Phomopsis stem canker

Diaporthe ueckeri is a significant fungal pathogen responsible for Phomopsis stem canker, a devastating disease of sunflower. This pathogen attacks the vascular system of the host plant, severely disrupting nutrient and water transport, which often leads to total crop failure in susceptible fields.

The primary host is Helianthus annuus (sunflower), although the fungus can survive on various wild species within the Asteraceae family. It is capable of infecting almost every part of the plant, but the most severe damage occurs on the stems and leaf stalks, which eventually collapse due to tissue necrosis.

The diagnostic symptoms include greyish-brown lesions on the lower leaves that progress to the petiole and eventually create large, necrotic girdles on the stems. These stem cankers weaken the structural integrity of the plant, causing it to snap under light wind conditions. Inside the stem, the pith becomes degraded and dark, which is a classic indicator of this fungal invasion.

Disease development is highly dependent on environmental conditions, particularly high humidity, heavy rainfall, and temperatures ranging from 20°C to 25°C. The fungus produces pycnidia and perithecia, releasing spores that are disseminated via wind and splashing water. Infected crop residues remain a source of inoculum for several years, making long-term field management essential.

Effective management requires a multi-faceted approach centered on prevention and chemical protection. Growers should prioritize an integrated pest management strategy to minimize the risk of infection. Key recommendations include:

• Enforcing long-term crop rotation cycles of 6 to 8 years.
• Selecting sunflower hybrids with documented resistance to Diaporthe species.
• Ensuring deep burial of infected stubble to accelerate the decay of the fungus.
• Applying fungicides during the critical growth stages (V4 to V8) to protect the plant.
• Removing volunteer sunflowers that may act as bridges for the disease.