White rust

White rust, caused by the oomycete Albugo tragopogonis, is a common and destructive plant disease that affects a wide variety of crops and ornamental species. Unlike true fungi, this organism belongs to the oomycetes, requiring specific management approaches in agronomic practice.

The pathogen hosts many important agricultural plants, including sunflower (Helianthus annuus), Jerusalem artichoke (topinambur), spinach (Spinacia oleracea), Indian mustard, sweet potato, and the ornamental Gerbera jamesonii. The economic impact ranges from aesthetic damage to total yield loss in sensitive cultivars.

The primary symptom is the development of white, powdery, or waxy pustules on the underside of leaves and stems. As the disease progresses, these pustules break through the epidermis, releasing mass amounts of sporangia. In many cases, infected leaves may show chlorotic spots on the upper side corresponding to the pustule location on the underside.

The disease cycle is heavily dependent on environmental conditions. High humidity, dew, or frequent rainfall are critical for the germination of sporangia and the infection of host tissues. Temperatures ranging between 15°C and 22°C are optimal for the rapid spread of the pathogen in field and greenhouse environments.

Management of white rust requires an integrated approach. Prevention includes the use of certified, disease-free seeds and the implementation of strict crop rotation. It is also crucial to remove and destroy infected plant debris, as the pathogen survives through dormant oospores in the soil. Chemical control involving fungicides containing metalaxyl or copper compounds can be effective if applied during early infection stages.