Plum rust

Plum rust is a fungal disease caused by the pathogen Tranzschelia pruni-spinosae. It is a common problem for various stone fruit trees, significantly affecting the foliage and potentially reducing the overall vitality of the orchard throughout the growing season.

The disease primarily targets trees within the Prunus genus. This includes plums, apricots, peaches, and almonds. The infection can spread rapidly within an orchard if environmental conditions are favorable and if primary sources of inoculum are not addressed.

The symptoms typically appear during the summer months. On the upper side of the leaves, small yellowish or reddish spots begin to develop. Correspondingly, the lower surface of the leaf displays rust-colored pustules, which represent the mass production of fungal spores ready for dispersal.

The development and spread of plum rust are heavily dependent on humidity and moisture. Periods of high humidity, frequent rainfall, and stagnant air within tree canopies promote the germination of spores. The fungus survives the winter primarily on fallen infected leaves, making sanitation a key aspect of management.

The harm caused by this disease is primarily due to premature defoliation, which impairs the tree's ability to photosynthesize and store energy reserves for winter. Effective control measures include the removal and destruction of leaf litter, maintaining proper tree spacing to ensure good air circulation, and the timely application of fungicides during the growing season.