Bacterial black spot of cherry

Bacterial black spot of cherry is a plant disease caused by the Pseudomonas syringae pathovar complex. It is a persistent threat to cherry orchards globally, affecting tree health and overall fruit yield by attacking foliage, shoots, and fruit tissue.

The pathogen is highly opportunistic, often entering the plant through natural openings such as stomata or wounds caused by pruning, insects, or environmental damage from frost and hail. Once inside, the bacteria multiply rapidly within the intercellular spaces.

Symptoms typically include dark brown or black angular spots on leaves, often surrounded by a chlorotic halo. As the infection progresses, the dead tissue may dry and fall out, creating a shot-hole effect. Shoot infection often leads to cankers that may ooze amber-colored sap (gummosis) and cause tip dieback.

The development of this disease is heavily dependent on wet, cool weather conditions. Periods of high humidity and rainfall promote the spread of the bacteria from infected plant debris or cankers to healthy tissues via water splash, rain, or tools.

The economic impact of bacterial black spot is significant, as it leads to defoliation, stunted growth, and potential tree death in cases of severe trunk infection. Weakened trees are also more susceptible to secondary pests and winter damage.

Effective management requires an integrated approach. Pruning and destroying infected branches during the dormant season is essential. Furthermore, applying copper-based sprays during the leaf-fall and early spring dormant periods helps reduce the bacterial inoculum level in the orchard environment.