Plum psyllid

The plum psyllid (Cacopsylla pruni) is a small insect belonging to the family Psyllidae, order Hemiptera. It is widely recognized as a major pest in stone fruit orchards, not only due to direct feeding damage but primarily because it serves as the essential vector for Candidatus Phytoplasma prunorum, which causes the severe "plum yellows" disease.

The host range of this pest focuses on the Prunus genus, particularly domestic plum, sloe, and occasionally apricot and peach. Both adults and nymphs feed on the phloem sap of the trees. By injecting saliva while feeding, they can transmit pathogens that cause chronic physiological disorders in the tree, leading to severe yield losses and tree decline over several years.

The life cycle of the plum psyllid is univoltine, meaning there is one generation per year. Adults hibernate in protected sites, often utilizing conifers or bark crevices as overwintering refugia. In early spring, as temperatures rise, they migrate to plum trees. The eggs are laid on developing buds, and the nymphs begin feeding as soon as they hatch, passing through five developmental stages.

Damage symptoms include leaf curling, yellowing, and the excretion of large amounts of honeydew. This sticky substance encourages the growth of sooty mold, which coats the foliage and hinders photosynthesis. Persistent infestation results in stunted shoot growth, premature fruit drop, and, in the case of phytoplasma infection, a progressive weakening of the entire canopy.

Managing Cacopsylla pruni requires a combination of monitoring and targeted intervention to maintain population levels below the economic threshold:

• Apply early spring insecticide treatments before the onset of flowering.
• Implement proper pruning practices to improve canopy airflow and reduce habitat suitability.
• Utilize yellow sticky traps to detect the arrival of adult psyllids early.
• Remove and destroy trees that show clear symptoms of phytoplasma infection.
• Promote biodiversity in the orchard to encourage natural predators, such as lacewings and ladybirds.