Plum rust mite

The plum rust mite (Epitrimerus alinae) is a microscopic pest belonging to the family Eriophyidae within the order Acariformes. These mites are elongated, worm-like in shape, and measure less than 0.2 mm in length, making them invisible to the naked eye and requiring microscopic analysis for accurate identification in an orchard setting.

This mite primarily attacks plum and cherry plum (mirabelle) trees, though it may also infest other stone fruit species in the Prunus genus. By feeding on the epidermal cells of leaves and young shoot tips, the mite causes significant physiological stress to the tree, reducing its overall photosynthetic capacity and vigor.

The overwintering phase occurs as adult females hiding in bark crevices or under the scales of dormant buds. As the trees break dormancy in early spring, the mites become active, migrating to the newly formed leaves where they begin to feed and reproduce, completing several generations throughout the warm summer months.

Typical symptoms of infestation include leaf curling, deformation, and the development of pale yellow or brownish discoloration (rusting) on the foliage. Heavy infestations can lead to stunted shoot growth, premature leaf drop in mid-summer, and a marked reduction in the size and quality of the fruit produced by the tree.

Effective management requires the application of targeted acaricides during the early stages of infestation to prevent population explosions. It is also essential to maintain proper orchard hygiene, including the removal of heavily infested prunings, and to monitor trees regularly to catch the initial signs of mite presence before significant damage occurs.