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Phloeospora robiniae

Yellowish brown leaf spots

Description

Phloeospora robiniae is a fungal pathogen responsible for leaf spot disease on black locust (Robinia pseudoacacia) and its cultivars. The fungus thrives in humid conditions, particularly after prolonged wet springs. It primarily infects leaves, but can also spread to petioles and young shoots, leading to growth disturbances and premature defoliation. The infection causes local tissue necrosis, which may result in leaf tearing, resembling gall mite damage. Severe infections can affect overall tree vitality by weakening the crown, especially in susceptible cultivars such as Robinia pseudoacacia ‘Umbraculifera’ and ‘Tortuosa’.

The fungus is widely distributed across Europe, particularly in regions with moderate to high humidity. Its fruiting bodies (acervuli) appear on the underside of infected leaves during summer, serving as a source of reinfection in the following seasons.

Symptom

On infected leaves, irregularly shaped, light brown spots with dark margins develop, usually 0.5–1 cm in size. As the infection progresses, leaf tissues may tear locally. Acervuli, small yellow-brown fungal fruiting bodies (about 0.1 mm), are visible on the lower leaf surface. Tips of the leaves are yellow, and become dark brown soon.

Tree Species: Black Locust

Part of a plant- attacked: Leaf / Needle, Branch

Pest significance: Harmful

Pest Category: Fungi

Invasive Species: No

Present in EU: Yes