Didymellina leaf

July 6, 2015

Fungal leaf spots

Pathogen

Didymellina poecilospora.

Hosts

Iris; most severe on rhizomatous iris.

Iris didymellina planting
Severe blighting of foliage. Most infections occur on the upper portion of the foliage.

Symptoms

The first symptoms are tiny, brown spots with water-soaked borders. As disease progresses, the water-soaked areas develop into irregular spots with grayish centers and dark borders. Foliage is killed, weakening the rhizomes. Disease severity worsens after bloom.

Iris didymellina leaf spot
Individual spots with grayish centers and darker borders surrounded by yellow halos.

Spread

Rain and splashing water disseminate spores to adjacent plants. The disease can easily be introduced on infected plant material.

Didymellina leaf spot
Necrotic tissue coalesces around the leaf spots.

Management

Good sanitation is important. Leaf debris should be removed in the fall to reduce inoculum, which overwinters on the dead foliage. If infected debris is left in the area in the spring, the pathogen can sporulate and reinfect developing foliage.

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