Viburnum-Powdery Mildew

Disease Information

Viburnum-Powdery Mildew

Cause Erysipheviburni (formerly Microsphaerasparsa), a fungus that becomes abundant in late summer, particularly on plants in shade. It is favored by a combination of warm days, cool nights, and humid conditions, but is inhibited by rain.

Symptoms

Symptoms The disease primarily affects young leaves and shoots. Affected plant tissues develop a powdery white growth of fungal mycelia. The fungus can be found on either leaf surface. Tiny black specks may be observed among the white mycelia in late summer. Developing leaves may be somewhat deformed by severe infections.

Management

Powdery mildew can be controlled by cultivar selection and sanitation. Since the fungus overwinters oninfected canes, in buds or on old leaves, it is important toprune infected plant parts and remove leaves before new growth starts in the spring. If you plant susceptible varieties,ensure the location is sunny with good air circulation.

Pruning rose canes to ensure good air circulation may alsohelp.

Fungicides may be required for susceptible varieties.

Fungicides active against powdery mildew include folpet,lime sulphur, sulphur, triforine, thiophanate-methyl andbenomyl.

 



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