Viburnums (Viburnum spp.) belong to the honeysuckle family. They are grown for their fragrant clusters of flowers and bright fruit. The evergreen or deciduous shrubs or small trees adapt to a range of growing conditions. Viburnums are likely to be infected with fungal disease that causes brown and yellow discoloured foliage.
Viburnums are susceptible to armillaria root rot caused by Armillaria mellea. Also referred to as mushroom, shoestring or oak root rot, the fungus infects the plant through the roots.
As infection spreads in the roots, it leads to rotting. There is often black, threadlike growth on roots. Foliage is stunted and turns yellow and brown. As disease progresses, leaves wilt and there is extensive leaf drop. The loss of foliage gives the plant a sparse look. In some cases, the plant dies without any symptoms at all.
Confirm cause of disease by examining roots and wood. Armillaria-infected plants have soft, fungal growth on roots and under the bark. Remove severely infected plants entirely with its soil, as this can infect new plants. Use resistant varieties.