As soon as you notice the black fungus on rhododendron shrubs, check the leaves carefully to determine which insect is responsible and treat it appropriately. leaves. This is a fungal disease that is characterized by white or gray blotches or coating on the leaves and other parts. The powdery mildew has since then been observed on leaves and seed pods of deciduous azaleas as well as evergreen rhododendrons, although the disease is more common on taxa of deciduous azaleas. It affects a wide range of plants and is caused by many different species of fungi. Powdery mildew affects various species of plants and is caused by a few closely related fung - 2ACCM64 from Alamy's library of millions of high resolution stock photos, illustrations and vectors. In 2002 a fungus causing powdery mildew on Rhododendron in Latvia was discovered and identi-fied as Erysiphe azaleae. For instance, the rhododendron cultivar 'Unique' shows almost no upper leaf change other than occasional very faint … Powdery Mildew. On rhododendrons PM often attacks new growth as well as more mature leaves and stems. Rhododendron : Powdery mildew (revision date: 3/10/2017) Use Integrated Pest Management (IPM) for successful plant problem management. Development of mature chasmothecia has been noticed at every location where … A puzzling aspect of this fungal disease is its varying appearance on different cultivars. Download this stock image: Powdery mildew on rhododendron (Rhododendron sp.) Powdery Mildew coats the trees leaves blocking the process of photosynthesis which turns light into food for trees and shrubs. On evergreen rhododendrons, light green or yellowish patches on the top of leaves sometimes accompanied by purple-brown areas on the backside of leaves are signs of powdery mildew. These newly produced leaves must then replenish the food supply through photosynthesis. You may also notice the affected leaves dropping off. These insects are flat, tan-colored discs on foliage and stems that at first glance appear to be growths on the leaves rather than insects. Photosynthesis is impaired, leaves turn yellow or reddish brown, distort, die and fall off. Every year trees and shrubs rely on their food reserves to push out new leaf growth. See: Rhododendron-Powdery Mildew. Erysiphe vaccinii (formerly Microsphaera vaccinii) has been found only on wild R. occidentale growing on the southern Oregon coast. On rhododendrons, the disease often fails to develop the distinctive powdery white growth normally associated with powdery mildews. This disease is mostly found in humid climates, and very rarely in cold weather. In severe cases, the growth of the plant may get stunted. Biology. Powdery mildew on rhododendrons is a fungal infection of the leaves. Cause The fungus Erysiphe azaleae (formerly Microsphaera azaleae) is found in western Oregon and Washington and southern British Columbia on garden azalea and rhododendron species and hybrids. Scale – Scale insects commonly cause black fungus on rhododendron. Subsequent growth is dwarfed and distorted, often covered with the mildew.