Or roots die and plants wilt without having leaf spots form. Leaf spot: the leaf spot fungus produces water-dispersed spores from fruiting bodies on the infections. When these germinate they infect the alternate host which is spruce (Picea spp.). Plants die rapidly. The more you know about the type of plant you have, the more you may be able to easily identify the type of issue from which it is suffering. Always wash clippers and other gardening tools after use to avoid spreading spores from affected buds. Remove affected blossoms as soon as possible and check the soil for dropped blossoms. Rhododendrons are favored for their year-round beauty. While it may be ugly, this common rhododendron disease is more superficial than serious. times, RHS Registered Charity no. Bud blast is spread by the rhododendron leafhopper. They are spread by water and potentially infect buds through wounds made by the rhododendron leafhopper when it punctures the bud to lay its eggs (although some recent research has cast a doubt on this link between the pest and disease). The most common include: Each unsightly fungus has its own set of issues with which a gardener needs to contend. The most common specific fungal diseases that affect rhododendrons include; They are also attacked by more generalist diseases such as; Bud blast: control of the leafhopper, to prevent infection by bud blast, is difficult because they are strong fliers and reinvade rapidly, but sprays of natural pyrethrum (e.g. Little is known about this pathogen. Bug Clear Ultra) from early August for as long as the pest is active may be helpful. While the bushy evergreen offers a spot of color in the garden all year long, it can be hiding problems that will pop up on the leaves or blooms as the weather warms. The fungus Exobasidium japonicum will cause unsightly disfiguration of the plant’s leaves, but it often won’t kill the plant entirely. And they wont grow in areas with chalky/limey soil unless in raised beds. Join the RHS today and support our charitable work, Keep track of your plants with reminders & care tips – all to help you grow successfully, For the latest on RHS Shows in 2020 and 2021, read more, RHS members get free access to RHS Gardens, Free entry to RHS members at selected times », Reduced prices on RHS Garden courses and workshops, Our Garden Centres and online shops are packed with unique and thoughtful gifts and decorations to make your Christmas sparkle, General enquiries If you see discoloration on the plant, mites are more than likely the issue and need to be removed with either a homemade or commercial insecticide. Signs of rhododendron distress can usually be traced to incorrect culture or siting. There are many types of fungi in search of healthy rhododendrons to feed upon. Preventing disease from the start is much easier than getting rid of it or controlling it from spreading to healthy plants. One of the most common creepy cruds that cause issues with azaleas and rhododendrons is a fungus known as water mold. Yellow Leaves And Green Veins Signal Iron Chlorosis If the pH (acidity/alkalinity) of the soil is greater than 5.5, your rhododendrons may develop an iron deficiency because it is not acid enough. Azaleas and rhododendrons like to have a layer of mulch to protect the shallow roots of the plants. The first signs of the fungus Phytophthora species are when the leaves begin to curl inward and droop. The main difference lies in the stamens. Of the few rhododendron insect problems that exist, most can be handled first through prevention or subsequent treatment with neem oil. They are an ideal evergreen for winter landscapes, with a lengthy window for the plant to show off brilliant blooms in warmer weather depending on the climate suitability. Rhododendron leaf spot. The bud eventually falls off and dies without blooming. However, there are a few fungal diseases that crop up. The symptoms of bud blast on rhododendrons start with the bud turning a silvery grey color before growing black bristles. Apply a fungicide to protect leaves before infection in the spring. Don't hose down the plant from the top down. Petal blight: the fungus causing petal blight produces wind-dispersed spores on old infected flowers which remain hanging on the plant from the previous season. Gall: the azalea gall fungus produces airborne spores on the white bloom that develops on the galls. Rhododendrons are quite easy to grow as long as you have well drained but moist acidic soil. Phytophthora thrives in wet soil or poorly drained areas where the plant is installed. The most frequent problems of rhododendrons mostly fall within nutritional imbalances or insect problems. 10). There are a number of different Rhododendron diseases, with the most serious being root rot and dieback of the branches. The hardy leaves of the rhododendron can lose their lovely appearance due to several diseases attacking the garden favorite. Azalea leafminer damage. If leaves have brownish raised areas on the underside of the leaf, it is often a fungal disease called rust. Stems have brown spots on which white masses of spores later form. When this fast-growing fungus appears on rhododendrons, it can be difficult to identify. Bud blast: the fungus causing bud blast produces its spores on the black fungal 'bristles' that appear on infected buds. Powdery Mildew Powdery mildew is a common fungal disease that’s easily recognized by the white, powdery spores that cover the leaf surfaces. Unfortunately, there isn’t a specific time period, as fungi will attack at any time of the year. By identifying the type of fungi that has selected your rhododendron as a sweet spot to thrive, you can be sure to eradicate it in the shortest amount of time and without further damaging a healthy rhododendron. Here are some common pests affecting this shrub: Spider mites – Spider mites feed off of bud and leaf … Westland Resolva Pest Killer) or acetameprid (e.g. This can leave the healthy plant open to even more serious diseases that can take it down to the roots. Rhododendron is a genus of plants with more than 850 species, from ground covers to shrubs and trees. Look for yellow leaves, scorched brown spots, powder or discoloration. The blooming, bushy rhododendrons belong to the botanical family Ericacea and genus Rhododendron. They wont tolerate deep and dry shade and poor drainage/heavy clay soil. When the infestation is severe, it can cause the petal-shaped leaves to drop from the plant. Fungal Diseases. Fig. After many years shrubs and trees deplete the naturally occurring calcium in the soil and it must be replaced. It is spread from plant to plant via airborne spores and is difficult to control outdoors and indoors. Pesticides for gardeners (Adobe Acrobat pdf document outlining pesticides available to gardeners) RHS members can get exclusive individual advice from the RHS Gardening Advice team. You’ve put in the work and waited all year for the blooms to begin on your rhododendron or azalea. Look for discolored roots or wilted branches. Winged pests can also create issues that often appear in spring and summer as they migrate from garden to garden. Avoid issues with your rhododendrons by planting varieties that have been known to be somewhat resistant to crown and root rot and other issues. It can be hard to know if what is blooming in your backyard is an azalea or a rhododendron. If an established rhododendron loses vigor after several years and there are no obvious insect or disease problems, it may be suffering from a lack of calcium. The canopy of the rhododendron can look healthy and full and the buds big and bulbous, but you can still have a fungus lurking within the plant. There are more than 800 species within the genus Rhododendron. Rhododendron Leaf Problems. 020 3176 5800 Rust: the rust pathogen releases airborne orange spores which spread the disease among Rhododendrons, then later it produces dark resting spores. However, there are many different types of rhododendron. The most significant are powdery mildew and bud blast. Two diseases, branch die-back and Phytophthora root rot in particular, are opportunistic this way. Treat rhododendrons for rust diseases by raking away infected leaves, pruning off diseased leaves, twigs and branches, and then destroying or discarding the infected plant parts.