Cercospora leaf spot (Cercospora handelii). Glomerella canker and dieback Glomerella cingulata Colletotrichum gloeosporioides [anamorph] Gray blight Pestalotia sydowiana. When Rhododendron occurs, there will be small brown spots on the leaf surface, which will gradually form irregular large spots, and then the leaves will fall off, affecting the flowering of the year and the development of flower buds in the next year. Exobasidium leaf spot Exobasidium burtii. Some sun is needed, dense shade will result in spindly plants that will rarely bloom. The hotter the region, the more shade these perennials need. It is uncommon to see necrosis occur out to the leaf tip. Powdery mildew on rhododendrons is a fungal infection of the leaves. The lacy wings (very distinctive) are held flat over the back and are transparent with two dark spots present. Leaf spots are most prevalent after periods of cool, wet spring weather. Cercospora leaf spot on Rhododendron. My mom says it might be rust. While leaf spots can be controlled with a fungicide, root and crown rot can be prevented to some extent by planting rhododendrons in well drained soil. Traditionally, botanists used to count the stamens when a plant was blooming, classifying those with 10 stamens as rhododendrons and those with five stamens as azaleas. 15/52 Spots. If you believe that your rhododendron has fungus on its foliage, then you need to take action, including reviewing the plant's cultural care. Several fungi cause leafspotting on rhododendron leaves, often as a secondary effect of the shrub being in poor condition from some other cause. Some have red-brown borders with silvery gray centers. The spot's upper surface may feel bumpy due to the fungal fruiting bodies (pycnidia). This condition is caused by several different species of phytophthora fungi, and each creates slightly varying symptoms. Leaf gall is a common springtime Rhododendron disease, but it is not particularly serious. When you ask, “Why does my rhododendron have yellow leaves”, the answer could be anything from improper irrigation to incorrect planting to inappropriate soil. Berkeley's Boalt Hall, and an MA and MFA from San Francisco State. Necrotic ring spot is a virus that causes light-colored spots or streaks on the rhododendrons leaves. symptoms are pale spots on upper leaf surface, with corresponding brown/grey patches underneath: Control with fungicide from late May onwards. Brown spot often occurs in rainy season and humid weather. known for their spots. Another test is the size of the flower and when they appear. Do Camellia Bushes Lose Their Leaves in Cold? Rhododendron Leaf Spot. The best soil will contain adequate humus and be moist to keep the shallow root systems of these plants from drying out. In general, most fungal leaf spots are not threatening to the health of the plant, although under severe conditions some defoliation can occur. 1 of 3. 8). To fix it, I usually clean up around the plant and try to cut back a few branches to reduce overcrowding and improve the air circulation. Wind burn, sunburn, drought, or winter damage may be the cause or these spots and they may disappear when warmer weather arrives. plants affected by it have leaves, buds, or stems that develop swollen, distorted growths in April or May. It is uncommon to see necrosis occur out to the leaf tip. Spots on rhododendron leaves. The rhododendron cultivar Unique, grown in a nursery showing necrotic leaf spots along the margins of the leaves. Every gardener with a shady corner loves rhodies. They are termed "queens of the shade garden" because they usually do not like full sun, preferring dappled or deep shade in most cases. One major cause of chlorosis is a deficiency of either iron or manganese. Any rose fungicide will do: myclobutanil (systhane), fungus fighter, roseclear etc. © Copyright 2020 Hearst Communications, Inc. Fungal dieback attacks new leaves first, causing brown spots, Fungal dieback then spreads to older foliage, causing spotting. Generally, rhododendron bush blooms are larger than azaleas, and they bloom later in the spring. Management. In fact, you should avoid any action that spreads moisture from leaf to leaf. Figure 1. symptoms are pale spots on upper leaf surface, with corresponding brown/grey patches underneath: Control with fungicide from late May onwards. Leaf spots caused by various fungi may be seen on rhododendrons and azaleas. Control rhododendron leaf spot, with the advice from our guide. My Encore Azalea Is Turning Brown in the Winter, When to Fertilize Magnolias and Camellias, The Old Farmer's Almanac: Growing Rhododendrons, Gardening Know How: Issues with Rhododendrons: Dealing With Rhododendron Insect Problems And Diseases, Clemson Cooperative Extension: Azalea & Rhododendron Diseases, Cooperative Extension: Rhododendrons with Brown Leaves. However, azalea varieties tolerate both chill and heat better than rhododendron bushes. Lophodermium leaf spot Lophodermium schweinitzii. Blisters form in this area of the lower leaf surface, and they rupture to expose typical yellow to orange-red pustules containing the urediniospores. Description. However, the occurrence and severity of these diseases are influenced by many factors, such as the … A fungal attack causes an outbreak of spots on the leaves. Black fecal spots will be present on the lower sides of stippled leaves. One of the most common fungal issues gardeners see on rhododendrons is referred to as "fungal dieback" or "Phytophthora dieback." However, the fungus is able to infect a broad array of landscape trees and shrubs, mostly as a minor pathogen. Most garden centers carry organic fungicides as well as conventional ones, so you’ll be able to find a product that meets with your gardening philosophy. Leaf spots. I have a rhododendron that has been doing very well for its first year in my back yard. Cause: Actual causes are not known. are Botrytis cinerea, Pestalotia sydowiana, P. rhododendri, Septoria azaleae, Colletotrichum azaleae (Glomerella cingulata), Cercospora handelii, Phyllosticta cunninghamii, and P. rhododendri. Also improve the growing conditions – add a mulch of well-rotted compost, and regularly feed and water. Troubleshoot your rhododendron by taking a small cutting to a local Master Gardener for a diagnosis. Here is some of the information from the PNW Plant Disease Management Handbook about Physiological leaf spot: "Cause Phyllosticta spp., a fungus found on wild as well as cultivated rhododendron. Best way to treat rust on a rhododendron? My rhododendron has leaves that are turning yellow, and some have spots that resemble The lacy wings (very distinctive) are held flat over the back and are transparent with two dark spots present. Management Recommendations. Why Does My Rhododendron Have Yellow Leaves? Do not forget to review your cultural practices in order to prevent the issues from happening again in the future. Small, black fruiting bodies may be visible on the upper or lower surfaces of the spots (Figure 3). Ovulinia petal blight Ovulinia azaleae Ovulitis azaleae [anamorph] Photo by Jennifer Parke, 2003. Rhododendrons perform best in protected sites with partial shade. Heavy infestations can cause leaves to turn brown and drop. Rhododendron Lace Bug, Stephanitis rhododendri. They often infect through wounds. Biology. Fungal Disease Powdery Mildew . The color may be yellow, brown or black and the size may range from ¼" to 1" in diameter depending on the causative agent. Control mainly consists of picking off the galls and disposing of them. Enjoy towering lilies with gigantic, scented blooms. To see if this disease is the problem, you'll need to do a little digging. The azalea leaf miner is a small yellowish caterpillar that mines inside the leaf tissues and later rolls the leaves. How Much Shade Can Rhododendrons Tolerate? Fungal Diseases. Exclusive offer from gardenersworld.com shopping deals, Get £10 off the fantastic 1000W Cooks Professional Stand Mixer, Whip up some of your best bakes yet with this powerful and easy-to-use stand mixer, Subscribe to BBC Gardeners' World Magazine and receive 12 issues for only £39.99 - saving 39%. Severe infections take their toll, denuding plants of their foliage and weakens plants, eventually killing them. The nymphs are black, spiny and smaller than the adults. Treat this disease by pruning off all diseased foliage and spraying the plant with an appropriate copper sulfate fungicide. Although it’s unsightly, leaf spot is only a significant problem on poorly growing or unhealthy plants, which might end up dropping a substantial number of leaves. Common insect pests on rhododendrons and azaleas include: Lace bug: If you notice leaves that look diseased, always look at the under side. Inclusion of a product does not indicate a recommendation or endorsement by the RHS. Insects, Diseases, and Other Plant Problems: Rhododendrons are susceptible to insect and disease problems. If the problem is severe or persistent, consider replacing the rhododendron with a more desirable variety. Infected leaves display dark brown spots which may cover up to half of the leaf surface. A rhododendron (Rhobodendron spp.) Leaves are the best indicators of plant problems. Rhododendron Leaf Spot When Rhododendron occurs, there will be small brown spots on the leaf surface, which will gradually form irregular large spots, and then the leaves will fall off, affecting the flowering of the year and the development of flower buds in the next year. What causes it? Even pests like aphids, bark beetles, spider mites, scales, weevils, and caterpillars can attack this plant. By BBC Gardeners' World Magazine Friday, 15 March, 2019 at 3:00 pm This disease, caused by the fungus Glomerella cingulata, results in rounded spots on the leaves. That why, before you begin to treat a fungal disease, it is a good idea to get a solid overview of your rhodie's cultural needs and growth requirements. While leaf spots can be controlled with a fungicide, root and crown rot can be prevented to some extent by planting rhododendrons in well drained soil. Cause: Actual causes are not known. Recognition and Life Cycle Adults are about 1/8-inch long. Cercospora leaf spot is most troublesome in late summer and fall, or whenever periods of warm temperatures and high humidity or leaf wetness occur. These spots may feel bumpy on the surface due to the presence of fungal structures. They have proven to be valuable garden mainstays in the spring thanks to their spectacular clusters of showy blooms. Phyllosticta leaf blotch is caused by several Phyllosticta species.. Rhododendron-Ramorum Leaf Blight and Shoot Dieback. She currently divides her life between San Francisco and southwestern France. Prevent this disease by watering carefully and avoiding splashing water on the foliage as you irrigate. The plants are able to survive and bloom for many years. Top the root area with several inches of an acidic mulch like pine bark chips or needles, but leave it a few inches from the rhododendron trunk. Brown spot often occurs in rainy season and humid weather. Rhododendrons and azaleas are both in the Rhododendron genus, and it can be hard to tell them apart. is called the queen of the shade garden since these flowering shrubs not only tolerate some shade but crave it. Rhododendron lace bug – Chlorotic spots on upper leaf surface, numerous dark spots of insect excrement on lower leaf surface; small, dark, spiny insects and slightly larger (3-mm), lacy insects on lower leaf surface. Generally, rhododendrons thrive in U.S. Department of Agriculture plant hardiness zones 4 through 9. Another cultivar, 'Virginia Richards,' gets brownish purple spots on both tops and bottoms of leaves. Rhododendrons are lovely plants with enchanting blooms that range from dark red to lavender. It is an upright shrub growing 5 to 8 ft. tall and 5 to 6 ft. wide. These include fungal leaf spots, leaf and flower gall, root rot, oedema, leaf flooding, winter injury, and chlorosis. Repeat the treatment every two weeks until the disease is under control. Keep deadheading. Unfortunately, the lovely plant is prone to disease and pests. Any rose fungicide will do: myclobutanil (systhane), fungus fighter, roseclear etc. Fungal Disease Powdery Mildew . Ask at your local garden center for a fungicide labeled for leaf-spot on Rhododendron and use according to directions. Brown Spots On The Leaves. It can enter through wounds. In the past week or two, the leaves have gone from a dark waxy green, to a mottled, dark … Symptoms First, light-yellow or yellow-green spots on the upper leaf surface and brown to purple spots on the lower surface. Symptoms Spots are dark brown, zonate, and frequently cover half the leaf area. Leaf and flower gall Exobasidium vaccinii = Exobasidium azaleae. … It’s a firm favourite with wildlife – pollinators and birds are drawn to this variety as it offers food and shelter. A second type of Rhododendron issue is brown spots on the leaves. Feed rhododendron only once a year, when buds swell in the spring. Azalea/Rhododendron > Leaves > Spots or blotches on leaves. Fungus Leaf Spot Symptoms: Spots are irregular in size and color (Fig.