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    • Easy Roses
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    • Portland's Rose Test Garden
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    • Rose Sawfly
    • Rose Bloom Balling
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Rhododendron Leaf Spot

Amanda's Garden Consulting Company

A Common Rhododendron Leaf Spot disease

Rhododendron Cercospora leaf spot,Cercospora handelii,plant diseases,brown leaves on rhododendrons,The Garden Website.com,Amanda's Garden Consulting,Amanda Jarrett,the garden website
Cercospora leaf spot infect the lower leaves first.
Rhododendron Cercospora leaf spot,Cercospora handelii,plant diseases,brown leaves on rhododendrons,The Garden Website.com,Amanda's Garden Consulting,Amanda Jarrett,the garden website
Drought contributes to this disease.
Rhododendron Cercospora leaf spot,Cercospora handelii,plant diseases,brown leaves on rhododendrons,The Garden Website.com,Amanda's Garden Consulting,Amanda Jarrett,the garden website
This rhodo is obviously suffering from lack of water, too much heat, too much sun and no mulch.
​It's not uncommon to see dark blotches on the leaves of rhododendrons and azaleas. This unsightly fungus is referred to as Cercospora leaf spot (Cercospora handelii). Severe infections take their toll, denuding plants of their foliage and weakens plants, eventually killing them.

Lower leaves show the first signs with irregular brown spots that develop a lighter tan eye in the center. Some spots show a yellow halo while others bear tiny dark pimples inside the larger spots. Those wee dimples are the vectors that spread the infection. 
 
A contributing factor that initiates and worsens this disease is drought. Rhododendrons have shallow roots so they dry out quickly, especially when it’s hot and dry. Accumulated drought stress over the years promotes this disease and eventually the plant will slowly decline. Water in the summer and any other time when there’s a lack of rainfall. When you do water, avoid wetting the foliage as this spreads the disease. Instead, thoroughly soak the ground past the canopy. 
 
A thick 3 inch layer of mulch is essential for rhodo health as it protects the soil from evaporation and insulates the soil from temperature extremes.
 
Avoid crowding rhodos as stagnant air also contributes to this disease. Remove neighbouring shrubs if they are just too close or thin out their stems. When planting rhododendrons, know their mature width and provide them with proper spacing to encourage good air circulation.
 
Remove infected stems that have died back to just above a set of healthy green leaves where there is no sign of infection. Prune out entire stems if they are fully infected to their base.  Don’t leave stubs: cut just above a leaf, stem, or right at a stems base. After each cut disinfect your pruners with rubbing alcohol – there’s no need to dilute or combine one part Pinesol or Lysol to 3 parts water. Place the disinfectant in a spray bottle as it makes it easier to treat the tools as you cut.  Rake up infected leaves when they eventually fall off and discard so they don’t reinfect.
 
With proper care, the infection should lessen. Don’t expect the damaged leaves to repair themselves and turn green. Once they are infected leaf tissues will not revert back, however new leaves should be healthy. 

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  • Home
  • About, Services, Contact
  • Amanda's Garden Blog
  • Ask Amanda
  • Roses
    • Types of Roses
    • Easy Roses
    • Climbing Roses
    • Portland's Rose Test Garden
    • Rose Insects & Diseases
    • Pruning Roses
    • Rose Sawfly
    • Rose Bloom Balling
  • Pruning Basics 101
    • Pruning Tools
    • Winter Pruning
    • Pruning Grapes
    • Pruning Clematis
    • Prune Your Own Garden Registration
  • Lawn Basics
    • Lawn Reno, Seed & Sod
    • Lawn Maintenance Schedule
    • Spring Lawn Care
    • Moss in Lawns
    • Lawn Grub Control
  • Mulching
    • Living Mulches - Groundcovers
  • Propagation
    • Growing Seeds Outdoors
    • Growing Seeds Indoors
    • Taking Cuttings
    • Saving Tomato Seeds
    • Seed & Plant Catalogues
  • How to Garden Topics
    • Planting Know-How
    • Soil Building
    • Drought Gardening
    • Sheet Mulching, Lasagna Gardening
    • Cover Crops
    • Composting
    • Compost Tea
    • Planting Spring Flowering Bulbs
    • Houseplant Winter Care
  • Growing Food
    • Spring Veggie Gardening
    • Crop Rotation, Succession & Companion Planting
    • Harvesting
    • Growing Potatoes
    • Winter Veggie Gardening
    • Taming Tomatoes
    • Speeding up Tomato Harvest
    • Tomato Tips
    • Tomato Troubles
  • Plant Pests 1
    • Plant Pests Part 2 - Controlling Insects
    • Viburnum Leaf Beetle
    • Dormant Oil/Lime Sulfur
    • Japanese Beetles
    • Peony Blotch/Measles
    • Slugs & Snails
    • Horsetail, the Weed
    • June Beetle
    • Powdery Mildew
    • Soil Solarization
    • Rhododendron Leaf Spot
    • Plant Rusts
  • Container Growing
    • Choosing a Container
  • Monthly Flower Arrangements
  • Feeding Plants 101
    • Fertilizers & Ratios
    • Nutritional Deficiencies & Toxicities
    • Organic Plant Food
  • Plant of the Month
    • Colourful Fall Plants
    • Aubretia, Rock Cress
    • Astilbes
    • Aucuba, Japanese Spotted Laurel
    • Autumn Crocus
    • Beautyberry, Callicarpa
    • Black-eyed Susans
    • Bleeding Heart, Lamprocapnos spectabilis
    • Dahlias
    • Devil's Walking Stick, Aralia spinosa
    • Dwarf Burning Bush
    • Fall Asters
    • Flowering Currants
    • Flowering Quince
    • Garden Phlox
    • Harry Lauder's Walking Stick
    • Heathers
    • Hellebores, Lenten roses
    • Himalayan Sweet Box
    • Jack-in-the-pulpit, cobra lily
    • Laurustinus viburnum, Viburnum tinus
    • Lavenders
    • Lily-of-the-Valley Shrub, Pieris japonica
    • Mediterranean Spurge
    • Montana Clematis
    • Mountain Ash
    • Oriental Poppies
    • Paperbark Maple
    • Pink Dawn Bodnant Viburnum
    • Poinsettia
    • Ornamental Kale
    • Peruvian Lily, Alstroemeria
    • Persian Silk Tree
    • Japanese Anemones
    • Japanese Forest Grass
    • Japanese Maples
    • Japanese Skimmia
    • Rose of Sharon
    • Winter Camellia, C. sasanqua
    • Strawberry Tree, Pacific Madrone
    • Stewartia
    • Torch Lily, Kniphofia uvaria
    • Tree Peonies
    • Tuberous Begonias
    • Virginia Creeper
    • Weigela
    • Winterhazel, Corylopsis
    • Wintergreen, Gaultheria procumbens
    • Witch Hazel
  • Garden Tour Blogs
  • Website Index