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    • Easy Roses
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    • Hummingbirds in Winter
    • Winterize Your Garden
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    • Fall Veggie Garden Clean-up
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    • Winter Veggie Gardening
    • Taming Tomatoes
    • Speeding up Tomato Harvest
    • Tomato Tips
    • Saving Tomato Seeds
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    • Tomato Troubles
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    • Plant Pests Part 2 - Controlling Insects
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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 Alternatives
    • Lawn Grub Control
  • Mulch & Mulching
    • Living Mulches - Groundcovers
  • Propagation
    • Growing Seeds Outdoors
    • Growing Seeds Indoors
    • Hardening Off Plants
    • Taking Cuttings
    • Seed & Plant Catalogues
  • How to Garden Topics
    • Fall Garden Chores
    • Planting Know-How
    • Soil Building
    • Soil pH
    • Watering Tips & Techniques
    • Drought Gardening
    • Sheet Mulching, Lasagna Gardening
    • Cover Crops
    • Composting
    • Compost Tea
    • Houseplant Winter Care
    • Hummingbirds in Winter
    • Winterize Your Garden
    • Ponds in Winter
  • Growing Food
    • Spring Veggie Gardening
    • Fall Veggie Garden Clean-up
    • Crop Rotation, Succession & Companion Planting
    • Harvesting
    • Growing Potatoes
    • Winter Veggie Gardening
    • Taming Tomatoes
    • Speeding up Tomato Harvest
    • Tomato Tips
    • Saving Tomato Seeds
    • Raspberries
    • Tomato Troubles
  • Plant Pests 1
    • Plant Pests Part 2 - Controlling Insects
    • Garden Inspections
    • Cloches
    • Helping Pollinators
    • Critters in the Garden
    • Black Sooty Mould
    • Brown Marmorated Stink Bug
    • Dogwood Anthracnose
    • 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
    • Black Knot
  • Container Growing
    • Choosing a Container
  • Feeding Plants 101
    • Fertilizers & Ratios
    • Nutritional Deficiencies & Toxicities
    • Organic Plant Food
  • Monthly Flower Arrangements
    • Christmas Wreaths
  • Plant of the Month
    • Spring Flowering Bulbs
    • Colourful Fall Plants
    • Abelia
    • American Sweetgum
    • Ash (Fraxinus) Trees
    • Astilbes
    • Azaleas, Deciduous
    • Aubretia, Rock Cress
    • Aucuba, Japanese Spotted Laurel
    • Autumn Crocus
    • Bear's Breeches
    • Beautyberry, Callicarpa
    • Black-eyed Susans
    • Bleeding Heart, Lamprocapnos spectabilis
    • Calla Lilies
    • Catalpas
    • Chinese Windmill Palm
    • Columbine
    • Chrysanthemums
    • Crocuses
    • Dahlias
    • Dawn Redwood
    • Daylily
    • Delphiniums
    • Devil's Walking Stick, Aralia spinosa
    • Doghobble, Leucothoe
    • Dwarf Alberta Spruce
    • Dwarf Burning Bush
    • Elderberries, Sambucus
    • Evergreen Clematis
    • English Daisies
    • Fawn Lilies, Erythroniums
    • Fall Asters
    • Flowering Currants
    • Flowering Quince
    • Fritillaria
    • Garden Peonies
    • Garden Phlox
    • Ginkgo biloba
    • Grape-hyacinths
    • Handkerchief or Dove Tree
    • Hardy Fuchsia
    • Harry Lauder's Walking Stick
    • Heathers
    • Heavenly Bamboo
    • Hellebores, Lenten roses
    • Himalayan Sweet Box
    • Hydrangeas, Mophead & Lacecap
    • Jack-in-the-pulpit, Cobra Lily
    • Japanese Anemones
    • Japanese Forest Grass
    • Japanese Maples
    • Japanese Skimmia
    • Japanese Snowbell
    • Japanese Spirea
    • Japanese Spurge
    • Kale, ornamental
    • Katsura Trees
    • Kousa Dogwood
    • Laurustinus viburnum
    • Lavenders
    • Lily-of-the-Valley Shrub, Pieris japonica
    • Mediterranean Spurge
    • Mexican Mock Orange
    • Montana Clematis
    • Mountain Ash
    • Oregon Grape Holly
    • Oriental Poppies
    • Oriental Lilies
    • Paperbark Maple
    • Pearl Bush
    • Persian Ironwood
    • Peruvian Lily, Alstroemeria
    • Phalaenopsis, Moth Orchids
    • Photinia, Fraser
    • Poinsettias
    • Primroses
    • Persian Silk Tree
    • Portuguese Laurel
    • Rose of Sharon
    • Saucer Magnolia
    • Shrubby Cinquefoil
    • Sneezeweed, Helenium
    • Snowberry
    • Snowdrops
    • Solomon's Seal
    • Star Magnolia
    • Strawberry Tree, Pacific Madrone
    • Stewartia
    • Torch Lily, Kniphofia uvaria
    • Tree Peonies
    • Tuberous Begonias
    • Variegated Wintercreeper
    • Viburnum, Pink Dawn Bodnant
    • Virginia Creeper
    • Weigela
    • Winterhazel, Corylopsis
    • Winter Camellia, C. sasanqua
    • Winter Daphne
    • Wintergreen, Gaultheria procumbens
    • Witch Hazel
    • Wood Anemones
    • Yews
  • Garden Tours & Such
    • NW Horticultural Society July Garden Tour 2024
    • Burnaby in Blooms
    • Burnaby's Century Gardens
    • South Delta Garden Club Tour 2023
    • Garden Club Events
  • Website Index
  • May Garden Chores 2025
  • Subscribe
  • Need Help?
    • Gift Cards