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  • Home
  • About, Services, Contact
  • 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
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    • Living Mulches - Groundcovers
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    • Taking Cuttings
    • Seed & Plant Catalogues
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    • Watering Tips & Techniques
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    • 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
    • Crop Rotation, Succession & Companion Planting
    • Harvesting
    • Growing Potatoes
    • Winter Veggie Gardening
    • Taming Tomatoes
    • Speeding up Tomato Harvest
    • Tomato Tips
    • Saving Tomato Seeds
    • Tomato Troubles
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    • Plant Pests Part 2 - Controlling Insects
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Black Knot

Amanda's Garden Consulting

An Ugly disease of the Rose Family

Picture
Picture
Picture
​Black tar-like, knobby swellings on the stems of plum and cherry trees are caused by a fungal disease called black knot (Apiosporina morbosa). This very prevalent disease affects members of the rose (Rosacea) family especially plums in the Pacific Northwest.
Causes: Pruning increases the chance of infection as the wounds are open to airborne spores. Weakened trees are vulnerable so provide good drainage and water during periods of drought. Stagnant air, high humidity, mild wet conditions also encourage this disease.
What to do: In winter, when plants are dormant, remove the growths by cutting the stems back to healthy wood at least 6 to 8 inches beyond the black knot. It’s imperative to disinfect pruning tools after each cut with 70% rubbing alcohol.
Destroy all infected parts from the plant and from the ground immediately. It’s recommended to burn all contaminated plant parts where possible. Severely infected trees should be removed. Avoid replacement plants that are members of the rose family: apples, apricots, cherry, nectarines, peaches, almonds, pears, raspberries, strawberries and roses.
Treatment: Spray with dormant oil/lime sulfur while plants are still dormant in late winter. Treat all members of the rose family in your garden with dormant oil to reduce the spread of the spores. Also apply it to the soil around and under the plants. On infected trees, apply neem oil when buds open. Repeat every 7 days.

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Copyright © 2017
  • Home
  • About, Services, Contact
  • 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
    • Taking Cuttings
    • Seed & Plant Catalogues
  • How to Garden Topics
    • Fall Garden Chores
    • Planting Know-How
    • Soil Building
    • 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
    • Crop Rotation, Succession & Companion Planting
    • Harvesting
    • Growing Potatoes
    • Winter Veggie Gardening
    • Taming Tomatoes
    • Speeding up Tomato Harvest
    • Tomato Tips
    • Saving Tomato Seeds
    • Tomato Troubles
  • Plant Pests 1
    • Plant Pests Part 2 - Controlling Insects
    • Garden Inspections
    • Helping Pollinators
    • 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
  • Plant of the Month
    • Spring Flowering Bulbs
    • Colourful Fall Plants
    • Abelia
    • American Sweetgum
    • Ash (Fraxinus) Trees
    • Astilbes
    • Aubretia, Rock Cress
    • Aucuba, Japanese Spotted Laurel
    • Autumn Crocus
    • Bear's Breeches
    • Beautyberry, Callicarpa
    • Black-eyed Susans
    • Bleeding Heart, Lamprocapnos spectabilis
    • Calla Lilies
    • Dahlias
    • Daylily
    • Delphiniums
    • Devil's Walking Stick, Aralia spinosa
    • Dwarf Alberta Spruce
    • Dwarf Burning Bush
    • Fall Asters
    • Flowering Currants
    • Flowering Quince
    • Fritillaria
    • Garden Peonies
    • Garden Phlox
    • Ginkgo biloba
    • Grape-hyacinths
    • Handkerchief or Dove Tree
    • Harry Lauder's Walking Stick
    • Heathers
    • Hellebores, Lenten roses
    • Himalayan Sweet Box
    • Jack-in-the-pulpit, Cobra Lily
    • Japanese Anemones
    • Japanese Forest Grass
    • Japanese Maples
    • Japanese Skimmia
    • Japanese Spurge
    • Laurustinus viburnum
    • Lavenders
    • Lily-of-the-Valley Shrub, Pieris japonica
    • Mediterranean Spurge
    • Mexican Mock Orange
    • Montana Clematis
    • Mountain Ash
    • Oriental Poppies
    • Oriental Lilies
    • Paperbark Maple
    • Pink Dawn Bodnant Viburnum
    • Poinsettias
    • Oregon Grape Holly
    • Ornamental Kale
    • Peruvian Lily, Alstroemeria
    • Phalaenopsis, Moth Orchids
    • Persian Silk Tree
    • Portuguese Laurel
    • Rose of Sharon
    • Sneezeweed, Helenium
    • Snowberry
    • Snowdrops
    • Star Magnolia
    • Strawberry Tree, Pacific Madrone
    • Stewartia
    • Torch Lily, Kniphofia uvaria
    • Tree Peonies
    • Tuberous Begonias
    • Virginia Creeper
    • Weigela
    • Winterhazel, Corylopsis
    • Winter Camellia, C. sasanqua
    • Wintergreen, Gaultheria procumbens
    • Witch Hazel
    • Wood Anemones
    • Yews
  • Garden Tour Blogs
  • Monthly Flower Arrangements
  • Website Index
  • Subscribe
  • Need Help?