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Anthracnose

FAST FACTS - ANTHRACNOSE
by Nanette Londeree, Master Rosarian

SIGNS

  • Tiny portions of the fungus (acervuli) may appear scattered on white center of leaf spots

    SYMPTOMS

  • Scattered or grouped spots on leaves that sometimes coalesce; usually circular
  • Young spots that are red, dark brown to purple on upper leaf surface
  • Center of spots turn white with a dark red margin as it ages
  • Center of spots on leaves have thin, papery membrane or no center at all, producing a “shot hole” appearance
  • Spots with ashen centers on stems and rose hips

    Anthracnose CAUSE

  • Spot anthracnose fungi, Sphaceloma rosarum
  • Also known as Purple Spotting or Shot-Hole fungus

    OPTIMAL CONDITIONS / HABITAT

  • Attacks wild roses, climbers and ramblers most often, though hybrid tea and bush-type roses also get the disease
  • Cool, moist spring and fall conditions
  • Mild temperatures and available water on surface of leaves and stems
  • Spread by air currents, splashing water from rain, sprinklers onto newly expanding leaves and stems

    TREATMENT

    Prevention:

  • Space plants to maximize sunlight and air circulation to help dry foliage
  • Good general garden sanitation as the fungus over-winters in old lesions on leaves and stems
  • A dormant spray with lime sulfur in late winter can be an additional preventive step for this disease

    Elimination:

  • Prune away affected parts, preferably in fall and winter and dispose of them in the trash, don’t add them to the compost pile
  • If you spray your roses, the materials you use for black spot are usually effective for anthracnose; products such as Banner Maxx, Clearys 3336F, Compass, Immunox, or Rose Defense are all good choices for control

    GOOD GUY / BAD GUY?

  • A pretty bad guy – it can cause leaf drop that weakens the plant; in extreme cases, it can result if complete defoliation


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    Last Modified: 08/06/2013