Antracnose

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

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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