Note: Marianna 2624 as a rootstock is reported to have Armillaria tolerance but has two drawbacks: it suckers profusely and has a shallow root system.
The bark has been peeled back to expose the cambium to show the white mats of the fungal mycelium.
OSU Extension Plant Pathology Slide Collection, 1982.
Cause Cercospora spp. have been found by the OSU Plant Clinic in Oregon, and Ramularia sp. have been reported in Washington. Prevalent in rainy seasons and in overcrowded plantings. Spores are airborne or transported in splashing water. These fungi generally overwinter in leaf debris in and around plants.
Cause The fungus Colletotrichum gloeosporioides (sexual: Glomerella cingulata) has been found a few times by the OSU Plant Clinic. Warm temperatures and stressed or weakened plants favor this fungus. Rain splashes spores onto weakened or damaged tissue. European privet is highly susceptible; Ligustrum amurense (Amur), L. ovalifolium (California), L.
Crown rot so severe that the top is easily pulled away from the roots.
OSU Plant Clinic Image, 2014.
Cause Primula mosaic virus and primula mottle virus have been found in a few primrose species. Both are potyviruses and can be spread by aphids or by mechanical inoculation. Several mottle viruses also have been described on primrose, but their occurrence in the Pacific Northwest is unknown.
Cause Several fungi can cause leaf spots on primrose. Ramularia primulae has been reported in Washington and isolated at the OSU Plant Clinic. Can be serious on cultivars grown in rock gardens. The fungus survives in soil and can be spread by soil movement as well as through airborne conidia. Conidia infect older, mature leaves.
Symptoms Yellow, angular blotches with ash-color centers on older leaves. A chlorotic halo may surround spots.
Note the necrotic lesions with yellow halos on the leaves in the lower part of this picture.
Note the dark, watersoaked spots on the flower petals.
Photo by Walter F. Mahaffee, 1996
Leaves may turn necrotic without showing the gray, fuzzy growth of the fungus.
Photo by Walter F. Mahaffee, 1996
Cause The bacterium Pseudomonas syringae pv. primulae can be a problem in cool, wet springs in the landscape. Has also been found as a greenhouse problem by the OSU Plant Clinic. Although the bacteria survive on the outside of the plant they must get inside and multiply in the space between plant cells (apoplast) to cause disease. These pathogenic bacteria inject several proteins and small-molecule toxins to get past host immune mechanisms.
Leaf spots due to Pseudomonas.
OSU Plant Clinic Collection, 2011.
Leaf blights with dark veins had Pseudomonas marginalis.
