Plant Disease Management Handbook

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.

See:

Greenhouse Plants, Ornamental - Impatiens Necrotic Spot

See:

Greenhouse Plants, Ornamental - Pythium Seed Rot, Damping-off, and Root Rot

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.

See:

Greenhouse Plants, Ornamental - Gray Mold

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.

By P. B. Hamm and C. M. Ocamb

Cause A phytoplasma transmitted by several species of leafhopper and within potato seed pieces.

By P. B. Hamm and C. M. Ocamb