Plant Disease Management Handbook

Cause Honeysuckle yellow vein mosaic virus (HYVMV) and honeysuckle yellow vein virus (HYVV) have been isolated from Japanese honeysuckle showing yellow vein symptoms. Both viruses have a monopartite DNA genome, and are transmitted in a persistent manner by whiteflies. These viruses have been reported infecting tomato in Korea and Japan. Japanese honeysuckle cultivars such as Gold Net and Yellow Net show yellow vein symptoms and are assumed infected with one or both viruses.

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Rhododendron - Phytophthora Root Rot

Notes Phytophthora has been found by the OSU Plant Clinic a few times in both nursery and landscape situations. There is little information on this problem and it is suggested to see other Phytophthora root rot diseases for possible management tactics.

Cause The fungus Erysiphe caprifoliacearum var. flexuosa (formerly Microsphaera caprifoliacearum var. flexuosa) has been reported from Idaho and Washington. The disease has been diagnosed twice at the OSU Plant Clinic. This fungus is favored by conditions that produce high humidity but dry leaves. It is a highly specialized pathogen that forms a close association with the host.

Cause Erysiphe ravenelii (formerly Microsphaera ravenelii), a fungus endemic to North America. Succulent new growth late in the season is particularly susceptible. Conidia are released in response to abrupt decreases in relative humidity. Wind blows conidia to healthy foliage where they start new mildew colonies. Too much water, such as flowing water or rain, destroys spores by causing them to burst. The fungus does not grow in a leaf but rather across the surface.

Cause Several fungi have been associated with a canker problem in the Pacific Northwest. Fusarium spp. and Phomopsis sp. have been associated with canker problems in nurseries. Nectria cinnabarina has been detected over the years from samples sent to the OSU Plant Clinic.

Cause Puccinia malvacearum, a fungus that overwinters in basal leaves, which may live through the winter, or on plant debris. Teliospores in association with plant debris remain viable at least 4 months in soil. Fungal mycelium may overwinter in young shoots of the host. Pycnia, aecia, and uredinia are not known for this fungus. Many other plants in the malvaceae can be infected.

Cause Fumago vagans, a nonpathogenic fungus that grows on the honeydew (excrement) of scale insects has been reported from the PNW. Several other fungi have been reported from southern states including Capnodium elongatum, Echidnodella angustiformis and E. prinoides. Sooty mold typically causes little damage to plants aside from an aesthetic problem.

Cause Sclerophoma sp., a fungus never identified to species. It does not sporulate readily in plant tissue under field or laboratory conditions but does in culture plates after exposure to ultraviolet light. Symptoms developed 3 months after artificial inoculation. Healthy plants placed in the field in June developed scab by September.

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Holly (Ilex spp.) - Boron Deficiency

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Rhododendron - Phytophthora Root Rot

Note Out of dozens of samples there has only been one diagnosed with Phytophthora root rot by the OSU Plant Clinic.