Plant Disease Management Handbook

Cause The fungus Elytroderma deformans is a serious needle cast of ponderosa and Jeffrey pine. Hosts also include Coulter, knobcone, lodgepole, and pinyon pine. Spores disperse in spring or early summer, infecting current-season needles. After infecting, the fungus can become systemic, growing through the needle into twigs where it can survive unfavorable conditions. It is most damaging along creeks and lakeshores or in drainages with moist environmental conditions.

By M. Agne

Cause Dothistroma septosporum (sexual: Mycosphaerella pini), a fungus reported in Oregon, Idaho and British Columbia. Dothistroma pini is found mostly in the North Central United States but has been reported from Idaho.

See:

Fir, Douglas and True - Damping-off

Spruce (Picea spp.) - Cylindrocarpon Root Rot

Cause A fungus, Cyclaneusma minus (formerly Naemacyclus minor). Hosts include Scots, Austrian, Virginia, lodgepole, mugo, and ponderosa pine. Spores are produced on both attached and fallen needles. Rain and wind disseminate spores any time of year when temperatures are above freezing. Spores infect needles through stomata any time from April through November.

Cause Phytophthora cinnamomi and Phytophthora tropicalis, fungus-like microorganisms. Other species may be involved as Phytophthora citricola and P. citrophthora have been reported in other regions and occur in the PNW. Poorly drained soil or media or flooding encourages disease development. It survives unfavorable periods in soil or media and infected plant debris.

See:

Rhododendron - Ramorum Leaf Blight and Shoot Dieback

Cause Alternaria alternata, Pestalotia sp., and Phyllosticta sp. have been found by the OSU Plant Clinic. Many leaf-spotting fungi overwinter in diseased leaves and are favored by wet weather. Alternaria gains entry to leaves through wounds.

Symptoms Circular to angular necrotic spots on leaves.

Cause A fungus-like organism, Phytophthora sp., has been found in rotted roots by the OSU Plant Clinic. Poorly drained soil or flooding encourages disease development. The organism survives unfavorable periods in soil and infected plant debris. Under favorable conditions, spores germinate and infect roots. After infection, the microorganism spreads mainly in the inner bark tissues of the root.

Cause The fungus Podosphaera pannosa (formerly Sphaerotheca pannosa) has been reported on photinia in Oregon. This fungus is a common problem on apple and pear. Conidia are readily disseminated by wind. Chasmothecia develop within the external hyphae and form appendages late in their development.