Plant Disease Management Handbook

Cause Unfavorable growing conditions, especially during heading. Frost, poor soil, and hot winds during flowering are common causes. Severe barley yellow dwarf virus infection also causes blast.

Symptoms Florets turn white, and parts or all of the kernels fail to develop. Panicle tips or bases are most often affected.

Cultural control Plant varieties recommended for the area.

Cause A bacterium, Pseudomonas syringae pv. coronafaciens, carried in seed or overwintered in old oat straw. Moist weather favors the disease. Resistant varieties are available elsewhere, but resistance of varieties common in the Pacific Northwest is unknown.

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Tanoak (Notholithocarpus densiflorus) - Sudden Oak Death

Cause Erysiphe calocladophora, Erysiphe penicillata and Phyllactinia alnicola, (formerly Microsphaera sp.), fungi that have been reported from Oregon and Washington. The conidia are readily wind disseminated. Chasmothecia develop within the external hyphae and form appendages late in their development. This fungus is favored by conditions that produce high humidity but dry leaves.

Cause Phoradendron villosum, a parasitic plant that affects white oak (Quercus garryana), black oak (Q. kelloggii), red oak (Q. rubra), scarlet oak (Q. coccinea), and pin oak (Q. palustris) and occasionally is on alder, aspen, birch, locust, manzanita, buckeye, sycamore, walnut and willow. Generally found in western Oregon.

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Maple (Acer spp.) - Leaf Scorch

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Peach (Prunus persica) - Leaf Curl

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Peach (Prunus persica) - Cytospora Canker

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Plants Resistant or Susceptible to Armillaria Root Rot

Cause Apiognomonia errabunda, a fungus widespread and common in western Washington, Oregon, and coastal British Columbia and found occasionally in eastern Washington. It is of little significance most years but can be serious in prolonged moist weather in spring and summer. Large trees can sustain severe disease without permanent damage. The disease can be a problem in production nurseries growing susceptible species.