Plant Disease Management Handbook

Cause Verticillium dahliae or V. longisporum, fungi that can survive as resistant mycelium in soil for many months to years.

Symptoms Unilateral wilting and death of aboveground plant portions. Sometimes, interveinal yellowing of lower leaves and plant stunting precede or accompany wilt. The root's vascular tissue becomes brown or black, reducing the grade of the product when harvested.

Cause An Ascochyta sp. has been reported from Washington, and a Ramularia sp. has been found in Oregon.

Symptoms Necrotic spots on leaves.

Cultural control None have been investigated in the Pacific Northwest.

Chemical control

Cause The fungus Erysiphe flexuosa has been reported in Washington and Idaho and observed in Oregon. Powdery mildews are highly specialized and form a close association with the host such that this fungus only infects species of Aesculus. The disease is favored by shade, warm conditions (60°F to 80°F) and cool nights. Overcrowding of plants is also favorable for disease development.

See:

Maple (Acer spp.) - Leaf Scorch

Cause Some trees will show symptoms of this nonparasitic problem year after year, regardless of the weather. Suggested causes have included high slat injury and heat but are not consistently associated with symptoms.

Cause The fungus Phyllosticta sphaeropsoidea (sexual Guignardia aesculi) overwinters in fallen leaves. Ascospores are produced in the spring and infect new leaves from budbreak through shoot elongation. The disease is favored by wet weather in spring. Although not formally reported from the Pacific Northwest, it has been detected on a few plant samples at the OSU Plant Clinic. It is an economic problem for nursery tree production.

By K. Eastwell and C. M. Ocamb

By K. Eastwell, D. H. Gent, and C. M. Ocamb

By C. M. Ocamb and D. H. Gent

Cause A fungus, Phomopsis tuberivora (syn. Phacidiopycnis tuberivora), that can survive in plant debris, on hop plants, or in soil as sclerotia. The fungus needs injured hop tissue for infection to occur. This disease was first reported in Australia in 1981 and recently confirmed in a hop yard in the Pacific Northwest in 2013.

By C. M. Ocamb and D. H. Gent