Common Diseases: Armillaria root rot categories: Common Diseases Common Problems last review date: 2026-03-27 11:02 White fungal mat of Armillaria root rot infecting trunk Photo by: C.R. Foss Biology Armillaria root rot is a fungal disease transmitted between plants by root contact. It is also spread by rhizomorphs. Armillaria is often found in newly cleared […]
Common Diseases: Botrytis blight (Gray mold) categories: Common Diseases Common Problems last review date: 2026-03-27 11:25 Botrytis sporulating on alder seedling Photo by: R.S. Byther Biology Water-soaked lesions appear and quickly become covered with a gray-brown mass of fungus and spores. Infection often occurs at injury sites. After initial infection, gray mold can spread into […]
Common Diseases: Cankers categories: Common Diseases Common Problems last review date: 2026-03-27 11:47 Black canker and peeling bark on madrone Photo by: R.S. Byther Biology Cankers are localized wounds or necrotic lesions, often sunken beneath the surface of the stem of a woody plant. Cankers can be caused by fungi, bacteria, or winter damage. Determining […]
Common Diseases: Crown gall categories: Common Diseases Common Problems last review date: 2026-03-28 09:30 Crown gall on roots Photo by: R.S. Byther Biology Crown gall is found on many ornamental plants, fruit trees, and caneberries. It is most commonly found on cherry, apple, peach, pear, plum, euonymus, rose, raspberry, and blackberry. Crown gall is caused […]
Common Diseases: Damping-off categories: Common Diseases Common Problems last review date: 2026-03-28 09:36 Damping-off of cucumber seedlings Photo by: R.S. Byther Biology Damping-off is caused by fungi that remain in the soil for long periods of time. Infected seeds decay without germinating. Seedlings may be infected and fail to emerge from the soil. Emerging seedlings […]
Common Diseases: Dead roots categories: Common Diseases Common Problems last review date: 2026-03-28 09:40 Dead roots and healthy roots in nursery plants Photo by: R.S. Byther Biology A plant showing symptoms of off-color, stunting, wilting, and death may be suffering from a root problem. Dead and discolored roots result from factors such as fungal root […]
Common Diseases: Dodder categories: Common Diseases Common Problems last review date: 2026-03-28 09:44 Dodder entwining fuchsia stem Photo by: R.S. Byther Biology The parasitic flowering plant dodder (Cuscuta spp.) attacks living plants by entwining them in its slender stems. Dodder is characterized by its tangle of leafless, yellow to orange threadlike stems. The stems encircle […]
Common Diseases: Downy mildew categories: Common Diseases Common Problems last review date: 2026-03-28 09:49 Lettuce leaf infected with downy mildew fungus Photo by: R.S. Byther Biology Downy mildew is a fungal disease of tender green tissues including leaves and shoots. Infected leaves show areas of slightly chlorotic to purplish red to dark brown discoloration on […]
Common Diseases: Dwarf mistletoe categories: Common Diseases Common Problems last review date: 2026-03-28 09:55 Dwarf mistletoe in conifer Photo by: R.S. Byther Biology Dwarf mistletoe is a parasitic plant that grows on the branches or occasionally on the trunk of a host tree, such as Douglas-fir, true firs, larch, pine, and junipers. It is yellow-green, […]
Common Diseases: Galls categories: Common Diseases Common Problems last review date: 2026-03-28 10:04 Camellia leaf gall Photo by: R.S. Byther Biology A gall is a swelling or overgrowth produced on a plant as a result of infection by certain pathogens or physiological stress. Galls may be found on leaves, stems, trunks or roots. They can […]
Common Diseases: Leaf spots and blights categories: Common Diseases Common Problems last review date: 2026-03-28 10:14 Madrone leaf spots Photo by: R.S. Byther Biology Leaf spots are localized lesions on host leaves consisting of dead and collapsed cells. Blights are general and extremely rapid browning of leaves, branches, twigs and floral organs resulting in their […]
Common Diseases: Nectria cankers categories: Common Diseases Common Problems last review date: 2026-03-28 10:26 Nectria canker fruiting bodies on branch Photo by: R.S. Byther Biology Nectria canker is a fungal disease affecting the twigs and branches of a wide variety of woody plants, including pear, maple, and apple (where it is called European canker). The […]
Common Diseases: Phytophthora root rot categories: Common Diseases Common Problems last review date: 2026-04-10 07:48 Phytophthora collar rot on madrone Photo by: R.S. Byther Biology Phytophthora root rot is caused by a fungal infection of the roots resulting in root death and overall plant decline. Infected plants may appear off-colored and stunted and may show […]
Common Diseases: Powdery mildew categories: Common Diseases Common Problems last review date: 2026-04-10 09:42 Powdery mildew infections on begonia leaves Photo by: R.S. Byther Biology White powdery growth on the surface of leaves and sometimes stems is characteristic of this easily diagnosed fungal disease. Young leaves and shoots may be stunted and distorted. Severe infection […]
Common Diseases: Pseudomonas bacterial canker categories: Common Diseases Common Problems last review date: 2026-04-10 10:12 Bacterial canker on tree trunk Photo by: R.S. Byther Biology Pseudomonas bacteria remain alive in old canker, in buds, and on plant surfaces of infected trees and on many kinds of plants, including weeds and grasses. Bacteria may be systemic […]
Common Diseases: Root rots categories: Common Diseases Common Problems last review date: 2026-04-10 10:32 Pansies dying from Rhizoctonia root rot Photo by: R.S. Byther Biology Many different fungi that infect root tissues cause similar symptoms: off-color foliage, stunting, wilting, and death. Laboratory isolation and microscopic examination are needed for specific diagnosis. Cylindrocladium, Fusarium, Rhizoctonia, and […]
Common Diseases: Rusts categories: Common Diseases Common Problems last review date: 2026-04-10 10:50 Hypericum rust fruiting bodies on underside of leaves Photo by: R.S. Byther Biology In general, rust diseases are easily diagnosed because of the abundant production of colorful powdery spores formed in tiny pustules. Microscopic examination may be necessary to identify specific rust […]
Common Diseases: Sclerotinia white mold categories: Common Diseases Common Problems last review date: 2026-04-13 07:05 Rotted petunia stem with sclerotia inside Photo by: R.S. Byther Biology Sclerotinia white mold is a fungal fungal affecting many herbaceous flowers and vegetable crops. A stem rot and white fungal growth appear at the base of infected plants. Infected […]
Common Diseases: Sudden oak death categories: Common Diseases Common Problems last review date: 2026-04-13 07:28 P. ramorum shoot blight symptoms on rhododendron Photo by: M. Elliott Biology Sudden Oak Death (SOD) is the common name for a disease caused by Phytophthora ramorum, a previously unknown and exotic plant pathogen. In California, it has killed hundreds […]
Common Diseases: Tubercularia canker categories: Common Diseases Common Problems last review date: 2026-04-13 09:35 Tubercularia canker fruiting bodies Photo by: R.S. Byther Biology Tubercularia canker is a fungal disease typically affecting twigs and branches, and occasionally trunks, of several species including elm, Russian olive, and Japanese maple. This disease is easily diagnosed by observing the […]