Plant Disease Management Handbook

By M. Putnam

Image related to Ginseng (Panax spp.)-Cylindrocarpon Root Rot (Disappearing Root Rot)

Note rust-colored lesions on the top two roots.

Photo by Melodie Putnam, 1983.

Note the few foliar symptoms associated with a root nearly completely rotted away, with only a hollow shell remaining.

Melodie Putnam, 1983.

Very early stages of the disease shown in cross sections to the left and center, and a severely affected root cross-section at the right. The disease progresses to the interior of the root, eventually completely decaying it.

Melodie Putnam, 1983.

By M. Putnam

Image related to Ginseng (Panax spp.)-Alternaria Leaf and Stem Blight

This picture shows the early stages of leaf and stem infection.

Melodie Putnam, 1982.

This picture shows later stages of leaf infection.

Photo by Melodie Putnam, 1983.

Cause Golovinomyces cichoracearum (formerly Erysiphe cichoracearum) is a fungus that is favored by moderate temperatures (68°F to 82°F) with alternating cool night and warm days and conditions that produce high humidity (80% to 90%) but dry leaves. A closed canopy and poor air circulation also promote disease development. It is a highly specialized pathogen that forms a close association with the host. Conditions that favor the host also favor the pathogen.

Powdery mildew can cover Gerbera leaves completely.

Jay W. Pscheidt, 2019.

See:

Geranium (Pelargonium spp.) - Mosaic (Impatiens Necrotic Spot)

This old large format slide is labeled "White Mesh" which is likely referring to a disease caused by a virus now know as Pelargonium vein clearing virus (or maybe yellow net virus).

OSU Extension Plant Pathology collection, circa 1950s.

Cause Verticillium dahliae, a soilborne fungus that survives in soil indefinitely. It can spread in infested soil, container media, irrigation water, or in symptomless infected cuttings. The fungus grows into the xylem where it colonizes the plant through mycelial growth and conidial production. Fluid movement in the xylem passively transports the conidia. Once in the xylem, this fungus partially blocks water movement and produces toxins that result in wilt symptoms.

The plant on the left is wilting due to Verticillium wilt, while plant on right has leaf spot and stem rot.

Photo by Jay W. Pscheidt, 1992.

Wedge-shape areas on affected leaves turn yellow; then the entire leaf turns yellow and wilts.

OSU Extension Plant Pathology collection, circa 1950s, color glass slide plate.

The stake in the pot reads sunburn, however, Verticillium wilt was found to be the cause of the wilting plants.

OSU Extension Plant Pathology collection, circa 1950s, from color glass slide plate.

See:

Greenhouse Plants, Ornamental - Shoot Proliferation and Leafy Gall

Multiple buds (areal gall) due to the bacteria Rhodococcus fascians.

OSU Plant Clinic image, 2010.

Cause Puccinia pelargonii-zonalis, an autoecious (can complete their life cycle on this one host) rust fungus that survives on living plants and plant debris. Movement of infected cuttings can also spread this fungus. Infections occur readily if leaves are wet 5 to 6 hours at 55°F to 75°F. Urediniospores may be infective at least 3 months. Considerable genetic variation exists from highly susceptible to immune cultivars.