Plant Disease Management Handbook

By C. M. Ocamb

Cause It is caused by a phytoplasma that is spread by leafhoppers, and the specific phytoplasma involved depends on the region. The dominate type of phytoplasma detected in hemp, including in Oregon, is Beet Leafhopper-transmitted Virescence Agent (BLTVA - group VI), but other types may be present. This disease can affect potato and tomato and also occurs on celery, radish, and Chinese cabbage. The phytoplasma overwinters on weeds or other crop hosts. The disease follows leafhopper migration.

Hemp leaves showing leaf cupping, curling, and deformation associated with phytoplasma infection.

Photo by C.M. Ocamb, Oregon State University, 2022

Hemp leaves showing a yellow coloration associated with infection by phytoplasma.

Photo by C.M. Ocamb, Oregon State University, 2022.

A hemp plant exhibiting an over-proliferation of meristem points on the tip of a branch on the upper right (witches’ broom).

Photo by C.M. Ocamb, Oregon State University, 2022.

By C. M. Ocamb

A detached hemp branch showing a stem lesion due to a Sclerotinia infection.

Photo by Hannah Rivedal, 2019.

Flower buds on a hemp plant that are infected by Sclerotinia sclerotiorum. Note the white-colored mycelium that is characteristic of this fungus.

Photo by Cynthia M. Ocamb, 2020.

Flower bud on a hemp plant that is infected by Sclerotinia sclerotiorum. The white-colored mycelium that is characteristic of this fungus is evident along with developing (white-colored) and maturing (black-colored) small, dense fungal masses known as sclerotia, which function as survival structures.

Photo by Cynthia M. Ocamb, 2020.

By K. Frost and C. M. Ocamb

Hemp shoot showing early symptoms due to infection by Hop latent viroid.

Photo by K. Frost, Oregon State University.

Hemp shoot showing later stage symptoms due to infection by Hop latent viroid.

Photo by K. Frost, Oregon State University.

Detached hemp leaves that are positive for Hop latent viroid.

Photo by C.M. Ocamb, Oregon State University, 2021.

By K. Frost and C. M. Ocamb

A hemp plant exhibiting symptoms of infection of Beet curly top virus in August. Note that some shoot portions appear unaffected while others show twisting and curling of leaflets characteristic of this disease.

Photo by C. M. Ocamb, Oregon State University, 2021.

Closer view of a hemp shoot exhibiting leaf curling and twisting due to Beet curly top virus.

Photo by C. M. Ocamb, Oregon State University, 2021.

Detached hemp leaves that exhibit twisting and deformities due to Beet curly top virus.

Photo by C.M. Ocamb, Oregon State University, 2021.

Detached hemp buds that exhibit twisting and deformities of leaf tissues due to Beet curly top virus.

Photo by C.M. Ocamb, Oregon State University, 2021.

See:

Hemp (Cannabis sativa) -Root and Crown Rot

By C. M. Ocamb

Cause The fungus, Fusarium proliferatum, which can survive in plant debris and has a broad host range. This can affect plants in the field, greenhouse, and vegetative propagation set-ups.

See:

Blueberry (Vaccinium corymbosum) - Rust

Willow (Salix spp.) - Rust

See:

Hazelnut (Corylus avellana) - Eastern Filbert Blight

Contorted hazelnut with eastern filbert blight canker.

Jay W. Pscheidt, 2019.

Red Dragon, a contorted filbert with red leaves and the single dominant gene for Eastern Filbert Blight resistance.

Jay W. Pscheidt, 2013.

Eastern filbert blight is also a disease on the ornamental contorted filbert.

Photo by Jay W. Pscheidt, 1996.

See:

Greenhouse Plants, Ornamental - Pythium Seed Rot, Damping-off, and Root Rot

Greenhouse Plants, Ornamental - Rhizoctonia Damping-off, Root and Stem Rot

These young Sedum plants had Fusarium crown and root rot with small, rotting root systems and decay extending into the crown.

Oregon State University Plant Clinic image, 2020.

Osteospermum with Fusarium basal rot where both roots and the base of the stem/root crown had decay.

Oregon State University Plant Clinic image, 2020.

Vascular discoloration develops inside the corm of this cyclamen with Fusarium wilt.

Oregon State University Plant Clinic image, 2018.

See:

Gooseberry and Currant (Ribes spp.) - Armillaria Root Rot

Phytophthora crown and root rot of gooseberry ‘Oregon Champ’. Note cut into vascular cambium showing health green tissue above and discolored diseased tissue below.

Oregon State University Plant Clinic image, 2013.

Cause Powdery mildew has been observed on Geum spp. in all states. Podosphaera aphanis, P. macularis and Erysiphe polygoni have been reported from Washington and Idaho. Disease appears to be worse in shaded areas of gardens.

Geum macrophyllum with white patches of powdery mildew scattered on this leaf and stem.

Jay W. Pscheidt, 2020.