Plant Disease Management Handbook

Cause Several fungi have been associated with a canker problem in the Pacific Northwest. Fusarium spp. and Phomopsis sp. have been associated with canker problems in nurseries. Nectria cinnabarina has been detected over the years from samples sent to the OSU Plant Clinic.

Dead branches due to canker on honey locust grown in Oregon.

Larry Moore collection, 1992.

This honey locust had Fusarium stem canker with dieback.

OSU Plant Clinic image, 2019.

Sunburst honey locust inoculated with Fusarium lateritium (left side images), Nectria cinnebarina (center) and Phomopsis sp. (right).

Larry Moore collection.

Image related to Honey Locust (Gleditsia spp.)-Canker

Fusarium cankers of various sizes on Imperial Honeylocust.

Sam Doane, 2008.

The slide is labeled Nectria canker but the exact cause is unknown. A classic canker has formed around this branch stub."

Photo by Ralph S. Byther

Canker on this 'Skyline' honey locust was due to Thyronectria austroamericana.

Larry Moore collection, 1991.

Cause Puccinia malvacearum, a fungus that overwinters in basal leaves, which may live through the winter, or on plant debris. Teliospores in association with plant debris remain viable at least 4 months in soil. Fungal mycelium may overwinter in young shoots of the host. Pycnia, aecia, and uredinia are not known for this fungus. Many other plants in the malvaceae can be infected.

Rust on Malva sp. with yellow puckered lesions on the top and brown pustules on the bottom of leaves.

Jay W. Pscheidt, 2008.

Lesions can also occur on Malva stems.

Jay W, Pscheidt, 2008.

Image related to Hollyhock (Alcea rosea)-Rust

Leaves develop numerous rust spots then become chlorotic and collapse.

Jay W. Pscheidt, 2002.

Tan spots with reddish borders develop on the upper surface, while gray to tan pustules are formed on the lower surface.

Photo by Ralph S. Byther

Rust on musk mallow, Malva moschata, with yellow puckered lesions on the top and brown pustules on the bottom of leaves.

Jay W. Pscheidt, 2013.

Cause Fumago vagans, a nonpathogenic fungus that grows on the honeydew (excrement) of scale insects has been reported from the PNW. Several other fungi have been reported from southern states including Capnodium elongatum, Echidnodella angustiformis and E. prinoides. Sooty mold typically causes little damage to plants aside from an aesthetic problem.

Image related to Holly (Ilex spp.)-Sooty Mold

Many black lower leaves on this holly tree.

Jay W. Pscheidt, 2012.

Lower older leaves have sooty mold which is growing on the excrement from the small long white cottony scale insects.

Jay W. Pscheidt, 2012.

Cause Sclerophoma sp., a fungus never identified to species. It does not sporulate readily in plant tissue under field or laboratory conditions but does in culture plates after exposure to ultraviolet light. Symptoms developed 3 months after artificial inoculation. Healthy plants placed in the field in June developed scab by September.

Image attempts to show scab on the upper and lower leaf surfaces.

OSU Extension Plant Pathology slide collection, 1971.

English holly has irregular, translucent to reddish black swollen areas on the leaf.

OSU Extension Plant Pathology Slide Collection.

Scab on the cultivar 'Brownell Special'.

Bill Brown, 1964.

Scab on the cultivars 'Escort Male' (left) and 'Rederly' (right).

Bill Brown, 1964.

See:

Holly (Ilex spp.) - Boron Deficiency

Note the spots along the leaf margins.

Photo by Jay W. Pscheidt, 1992.

Leaf spotting due to copper-based pesticide (left), the fungal disease scab (middle) and another pesticide called Nabam (right).

OSU Extension Plant Pathology slide collection, 1963.

See:

Rhododendron - Phytophthora Root Rot

This Ilex × meserveae 'Blue Princess' has crown and root rot due to Phytophthora sp. Note the cut made at the base of the plant revealing necrotic discolored tissue.

OSU Plant Clinic Image, 2016.

Cause Phytophthora ilicis, a fungus-like microorganism. The disease develops in cool, rainy weather of fall and winter and subsides in warm, dry summer months. It may be very severe in dense orchards where air circulation is poor. In some orchards on the Oregon coast, the disease has caused almost complete defoliation and severe twig blighting, particularly on lower limbs.

Image related to Holly (Ilex spp.)-Phytophthora Leaf and Twig Blight

Fruit, which turn a dark color, can also be infected.

OSU Extension Plant Pathology Slide Set, 1962.

Notice the defoliation, shoot dieback and necrotic berries.

Photo by Jay W. Pscheidt, 1994.

Japanese holly plants that tested positive with ELISA for Phytophthora (the twigs).

Lyle J. Feilmeier, Collier Arbor Care, 2006.

Splashing water from a roadway has encouraged severe defoliation from leaf and twig blight.

Robin Rosetta, 2007.

Defoliation and twig dieback are common.

Jay W. Pscheidt, 1990s.

See:

Holly (Ilex spp.) - Scab

Holly leaf spotting due to Trochila ilicina.

OSU Extension Plant Pathology slide collection.

Cause Green algae. This elementary plant grows on leaves, twigs, and trunks in wet or humid weather. Algal growth on conifer needles is a response to high nitrogen deposition and may be the same for holly.

Symptoms Yellow-green powdery layer on leaf surfaces, twigs, and trunk, usually appearing first on the north side of the lower trunk and gradually spreading up and out to twigs and leaves.

Dull, green, algal colonies develop on leaves.

Photo by Jay W. Pscheidt, 1993.

See:

Holly (Ilex spp.) - Red Leaf Spotting

Cause Many commercial holly plantings have incipient boron deficiency. PNW soils west of the cascades are naturally low in boron. Many crops in these areas need supplemental boron.