Plant Disease Management Handbook

Cause Septoria exotica is a fungus that is favored by conditions that keep leaves wet. Pseudophaeophleospora atkinsonii (formerly Kirramyces hebes) has been described, which has similar symptoms but larger sized leaf spots. It is not known which might occur in the PNW.

Image related to Hebe-Septoria Leaf Spot
The first symptoms are small black spots on the leaves, which enlarge and form an ash-colored center.
Photo by Neil Bell, 2004
Image related to Hebe-Septoria Leaf Spot
Small spots are Septoria sp. but the larger necrotic areas and leaf deformation are due to downy mildew.
Photo by Neil Bell, 2004

Cause There have been several organisms associated with root rots and resulting branch diebacks in Oregon including Phytophthora sp., Macrophomina phaseolina (Charcoal rot) and Fusarium oxysporum. Both Phytophthora and Fusarium are favored by excessively wet soils but Phytophthora is favored by cool soils conditions while

Image related to Hebe-Root Rot
Phytophthora sp. on the cultivar 'Red Edge'.
Photo by Neil Bell, 2005

This Hebe 'McKeanii' had dieback and black root rot (Berkeleyomyces sp. (formerly Thielaviopsis basicola)).

OSU Plant Clinic Image, 2017.

See:

Veronica - Downy Mildew

Image related to Hebe-Downy Mildew
Note the discolored areas on the leaves.
Photo by Neil Bell, 2004

See:

Oregon Grape (Mahonia aquifolium) - Powdery Mildew

Image related to Heavenly Bamboo (Nandina domestica)-Powdery Mildew

Powdery mildew may start out as widely scattered individual colonies.

Jay W. Pscheidt, 2012.
Image related to Heavenly Bamboo (Nandina domestica)-Powdery Mildew

Entire shoots may be covered with the sporulation of this fungus.

Jay W. Pscheidt, 2012.
Image related to Heavenly Bamboo (Nandina domestica)-Powdery Mildew

Many shoots may be covered with this disease.

Jay W. Pscheidt, 2012.

Cause Mosaic symptoms may be due to any of 3 viruses including cucumber mosaic virus (CMV), plantago asiatica mosaic virus (formerly nandina mosaic virus) and/or nandina stem pitting virus (NSPV). All of these viruses are easily transmitted through vegetative propagation of the host. CMV can also be vectored by a wide variety of aphids. None are seed transmitted.

Image related to Heavenly Bamboo (Nandina domestica)-Mosaic

'Tuscan Flame' with CMV.

OSU Plant Clinic Image, 2013.

Cause The fungus-like microorganism Phytophthora cinnamomi has been reported frequently in Oregon. Waterlogged soils and warm temperatures favor the disease. It survives unfavorable periods in soil and within plant debris. Under favorable conditions, spores germinate and infect roots. After infection, the fungus-like microorganism spreads mainly in the inner bark tissues of the root and stems. They survive as various spores in the soil, container media, or infected roots.

Image related to Heather (Calluna spp.)-Root Rot

Dieback of 'Darleyesis Kramer Red' heather due to root rot from Phytophthora sp.

OSU Plant Clinic Collection, 2011.

Image related to Heather (Calluna spp.)-Root Rot

Crown rot of 'Svenja' heather due to Phytophthora sp.

OSU Plant Clinic Image, 2014.

Shoot dieback due to Phytophthora sp. on this Calluna vulgaris 'Svenja'.

OSU Plant Clinic Image, 2016.

See:

Tree Wound Paints

Heart rot fungi have colonized this trunk as evidenced by the fruiting bodies seen in this picture.

Jay W. Pscheidt, 2007.

Image related to Hazelnut (Corylus avellana)-Wood Decay

Fruiting bodies of Trametes versicolor commonly called Turkey Tail.

OSU Plant Clinic Image, 2014.
Image related to Hazelnut (Corylus avellana)-Wood Decay
There are two different heart rot fungi fruiting at the base of this hazelnut tree. The hoof shaped structure on the left is a Ganoderma sp. while the smaller ones on the right are Trametes versicolor.

Jay W. Pscheidt, 2014.

Pycnoporus cinnabarinus is a saprophytic, white-rot decomposer.

OSU Plant Clinic, 2020.

Cause Unknown. Witches' brooms in hazelnut are an oddity that is seen every few years. Growers are curious about the problem but do not report that it affects production in any way.

Witches' broom symptoms were associated with hazelnuts infected with Candidatus Phytoplasma fragariae in Slovenia but trees with the same pathogen in the UK only had yellowing leaf symptoms.

Affected branches stand out from all the other branches.

Jay W, Pscheidt, 2002.

Normal branch becomes swollen and then numerous small branches emerge from that point.

Jay W, Pscheidt, 2000.

Image related to Hazelnut (Corylus avellana)-Witches' Broom
Leaves and stems may look normal green but are still stunted in growth.
Jeff Olsen, 2008.

Cause Hazelnuts will not tolerate saturated soil conditions for extended periods of time during the winter. Trees grow poorly under these wet conditions for years and eventually may die.

Image related to Hazelnut (Corylus avellana)-Wet Feet
Notice how the trees get smaller and stunted down the hill to where water is standing.
Jay W. Pscheidt, 2012

Stunted trees are often found in areas where water collects and drains from fields. These stressed trees may die from other causes such as Bacterial blight.

Jay W. Pscheidt, 2007

Damaged cambium may show up as a dark wet spot on the bark where brown liquid oozes from the wound. In this case, due to Phytophthora root rot.

Jay W, Pscheidt, 2008.

The damaged cambium of Phytophthora root rot is seen here where the bark has been cut away. Root rot will kill the cambium from the bottom up.

Jay W, Pscheidt, 2008.

This hazelnut was positive for Phytophthora root rot.

OSU Plant Clinic image, 2012.

See:

Hazelnut (Corylus avellana) - Wood Decay

Sunburned leaves become yellowed starting between veins or on the margins. Leaves can roll downward and can become brown and necrotic.

Jay W. Pscheidt, 2018.

Sunburned leaves and trunks are generally on the south and/or southwest side but can burn anytime tissue is exposed to strong sunlight.

Jay W. Pscheidt, 2018.

Leaves exposed to sunlight during thinning in June. Note shaded portions are still green.

Jay W. Pscheidt, 2020.