Black stain root disease

Last updated on January 30, 2025

Leptographium wageneri

There are two distinct strains of the fungus in British Columbia that cause black stain root disease, one on Douglas-fir and one on pines. Unlike other root diseases, this fungus does not decay wood but acts as a vascular wilt clogging up tracheids.

The disease spreads via root contact or by root weevils or secondary bark beetles. Black stain root disease is often associated with disturbed sites that attract the insects that vector the pathogen.

Description

Black stain root disease affects Douglas-fir trees of all ages (including newly planted seedlings). On pine, it typically infects trees greater than 60 years of age but has been found in young stands. Sublethal infection of black stain root disease may contribute to symptoms of decline and reduced growth in Douglas-fir stands.

Black stain root disease is often found in association with laminated and Armillaria root diseases.

Host tree species

The Douglas-fir strain affects primarily Douglas-fir and the pine strain affects ponderosa pine, lodgepole pine, and western white pine.

Damage symptoms

Black stain root disease causes typical root disease symptoms including reduced height growth, thinning and yellowing foliage, and stress cones. A black to brownish-purple stain is revealed if the sapwood is cut open. This stain follows the annual rings and is present in the lower bole and roots. Positive identification of black stain requires chopping into the roots of symptomatic or freshly killed trees since the stain fades over time in the sapwood.

Tree mortality from black stain root disease is often attributed to other forest health agents such as primary or secondary bark beetles. L. wageneri produces droplets of sticky spores that get transported on the surface of some species of root weevils and secondary bark beetles. These insects are attracted to stressed and dying trees, often resulting from disturbance caused by soil disturbance and compaction, drought, flooding, or harvesting. We may see increased amounts of black stain root disease as a result of more frequent droughts associated with climate change.

Black stain root disease is often associated with roads and right of ways. Repeated or adjacent stand entries (for example progressive harvesting along a new or reactivated road system) could lead to build-up of the secondary insects as they move from one block to the next in progression. Harvesting and road building during mid to late summer will avoid peak periods of insect vector dispersal in the spring and give slash more time to dry out and become a less attractive food source.

Read a detailed list of black stain root disease symptoms (PDF, 205KB)

Management

Regenerating with less susceptible species that are ecologically appropriate is the recommended treatment for black stain root disease. Read a detailed guide on root disease management. https://www2.gov.bc.ca/assets/gov/farming-natural-resources-and-industry/forestry/forest-health/forest-health-docs/root-disease-docs/rootdiseaseguidebookjune2018_4.pdf

Identification images

black stain root disease shown on exposed tree fibre

black stain tree effects

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