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Black Stain Root Disease (Leptographium wagneri)

Trees Affected
Cross-section of tree affected by black stain root disease. Source: USDA Forest Service - Forest Health Protection Intermountain Region, Bugwood.org

Common: Douglas fir, ponderosa pine, Jeffrey pine

Occasional: Lodgepole pine, knobcone pine, western white pine, sugar pine, western hemlock, mountain hemlock

Summary

Black Stain Root Disease Crown Decline. Source: Source: USDA Forest Service
Black stain root disease is caused by a fungus that grows through the vascular system of its host and causes relatively rapid wilt-like crown decline. It spreads from the roots of one tree to another on root-feeding insects, and subsequently grows up through the vascular system of the tree, cutting off access to water and nutrients as it goes. Symptoms include resin on roots and on the lower bole as well as crown yellowing and thinning, often with stunted branches at the top. These symptoms frequently give declining trees a more rounded top compared to healthy trees of the same species. Although this fungus does not rot its host’s wood, it does produce vertical black staining on roots and root collar sapwood that is diagnostic of the disease.

 

Local Distribution

Black stain root disease is present in a variety of locations throughout the north coast. Although the following list is not exhaustive, this disease has been observed at the following locations:

  • Along highway 299 near Ellis summit
  • In the hills around Ferndale
  • Jackson State Forest

Management Strategies

Black Stain Root Disease Sapwood Damage. Source: William Jacobi, Colorado State University, Bugwood.org
Black stain root disease cannot enter or infect healthy, unwounded roots, so avoiding actions that result in root injury or soil compaction can reduce the occurrence of this disease (for more specific management recommendations see USFS recommendations here). However, since this fungus occurs across this region and some root injury is inevitable, planting mixed species stands with some resistant species in high-risk areas is also recommended.

Pests and Pathogens with Similar Symptoms

Armillaria Root Disease: Both of these pathogens may cause top down decline and other symptoms associated with root disease. However, Armillaria root disease can be distinguished from most other root diseases (including black stain root disease) by the presence of black root-like cords called rhizomorphs under the bark of the affected tree. Additionally, Armillaria root disease produces a white, spongy rot and does not produce the signature vertical black staining of black stain root disease. However, it is possible for these pathogens to co-occur at a site, so the presence of one does not rule out the possibility of the other.

Further Reading

Overview and management:

https://www.fs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb5187236.pdf

Overview and symptoms (with pictures):

https://www.fs.fed.us/foresthealth/docs/fidls/FIDL-145-BlackStainRootDisease.pdf