Black-stain root disease is a vascular wilt restricted to western North America that infects roots and can move some distance up the base of the stem. Although it is now an important disease, it was first reported in 1961 , and wasn’t reported on Pseudotsuga menziesii until 1967 .
Various western conifers in three distinct host groups are susceptible. Other tree species are seldom infected .
- Pseudotsuga menziesii (Douglas-fir).
- The hard pines Pinus ponderosa and P. jeffreyi, and P. contorta (lodgepole pine).
- The piñons P. edulis (piñon) and P. monophylla (singleleaf piñon).
The pathogen is Leptographium wageneri, an ascomycete closely related to Ophiostoma stain fungi. Thus far no sexual fruting has been found with certainty. Like blue-stain fungi, this pathogen has dark hyphae, but unlike them, it grows predominantly in tracheids rather than ray parenchyma and epithelial cells of resin canals as blue-stain fungi do.
The pathogen is almost certainly insect vectored for long-distance dispersal, but it grows root-to-root for secondary spread as many root pathogens do.
Three types have been described as varieties or subspecies. They are physiologically and, to a slight degree, morphologically distinguishable. The most important point is they are host-specialized:
|L. wageneri var. wageneri||Pinus edulis|
|This is the type variety of the species; the species was described based on an isolate from piñon.|
|L. wageneri var. ponderosum||P. ponderosa|
|Distinguished based on morphology and host range.|
|L. wageneri var. pseudotsugae||Pseudotsuga menziesii|
Distribution and Damage
Trees develop thin, chlorotic crowns and eventually die in expanding disease centers. If you cut into roots and the lower stem, you will be thrilled to find dramatic streaks of black stain.
In Douglas-fir, vectors are known, root-feeding weevils. They are attracted to fresh wounds and stumps, so thinning initiates disease in some stands. In pines, damage is associated with slightly wetter conditions, flats and drainages.
- Avoid undue wounding or disturbance
- Avoid creating wet areas
- Avoid or delay precommercial thinning
- Conduct operations in summer to avoid peak times of vector activity
- Manage for nonhosts of the pathogen variety on the site
References1.Cobb FW, Platt WD. 1967. Pathogenicity of Verticicladiella wageneri to Douglas-fir. Phytopathology 57(9):998–999.2.Hessburg PF, Goheen DJ, Bega RV. 1995. Black Stain Root Disease of Conifers. Forest Insect & Disease Leaflet 145 (revised)., Vol. 145 Washington, DC: USDA Forest Service. [PDF]3.Wagener WW, Mielke JL. 1961. A staining-fungus root disease of ponderosa, Jeffrey, and pinyon pines. Plant Dis Rep 45(11):831–835.