The black stain fungus infects and kills several species of western conifers. The fungus colonizes water conducting tissues of the hosts roots, root collars, and lower stems, ultimately blocking the movement of water to foliage. Severely infected trees exhibit wilting symptoms. Black stain kills young trees within a year or two of infection. Older infected trees decline more slowly (over 2 to 8 years) and are often predisposed to bark beetle infestation. Tree mortality associated with the disease is often mistakenly attributed to other, more easily identified root disease or to bark beetles, which are commonly associated with the rapid decline and death of black stain-infected trees.

Trees infected by the black stain fungus usually exhibit symptoms of gradual decline before they die. In early stages of decline, terminal growth is reduced and older needles become chlorotic. As the disease progresses, older needles are shed prematurely, new needles are somewhat stunted and yellow, and reduced growth is evident on lateral branches. In advanced stages, new growth is compact and chlorotic, with a tufted appearance, and tree crowns exhibit very sparse foliage. They also bear "distress" cone crops. Very small trees, or those affected by other significant stress factors, may succumb quickly without exhibiting gradual decline symptoms; foliage may change rapidly from green to yellow or reddish brown.

Crown symptoms of trees affected by black stain root disease are very similar to those associated with other root diseases. Black stain can be distinguished from other root diseases by the distinctive chocolate brown to purple- black stain in the sapwood of roots and lower stems of infected trees. When observed in cross-section, the black stain appears in arcs roughly concentric with the growth rings. In contrast, blue stains, which are sometimes confused with black stain, are usually a lighter color and typically are wedge-shaped in cross-section or they discolor the entire sapwood radius.

Black stain root disease affects groups of trees in distinct infection centers. Typical infection centers have trees in various stages of decline near the perimeter and dead trees in the interior nearer the origin of initial infection.

Long-distance spread of the black stain fungus involves insect vectors, such as root-feeding bark beetles or weevils. Black stain infection centers are most prevalent in areas where substantial tree damage or site disturbance has occurred, especially along roads, trails, and soil disturbance. The appearance of infection centers in areas of disturbance reflects the insects preference for stressed trees.

Once established, the black stain fungus colonizes root and stem sapwood, reducing water uptake and the vertical ascent of sap by clogging water conducting vessels. Infected trees die (usually in summer. when soil moisture is depleted) because of the inability to take up water.

Once a new infection center is established, spread of the infection from tree to tree occurs through root grafts between healthy and diseased trees. Infection centers in ponderosa pine and pinon trees enlarge on the margin at an average rate of one meter per year (3 to 5 times faster than that of other common root diseases). Black stain root disease remains active for a short time period, usually no more than 1 to 3 years after the host tree dies.

In recent years, black stain root disease has been detected in many new areas, often causing locally severe damage. Incidence appears to be steadily increasing. At the present time, there is no effective cure for already diseased trees. Current management strategies for control of black stain root disease are either preventive or corrective.

1. Minimize site disturbance - Management treatments for disease-prone areas should be those that cause the least site disturbance, particularly avoiding soil compaction and changes in the soil profile. Avoid the use of heavy equipment or vehicles on muddy soil. Avoid road construction within a mile of black stain disease centers. Injured trees and those with root collars partially covered by fill should be removed. Damaged and partially buried trees are often weakened and are attractive to insect vectors of black stain.

2. Minimize tree injury - Special care should be taken to avoid damaging remaining trees while thinning or cutting of dead or diseased trees. Avoid fills around root zones. Don't place nails, signs, hammocks, or any wire on or around trees. Provide supplemental water during droughts - but don't over water trees, especially pinon pines.

When establishing new trees near areas of black stain root disease, a mix of species should be used (the 3 varieties of the fungus generally do not infect other host trees, i.e. the pinon variety of black stain is not believed to infect ponderosa pine or Douglas-fir trees).

Thinning should be avoided within or adjacent to known infection centers. Patch-cutting of the entire disease center and an additional 50 foot buffer around its edge is preferred to thinning.

Where bark beetles (especially LPs engraver beetles) are present, follow recommendations such as winter cutting and prompt slash treatment.

Note: This information was summarized for residents of Log Hill Mesa, Ouray County, Colorado Forest Pest Workshops, February 22, 1997

For more complete information, interested parties should obtain and read the source document: Black Stain Root Disease in Conifers, USDA Forest Service publication: Forest Insect & Disease Leaflet 145

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