Root Disease
Black Stain Root Disease
Leptographium wageneri (W.B. Kendr.) M.J. Wingf.

Hosts:  Piñon and Douglas-fir

Figure 278. Figure 278. Black stain of piñon caused by Leptographium wageneri.

Symptoms/signs:  Like other root diseases, black stain usually exhibits symptoms of gradual crown decline before tree death. In the 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 internodal growth is evident on lateral branches. Very small trees may succumb quickly without exhibiting gradual crown decline symptoms.

Black stain root disease is distinguished from other root diseases by the dark-brown to purple-black discoloration in the sapwood of the lower bole and root collar. When observed in cross section, the black stain appears in arcs roughly concentric with the growth rings.

Biology:  The Southwestern Region has two physiologically and morphologically distinct variants of black stain root disease. Leptographium wageneri var. wageneri is pathogenic to piñons and L. wageneri var. pseudotsugae T.C. Harr. & F.W. Cobb causes black stain in Douglas-fir. Both of these have been found in New Mexico but not in Arizona. A third variety L. wageneri var. ponderosum infects hard pines in California but has not been found in the Southwest.

Effects:  Black stain root disease fungi grow in sapwood and plug tracheids, which prevents water transport and causes a wilting and rapid tree decline and death. Unlike species of Armillaria and Heterobasidion, L. wageneri does not cause wood decay and dies with its host.

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 where infection originated.

Similar Insects and Diseases:  Blue stain fungi, which are often confused with black stain fungi, are usually a lighter color and typically are wedge-shaped in cross-section, and they can discolor the entire sapwood radius.

References:  38, 93