Black Stain Root Disease of Conifers Paul F. Hessburg, Donald J. Goheen, and Robert V. Bega

The black stain fungus—Lep- the disease was often mistakenly at- tographium wageneri (Kendrick) tributed to other, more easily identi- Wingfield*—infects and kills several fied root diseases or to bark , species of western conifers. The fun- which are commonly associated with gus colonizes water-conducting tis- the rapid decline and death of black sues of the host's roots, root collars, stain-infected trees. and lower stems, ultimately blocking the movement of water to foliage. Black stain occurs in many locations Severely infected trees exhibit wilting throughout the western United States. symptoms characteristic of vascular At present, the greatest development of wilt diseases. Black stain kills young the disease occurs in southeastern and trees within a year or two of infection. northwestern California, southwestern Older infected trees decline more and east-central Oregon, the central slowly (over 2 to 8 years) and are often Sierra Nevada, and southern Colorado. predisposed to bark infestation. In recent years, reports of black stain in young, intensively managed stands Distribution have increased dramatically, espe- cially in Oregon and California. The Black stain root disease is thought to disease affects trees in high-use recre- be native to western coniferous ation areas and areas important for forests. Although the disease was first wildlife management as well as those discovered in 1938, further spread on lands dedicated to timber produc- went virtually undetected until the tion. 1970s. Tree mortality associated with ————————————— Paul Hessberg is research plant pathologist at the USDA Forest Service's Pacific Northwest Research Sta- tion, Forestry Sciences Laboratory, Wenatchee, Washington; Donald Goheen is plant pathologist/entomolo- gist at the USDA Forest Service's Southwest Oregon Forest and Disease Technical Center, Rogue River National Forest, Medford, Oregon; and Robert Bega retired as a research plant pathologist from the USDA Forest Service's Pacific Southwest Forest and Range Experiment Station, Berkeley, California. *Other names have been given to the fungus that causes black stain root disease: Ophiostonia wagneri (Goheen and Cobb) Harrington is the name of the sexual stage; Ceratocystis wageneri, and Verticicladiella wageneri are no longer considered taxonomically correct.

1 Hosts ponderosum) attacks hard pines and The principal hosts of L. wa- occasionally hemlocks. Although lim- generi are Douglas-fir, ponderosa ited cross-over has been shown experi- pine, Jeffrey pine, pinyon, and sin- mentally with the Douglas-fir and hard gleleaf pinyon. Seldom-damaged pine variants, natural occurrences have hosts in the United States include not been detected. For purposes of lodgepole pine, western hemlock, resource management, each of the mountain hemlock, sugar pine, west- variants can be considered host spe- ern white pine, and knob-cone pine. cific. Tree species highly resistant or im- mune to infection are "cedars" (Alaska Black stain root disease occurs over a yellow-cedar, Port-Orford-cedar, wide range of environmental condi- western redcedar, and incense-cedar), tions, from the hot and semi-arid spruce, larch, junipers, and true firs. Southwest to cool Pacific coastal ar- eas. Soil type does not appear to be a Recent research indicates that there major factor in the distribution of the are three distinct variants of L. wa- disease. Soil moisture and tempera- generi, each with specific host prefer- ture, however, may influence disease ences. One (var. wageneri) attacks distribution significantly. Cool, moist pinyon, another (var. pseudotsugae) soil conditions in spring and early attacks Douglas-fir, and the third (var. summer are ideal for infection,

Figure 1 — Crown symptoms of black stain Figure 2 — Faded, sparse crown of pon- root on young Douglas-fir. derosa pine with black stain root disease.

2 growth, and tree-to-tree spread of the pathogen.

Symptoms and Damage Trees infected by the black stain fungus usually exhibit symptoms of gradual de- cline before they die (figures 1 and 2). 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 re- duced internodal growth is evident on lat- eral 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 fac- tors, may succumb quickly without exhibit- Figure 3 — Typical dark sapwood stain as- sociated with black stain root disease.

Figure 4 — Cross section through affected root showing arc-shaped pattern of black stain.

3 hibiting gradual decline symptoms; fo- liage may change rapidly from green to yellow or reddish brown.

Crown symptoms of trees affected by black stain root disease are very simi- lar usually a lighter color and typically are wedge-shaped in cross-section or they discolor the entire sapwood ra- dius.

Black stain root disease affects groups of trees in distinct infection centers (figures 5-7). 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. Infection centers usually oc- cur in well-stocked stands where a preferred host predominates or occurs Figure 5 — Black stain root disease center in in unmixed clumps. In stands where a second-growth ponderosa pine plantation. species composition is well mixed,

Figure 6 — Typical black stain root disease center in a Douglas-fir plantation.

4 Figure 7 — Black stain root disease center in singleleaf pinyon.

Figure 8 — Insect vectors of the black stain root disease fungus on Douglas-fir: nigri- nus, Steremnius carinatus, and Pissodes fasciatus.

5 infection and mortality are less com- roots of recently dead or dying host mon, but isolated trees or tree clusters trees including those infected by L. can be infected. wageneri. Several vector species—H. nigrinus, P. fasciatus, and S. carina- Disease Cycle tus—also breed in Douglas-fir stumps, Long-distance spread of the black which are susceptible to infection by stain fungus involves insect vectors L. wageneri for up to 7 months after (figure 8). The root-feeding barkbee- stems have been severed. tles Hylastes macer LeConte and H. nigrinus (Mannerheim) are believed to Leptographium wageneri sporulates be the primary vectors of the fungus readily inside insect galleries in in- on ponderosa pine and Douglas-fir, fected roots and root collars. Stalked, respectively. Two weevils—Sterem- microscopic fruiting bodies nius carinatus (Boheman) and Pis- (conidiophores) form on gallery sodes fasciatus LeConte—have also walls, each bearing a sticky spore been implicated as vectors in Douglas- droplet that protrudes into the gallery. fir, but their involvement in local and These sticky spore droplets are well long-distance spread of the pathogen suited to insect dispersal (figure 9). is still poorly understood. During emergence, some young adult beetles are contaminated with spores Vector commonly breed in as they brush against spore droplets in galleries or pupal chambers. Contami-

Figure 9 — Enlargement (25x) of fruiting bodies of the black stain root disease fungus in an insect gallery, showing sticky spore masses.

6 -nated beetles fly (or walk) from brood the pathogen through soil. Small trees, burrow through the duff and soil, rootlets (< 5 mm., or .2 in diame- visit roots of healthy, recently dead, or ter) serve as infection courts where dying trees, and deposit spores on root roots are not grafted. Infection sapwood exposed during feeding. centers in ponderosa pines and Wounds that expose sapwood xylem pinyons enlarge on the margin at are required for infection, because L. an average annual rate of 1.0 m/yr wageneri hyphae are unable to pene- (3.2 ft/yr). Infection centers in trate live bark and cambial tissues. Douglas-fir enlarge at a rate of 0.8 to 1.5 m/yr (31.5 to 59.1 in/yr), but Once established, the black stain fun- enlargement of infection centers gus colonizes root and stem sapwood with this host often decreases xylem, reducing water uptake and the markedly when stands reach 30 to vertical ascent of xylem sap by clog- 35 years of age. The rate of en- ging water conducting vessels with hy- largement of black stain infection phae and host reaction compounds. In centers is 3 to 5 times faster than live trees, the fungus is confined to that of other common root dis- tracheids; parenchymatous tissues are eases. not invaded. Infected trees die (usually in summer, when soil moisture is de- Leptographium wageneri is rela- pleted) because of inability to take up tively nonpersistent in infected water. root systems, remaining active usually no more than 1 year after Black stain infection centers are most its host dies. prevalent in areas where substantial tree damage or site disturbance has Management and Cultural occurred, especially along roads and Controls skid trails, in areas having a history of In recent years, black stain root disease tractor logging and resultant soil com- has been detected in many new areas, paction, and in areas that have been often causing locally severe damage. precommercially thinned. The appear- Incidence appears to be steadily in- ance of infection centers in areas of creasing. At the present time, there is disturbance reflects vector insect pref- no effective cure for already diseased erence for stressed trees. trees, and genetically resistant host genotypes have not been identified. Once a new infection center is Current management strategies for established, spread of the infection control of black stain root disease are from tree to tree occurs through either preventive or corrective. root grafts between healthy and diseased trees and through inti- mately associated roots via limited growth (< 15 cm, or about 6 in) of

7 Preventive Management tially covered by fill or side cast from Black stain root disease is favored by the right-of-way after construction several traditional management and should be removed. Damaged and par- road maintenance activities that are tially buried trees are often weakened used throughout the range of its hosts. and have been shown to be attractive By modifying or eliminating some of to insect vectors of black stain. Many these influences and by minimizing new infection centers begin in rights- site disturbances, tree injuries, and the of-way cut for roads. Special care opportunity for successful insect vec- should be exercised in road and site toring, further spread of the pathogen construction when developing new can be reduced. recreation sites.

Minimizing site disturbance: Minimizing tree injury: During road Management treatments for disease- building and maintenance, recreation prone areas should be those that cause site development, and timber harvest the least site disturbance, particularly activities, creating flooded or poorly avoiding soil compaction and disrup- drained areas in or around Douglas-fir tion of the soil profile. Where timber plantations or second-growth stands of is being harvested, high-lead and sky- ponderosa pine should be avoided. line yarding are preferable to tractor Vectors of black stain root disease logging and should be selected when often visit trees with roots in flooded an option exists. When tractor- or poorly drained soils. Using rotary- logging, the area covered by skid trails blade brush-cutting machinery to clear should be minimized, and yarding roadsides adjacent to Douglas-fir plan- should be restricted to the dry season tations is another practice to avoid, for (mid to late summer), when the risk of newly created tree stumps and trees serious soil compaction is reduced. that are damaged but not severed by Skid trails should be designated on the the blades are attractive to vectors. ground before beginning falling activi- Special care should also be taken to ties, and tree falling should be done to avoid damaging young plantation trees the yarding lead. Soils particularly when harvesting sawtimber in adja- prone to compaction by heavy equip- cent stands. ment should not be tractor-logged. Modifying silvicultural practices: New road construction through estab- Precommercial thinning in Douglas-fir lished young Douglas-fir plantations plantations should be done after the (<30 years old) or second-growth vectors of black stain have emerged stands of ponderosa pine should be and established themselves for breed- avoided, especially within 1.6 km (1 ing in other dead, dying, or down ma- mile) of known black stain disease terials. Vectors usually emerge in the centers. If new roads must be estab- spring or early summer. In areas where lished or old roads re-opened, injured black stain is a potential probem, pre- trees and those with root collars par- commercial thinning should be sched- 8 uled between the last of June and the trol guidelines for that species. first of September to ensure that thin- ning slash will be red and dry by fall. When resistant species selections are This will limit opportunities for insect lacking and precommercial thinning is vector population build-up. In areas necessary, avoid thinning in active in- where summer months are often dry fection centers and in buffer zones and droughty, the period of precom- adjacent to them. Thinning in active mercial thinning may be extended into infection centers should be avoided, be- late September. cause odors from freshly cut stump surfaces of infected trees are more Corrective Management attractive to vectors than odors from Where black stain root disease is al- cut surfaces of healthy trees. This ready established, a few silvicultural leads to increasing disease in crop remedies are available. Cultural con- trees adjacent to active infection cen- trols should be incorporated into silvi- ters. cultural prescriptions and should not disrupt the normal management sched- In the central Sierra Nevada of Cali- ule unless incidence in stands is mod- fornia, mixed conifer stands of pon- erate or worse (more than 5% of trees derosa pine, incense-cedar, and firs affected). often progress to a more advanced seral stage when black stain root dis- When establishing new plantations ease is active in the pine, because near areas where black stain is a death of the pines favors the other re- known management concern, a mix of sistant species. When ponderosa pine species should be planted to provide is the dominant species in such stands, future options for species manipula- a mixture of resistant tree species tion. Where black stain is already should be favored in and around black causing significant mortality in young stain centers during precommercial Douglas-fir stands, resistant or im- and commercial thinnings. Patch cut- mune tree species should be favored ting and creation of 15.2-m (50-ft) over Douglas-fir in precommercial buffers around disease centers is often thinning or cleaning operations, espe- recommended during intermediate or cially in active infection centers and in selective harvest entries in ponderosa buffer zones immediately adjacent to pine stands to prevent the continued them. The width of buffer zones spread of the pathogen. Patch cutting in should be based on the number of infected pinyon in recreation areas has years before the next scheduled entry also been recommended but does not and a potential pathogen spread rate of appear to be effective unless buffers 1.5 m/yr (4.9 ft/yr). Buffer zones are much wider than 15.2 m (50 ft) are typically two to five normal tree spac- used. ings wide, depending on the tree species, size class, and stocking con-

9 Assistance nal of Forest Research 16:1250- 1254.

Technical assistance in recognizing Hessburg PF, Hansen EM. 1987. black stain root disease and develop- Pathological anatomy of black stain ing vegetation management prescrip- root disease on Douglas-fir. Cana- tions to reduce or eliminate losses is dian Journal of Botany 65:962-971. available from USDA Forest Service, Forest Pest Management (FPM), or Landis TD, Helburg LB. 1976. Black other extension, municipal, or State stain root disease on pinyon pine in forestry offices. Colorado. Plant Disease Reporter 60:713-717. Rcferences Cobb FW Jr, Slaughter GW, Wagener WW, Mielke JL. 1961. A Rowney DL, Dernars CJ. 1982. staining fungus root disease of pon- Rate of spread of Ceratocystis wa- derosa, Jeffrey, and pinyon pines. generi in ponderosa pine stands in Plant Disease Reporter 45:831-835. the central Sierra Nevada. Phy- topathology 72:1359-1362. Witcosky JJ, Schowalter TD, Hansen EM. 1986. Influence of Goheen DJ, Hansen EM. 1978. time of precommercial thinning on Black stain root disease in Oregon the colonization of Douglas-fir by and Washington. Plant Disease Re- three species of root-colonizing in- porter 62:1098-1102. sects. Canadian Journal of Forest Research 16:745-749. Harrington TC, Cobb FW Jr. 1988. Leptographium root diseases of Witcosky JJ, Schowalter TD, conifers. St. Paul, MN: American Hansen EM. 1986. Hylastes nigri- Phytopathogical Society. 149 p. nus, (Coleoptera: Scolytidae), Pis- sodes fasciatus, and Steremnius car- Harrington TC, Reinhart C, Thorn- inatus (Coleoptera: ) burgh DA, Cobb FW Jr. 1983. as vectors of black stain root disease Association of black-stain root dis- of Douglas-fir. Environmental Ento- ease with precommercial thinning mology 15:1090-1095. of Douglas-fir. Forest Science 29:12-14.

Hessburg PF, Hansen EM. 1986. Mechanisms of intertree transmis- sion of Verticicladiella wageneri in young Douglas-fir. Canadian Jour-

10 Pesticides used improperly can be injurious to humans, , and plants. Follow directions and read all precautions on the labels. Consult your local forest pathologist, county agricultural agent, or State extension agent about restrictions and registered uses of particular pesticides.

The U.S. Department of Agriculture (USDA) prohibits discrimination in its programs on the basis of race, color, national origin, sex, religion, age, disability, political beliefs, and marital or familial status. (Not all prohibited bases apply to all programs.) Persons with disabilities who require alternative means for communication of program information (braille, large print, audiotape, etc.) should contact the USDA Office of Communications at (202) 720-5881 (voice) or (202) 720-7808 (TDD).

To file a complaint, write the Secretary of Agriculture, U.S. Department of Agriculture, Washing- ton, DC 20250, or call (202) 720-7327 (voice) or (202) 720-1127 (TDD). USDA is an equal employment opportunity employer.

Revised March 1995 Formatted for the Internet April 2000 by Gloria Perez

11