May 2004 Forest Health Protection and State Forestry Organizations

11.5 WEB July 2020 Management Guide for Schweinitzii Root and Butt Rot By James T. Hoffman US Forest Service schweinitzii (Fr.) Pat.

Topics Primary hosts— The most common heartwood  Douglas- decay organism of in Overview 1  Engelmann Montana and Idaho.  Ponderosa Life History 2 As a root disease, it results in Silvicultural 3 little direct tree mortality except Alternatives on the poorest sites.

Other Reading 3 Field Guide Butt decay and windthrow are common effects Management Guide Index Butt rot from this is stem breakage. Brown cubical decay common and can be seen in virtually in the structural roots often extends all western conifers but is considered about 8 feet up the tree stem causing economically significant in only a significant cull of the commercially few situations— mature and important butt log. overmature Douglas-fir stands in As a root parasite on Douglas- Idaho and Montana; spruce stands fir, it predisposes trees to infection Key Points infected with tomentosus root rot; by Armillaria ostoyae, or attack by  Douglas-fir is the and ponderosa pine but in Nevada Douglas-fir beetle. Root disease most commonly damaged species around Lake Tahoe. caused solely by this fungus results in western United The fungus causes extensive in little direct tree mortality except States and decay of host root and butt on the poorest sites. Canada. heartwood. In addition, root ends are Although trees typically become  Cull from butt rot killed causing them to terminate in infected at a very young age, they and windthrow gall-like swellings, which greatly seldom show significant effect until cause most reduces structural support of roots. they are 100 years-old or more. losses. Consequently infected trees are more Generally, if one tree in a stand is  Direct mortality is susceptible to uprooting and lower- infected, nearly all others are as well. rare.

 Trees may be predisposed to Douglas-fir beetle Management Overview and Armillaria root disease.  Prevent over maturity  Avoid basal stem damage  Maintain growth and vigor  Favor less-susceptible species  Accept damage as a natural occurrence that can have positive effects Page 2 Back to menu Schweinitzii Root and Butt Rot 11.5

Life History Infection occurs through small of this disease. These are roots, in laboratory tests. Growth particularly evident in trees of the mycelium through duff and, uprooted because of their perhaps direct infection by compromised root systems. Trees Schweinitzii germinating spores probably infected with P. schweinitzii root and butt accounts for most infections. Field display above-ground symptoms, rot generally is considered a evidence suggests that this may be such as thinning crowns with disease of old the most important means of branch dieback and shortened trees. infection of Douglas-fir and grand terminal growth, only after the root fir. system has been seriously Infections can Infections are also thought to degraded. Trees on very poor sites, be detected in occur directly though deep basal such as at the margins of forest and saplings but stem, or root wounds associated grasslands, are most likely to little damage is with a stand disturbance such as display crown symptoms typical of evident in fire or logging. Even if the other root diseases. Decades after young trees. infection didn’t originate with the root infection, decay may become wound, such scars almost certainly evident in the lower stem. increase the extent of decay, presumably by aerating the infected Fruiting bodies produced by the heartwood, as seen in other heartrot fungus area annual, spongy to diseases . leathery conks. They develop Incidence of Schweinitzii root during periods of moist weather in and butt rot is very high in fire- late summer. The upper surface of Basal scarred Douglas-fir stands. Old conks are reddish-brown and wounding, basal wounds, often mined by velvety with concentric rings; the including fire carpenter ants, are a fairly reliable lower surface is pored, green when scars, can indication that the tree also has fresh and becoming brown with greatly brown cubical root and butt rot. age. Conks on the ground emanate increase from either decaying roots, or from severity of butt After infection, the fungus grows the base of severely infected stems. decay. directly into the center of roots and Conks occasionally form on the cut is seldom found in the outer tissues. end of logs with brown cubical It decays the root heartwood and heartrot. spreads from root to root through heartwood, also using grafted roots to move from tree to tree. In the early stages the decay is punky and only slightly discolored. In the advanced stages, the decay is red-brown with cubical cracking. Terminal ends of many of the larger roots eventually become stubbed; forming large gall-like swellings which can be diagnostic 11.5 Back to menu Schweinitzii Root and Butt Rot Page 3

Silvicultural Alternatives Prevent overmaturity— and western , whenever For existing Douglas-fir stands and wherever, possible. on affected sites, plan stand rotations of 100- to 120-years to Appreciate the positive ecological both minimize Schweinitzii root functions of the pathogen— disease severity and subsequent Realize that P. schweinitzii is a -Web Resource- attacks by Douglas-fir beetle. common, native pathogen that can not be removed from infested sites. Ecology and Prevent basal stem damage— The fungus plays an ecological role Management of Avoid basal stem and root in recycling aging trees. It also Phaeolus damage to residual trees to reduce produces habitat for cavity nesting Schweinitzii the disease and decay hazards birds and other animals, and for Susan K. Hagle decay-inhabiting insects. Each of 1989 Maintain growth and vigor— these roles and many others have Thin stands early, particularly evolved with the evolution of on poor sites which can not support forests and contribute to dense tree growth. ecological diversity and stability.

Favor less-susceptible species—Management should be planned to favor less-susceptible species, especially seral species like

Other Reading Forest Health Protection and State Forestry Organizations Allen, E.A., Morrison, D.J., and G.W. Wallis. 1996. Common tree diseases of Assistance on State Assistance on British Columbia. Natural Resources And Private Lands Federal Lands

Canada, Canadian Forest Service. 178p. Montana: (406) 542-4300 US Forest Service Region One Dubreuil, S.H. 1981. Occurrence, Idaho: (208) 769-1525 Missoula: (406) 329-3605 symptoms, and interactions of Phaeolus Coeur d’Alene: (208) 765- schweinitzii and associated fungi causing Utah: (801) 538-5211 7342

decay and mortality of conifers. Nevada: (775) 684-2513 US Forest Service

University of Idaho, PhD Thesis, 157p. Region Four Wyoming: (307) 777-5659 Ogden: (801) 476-9720 Scharpf, R.F. 1993. Diseases of Pacific Boise: (208) 373-4227 coast conifers. USDA Forest Service, Agricultural Handbook 521. 199p.

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