Armillaria Root Disease Research Articles

Assessing Potential Risks of White Pine Blister Rust on Western White Pine from Increased Cultivation of Currants

Introductions of white pine blister rust (WPBR, causal fungus: Cronartium ribicola J.C. Fischer) to eastern and western North America before 1915 caused such extensive damage that western white pine (Pinus monticola D. Don) was essentially abandoned as a manageable forest tree species for over 60 years. Recent results from WPBR resistance selection and breeding programs, and from field trials of tree spacing, pruning and bark excision treatments have supported efforts to increase establishment and to intensively manage western white pine. Western white pine is a desirable component in many forested areas because of its faster growth and much higher value compared to many other associated tree species. It also has a low susceptibility to armillaria root disease caused by Armillaria ostoyae (Romagnesi) Herink and laminated root rot, caused by Phellinus weirii (Murr.) Gilb. Some regulations, e.g., Forest Practices Code of British Columbia (BC) Act, require anyone who harvests timber on provincial forestland and uses western white pine for reforestation to either plant genetically resistant western white pine stock or prune susceptible young trees for protection. Risks of increased WPBR associated with increased commercial cultivation of gooseberries and currants (Ribes L.) have yet to be determined. However, major threats appear to include 1) increase in local amounts of spores for nearby infection of pines; and 2) possible introductions or development of new, virulent races of C. ribicola, particularly from eastern to Pacific northwestern North America. In view of these possible threats, we recommend that existing regulations and legislation should be amended, or possibly new measures enacted, to permit propagation and commercial cultivation only of varieties of Ribes that are immune or highly resistant to WPBR.

Inoculation of stumps with <i>Hypholoma</i> <i>fasciculare</i> as a possible means to control armillaria root disease

Hypholoma fasciculare (Huds. ex Fr.) Kummer was paired with Armillaria ostoyae (Romagn.) Herink in a variety of ways in the laboratory and then it was inoculated onto A. ostoyae infected stumps in ...

Precommercial Thinning in a Ponderosa Pine Stand Affected by Armillaria Root Disease in Central Oregon: 30 Years of Growth and Mortality

Abstract A 30-yr-old stand of ponderosa pine was precommercially thinned in 1966 to determine the effects of thinning on tree growth and mortality caused by Armillaria root disease in central Oregon. After 30 yr, crop tree mortality was significantly (P = 0.02) less in thinned plots than in unthinned plots. Tree diameter growth was not significantly (P = 0.17) increased by thinning. Crop-tree basal area/ac growth was significantly (P = 0.03) greater in thinned plots. Apparently, from a root disease perspective, precommercial thinning of pure ponderosa stands significantly decreases the incidence of crop-tree mortality after 30 yr and significantly increases basal area/ac growth but not individual tree diameter growth. Recommendations for thinning based on stand density index (SDI) are given. West. J. Appl. For. 14(3):144-148.

Effect of water potential on radial colony growth of Armillaria mellea and A. gallica isolates in culture

Increased incidence of Armillaria root disease on orchard and landscape trees in northern California may be related to changes in irrigation practices. Continuously moist soil from sprinkler irrigation may favor survival and growth of the fungus. The effects of water potential on radial colony growth were tested for two species of Armillaria. Isolates were tested on malt extract agar amended with either KCl or sucrose to control osmotic potential and produce six different water potentials from -0.5 to -8.5 MPa. Eleven Armillaria mellea isolates from orchard crops and hardwood forest trees and three isolates of A. gallica from hardwood forest trees in California grew well between -0.5 and -1.5 MPa water potential. Rates of mycelial growth were 7–10 mm/wk. Below -1.5 MPa mycelial growth of all isolates declined with decreasing water potential. In this study, A. mellea, and to a lesser extent A. gallica, were sensitive to changes in water potential in culture.

The effect of Armillaria root disease on lodgepole pine tree growth

Growth of lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) trees infected with Armillaria ostoyae (Romagn.) Herink growing in disease centres were compared with the growth of uninfected trees from two stands in west-central Alberta. Sample trees were measured (height, diameter at breast height, and height to live crown) and disks removed for stem analysis. The standing wood volumes inside disease centres of the two sites were 54 and 15% of the volume in surrounding stands. There were no significant differences in height or diameter at breast height between infected and uninfected trees. Expected growth rates determined by stem analysis revealed, however, that there were conservative losses of 43% in annual volume increment, 32% in specific volume increment, and 23% in height increment. The pattern of stem growth of infected individuals was that typically found in open-grown trees, in marked contrast to the pattern found in uninfected trees growing outside the disease centre. Tree growth chronologies suggested that disease centres were present early in the stands' development as trees grew rapidly before they became infected; however, the characteristic open-grown pattern of trees found in disease centres did not change after they became infected.

The effect of Armillaria root disease on lodgepole pine tree growth

The effect of Armillaria root disease on lodgepole pine tree growth

Armillaria Root Disease Inoculum Remaining in Young Ontario Conifer Plantations Following Root Raking or Madge Rotoclearing

Abstract Armillaria ostoyae causes a destructive root disease in northern conifers. Most infections result from root invasions by rhizomorphs growing through the soil from previously colonized stump and woody root debris. Armillaria longevity in woody debris is related to the colonized volume. Stump and root removal by root raking alone often does not satisfactorily reduce subsequent root disease mortality. This investigation characterized residual woody debris volumes in three conifer seed orchards in northern Ontario. Site preparation for stump and root removal in two of the orchards consisted of root raking alone, vs. Madge Rotoclear™ treatment ("rotoclearing") in the third orchard. Fallow periods between site preparation and planting were 1, 5, and 8 yr in the three orchards, respectively. Mortality related to colonized residual woody debris is continuing in the raked orchards, but appears to have ended in the rotocleared orchard. Root systems of 32 orchard trees recently killed by Armillaria root disease and 9 apparently healthy (otherwise comparable) trees were excavated. Regardless of site preparation method, Armillaria-killed trees were associated with greater total volumes of residual woody debris (comprising larger pieces on average) than were healthy trees. Also, healthy trees in the rotocleared orchard were associated with smaller debris pieces on average than were healthy trees in the root-raked orchard. Size of individual woody debris pieces which contained viable A. ostoyae was highly variable. Even small pieces of colonized debris close to a root crown were apparently capable of causing lethal infection. Nevertheless, compared to root raking, rotoclearing apparently breaks A. ostoyae-colonized woody debris into smaller pieces resulting in more rapid displacement of A. ostoyae. We conclude that rotoclearing followed by a fallow period of 8 yr before planting merits consideration as an inoculum reduction treatment for site preparation. A 10 yr fallow period might have prevented nearly all root disease mortality under the conditions of this study. North. J. Appl. For. 15(4):191-196.

Spatial Distribution of Armillaria mellea in Pear Orchards.

Pears have traditionally been considered to be highly resistant to Armillaria root disease (causal agent: Armillaria mellea). In recent years, however, the incidence of Armillaria root disease in pears has increased in California. To determine the spatial distribution of Armillaria root disease in the field, a total of 156 isolates of Armillaria were collected from dead and dying pear trees located within two orchards in Lake County. All isolates from these two orchards, as well as from an additional 10 pear orchards, were identified as Armillaria mellea sensu stricto. Based on pairings among 102 Armillaria isolates, four somatic incompatibility groups (SIGs) were identified at orchard 1. Three of the four SIGs at this site were over 100 m in length; the largest SIG was at least 200 m in length. Pairings among 54 isolates identified five SIGs at orchard 2. The SIGs at orchard 2 were generally smaller than those detected at orchard 1 and ranged from 20 to 60 m in length. The size of the SIGs points toward long-term establishment of the fungus on the two sites, most likely predating the establishment of the pear orchards. Extensive root excavations of 19 trees indicated that the primary means of secondary spread of Armillaria was via rhizomorphs, as opposed to root-to-root contact.

Influence of Forest Structure and Diseases on Nest-Site Selection by Red-Breasted Nuthatches

Empirical studies of the effects of forestry on cavity-nesting birds largely neglect weak cavity excavators and instead focus on large, strong cavity excavators such as woodpeckers (Picidae). Weak cavity nesters tend to be smaller and may be less limited by the availability of large trees but more dependent on suitably softened wood. In this paper, we describe availability, use, and preference for nesting habitat of a small cavity-nesting bird, the red-breasted nuthatch (Sitta canadensis), in mature coniferous forest in southeastern British Columbia. We describe nesting habitat at 3 spatial scales: (1) the level of forest stands proposed for logging (cutblocks), which ranged from 8.1 to 18.4 ha in size; (2) the level of 0.04-ha patches of forest centered on nest trees (nest plots); and (3) the level of individual nest trees. In addition to considering basic structural habitat features, we analyzed the relation between nesting use and several factors related to forest health, including Armillaria root disease (Armillaria ostoyae), stemwood decay, mountain pine beetle (Dendroctonus ponderosae) infestation, and dwarf mistletoe (Arceuthobium spp.). Red-breasted nuthatches nested at higher densities on cutblocks with more dead trees (snags) and higher levels of root disease. Within nest plots, we also detected a preference for nesting in Armillaria-infected trees. Cavity nesting of nuthatches was influenced by both forest structure and the disease agents that contribute to it. We recommend that standing diseased and dead trees be retained in patches during logging operations. Retention of such trees in distinct patches more likely satisfies requirements for worker safety and for limiting the spread of diseases than does retention of single dead and diseased trees throughout cutblocks. Wildlife values not only should be incorporated into timber harvesting regulations but also should be considered when planning activities designed to improve forest health for timber production.

Armillaria root disease, stand characteristics, and soil properties in young lodgepole pine

Thirty six lodgepole pine stands in west-central Alberta, ranging in age from 9 to 28 yr of age, were surveyed for Armillaria root disease mortality. Selected stand characteristics and edaphic factors were recorded in each stand to determine if there was a relationship between these factors and Armillaria root disease. Data was analysed using a multivariate linear regression. A statistically significant relationship was found between sand content, ammonium (NH 4 +) concentration and Armillaria root disease. The incidence of Armillaria root disease increased significantly with increasing sand content of the surface mineral horizon and decreasing NH 4 + concentration of the surface organic horizon (LFH). Stand age, density, elevation, soil pH, depth of the surface organic horizon (LFH), calcium (Ca), phosphorus (P), potassium (K), magnesium (Mg), and sulfur (S) did not have a significant effect on the amount of mortality.

Tree vigour and the susceptibility of Douglas fir to Armillaria root disease

SummaryIn this study the effects of thinning, fertilization and pruning on the vigour of Douglas fir (Pseudotsuga menziesii) and its susceptibility to Armillaria root disease were explored. Tree vigour was defined as the relative capacity for tree growth, expressed as the above‐ground biomass increment per unit of photosynthetic tissue, or growth efficiency (GE). It has been hypothesized that trees with higher GE can better resist pathogen attack, and that GE can be used as a predictor of tree susceptibility to disease. In a previous study, four Douglas fir plantations were thinned, fertilized and pruned in all combinations, and the effects of these treatments on tree vigour were measured after 10 years. Root disease was not a factor in the initial study design, and mortality was ignored until 8 years after the treatments were applied. The results of an earlier study were utilized and the correlation between Armillaria root disease incidence and the effects of earlier stand treatments on tree growth was tested. Armillaria ostoyae was the primary mortality agent in the study area. Disease incidence on infested subplots ranged from 2 to 20%. Armillaria ostoyae incidence was the highest at medium tree density (6.1%), slightly lower on the low density (5.6%), and lowest on the unthinned plots (3.8%). There were no significant correlations between disease incidence and previous tree growth. The vigour of trees that became symptomatic or died by 1993 was not significantly different in 1983–85 from the vigour of trees that remained asymptomatic. On these sites, in areas of infestation, A. ostoyae is killing the largest, fastest growing trees, as well as less vigorous trees. Armillaria continues to cause mortality, regardless of the growth efficiency or growth rate of the host.

Comment-Using spatial and temporal patterns of Armillaria root disease to formulate management recommendations for Ontario's black spruce (Picea mariana) seed orchards

Comment-Using spatial and temporal patterns of <i>Armillaria</i> root disease to formulate management recommendations for Ontario's black spruce (<i>Picea mariana</i>) seed orchards

Distribution, Severity, and Spread of Armillaria Root Disease in Kenya Tea Plantations.

Surveys for Armillaria root disease severity were conducted over a 5-year period in small tea farms (0.5 to 1.0 ha) in the 12 tea-growing districts of Kenya. The disease occurred in all tea districts, but severity was greater in the districts east of the Rift Valley. Disease severity was associated with relative amounts of residual woody debris, especially roots, from trees and shrubs present when the land was converted to tea plantations. Excavation of tea bushes in disease centers showed that infection of tea bushes occurred primarily by mycelial growth from residual tree roots and from infected tea roots rather than from rhizomorphs. Rhizomorphs were scarce, and rarely involved in infection. They were confined mostly to the surface of the residual tree roots and were found growing freely in the soil in only one tea district. Rhizomorphs were more abundant in higher elevation plantations than in lower elevation plantations, where they occurred only on residual tree roots in the deeper, cooler, moister levels of the soil. Inoculum from residual tree debris in the soil was the most important source of infection in plantations of seed origin. Secondary spread from infected tea plants to healthy ones was limited and disease centers were small. In tea plantations derived from clonal cuttings, secondary disease spread from infected to healthy tea plants was more important resulting in large disease centers or gaps due to plant death and removal. Currently, soil sanitation by thorough removal of roots of forest trees and prompt removal of infected tea bushes is the best available management practice.

Silvicultural management of armillaria root disease in western Canadian forests

Silvicultural management of armillaria root disease in western Canadian forests

Using spatial and temporal patterns of Armillaria root disease to formulate management recommendations for Ontario's black spruce (Piceamariana) seed orchards

Between 1982 and 1989, 22 black spruce (Piceamariana (Mill.) BSP) seed orchards were established on cleared jack pine (Pinusbanksiana Lamb.) forest land in northwest Ontario. These orchards were located on stressful sites for black spruce to hasten seed production. Mortality caused by Armillariaostoyae (Romagn.) Herink was observed in most of these orchards within 3 years of establishment. This study was initiated to quantitatively describe the temporal progress and spatial patterns of Armillaria root disease mortality in five representative orchards, to determine future operational management implications. In the four orchards where epidemics developed, temporal disease progress was nonlinear and was better described by the monomolecular function than by the Gompertz or logistic functions. Monomolecular rates of disease increase were 0.0062–0.0346. Applying these rates, we estimated that cumulative Armillaria root disease mortality will be 9–41% and 25–79%, at 20 and 50 years after planting, respectively. Armillaria root disease mortality was spatially aggregated in all four orchards. Trees adjacent to Armillaria-killed trees had an increased probability of mortality from Armillaria root disease. Successive epidemics may develop in these orchards; their timing and severity will be affected by orchard management practices. Measures of spruce family performance in these orchards are compromised by the aggregated distributions of different A. ostoyae genets and the root disease they cause.

Forest health research needs in British Columbia

To determine the needs and priorities for research on specific topics concerning forest health in British Columbia, a questionnaire was developed and distributed to forest management agencies, forest industry and other research agencies. Response was received from all groups contacted (Pacific Forestry Center [Canadian Forest Service]; BC Ministry of Forests; BC Ministry of Environment Lands &amp; Parks; Industry; and Universities) throughout the province. Forty-two insect, disease, and mammal pests were identified for research. Research priorities for insects and diseases were equally distributed and of greater importance than mammals. Diseases most frequently identified included Armillaria root disease and tomentosus root disease, while the mountain pine beetle and the white pine weevil were foremost among insects. Broadly based issues included pest responses to alternative silvicultural systems, quantification of pest caused losses, and standardized survey methodology between agencies. Lower profile research concerns included the pinewood nematode, nursery pests, and hardwood diseases. The potential introduction into the province of exotic pests such as the Gypsy moth was identified as an emerging issue. Key words: forest health, research priorities, forest insects, disease, mammal pests

The spatial distribution of Armillaria root disease in an uneven-aged, spatially clumped Douglas-fir stand

The location, species, and infection status of all trees and stumps in nine 40 by 40 m plots located in a single large Armillaria root disease (caused by Armillariaostoyae (Romagnesi) Herink) infested area in the Interior Douglas-fir Zone in British Columbia were recorded. The area was logged to a diameter limit in 1963 and then left undisturbed. Spatial analysis using variance over mean ratios of number of trees per grid square for a series of grid sizes showed that stumps were randomly distributed, trees were strongly clumped, and infected trees occurred in small clumps that were themselves randomly distributed. Analysis of intertree distances showed that clumps of infected trees ranged from 1 to 29 trees (average 3.2 trees). Incidence of infection did not decline with distance from old stumps. Infection incidence in spatial domains surrounding each stump ranged from 0 to 100%. Nevertheless, variation in incidence among stump domains could not be attributed to variation in inoculum potential at the time of logging. It is concluded that in the experimental area, 30 years after the last major disturbance by partial cutting, Armillaria occurs in small domains, largely on the root systems of trees regenerated since logging. In these circumstances, bridge tree removal spacing, which removes all trees from a band around each infected tree, may isolate most of the viable Armillaria inoculum colonies from the remainder of the stand.

Precommercial thinning in Pseudotsuga, Tsuga, and Abies stands affected by armillaria root disease: 10-year results

Four 10- to 20-year-old stands were precommercially thinned to determine the effects of thinning on tree growth and mortality caused by armillaria root disease in the Cascade Range of western Oregon and Washington, U.S.A.: one stand of Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco var. menziesii) and noble fir (Abiesprocera Rehd.), one of Douglas-fir and western hemlock (Tsugaheterophylla (Raf.) Sarg.), one of Douglas-fir alone, and one of Shasta red fir (AbiesmagnificaA. Mutt. var. shastensis Lemm.) and mountain hemlock (Tsugamertensiana (Bong.) Carr.). After 10 years, differences in crop-tree mortality between thinned and unthinned plots were not significant in any of the four stands. Tree radial growth was significantly increased by thinning in 6 of 15 plots. Crop-tree basal area (per hectare) growth was significantly greater in thinned plots. Basal area (per hectare) growth of all trees was significantly greater in unthinned plots. Apparently, from a root-disease perspective, precommercial thinning does not affect the incidence of crop-tree mortality after 10 years, but tree growth increases significantly.

Chemical and nutritional status of dwarf mistletoe, Armillaria root rot, and Comandra blister rust infected trees which may influence tree susceptibility to bark beetle attack

The terpenoid and phenyl propanoid content of xylem resin as well as phloem nitrogen and carbohydrate levels of lodgepole pine trees infected with Armillaria root disease, Comandra blister rust, and dwarf mistletoe and check (asymptomatic) trees were determined. Comparisons were made to determine if differences existed that might influence their susceptibility to bark beetle attack. These variables were also contrasted with respect to aspect (north and south). Five volatiles (tricyclene, α-pinene, camphene, γ-terpinene, and bornyl acetate) were significantly higher in trees with one or more diseases than in check trees. Four volatiles (myrcene, camphor, 4-allylanisole, and γ-terpineol) were significantly lower in diseased trees. Camphene was the only resin constituent found to differ with respect to aspect, with a higher concentration on the north aspect of check trees. There were no significant differences in carbohydrate or nitrogen content with respect to aspect. The check trees were found to have significantly higher starch, total nitrogen, and free amino-N contents than diseased trees. Trees infected with Comandra blister rust were found to contain lower levels of reducing and nonreducing sugars than the other diseased trees and the check trees. Changes in terpenoids and phenyl propanoids in trees susceptible to mountain pine beetle attack suggest a biochemical basis for host selection. Key words: mountain pine beetle, lodgepole pine, Comandra blister rust, dwarf mistletoe, Armillaria root disease, resin chemistry, susceptibility.

Spatial and temporal characteristics of canopy gaps caused by Armillaria root disease and their management implications in lowveld forests of South Africa

AbstractRoadside reconnaissance and aerial photo surveys were used to characterize the frequency and size of canopy gaps caused by Armillaria root disease in 1763 stands of Pinus spp. in the eastern Transvaal, South Africa. Root disease occurred in 290 stands, most of which grew at altitudes 1000 m. Pinus elliottii was the most commonly infected host, followed by P. kesiya, P. roxburghii, P. caribaea, P. taeda, and P. patula. Disease severity (proportion of stand area with gaps) increased rapidly to age 3, remained nearly constant between ages 6–17, increased rapidly again between 17–28, and then decreased abruptly between ages 28–40. Gap incidence (proportion of all stands with gaps) rapidly increased to age 10, after which it remained nearly constant. Host species present in previous stands influenced whether disease developed in current stands.