Incidence of Heterobasidion annosum in precommercial thinning stumps in coastal British Columbia

Coniferous stumps in 83 stands in coastal British Columbia were sampled 3-5 years after precommercial thinning. The percentage of stumps and surface area colonized by Heterobasidion annosum were determined for 25 stumps of each species in each 5-cm diameter class present in each stand. There were significant differences among species in the percentages of stumps and surface area colonized, with Douglas-fir (Pseudotsuga menziesii) having the lowest values, amabilis fir (Abies amabilis) and Sitka spruce (Picea sitchensis) the highest and western hemlock (Tsuga heterophylla) being intermediate. For stumps of each species 5–20 cm in diameter, both the percentage of stumps and surface area colonized increased with increasing diameter. In stumps that were grafted to an adjacent tree, there was decreased incidence of H. annosum for Douglas-fir and Sitka spruce and increased incidence for western hemlock and amabilis fir. There were trends in the percentage of stumps and area colonized for season of thinning and biogeoclimatic subzones with the values for most species decreasing as the amount of precipitation increased. Colonization of precommercial thinning stumps by H. annosum occurs throughout the coastal region of British Columbia, and this will increase the amount of inoculum and will likely increase the incidence of butt rot. The results of this study suggest that the increase in inoculum can be minimized by thinning before age 15, by cutting only trees less than 10 cm in diameter and by thinning during low risk seasons.     

Untersuchungen zur biologischen Bekämpfung von Heterobasidion annosum an Fichte (Picea abies) mit antagonistischen Pilzen II. Interaktionstests auf Holz

Investigations on biological control of Heterobasidion annosum in Norway spruce with antagonistic fungi. II. Interaction experiments in wood . Seventeen fungal species were examined for antagonism against H. annosum in wood. After inoculation of stem sections and stumps by conidia and dowels, the distribution patterns of the mycelia within the wood were recorded. In spruce-wood antagonism was shown only by Hypholoma capnoides, Bjcrkandera adusta, Resinicium bicolor and Trichoderma spp. near the site of inoculation. As the distance from this site increased H. annosum became more dominant. Inoculations by dowels yielded more infections than inoculations by spores. The patterns of myeelial distribution within the wood were similar in stem sections and in stumps. Spruce stumps were colonized naturally mainly by Resinicium bicolor, Armillaria mellea s. I. and Nectria fuckeliana. In stem sections of Pinus sylvestris, however, Phlebiopsis gigantea displaced H. annosum effectively.     

Stump treatment against Heterobasidion with Phlebiopsis gigantea and some chemicals in Picea abies stands in the western Alps

The effectiveness against Heterobasidion natural airborne infections on Norway spruce stumps was tested for six treatments: aqueous suspension of Phlebiopsis gigantea oidiospores, 10%, 20% and 30% aqueous urea solutions, 4% copper oxychloride aqueous solution, and borax powder. The experiment was carried out in four naturally regenerated forests in the western Alps, each characterized by a different airborne inoculum potential. Within each stand, all treatments, with the exception of urea 10%, were effective and resulted in colonized areas of stumps significantly lower than controls. The effect of ambient spore loads on the stump colonization is discussed.     

Biological control of Heterobasidion annosum (Fr.) Bref. (Fomes annosus) in Finland

Fresh stumps of Norway spruce (Picea abies) were inoculated with Peniophora gigantea (Fr.) Massee, Botrytis cinerea Pers. ex Fr., Gliocladium deliquescens Sopp, Trichoderma viride Pers. ex Fr. ex S. F. Gray aggr. and Verticicladiella procera Kendrick in order to study their effect on infection by Heterobasidion annosum (Fr.) Bref. The organisms colonizing spruce stumps under natural conditions were identified by collecting samples in the field. In addition, the effect of season of the year, air temperature, precipitation and relative air temperature on fungal colonization of the stumps was investigated.     

The choice of definition has a large effect on reported quantities of dead wood in boreal forest

A survey was conducted to assess the impact of the choice of definition on reported quantities of dead wood in Swedish forests, which to more than 90% are located in the boreal zone. The data collection was made on a subsample of the permanent plots of the Swedish national forest inventory. The objects included were standing dead trees and snags down to 5-cm diameter at breast height, dead lying stems and branches down to a threshold diameter of 1 cm and stumps down to a threshold diameter of 5-cm at normal stump height. Standing trees, snags and stumps were inventoried on 10-m radius circular plots while the downed objects were inventoried using both circular plots and line intersect sampling; thin objects (diameter 1–5 cm) were assessed only through line intersect sampling. The results showed that the estimated volume of dead wood was as high as 25 m³ ha^?1 when all components were included. With the standard Swedish definition, the corresponding estimate was only 10.9 m³ ha^?1, or 43% of the total value. Since definitions of dead wood vary greatly between countries we conclude that great caution must be exercised when figures are compared in connection with international reporting. For example, adding stumps to the Swedish definition would increase the amounts of dead wood from 10.9 to 15.7 m³ ha^?1, i.e. with 44%.     

Evaluation of the biological control agent Rotstop in controlling the infection of spruce and pine stumps by Heterobasidion in Latvia

The biological control agent Rotstop^® composed of a suspension of spores of Phlebiopsis gigantea (Fr.) Jül. is widely used for protecting conifer stumps from aerial infection by Heterobasidion species. The efficacy of Rotstop application on Norway spruce (Picea abies) and Scots pine (Pinus sylvestris) stumps was determined in several locations and at different seasons in Latvia. Mean efficacy in controlling natural infection by Heterobasidion spp. in spruce stumps was 64%, calculated on the basis of number of infected stumps, and 89%, calculated on the basis of area of infected wood on sample discs cut from the stumps. Corresponding proportions for pine were 82% and 95%. The results show that Rotstop can be successfully used for stump treatment in Latvia, although improved efficacy is desirable, particularly in spruce. A Latvian isolate of P. gigantea, selected from numerous isolates in preliminary tests, was included in one experiment and was shown to be as effective as the Rotstop isolate. In untreated spruce stumps Heterobasidion spp. and P. gigantea were present in the same stump three times more frequently than in untreated pine stumps. Heterobasidion spp. infection in untreated spruce stumps was low when P. gigantea covered more than 10% of stump dissection.     

Colonization of Phellinus weirii-infested stumps by Trichoderma viride.

Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] stumps infested with Phellinus weirii (Murr.) Gilb. were inoculated with pellets formulated from fermented barley and spores of three isolates of Trichoderma viride Pers.: Fr. After one year, Trichoderma spp. were isolated from stumps inoculated in June less frequently (12 %) than those inoculated in February (23 %) or in October (29 %). Isolations of Trichoderma spp. from stumps with advanced decay were more frequent (46 %) than from stained stumps (12 %) or from sound stumps (2 %). Isolation success was directly related to wood decay at point of sampling, nearness to source of inoculum, and nearness to stump surface.     

Effect of inoculum density and borate concentration in a stump treatment trial against Heterobasidion annosum

The effectiveness of disodium octaborate tetrahydrate (DOT) as a stump treatment chemical for Sitka spruce in Britain was tested on six occasions by inoculating treated and untreated stumps with basidiospores of Heterobasidion annosum at three concentrations ranging from an average 49 viable spores/ml to 4.9 × 10⁵/ml of water. The extent of colonization of heartwood by H. annosum was measured and, along with the incidence of infected stumps, provided a measure of the combined effects of spore concentration and of the two DOT treatments (15 and 30 g/m²) on the trial results. On untreated stumps, both the incidence of infection and the cross‐sectional area of stump heartwood colonized by the fungus increased with inoculum density. The same effect was evident in treated stumps, but it was reduced by increasing DOT application. Infection was at its lowest in stumps treated with DOT at 30 g/m², being entirely absent from those 60 stumps that were inoculated with the fewest spores. The implications of these findings for the design of trials of control agents that rely on artificial inoculation with H. annosum and for the selection of dose rates to use in harvesting operations are discussed.     

Impact of armillaria root disease and the effect of thinning in a late‐rotation Pinus radiata plantation

In a search for alternative methods for managing armillaria root disease in Pinus radiata plantations in New Zealand, a thinning trial was established in a 1985 planted stand infested by Armillaria novae‐zelandiae. The incidence of chronic (non‐lethal) infection rose significantly following a first thinning at age 7 years that provided additional inoculum in the form of colonized stumps. However, this effect diminished before age 19 years when the small stumps had decomposed and, contrary to expectations, a further increase in infection did not follow a second thinning at age 13.5 years, despite a high incidence of larger colonized second thinning stumps. Apparently the increased vigour and associated resistance in the released older trees was sufficient to counter any increase in inoculum potential following treatment. It therefore now appears that thinning may not be detrimental to the final crop volume in contemporary diseased second‐rotation plantations. However, this treatment furnishes no disease control benefit, and should still be deployed judiciously in heavily infested stands. There was a small, but significant reduction in volume growth on the more severely infected trees during the first 13 years in this trial, but on the larger trees later in the rotation at age 19 years there was no difference in stem volume between infection severity categories. A previous assessment based only on the earlier data therefore overestimates the impact of Armillaria in present and future pine plantations in New Zealand. Nevertheless, its widespread distribution and its demonstrated pathogenicity indicate that forest owners should be conscious of the presence of Armillaria during plantation management.     

In vitro interactions between bacteria isolated from Sitka spruce stumps and Heterobasidion annosum

Culture medium composition affected antagonism by bacterial isolates from Sitka spruce (Picea sitchensis) stumps against Heterobasidion annosum. Fifty percent of bacterial isolates inhibited H. annosum growth on sporulation agar or yeast–dextrose–peptone agar; only 10% of isolates caused inhibition on both media. Proportions of isolates inhibiting H. annosum varied with stump age; fewer isolates from 4‐ or 6‐year‐old stumps exhibited antagonism than isolates from older or younger stumps. Fifteen isolates showing antagonism on sporulation agar were tested against H. annosum in spruce wood cubes. None of the bacterial isolates alone caused a significant weight reduction in inoculated cubes. Relative inoculation times of bacterial isolates and H. annosum had an effect on weight loss in interactions; simultaneous inoculation with isolates and H. annosum inhibited weight loss caused by H. annosum compared with bacteria‐free controls. Inoculation with bacterial isolates 10 days before H. annosum had no effect on the decay rate. In contrast, inoculation with H. annosum 10 days before bacteria increased weight loss of cubes by 200% relative to cultures lacking bacteria. The effect of a mixed bacterial inoculum on weight change in 0.2‐mm spruce wood slips co‐inoculated with H. annosum, Resinicium bicolor, Hypholoma fasciculare, Stereum sanguinolentum or Melanotus proteus differed between different fungi.     

Effect of planting Scots pine around Norway spruce stumps on the spread of Heterobasidion coll.

Management of a Norway spruce stand planted on a site infected by Heterobasidion coll. is problematic because the fungus spreads vegetatively from the colonized stumps of the previous generation to the new seedlings. Growing of mixed stand with more resistant tree species has been suggested to decrease the economic losses caused by butt rot in Norway spruce trees. The mechanistic simulation model Rotstand describing the spread of Heterobasidion coll. in coniferous stands of southern Finland was used to study the effect of planting Scots pines around colonized clear‐felling stumps of Norway spruce of the previous generation. Planting of Scots pines in clusters around colonized stumps markedly decreased the butt rot of Norway spruce trees at the age of 20 years and at clear felling. If the same number of Scots pines were planted randomly, the effect was weak. When the average diameter of colonized clear‐felling stumps was 30 cm, a Scots pine circle with a radius of 3 m resulted in the highest soil expectation value (SEV) at 2% discounting rate, whereas with 40‐cm stump diameter, a 4‐m radius produced the highest SEV. When the proportion of Heterobasidion parviporum in the old colonized stumps was 50% instead of 95%, planting pines around colonized stumps still clearly decreased the butt rot at the age of 20 years and in final felling.     

Heterobasidion annosum infection of Picea abies following manual or mechanized stump treatment

Heterobasidion annosum (Fr.) Bref. s. l. colonization following thinning was studied in 1246 stumps of Picea abies (L.) Karst. trees from 14 previously unthinned stands in Sweden. Treatments included mechanized and manual application of (1) 35% urea solution, (2) Phlebiopsis gigantea (Fr.) Jül. spores, and (3) 5% solution of disodium octaborate tetrahydrate (DOT), and untreated stumps, cut in the summer and winter. Compared with untreated stumps cut in the summer, all stump treatments and winter cuttings significantly reduced the colonized stump area 6–7 weeks after thinning by 88–99%. Mechanized stump treatment provided as good protection as manual treatment against H. annosum infections. The probability of spore infection (p _ij ) was reduced by 53–83% in mechanized treatment and 79–98% in manual treatment compared with untreated summer thinning. In terms of p _ij , urea had significantly higher control efficacy than P. gigantea and manual treatment performed better than mechanized treatment.     

Treatment of wounds on Acer rubrum with Trichoderma viride1

Wounds on 90 Acer rubrum trees were inoculated with Trichoderma viride in July and August 1973 to determine the effect of the fungus on the development of decay. The trees were 45 years old and 15 cm diam at 1.4 m aboveground. Each tree had 12 wounds, 1.4 cm in diam and 5 cm deep. After a year 28 trees were harvested and isolations were made from the discolored, and decayed wood associated with each wound. Trichoderma viride was reisolated from all wounds that were inoculated with it. Hymenomycetes were isolated frequently from decayed wood associated with wounds not inoculated with T. viride. No Hymenomycetes were isolated from wounds inoculated with T. viride.     

Swiss stone pine trees and spruce stumps represent an important habitat for Heterobasidion spp. in subalpine forests

In the Western Italian Alps (WIA), the three European species of the forest pathogen Heterobasidion spp. can coexist in the same area. Heterobasidion parviporum Niemelä & Korhonen and Heterobasidion abietinum Niemelä & Korhonen are normally found in areas with a significant presence of their respective primary hosts, spruce (Picea spp.) and fir (Abies spp.). The host/niche occupied by Heterobasidion annosum (Fr.) Bref. in the region still remains unclear. Although Scots pine (Pinus sylvestris), a major host for this fungal species in other parts of Europe, is abundant in the region, little or no evidence of disease caused by H. annosum is visible in this tree species. Two different, but not mutually exclusive, hypotheses can explain the presence of H. annosum: (1) Scots pines are infected but largely asymptomatic and (2) H. annosum has adapted to different hosts. An analysis of Heterobasidion species was performed in two natural, mixed‐conifer forests using traditional isolation techniques and novel direct molecular diagnosis from wood. In a subalpine stand of mixed spruce (Picea abies), larch (Larix spp.), and Swiss stone pine (Pinus cembra), 18 naturally infected spruces and larches only yielded H. parviporum. A Swiss stone pine in the same stand was extensively colonized by both H. parviporum and H. annosum. In a second subalpine stand, an analysis of 18 spruce stumps and nine Swiss stone pine stumps yielded both H. parviporum and H. annosum isolates. Pine stumps had been mostly colonized by H. parviporum prior to tree felling, suggesting that this species may be secondarily infected by the locally predominant Heterobasidion species (i.e. H. parviporum). Results of our analysis also indicated that primary colonization of spruce stumps (e.g. through basidiospores) was caused by both H. parviporum and H. annosum, while secondary infection of such stumps was mostly because of H. parviporum.     

The effect of wood moisture on infection of Sitka spruce stumps by basidiospores of Heterobasidion annosum

In an inoculation experiment to test the effect of wood moisture content on infection of Sitka spruce (Picea sitchensis) stumps by basidiospores of Heterobasidion annosum, exposure to high rainfall increased infection in the heartwood and reduced sapwood infection compared to covered stumps. This was associated with a greater moisture content in both wood types. Within-treatment variation in the amount of infection was high and it is suggested that endogenous factors in stumps may have a greater influence on infection than the environment or the availability of spores.     

Rhizomorph production and stump colonization by co‐occurring Armillaria cepistipes and Armillaria ostoyae: an experimental study

In managed spruce forests, Armillaria cepistipes and A. ostoyae are efficient stump colonizers and may compete for these resources when they co‐occur at the same site. The aim of this experiment was to quantify the mutual competitive ability of the two Armillaria species in producing rhizomorphs and in colonizing Norway spruce (Picea abies) stumps. Five isolates of A. cepistipes and two isolates of A. ostoyae were simultaneously inoculated pair‐wise into pots containing a 4‐year‐old spruce seedling. For comparison, each isolate was also inoculated alone. One year after inoculation, stumps were created by cutting down the seedlings. Six months after creation of the stumps, rhizomorph production and stump colonization were assessed. Armillaria spp. were identified from 347 rhizomorphs and 48 colonized stumps. Armillaria cepistipes dominated both as rhizomorphs in the soil and on the stumps. Nevertheless, A. ostoyae was relatively more frequent on the stumps than in the soil and A. cepistipes was relatively more frequent in the soil than on the stumps. In both species, the ability to colonize the stumps in simultaneous inoculations was significantly reduced compared with single inoculations. In respect to rhizomorph production, simultaneous co‐inoculations had a slightly stimulatory effect on A. cepistipes and no significant effect on A. ostoyae. Our study suggests a rather neutralistic co‐existence of A. cepistipes and A. ostoyae as rhizomorphs in the soil. Concerning the ability to colonize stumps, the two species experience a mutual negative effect from the interaction, probably because of interspecific competition.     

Hydrothermal and organosolv pretreatments of poplar wood and wheat straw for saccharification by a Trichoderma viride cellulase

Summary Two types of processes have been applied for the pretreatment of lignocellulosic materials in order to render them easily degradable by the cellulase of Trichoderma viride. They were compared at different temperatures, with regard both to the residual dry mass and the improvement in accessibility to the enzyme complex. The latter was measured in terms of glucose liberated, which was quantified by HPLC. Hydrothermolysis proved more effective than the organosolv process for the pretreatment of wheat straw, and vice versa for poplar wood. In terms of the percentage of glucan enzymatically converted to glucose, yields up to 90% could be achieved.One of the authors (H.H.) would like to thank the Austrian Research Center Seibersdorf for granting a bursary. We are also grateful to Mr. Josef Huber for his kind assistance in preparing the three-dimensional plot     

Infection of Picea sitchensis and Pinus contorta stumps by basidiospores of Heterobasidion annosum

Infection of Pinus contorta and Picea sitchensis stumps by basidiospores of Heterobasidion annosum is extremely variable, both within and between sites, but in general P. sitchensis stumps are less sus-ceptible than those of P. contorta. Measurement of the cross-sectional area occupied by H. annosum on each stump provides a more sensitive test of species susceptibility than assessment of the proportion of stumps infected. P. sitchensis stumps become infected on a variety of soils but there is evidence to suggest that infection may be reduced by high rainfall. In some infected stumps, H. annosum is confined to the lower stump tissues. Its absence from the upper portion of the stump may be due to replacement by other micro-organisms or, alternatively, physical conditions in the upper stump tissues may prevent its continued survival after infection has taken place. In both species, but more commonly in P. sitchensis, some stumps remain alive for at least two years after felling, particularly on peat soils, due to the presence of root grafts with neighbouring trees. Results for P. sitchensis suggest that infection occurs more readily in living stumps than in those which die rapidly after felling. The viability of H. annosum basidiospore suspensions can be determined more accurately and more rapidly on a selective agar medium than on conifer stem sections.     

Hymenoscyphus fraxineus can directly infect intact current‐year shoots of Fraxinus excelsior and artificially exposed leaf scars

Hymenoscyphus fraxineus, the causal agent of ash dieback, was inoculated onto intact, unwounded current‐year shoots and leaf scars of 4‐year‐old, potted Fraxinus excelsior seedlings. Pieces of ash wood colonized by the fungus were used as inoculum. Three of 25 (12%) of the inoculated intact shoots and nine of 25 (36%) of the inoculated leaf scars were infected by H. fraxineus and developed typical symptoms of ash dieback, including necrotic lesions on the shoot surface and wood discoloration as well as shoot and leaf wilting distal to the inoculation site. No symptoms occurred on control seedlings, which had been inoculated in the same way but with sterile wood pieces. Visible necrotic lesions on shoots and wood discoloration were statistically significantly longer in proximal than in distal direction from the inoculation site, a pattern which resembles symptoms after natural infection. The ash dieback pathogen was re‐isolated from nine of 12 (75%) of the symptomatic seedlings. These results provide indirect supportive evidence that the fungus infects shoots via leaves and shows that it is able, under experimental conditions using a massive mycelial inoculum, to directly infect intact, unwounded current‐year shoots of its main host in Europe.     

Torque required to twist and cut loose Scots pine stumps

Abstract

Stump wood is a possible source of renewable energy, but before its potential as a fuel can be utilised to a high degree, new harvesting techniques should be developed to reduce the environmental impact (notably ground disturbance) of harvesting stumps. The forces required to lift and drag stumps out of the soil are known. In this study, two unknown and important parameters were addressed: the torque required to uproot stumps by twisting them and the torque required to cut lateral roots around stumps. A new, improved stump-twisting rig was designed and used in trials with 28 Scots pine (Pinus sylvestris) trees (breast-height diameter over bark, 153–427 mm). The measured torque requirements ranged from 10 to 50 kNm. Twisting stumps required more torque than cutting lateral roots around stumps and the required torque increased with increases in stump size. The results indicate that a wrist on a big feller-buncher, but not a conventional rotator used on forest machines, should be able to generate sufficient torque to cut the roots around stumps such as those used in this study.