The pine wood nematode Bursaphelenchus xylophilus (Steiner and Buhrer) Nickle (=B. lignicolus Mamiya and Kiyohara): an assessment of the current position

Pine wood nematode, Bursaphelenchus xylophilus (Steiner andBuhrer) Nickle, is the casual organism of pine wilt disease,a major tree killer in the Far East. This paper describes thebiology of B. xylophilus, particularly its inter-relationshipswith vector insects in the genus Monochamus (Coleoptera: Cerambycidae),tree species and environmental conditions. The principal methodof transmission, and hence of international plant health significance,is introduction of nematodes to susceptible dying or dead treesduring female oviposition. This occurs in all countries wherethe nematode occurs but is the only significant method of transmissionand survival of B. xylophilus in North America. Extensive treemortality in Japan and China is associated with presence ofhighly susceptible tree species, suitable vector species andhigh summer temperatures. Pest risk assessments have been carriedout to determine the risks to Europe; it is concluded that thenematode would undoubtedly survive in Europe but that tree mortalityis likely only in the warmer southern countries. Methods toprevent transfer of nematodes to Europe are discussed in relationto European Union legislation.     

Silviculture of Weymouth Pine

The advantages of being able to grow Weymouth pine (Pinus strobusL.) on a commercial scale are indicated. The growth of thisspecies in Thetford Forest is described, and the point is madethat serious infection from White Pine Blister Rust (Cronartiumribicola J. C. Fischer) has occurred in dense unthinned plantationsonly. Maintenance of vigour by early heavy thinning, and earlybrashing and high pruning to remove moribund branches, are suggestedas means of minimizing deaths from the disease. Whilst individualWeymouth pines in pure plantations treated in this way are nomore susceptible to Blister Rust than individuals in mixturewith other species, mixed plantations have the advantage ofproviding alternative species for the final crop if the Weymouthpine fails.     

Control of the Pine Weevil, Hylobius abietis L., and of Hylastes species

Dipping the tops of plants, prior to planting, in a 5 per centoil-based emulsion formulation of DDT has given good controlof Hylobius but does not control Hylastes and may involve damagedue to phytotoxicity in some circumstances. Experimentationwith newly introduced water-based formulations of DDT and BHCconfirmed earlier findings that there are few significant differencesbetween possible materials. The need to dip whole plants inorder to control Hylastes, with minimum risk of phytotoxicity,has led to the use of 1.6 per cent water-based BHC on a fieldtrial scale with promising results.     

Control of the Large Pine Weevil and Bark Beetles of the Genus Hylastes

Since 1968 a water-based formulation of gamma BHC (Gammacol)has largely replaced DDT as a plant-dipping treatment againstthe large pine weevil Hylobius abietis L. and Hylastes spp.beetles. With Sitka spruce in high rainfall areas, BHC at 1•6 percent is as effective as DDT at 2•5 per cent in controllingthese insects. Neither chemical has proved adequate where exceptionallyhigh populations of Hylobius occurred, though control of Hylasteshas been very good. Plants were dipped in Gammacol, and then stored in sealed polythenebags for 28 days. Provided that the plants were dried sufficientlybefore storing, they subsequently suffered only a slight reductionin height-growth but received adequate protection against beetles.This technique should enable forest nurseries to supply ready-treatedplanting stock. Chlorpyrifos (Dureban) may prove a useful alternativeto BHC.     

NATURAL REGENERATION OF PINE AND BIRCH ON THE HEATHER MOORS OF NORTH-EAST YORKSHIRE

Both pine (Pinus sylvestris L.).and birch (Betula pubescensEhrh.) usually invade after a fire, the invasion reaching greatestforce after 3 to 5 years, then falling off rapidly probablywith the return of the heather (Calluna). Pine seedlings onlygrow vigorously if their tap-roots reach the pan, when secondaryroots are developed extensively. In birch the tap-root is notwell developed, but secondary roots spread vigorously sendingdown sinkers to penetrate the pan. Regeneration of birch ishelped by rotten stumps and roots which its mycorrhizal rootsexplore. The root forms are compared and contrasted and thefindings compared with the work of Laitakari and Erteld.     

The relative efficacy of herbicides for the control of Deschampsia flexuosa (L.) Trin. in woodland establishment in the UK

Deschampsia flexuosa is a commonly occurring calcifuge grasswhich can be detrimental to tree regeneration. In the work reportedhere, two experiments using pot-grown plants and one field experimentwere set up to investigate the relative efficacy of variousherbicides in controlling D. flexuosa. Cycloxydim, glyphosateand imazapyr applied in the summer killed virtually all pot-grownplants of D. flexuosa within 1 year of treatment. Hexazinoneand propyzamide were also effective at the recommended doses.Mixture B enhanced the efficacy of several herbicide treatmentsbut pre-spraying plant moisture stress had no effect on subsequentherbicide activity. Cycloxydim and imazapyr applied in springor summer gave excellent long-term control in the field. Itis concluded that if non-chemical approaches such as canopymanipulation or cultivation fail to give adequate control ofD. flexuosa and herbicide use becomes necessary to allow treeregeneration, then cycloxydim applied at 0.45 kg a.i. ha^–1appears to be an effective alternative to the use of more broad-spectrumproducts, and gives very good tree tolerance. If herbicide useis required prior to tree establishment, glyphosate may be acheaper option and will control a broader spectrum of weeds,although it is slightly less effective than cycloxydim on D.flexuosa.     

Frost Hardiness of Red Alder (Alnus rubra) Provenances in Britain

The phenology and frost hardiness of shoots of 15 provenancesof Alnus rubra growing in Scotland were measured over one autumn,winter and spring. Dates of budset (in September) and the onsetof rapid frost hardening (in October-November) occurred about2 days earlier for each degree latitude of origin northwards,except for an Idaho provenance. However, all provenances dehardenedat about the same time in March and burst their buds between8 and 14 April. Assuming that rapid frost hardening in the autumnwas triggered primarily by shortening daylengths, Alaskan provenancesof A. rubra seemed better adapted to British conditions thansouthern British Columbian provenances, which have been mostcommonly planted. However, even Alaskan provenances are proneto spring frost damage. Scottish A. glutinosa and Alaskan A.sinuata set buds and frost hardened 1–2 weeks before eventhe Alaskan A. rubra, and burst their buds 2–3 weeks laterin April-May. All three species were hardy to below –30°Cfrom December to mid-March.     

Root anchorage and stem strength of black spruce (Picea mariana) trees in regular and irregular stands

A tree winching experiment was conducted, simulating wind actionand resulting damage, in order to assess mechanical resistanceof black spruce (Picea mariana (Mill.) B.S.P.) trees in standsof regular and irregular structures. The critical bending moment(M_c) of winched trees was determined and the relationship betweenM_c and tree and stand characteristics was investigated throughstatistical analyses. Stem mass (SW), average spacing betweentrees (S) and height:diameter ratio (H/d.b.h.) were initiallyselected by a screening procedure to predict M_c. Potential differencesbetween stand structures were tested in mixed models using differentsubsets of the data. Included fixed effects varied between thedifferent models. SW was the most useful and significant variablein all models and H/d.b.h. was significant only when snappedtrees were included in the analysis. When decayed samples wereexcluded, resistance to uprooting was higher in irregular stands.Decay seemed to play an important role in irregular stands andshould be investigated further. Since no difference was observedin the relationship between stem mass and critical turning momentbetween distant sites, relationships should be applicable acrosswide regions. This study provides some of the basic relationshipsrequired to model windthrow risk in irregular stands. However,the effects of stand structure on wind load for individual treeswill also need to be considered.     

The threat of the ambrosia beetle Megaplatypus mutatus (Chapuis) (=Platypus mutatus Chapuis) to world poplar resources

We describe the life cycle of Megaplatypus mutatus (Chapuis)(=Platypus mutatus) and the damage it causes to poplar resourcesin Argentina. This insect, native to the subtropical and tropicalareas of South America, has extended its range into temperateregions, reaching as far south as Neuquén in ArgentineanPatagonia. The damage is caused by the adult insects, whichbore large gallery systems into living poplars (Populus spp.),willows (Salix spp.) and many other broadleaf species, includingimportant fruit trees species such as apples (Malus spp.), walnuts(Juglans spp.) and avocados (Persea spp.). The galleries degradethe lumber and weaken the tree stems, which often then breakduring windstorms. A recent introduction of M. mutatus to Italydemonstrates that this insect can be transported long distancesbetween countries, and therefore presents a threat worldwide—particularlyto poplar cultivation. We review the taxonomic nomenclaturefor this pest, provide a summary of the life cycle, hosts anddamage and summarize actions taken to reduce the risk of introductionof M. mutatus to Canada.     

Controlled Pollination Studies with Shining Gum (Eucalyptus nitens (Deane & Maiden) Maiden)

Intraspecific and interspecific controlled pollinations wereattempted on 12 E. nitens trees representing a range of provenances.Over consecutive flowering seasons there were consistent differencesin the relative flowering times of five genotypes on one site.Of 24 intraspecific combinations attempted in 1985 62 per centset seed, and overall 45 per cent of flowers pollinated setseed. All but one of 10 interspecific combinations succeededwith 33 per cent of flowers pollinated setting seed. The maternalinfluence was generally stronger than the paternal, in termsof number of seed set and seed weight. For all mothers, themean number of seeds per capsule from self-pollinated and open-pollinatedflowers were only 2.2 and 3.8, compared with 6.8 and 7.9 forflowers hand-pollinated with E. gunnii and E. nitens pollenrespectively. Implications of various aspects of the reproductivebiology of these species on breeding programmes are discussed.Two previously identified forms of E. nitens showed consistentdifferences in floral morphology, flowering time and seed maturity.Their taxonomic status is commented on.     

CONTROL OF CUTWORM IN FOREST NURSERIES

Larvae of Agrotis segetum Schiff (cutworms) damaged seedlingson a light loam soil at Ken nington Nursery, Oxford. Experimentscarried out in 1955–7 investigated the effect of BHC,DDT, aldrin, and dieldrin on cutworms and their phytotoxicityto Sitka spruce (Picea sitcbensis) seedlings. A spray containing 3 lb. aldrin per acre (as a 30 per cent,miscible oil) or 1? lb. dieldrin per acre (as a 15 per cent,miscible oil) gave excellent control of Agrotis segetum larvaeand did no damage to the seedling crop. Both insecticides wereapplied in 100 gallons water per acre. Immediate control ofcutworm was obtained with applications at time of expected larvalemergence (mid-June) or at time of first visible crop damage(mid-July); applications one month later gave good control after3 days. Stock beds containing seedlings of all the conifers commonlyused in Britain have been sprayed in mid-July with aldrin anddieldrin at half the rate used in the experiments. No specieswas damaged and control of cutworm was good.     

The Ecology of Armillaria mellea Vahl (ex Fries) in the Indigenous and Exotic Woodlands of Rhodesia

A. mellea is the cause of severe killing in young plantationsof Pinus elliottii in Rhodesia. P. patula is more resistantthough it may act as a carrier of the fungus; its resistancemay be overcome when planted in conditions of high inoculumconcentration such as clear-felled areas of P. elliottii whichhave a previous disease history. The source of infection isthe stumps of felled indigenous trees. Subsequent spread inthe pine is from tree to tree by root contact. The rate of increasein the incidence of the disease up to thirteen years from plantinghas been plotted. An initially logarithmic increase of killingshows a significant decline when the plantation is eight toten years of age. Viable basidiospores of A. mellea are presentin the air spora but little evidence of their importance inthe spread of A. mellea could be found.     

Lypha dubia (Fall.)(Dipt.: Tachinidae) as a Parasite of the European Pine Shoot Moth,Rhyacionia buoliana (Schiff.)Lep.: Eucosmidae) in Europe

Ohne Zusammenfassung

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Lypha dubia (Fall.)(Dipt.: Tachinidae) as a Parasite of the European Pine Shoot Moth,Rhyacionia buoliana (Schiff.)Lep.: Eucosmidae) in Europe

     

Long-term ecology of native pinewood communities in East Glen Affric, Scotland

Fossil pollen, stomata and charcoal were examined from a lakesedimentary sequence in the Glen Affric National Nature Reserve,one of the largest areas of remnant native pine woodland inScotland, in order to assess ecosystem dynamics over the last11 000 years. Results reveal that pinewood communities havebeen continuously present in East Glen Affric for the last 8300years. Pinus sylvestris first arrived in the area around 9900cal. BP, but occurred in only low abundance for the subsequent1600 years. Pine populations expanded around 8300 cal. BP andremained in relatively constant abundance throughout the remainderof the Holocene. There is no evidence of a hypothesized regionalmid-Holocene ‘pine decline’ at the site. Charcoalresults reveal that pinewood communities in East Glen Affricdo not appear to have been dependent on fire for either theirestablishment or their maintenance as has previously been suggested.     

Fomes annosus Butt-Rot of Sitka Spruce IV. Observations on the Distribution of Cryptosporiopsis abietina (Petrak) in the Stems of Rotted Trees

Cryptosporiopsis abietina was isolated from the heartwood of12 out of 18 Sitka spruce suffering from butt rot caused byFomes annosus, but from none of eight healthy trees from thesame plantations. C. abietina was present in a distinct zoneabove the tissue colonised by F. annosus. It was present inboth sound wood, and in wood with stain or incipient decay. C. abietina inhibited the growth of F. annosus on malt agar,and to a lesser extent in autoclaved Sitka spruce heartwood.The possible influence of this potentially antagonistic funguson infection by F. annosus is briefly discussed.     

Insecticidal Control of the Pine Looper Moth in Great Britain: III. Aerial Spraying with Tetrachlorvinphos

In 1969 the routine annual survey of pupal populations of Bupaluspiniarius L., the Pine looper moth, did not include the forestareas of Wykeham and Langdale where, unnoticed, a build-up ofthe population to epidemic proportions had taken place resultingin the complete defoliation of 150 acres (61 ha). Surveys carriedout in these and the surrounding areas in 1970 revealed extremelyhigh counts, indicating the strong possibility that insecticidalcontrol would be necessary. Alternative insecticides to DDTwere screened and the more promising were field tested resultingin the selection of tetrachlorvinphos. Egg counts were usedto confirm the presence of a damaging population and to defineits boundaries for control spraying which was carried out over1,300 acres (526 ha). Estimates of larval mortality and laterassessments of pupae indicate that the control operation wassuccessful.     

Growth and provenance of Norway maple (Acer platanoides) in lowland Britain

The results of an experiment to investigate the early growthand form of ten different provenances of Norway maple (Acerplatanoides L.) are described. Two sites were planted and after8 years survival was 88 per cent and 95 per cent and heightincrement was 402 cm and 201 cm; confirmmg the potential ofNorway maple to be a productive forest tree. Provenances thatperformed well were from Germany, the Netherlands, Denmark andYugoslavia; exact locations were not known for all seed collections.A provenance from Russia was included, material from this fareast has rarely been tested in Britain. However, as expected,its performance was relatively poor. The main constraint tofurther planting of Norway maple is the palatability of thebark to grey squirrels (Sciurus carolinensis Gmelin.). However,it is a useful tree for high pH and heavy soils and as an alternativespecies to sycamore (Acer pseudoplatanus L.).     

Future outlook for Pinus patula in South Africa in the presence of the pitch canker fungus (Fusarium circinatum)

Approximately 50% of the area planted to softwood trees in South Africa has been established with Pinus patula, making it the most important pine species in the country. More effort has gone into developing this species for improved growth, tree form and wood properties than with any other species. This substantial investment has been threatened in the last 10 years by the pitch canker fungus, Fusarium circinatum. The fungus infects and contaminates nursery plants and, once transferred to the field, causes severe mortality of young trees in the first year after establishment. Although nurserymen have some control of the disease, it is recognised that the best long-term solution to mitigate damage because of F. circinatum infection is to identify tolerant species, clones and hybrids for deployment in plantations in the future. Research has shown that alternative species such as P. tecunumanii, P. maximinoi and P. elliottii are suitable for warm sites. Pine hybrids, particularly between P. patula and the high-elevation sources of P. tecunumanii, appear to be a suitable replacement on subtemperate and temperate sites. Although these alternative species and hybrids are more sensitive to subfreezing temperatures than P. patula, their planting range can be increased by including cold tolerance as a selection criterion. Future breeding efforts will most certainly focus on improving the tolerance of pure P. patula to F. circinatum, which can be achieved by identifying specific family crosses and tolerant clones. The commercial deployment of disease-tolerant control-pollinated P. patula and hybrid families will most likely be established as rooted cuttings, which requires more advanced propagation technology. In the long term, new seed orchards comprised of P. patula clones tolerant to F. circinatum could be used to produce seed for seedling production.     

Significance and Control of Attack by the Ambrosia Beetle Trypodendron lineatum (Oliv.) (Col. Scolytidae) in Argyllshire Forests

Following damage to saw-logs in Argyllshire forests methodsof controlling attack by the ambrosia (pinhole borer) beetleTrypodendron lineatum (Oliv.) have been studied. Attack beginsin April, reaches a peak in May but then declines rapidly, beingof negligible importance after August. Trees felled betweenNovember and January are more susceptible but few logs leftat stump are attacked. Damage is much more widespread in logsstacked in the forest or at the milt. Good protection can be provided economically by spraying stackedtimber with an emulsion of 0?75 per cent, gamma BHC. A freshtreatment is advisable if logs are restacked or the outsideones removed from a stack between April and August. These treatments,combined with rapid extraction and conversion of logs duringthe summer, should reduce the incidence of damage. Suspensionof felling during this period appears unjustified if these measuresare followed; moreover, freshly felled timber is less susceptibleto attack. Although the Lymexylid beetle Hylecoetus dermestoides L. isalso widespread, damage is less apparent due to the absenceof associated staining. The control measures recommended forTrypodendron appear suitable for Hylecoetus.     

NOTE ON THE FIRST BRITISH OCCURRENCE OF IPS CEMBRAE HEER (COL. SCOLYTIDAE)

During 1955 the larch bark beetle, Ips cembrae Heer, was discoveredin twenty-nine localities in Moray, Nairn, Banff, and Inverness.These are the first British records for this species. It isassumed that I. cembrae entered the country in post-war shipmentsof German timber and has persisted in small numbers until thedamage to woodlands caused by the gale in 1953 provided favourableconditions for its increase. A conspicuous feature of attackis the twig tunnelling of the adult beetles which produces crownpruning. In one locality I. cembrae succeeded in breeding inand killing standing European larch of some 45 years of age.