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Eastern Australia was subject to its hottest and driest year on record in 2019. This extreme drought resulted in massive canopy die-back in eucalypt forests. The role of hydraulic failure and tree size on canopy die-back in three eucalypt tree species during this drought was examined. We measured pre-dawn and midday leaf water potential (Ψleaf ), per cent loss of stem hydraulic conductivity and quantified hydraulic vulnerability to drought-induced xylem embolism. Tree size and tree health was also surveyed. Trees with most, or all, of their foliage dead exhibited high rates of native embolism (78-100%). This is in contrast to trees with partial canopy die-back (30-70% canopy die-back: 72-78% native embolism), or relatively healthy trees (little evidence of canopy die-back: 25-31% native embolism). Midday Ψleaf was significantly more negative in trees exhibiting partial canopy die-back (-2.7 to -6.3 MPa), compared with relatively healthy trees (-2.1 to -4.5 MPa). In two of the species the majority of individuals showing complete canopy die-back were in the small size classes. Our results indicate that hydraulic failure is strongly associated with canopy die-back during drought in eucalypt forests. Our study provides valuable field data to help constrain models predicting mortality risk.

In Australia, Phytophthora cinnamomi is the only species reported as the causal agent of stem canker and root rot in macadamia. In other countries, five Phytophthora species have been reported to cause diseases in macadamia, which led us to question if more than one Phytophthora species is responsible for poor tree health in macadamia orchards in Australia. To investigate this, samples were collected from the rhizosphere, stem, and root tissues of trees with and without symptoms, nurseries, and water sources from 70 commercial macadamia orchards in Australia. Phytophthora isolates were identified based on morphological characteristics and DNA sequencing. P. cinnamomi was the most predominant and widely distributed species, and was obtained from the different types of samples including symptomless root tissues. In addition to P. cinnamomi, only P. multivora was isolated from diseased tissue (stem canker) samples. Six other Phytophthora species were obtained from the rhizosphere samples: P. pseudocryptogea, P. citrophthora, P. nicotianae, P. gondwanense, P. sojae, and a new Phytophthora taxon. Only P. cinnamomi was obtained from macadamia nursery samples, while five Phytophthora species were obtained from water sources. Of the heterothallic Phytophthora species, mating type A2 isolates were dominant in P. cinnamomi isolates, whereas only mating type A1 isolates were obtained for P. nicotianae, P. pseudocryptogea, and P. citrophthora. Pathogenicity assays revealed that P. cinnamomi and P. multivora caused significantly larger stem and leaf lesions than P. citrophthora, P. nicotianae, and P. pseudocryptogea. Phytophthora sp. and P. sojae were nonpathogenic towards leaves and stems.

Spotted lanternfly (SLF), Lycorma delicatula (Hemiptera: Fulgoridae) is an invasive phloem-feeding planthopper currently being quarantined in a 24 000 km2 area in eastern Pennsylvania, New Jersey, Maryland, and Delaware, with a second population under quarantine in a 46 km2 area in Virginia. Because this insect feeds on over 70 species of plants, it has the potential to impact a wide range of sectors, and as a result, there has been great public speculation that the economic impact of SLF could be severe. SLF is a large-bodied voracious feeder that reduces plant resources directly by feeding, and indirectly, from sooty mold that grows on its excrement and blocks photosynthesis. SLF is causing severe damage to vineyards from feeding, and is a significant nuisance pest. It has high potential for spread via human-mediated transport, particularly of egg cases, and may therefore significantly impact commerce in the near future. The ultimate impacts of this insect are not yet known, and will depend upon its longer term impacts on plant and tree health, and the extent to which its range expands. © 2019 Society of Chemical Industry.

This work is based on the research supported by the National Research Foundation of South Africa (NRF; grant 91570). The members of the Tree Protection Co-operative Programme (TPCP), the THRIP initiative of the Department of Trade and Industry, the DST/NRF Centre of Excellence in Tree Health Biotechnology (CTHB) of the Forestry and Agricultural Biotechnology Institute (FABI), University of Pretoria, South Africa.

Summary Forest pests drive tree mortality through disruption of functional traits linked to nutrient acquisition, growth, and reproduction. The impacts of attack by individual or multiple aboveground herbivores on root functional traits critical to tree health have received little attention. This is especially true for exotic herbivores, organisms often found in disturbed forests. We excavated whole-root systems from eastern hemlock (Tsuga canadensis) individuals experimentally infested with hemlock woolly adelgid (HWA: Adelges tsugae) and elongate hemlock scale (EHS: Fiorina externa) individually, or in combination, for periods of two and four years. Belowground root biomass, functional traits, and storage nutrients were measured to assess impacts of herbivory. We also quantified ectomycorrhizal fungal (EMF) colonisation of fine roots and used culture-independent methods to examine EMF diversity. Trees infested with HWA had a greater root mass fraction (root to total biomass ratio), although feeding had no observable effects on root functional traits (e.g., specific root length) or on resource allocation to roots. HWA feeding did significantly reduce EMF colonisation of hemlock fine roots, though surprisingly, EMF diversity and that of other fungal associates were unaffected. In contrast to HWA, EHS (alone or in conjunction with HWA) feeding had no observable effect on belowground traits or EMF colonisation alone; however, its presence mediated HWA effects when trees were co-infested. Simultaneous infestation within the same year yielded significant reductions in EMF colonisation, while prior EHS attack weakened HWA effects. Our results collectively suggest that prior EHS attack dampens the impact of HWA on belowground functional traits. This highlights how the timing and sequence of herbivore arrival can alter plant-mediated interactions between herbivores and their effects on above-belowground linkages and associated tree health. This article is protected by copyright. All rights reserved.

Winter is an understudied but key period for the socioecological systems of northeastern North American forests. A growing awareness of the importance of the winter season to forest ecosystems and surrounding communities has inspired several decades of research, both across the northern forest and at other mid‐ and high‐latitude ecosystems around the globe. Despite these efforts, we lack a synthetic understanding of how winter climate change may impact hydrological and biogeochemical processes and the social and economic activities they support. Here, we take advantage of 100 years of meteorological observations across the northern forest region of the northeastern United States and eastern Canada to develop a suite of indicators that enable a cross‐cutting understanding of (1) how winter temperatures and snow cover have been changing and (2) how these shifts may impact both ecosystems and surrounding human communities. We show that cold and snow covered conditions have generally decreased over the past 100 years. These trends suggest positive outcomes for tree health as related to reduced fine root mortality and nutrient loss associated with winter frost but negative outcomes as related to the northward advancement and proliferation of forest insect pests. In addition to effects on vegetation, reductions in cold temperatures and snow cover are likely to have negative impacts on the ecology of the northern forest through impacts on water, soils, and wildlife. The overall loss of coldness and snow cover may also have negative consequences for logging and forest products, vector‐borne diseases, and human health, recreation, and tourism, and cultural practices, which together represent important social and economic dimensions for the northern forest region. These findings advance our understanding of how our changing winters may transform the socioecological system of a region that has been defined by the contrasting rhythm of the seasons. Our research also identifies a trajectory of change that informs our expectations for the future as the climate continues to warm.

Following a request from the European Commission, the EFSA Panel on Plant Health performed a pest categorisation of Cronartium harknessii, Cronartium kurilense and Cronartium sahoanum, which are well-defined and distinguishable tree fungal pathogens of the family Cronartiaceae. In 2018, these species were moved from the genus Endocronartium to the genus Cronartium. These pathogens are not known to be present in the EU and are regulated in Council Directive 2000/29/EC (Annex IAI) (as non-European Endocronartium spp.) as harmful organisms whose introduction into the EU is banned. These three fungi are autoecious rusts completing their life cycle on Pinus spp. C. harknessii is known as the western gall rust or pine-pine gall rust in North America (Canada, the USA and Mexico). C. kurilense and C. sahoanum are reported from Russia (North Kuril Islands) and Japan. The pathogens could enter the EU via host plants for planting and cut branches. The pathogens could establish in the EU, as climatic conditions are favourable and Pinus spp. are common. The pathogens would be able to spread following establishment by movement of host plants for planting and cut branches, as well as natural spread. Should these pathogens be introduced in the EU, impacts can be expected on pine forests, plantations, ornamental trees and nurseries. The pathogens cause formation of stem galls, which kill young trees and result in stem defect in older trees. The main knowledge gap concerns the limited available information on C. kurilense and C. sahoanum compared to C. harknessii. The criteria assessed by the Panel for consideration of C. harknessii, C. kurilense and C. sahoanum as potential quarantine pests are met, whilst, for regulated non-quarantine pests, the criterion on the pest presence in the EU is not met.

Following a request from the European Commission, the EFSA Panel on Plant Health performed a pest categorisation of Melampsora farlowii, a well-defined and distinguishable fungus of the family Melampsoraceae. M. farlowii is the causal agent of a leaf and twig rust of hemlocks (Tsuga spp.) in eastern North America. The pathogen is regulated in Council Directive 2000/29/EC (Annex IAI) as a harmful organism whose introduction into the EU is banned. M. farlowii is not reported to be present in Europe and could enter the EU via host plants for planting and cut branches. Cones and fruits are listed as plant parts that can carry the pest in trade and transport, but are not regulated. The pathogen could establish in the EU, as climatic conditions are favourable and Tsuga spp. have been planted as ornamentals and in plantations in several EU countries. M. farlowii would be able to spread following establishment by human movement of host plants for planting and cut branches, as well as natural spread. Should the pathogen be introduced in the EU, impacts can be expected on Tsuga spp. plantations, ornamental trees and especially nurseries. Hemlock rust is considered a destructive rust attacking Tsuga spp., particularly Tsuga canadensis in nurseries. The main uncertainties concern whether the impact of the pathogen in plantations under European conditions could be different than observed in eastern North America, whether fruit/cones of Tsuga can be a pathway of entry, and the dissemination potential of the pathogen under European conditions. However, M. farlowii is found in North America in most of the natural distribution range of T. canadensis, suggesting little dispersal limitation of the pathogen. The criteria assessed by the Panel for consideration as a potential quarantine pest are met, whilst, for regulated non-quarantine pests, the criterion on the pest presence in the EU is not met

Trees are natural repositories of valuable environmental information that is preserved in the growth and structure of their stems, branches and roots. Dendrochronological analyses, based on the counting, crossdating and characterisation of incrementally formed wood rings, offer powerful insights for diverse fields including ecology, climatology and archaeology. The application of this toolset is likely to increase in popularity over coming decades due to advances in the field and a reduction in the cost of analyses. In research settings where the continued value of living trees subject to dendrochronological investigation is important, the use of an increment bore corer to extract trunk tissue is considered the best option to minimise negative impacts on tree health (e.g. stress and fitness). A small and fragmented body of literature, however, reports significant after-effects, and in some cases fatal outcomes, from this sampling technique. As it stands, the literature documenting increment bore coring (IBC) impacts lacks experimental consistency and is poorly replicated, making it difficult for prospective users of the method to assess likely tree responses to coring. This paucity of information has the potential to lead to destructive misuse of the method and also limits its safe implementation in circumstances where the risk of impacts may be appropriate. If IBC is to fulfil its potential as a method of choice across research fields, then we must first address our limited understanding of IBC impacts and provide a framework for its appropriate future use. Firstly, we review the historical context of studies examining the impacts of IBC on trees to identify known patterns, focal issues and biases in existing knowledge. IBC wound responses, particularly those that impact on lumber quality, have been the primary focus of prior studies. No universal treatment was identified that conclusively improved wound healing and few studies have linked wound responses to tree health impacts. Secondly, we build on literature insights using a theoretical approach to identify the most important factors to guide future research involving implementation of IBC, including innate tree characteristics and environmental factors. Thirdly, we synthesise and interrogate the quantitative data available through meta-analysis to identify risk factors for wound reactions. Although poor reporting standards, restricted scopes and a bias towards temperate ecosystems limited quantitative insight, we found that complete cambial wound closure could still harbour high rates of internal trunk decay, and that conditions favouring faster growth generally correlated with reduced indices of internal and external damage in broadleaved taxa. Finally, we propose a framework for guiding best-practice application of IBC to address knowledge gaps and maximise the utility of this method, including standardised reporting indices for identifying and minimising negative impacts on tree health. While IBC is an underutilised tool of ecological enquiry with broad applicability, the method will always incur some risk of negative impacts on the cored tree. We caution that the decision to core, or not to core, must be given careful consideration on a case-by-case basis. In time, we are confident that this choice will be better informed by evidence-based insight.

Tree Protection Co-operative Program (TPCP), the THRIP initiative of the Department of Trade and Industry, the DST/NRF Centre of Excellence in Tree Health Biotechnology (CTHB) of the Forestry and Agricultural Biotechnology Institute (FABI), University of Pretoria, South Africa and the Kenya Forestry Research Institute (KEFRI).

The rapid emergence of Acacia mangium as the key industrial plantation species in Indonesia has been followed by the equally rapid emergence of red root rot ( Ganoderma philippii ) as its potential nemesis. As a consequence, and on severely affected mineral soils in equatorial tropical environments in particular, A . mangium may no longer be capable of producing commercial yields after three rotations. In this experiment, 100-tree plots were established in commercial plantings of A . mangium at five sites which represented the range of growing conditions used for plantation establishment in Indonesia. Repeated monitoring at approximately 6-month intervals of above- and below-ground variables was used to explore relationships between measures of tree health and root rot. Crown colour and density were poor predictors of either the presence or severity of infections. Tree mortality increased more or less linearly with time and led to the progressive coalescence of initially discrete disease gaps. The average rate of disease development was about 0.3% per month, and average time from infection to tree death was conservatively estimated at around 1 year. Trees with more than four dead/missing neighbours had a >50% chance of being dead by the following monitoring. By the end of the monitoring period >40% of trees were classified as dead/missing, although this value varied from 20 to 70% depending on site, tree age and rotation. Canonical discriminant analysis correctly allocated >90% trees into their correct group on the first monitoring and similarly classified whether trees would be dead or missing in the following monitoring.

Newly-established populations of invasive wood-inhabiting insects provide an opportunity for the study of invasion dynamics and for collecting information to improve management options for these cryptic species. From 2011 to 2013, we studied the dynamics of the goldspotted oak borer Agrilus auroguttatus Schaeffer (Coleoptera: Buprestidae), a new pest of oaks in southern California, at six sites that had been colonized recently. At all sites, the percentage of coast live oaks Quercus agrifolia Nee, colonized by A. auroguttatus increased between 2011 (6-33%) and 2013 (23-40%), although beetle densities did not grow rapidly at most sites. From 2011 to 2013, there were minor changes in signs and symptoms of A. auroguttatus infestation (adult emergence holes, bark staining, and evidence of woodpecker foraging), except at one site where an outbreak occurred. At some sites, noticeable negative changes in oak crown health occurred 1 year prior to positive A. auroguttatus population growth. Among sites, most of the A. auroguttatus population density (66-93%) was produced by a small number of heavily-infested trees (= brood trees). Early identification and removal of brood trees in newly-invaded areas could slow the growth of A. auroguttatus populations.

The Department of Science and Technology (DST)/National Research Foundation (NRF) Centre of Excellence in Tree Health Biotechnology (CTHB) and members of the Tree Protection Co-operative Programme (TPCP), South Africa.

Eucalyptus grandis and its hybrids, as well as Acacia mearnsii, are important non‐native trees commonly propagated for forestry purposes in South Africa. In this study, we conducted pathogenicity trials to assess the relative importance of five commonly isolated Phytophthora spp. (Phytophthora alticola, P. cinnamomi, P. frigida, P. multivora and P. nicotianae) from the plantation environment on E. grandis and A. mearnsii seedlings. Overall E. grandis was more susceptible to the tested Phytophthora spp. than A. mearnsii. Phytophthora cinnamomi was the only pathogen that had a significant negative effect on both the host tree species, leading to a reduction in root and shoot weight as well as to death in the case of E. grandis. Phytophthora alticola and P. nicotianae exclusively affected E. grandis and A. mearnsii, respectively. This study updated the current knowledge on the pathogenicity of Phytophthora spp. on two important non‐native commercially propagated tree species from South Africa.

Huanglongbing (HLB) is a systemic disease of citrus caused by phloem-limited bacteria ‘Candidatus Liberibacter’ spp. with ‘Ca. Liberibacter asiaticus’ (Las) the most widespread. Phloem-limited bacteria such as liberibacters and phytoplasmas are emerging as major pathogens of woody and herbaceous plants. Little is known about their systemic movement within a plant and the disease process in these tissues. Las movement after initial infection was monitored in leaves and roots of greenhouse trees. Root density, storage starch content, and vascular system anatomy in relation to Las presence in field and greenhouse trees, both with and without symptoms, showed the importance of root infection in disease development. Las preferentially colonized roots before leaves, where it multiplied and quickly invaded leaves when new foliar flush became a sink tissue for phloem flow. This led to the discovery that roots were damaged by root infection prior to development of visible foliar symptoms and was not associated with carbohydrate starvation caused by phloem-plugging as previously hypothesized. The role of root infection in systemic insect-vectored bacterial pathogens has been underestimated. These findings demonstrate the significance of early root infection to tree health and suggest a model for phloem-limited bacterial movement from the initial insect feeding site to the roots where it replicates, damages the host root system, and then spreads to the rest of the canopy during subsequent leaf flushes. This model provides a framework for testing movement of phloem-limited bacteria to gain greater understanding of how these pathogens cause disease and spread.

The Tree Protection Cooperative Programme (TPCP) and the Department of Science and Technology (DST)/ National Research Foundation (NRF) Center of Excellence in Tree Health Biology.

Eucalypt woodlands have been extensively cleared in southern Australia for agricultural production and the scattered trees that remain ("paddock trees") are at risk of extinction without conservation action to lift recruitment rates. Here we assessed the reproductive, demographic, and genetic structure of trees from two vegetation types (paddock vs. intact vegetation fragments) for each of two species of eucalypts to characterize post-clearance population structure and to evaluate paddock trees as seed sources for revegetation. Paddock trees of both species were structurally larger than trees in vegetation fragments, but seedlings and saplings were completely absent in paddocks due to ongoing agricultural land use. Eucalyptus leucoxylon paddock trees had high mortality, but overall paddock trees were not in poorer condition than fragment trees. E. leucoxylon paddock trees had lower reproductive output than trees in fragments, and Eucalyptus camaldulensis paddock trees had higher. Levels of genetic diversity of adult trees were very similar in the two vegetation types, and there was no genetic differentiation between paddock trees and remnant vegetation across our survey sites. These results suggest that paddock trees represent a potential source of seed to contribute to genetically diverse woodland restoration plantings, though further trials will be required to evaluate seedling survival on agriculturally modified land and under predicted future climate conditions.

Summary Allochthonous Norway spruce stands in the KysuckeBeskydy Mts. (north-western Slovakia) have been exposed to substantial acid deposition in the recent past and grow in acidified soil conditions with mean pH of about 4.0 in the topsoil. We selected 90 spruce trees representing 30 triplets of different crown status: healthy, stressed and declining to assess the relationship between crown and fine root status. Sequential coring and in-growth bags were applied to each triplet to investigate fine root mass and growth in the soil depths of 0-10 and 10-20 cm. Fine root quantity (biomass and necromass), turnover (production over standing stock), morphological features (specific root length, root tip density) and chemical properties (Ca:Al molar ratio) were compared among the abovementioned health status categories. Living fine root biomass decreased with increasing stress, while the ratio of dead to living biomass increased. Annual fine root production decreased and specific root length increased in stressed trees when compared to healthy or declining trees, a situation which may be related to the position of trees in the canopy (healthy and declining - dominant, stressed - co-dominant). The Ca:Al ratio decreased with increasing crown damage, indicating a decreased ability to filter out aluminium. In conclusion, fine root status appears to be linked to visible crown damage and can be used as a tree health indicator.

Summary 1 This paper assesses whether tree-ring patterns found in recently dead mountain pines (Pinus mugo Turra) infected by Armillaria spp. differ from those infected by Heterobasidion annosum, and determines whether and to what extent tree rings may be used as indicators of tree-decline history (i.e. tree health conditions in relation to disease history) prior to death. 2 Dendroecological and phytopathological analyses were undertaken in the Swiss National Park. The calendar year of death of the standing dead trees was determined by cross-dating ring-width patterns of dead trees to reference chronologies from living trees. This procedure is not, however, exact as there may be multiple intermittent missing rings. 3 A remarkable discrepancy (up to 31 years) was found between the tree-death year estimated through crown condition assessment (i.e. the presence or lack of green needles) and the date of the outermost tree ring (when tree-ring production ceased). New needles may form and existing ones remain green for some years after the cambium at different heights along the stem has ceased activity and no new wood cells are being formed. 4 Ring-patterns in trees infected by Armillaria differ from those in trees infected by H. annosum. All dead trees infected by Armillaria had a slow growth decrease indicating suppression for several decades, and suggesting that Armillaria attacked trees that were already weakened by competition. In contrast, trees infected by H. annosum died over a very short period of time, although they may have been infected a long time previously. Nevertheless H. annosum seems to infect and kill trees directly , whereas Armillaria, at this site, is a secondary pathogen. 5 This study demonstrates that tree rings may be used as indicators of the history of tree decline prior to tree death. However, the history of tree disease is difficult to reconstruct fully, e.g. tree rings do not enable the onset of infection to be dated.

Assessment of forest health on a national scale is a difficult task. One pa- rameter used to rapidly classify tree health is crown transparency, or the amount of sky seen through the crown. Previous investigations of sources of error in estimating crown transparency concentrated on observer experience and perception, and on lighting condi- tions, showing that the error can be as much as + 15%. Here we tested the hypothesis that crown dimensions, which determine the path-length of the line of sight of the observer through crowns, introduce a large bias in estimates of crown transparency. Both theoretical and empirical results show that crown transparency is highly sensitive to crown dimensions. Crowns of trees with path-lengths >10 m are always likely to be rated 80% transparent. The misclassification of tree health is further exacerbated by the reduction in the rate at which transparency decreases per unit of path-length as the path-length increases, reflecting a lower average leaf density with increasing crown size. Thus we propose that available crown transparency data may be used to rank relative tree health within narrow intervals of path-length, thereby incorporating the effects of crown dimensions on transparency.

The cause of tree disease in any location is difficult to diagnose because of the multiplicity of potential causes. Spatial analysis provides useful evidence on the significance, scale and shape of patterns for disease diagnosis. This study explores the causes of dieback through spatial analysis of tree health at Coranderrk Reserve, an example of an important conservation reserve on the urban fringe of Melbourne, Victoria. Ca. 200 trees were sampled at two sites and measured for position, diameter and height in each of two different commu- nity types. An index of tree health was developed, and each tree was assigned a value of health. Dead trees were catego- rized based on state of decay. Correlograms using Moran's I found significant spatial structure at both study sites. The study employed a method of analysis that compares the spatial patterns in dead and living trees. When all dead trees were eliminated from the analysis, significant spatial pattern was found only at one site. The spatial structures obtained were compared with those expected from the different possible causes of tree dieback. Some potential explanations were eliminated. The results illustrate how spatial analysis may make useful contributions to disease diagnosis if employed systematically together with other modes of investigation.

Mistletoes are hemiparasites that occur worldwide in many types of forest, woodland and shrubland ecosystems (Watson 2001). Some species are regarded as pests due to their detrimental effects on host species (Hawksworth 1983; Reid & Yan 2000). Heavy infestations can affect the growth, productivity and form of host trees, and may cause host death (Reid et al . 1994; Shaw et al .2004, 2008). In south-eastern Australia, mistletoes often are visibly obvious in trees along roadsides, in paddocks and on the margins of open forests; and concerns have been expressed about their potentially detrimental effects on host trees.Despite this, little quantitative information is available on the effects of mistletoes on tree health and mortality (Reid et al . 1994). Are detrimental effects widespread or localized? A first step is to assess whether trees parasitized by mistletoe are less healthy than those without such parasites. Here, we investigate the relationship between parasitism by Box Mistletoe ( Amyema miquelii (Lehm. ex Miq.) Tiegh.), a common species in south-eastern Australia, and the health of trees of a widespread host species, Grey Box ( Eucalyptus microcarpa (Maiden) Maiden), across a large geographic region.

Cambial electrical resistance (CER) was used as an objective measure of vitality of silver fir (Abies alba Mill.) in the forests of Slovenia. Trees were rated during the growing season by CER and a subjective crown status index (CSI). Both CER and CSI were inversely correlated to annual ring width increment. Using both CER and CSI, fir were assigned to vitality and vigor categories. Inferences made from these categories and radial growth trends indicated that ring growth decreased prior to the development of canopy symptoms. This decrease in ring growth would have been detected as an increase in CER. This pattern of decline is consistent with the decline of trees due to chronic belowground stress. Variation in CER was due both to the vascular cambium and to the thickness of the nonconducting phloem.

In January 2016, Science and Advice for Scottish Agriculture received shoots of Rhododendron ponticum submitted by a Forestry Commission Scotland Tree Health Officer. The samples had been collected during a survey for P. ramorum from an …

Apricot (Pruntts armeniaca) and almond (P. dulcis) trees at the first leaf stage were planted in soil infested with Verticittium dahliae and mulched with transparent or black polyethylene film, or not mulched, in the San Joaquin Valley of California, March-August 1990. During the 19-week mulching treatment, summer soil temperatures reached as high as 46,41, and 33 C at 18 cm depth; and 41,37, and 32 C at 30 cm depth under clear film, black film, and no film, respectively. Trees mulched from the time of planting with transparent polyethylene (solarization) did not survive or grow as well as those mulched with black film or not mulched. Incidence of foliar symptoms due to Verticillium wilt was reduced by 86-100% in both apricot and almond trees by black, as well as transparent film mulch the following season. Incidence of vascular discoloration symptoms of trunks and primary scaffolds due to Verticillium wilt was similarly reduced by both mulches. Mulching with black polyethylene film gave better overall results than solarization with transparent film. The intermediate soil temperatures produced did not chronically harm trees, as judged by tree survival and annual growth of trunk diameter, yet the prolonged period of soil heating provided control of Verticillium wilt equivalent to that of solarization with transparent polyethylene. These studies provided further evidence that in-season mulching can be used to conserve water during establishment of neW orchards or replant trees in warm, arid climates.

A well-defined gradient of wet atmospheric depositions characterized by SO4, NO3, H, and NH4 ions has been described in north-central Pennsylvania. The forests of this region are of the oak/hickory type as they extend across the Allegheny Plateau. Sulfate levels along a 160-km west-east gradient varied from approximately 40 kg/ha to 25 kg/ha in the western and eastern portions, respectively. The objective of this research project was to determine if forest trees along the gradient showed anomalous characteristics that might be related to acidic atmospheric deposition. Trees were relatively healthy across the gradient, as measured by observations of crown transparency, twig dieback, and trunk condition. No general relationship was apparent between overall tree health and deposition patterns. Specific disorders noted at greater frequencies at the high deposition portion of the gradient included the presence of insect borers on white oak trunks and early fall coloration of red maple. Disorders observed at greater frequencies at the low deposition portion of the gradient included twig and branch dieback of red oak, white oak, and red maple; chlorosis of red oak; and thrips injury of red maple. A direct cause-and-effect relationship between the pollution gradient and these disorders has not been established.

Insect defoliation is commonly associated with and assumed to be a cause of mortality in Australian eucalypts, particularly in rural regions where trees suffer from the eucalypt dieback syndrome. To test this, leaf growth and defoliation were measured in the canopies of Eucalpyptus trees from June 1982 to June 1986, and related to tree health and eucalypt dieback. Over 5000 leaves were monitored, including replicates of branches, canopy heights, individual trees, species, and sites. Three types of sites were selected, representing the most common conditions in the eastern Australian tablelands: woodlands (comprised of healthy trees but with slight signs of dieback), healthy trees in pastures, and dying trees in pastures. Within each site the commonest native tree species were selected for study; species were not always the same between adjacent sites because of interspe_kw canopy See full-text article at JSTOR

Scots pine trees, P. sylvestris, were sprayed with simulated acid mist in the laboratory to test the effects on the nymphal and population growth rates of three species of pine aphid, S. pineti, E. agilis and C. pini. The acid treatment was found to promote the mean relative growth rates of both S. pineti and C. pini, while population growth rates were significantly enhanced in S. pineti and E. agilis. The acid treatment was also found to cause necrosis and chlorotic mottling of needles. The only significant adverse effect of aphids on needles was shown by E. agilis, which was found to further exacerbate the chlorotic mottling of needles caused by acid mist. The possible implications of these findings for field populations of aphids and trees are discussed. Zusammenfassung Zum Einflus von simulierten sauren Niederschlagen auf die Entwicklungsrate von Nadelholzlausen im Zusammenhang mit den neuartigen Waldschaden Pinus sylvestris wurde im Labor mit kunstlichen sauren Niederschlagen behandelt, um deren Wirkung auf die Nymphen- und Populationsentwicklung von S. pineti, E. agilis und C. pini zu untersuchen. Die Behandlung begunstigte die durchschnittliche relative Wachstumsrate von S. pineti und C. pini, wahrend die Wachstumsrate der Population von S. pineti und E. agilis signifikant erhoht wurde. Die Saurebehandlung verursachte nekrotische und chlorotische Nadelfleckungen. Nur fur E. agilis konnte ein signifikant negativer Einflus der Lause auf die Nadeln nachgewiesen werden. Durch die Saugtatig-keit dieser Art wurden die durch die Saaurebehandlung verursachten chlorotischen Fleckungen verstarkt. Die Bedeutung dieser Ergebnisse fur Freilandpopulationen wird diskutiert.