Subsequent Defoliation Research Articles

A novel method for assessing the threat to oak stands from geometrid defoliators

Oak forests are of great ecological and socioeconomic values but are declining in many regions due to abiotic and biotic factors, including crown damage by defoliating insects. In Europe, several geometrid species reach outbreak densities and are then able to cause severe oak defoliation. Prior to control measures, the threat posed by defoliators must be reliably assessed to limit the treated area and consequently to minimize the negative environmental impacts and the costs of the insecticide application. Few methods have been developed so far to assess the threat to oak forests from geometrids, most of which have proven to be unreliable and/or labour-consuming. In this paper, we present a new method for predicting crown damage from geometrid defoliators based on the density of their flightless females assessed with the use of collar traps installed on tree trunks. The studies were conducted in 2014–2020 in 68 oak stands in Poland. Using beta regression, we estimated the relationship between the density of geometrid females (from genera: Operophtera, Erannis, Agriopis, Alsophila and Apocheima) in collar traps and subsequent defoliation caused by their progeny (i.e. larvae). We then proposed threshold numbers of female density to predict different levels of defoliation and calculated the numbers of collar traps that would be required to detect the threshold density of geometrid females indicating expected defoliation >30%. The new method allows forest managers to monitor populations of different species and phenological groups of geometrids and predict the threat (expected defoliation) to oak forests from these insects.

An examination of the effect of autumn closing date on over-winter herbage production and spring yield

Altering autumn management affects the herbage mass available in spring. An experiment was established to determine the effect of five autumn closing dates (CDs) on herbage production, herbage quality, leaf, stem and dead proportions and tiller density over winter. In the study 50% of the herbage available in spring was accounted for by autumn CD. Each 1 d extra a sward was closed from 25 September to 9 December increased herbage mass by 16 kg DM/ha in spring. Swards closed earlier (25 September–26 October) had consistently higher herbage masses in spring (1,301 kg DM/ha) compared to swards closed later (11 November–9 December; 703 kg DM/ha). Later closed swards had greater herbage quality compared to earlier closed swards (organic matter digestibility = 852 and 825 g/kg DM, respectively) due to increased stem and dead material in the grazing horizon of earlier closed swards. There was no effect of autumn CD on sward quality in the subsequent defoliation in spring. However, following the initial spring grazing there was an effect of autumn CD on subsequent grass growth rates; swards closed in October had a lower growth rate (33 kg DM/ha per day) compared to swards closed in November and early December (49 kg DM/ha per day). Results indicate that earlier autumn closing is beneficial to meet high-feed demand in spring but can affect sward quality and growth rates in spring.

No evidence that rapid adaptation impedes biological control of an invasive plant.

Biological control is a popular tool for invasive species management, but its success in nature is difficult to predict. One risk is that invasive plants, which may have adapted to lower herbivore pressure in the introduced range, could rapidly evolve defences upon re‐association with their biocontrol agent(s). Previous studies have demonstrated that populations of the invasive plant purple loosestrife (Lythrum salicaria) exposed to biocontrol exhibit traits consistent with the rapid evolution of defence. However, to date, no one has tested this hypothesis under field‐natural levels of herbivory. Using seed from 17 populations of purple loosestrife growing in eastern Canada, that varied in their history of exposure to their biocontrol agent, the leaf beetle Neogalerucella spp., we transplanted 1,088 seedlings from 136 maternal families into a common garden under ambient herbivory. Over the following three and half years, we assessed plant performance in the face of biocontrol by measuring early‐season plant size, defoliation, flowering, and season‐end biomass. We discovered that a population history with biocontrol explained little variation in herbivory or plant performance, suggesting that adaptation is not hindering biocontrol effectiveness. Instead, plant size, subsequent defoliation, and spatio‐temporal variables were the main predictors of plant growth and flowering during the study. The high individual variability we observed in plant performance underscores that flexible strategies of allocation and phenology are important contributors to the persistence of invasive plants. Our findings suggest that plant adaptation to biocontrol is unlikely to be a strong impediment to biological control in this species, however, the high survival and variable defoliation of plants in our study also indicate that biocontrol alone is unlikely to result in significant population decline. We recommend that the application of multiple forms of control simultaneously (e.g. thinning plus biocontrol) could help to prevent the existence of refuges of large, reproductive individuals.

Effect of White Spruce Release on Subsequent Defoliation by the Yellowheaded Spruce Sawfly, Pikonema Alaskensis (Hymenoptera: Tenthredinidae)

Effect of White Spruce Release on Subsequent Defoliation by the Yellowheaded Spruce Sawfly, Pikonema Alaskensis (Hymenoptera: Tenthredinidae)

Phenology-dependent variation in the non-structural carbohydrates of broadleaf evergreen species plays an important role in determining tolerance to defoliation (or herbivory)

Two broadleaf evergreen canopy species (Schima superba and Engelhardia roxburghiana) with different phenologies in a subtropical region of southern China were used to determine the influence of leaf phenology on the impact of an insect pest attack. S. superba regenerates its leaves in February, while E. roxburghiana regenerates its leaves in May. The moth Thalassodes quadraria attacked the two broadleaf evergreen species in March to April, and the newly produced leaves were removed for S. superba but not for E. roxburghiana. The young trees were artificially defoliated to imitate an insect pest attack during March 2014. Nonstructural carbohydrate (NSC) and growth measurements and a retrospective analysis based on the radial growth of mature trees were conducted in January 2015. The results showed that NSC concentrations decreased in S. superba during canopy rebuilding, and the subsequent defoliation severely inhibited leaf and shoot growth, prevented NSC restoration in roots and stem xylem, and caused high mortality. The insect outbreaks reduced the radial growth of S. superba. In contrast, E. roxburghiana experienced less growth retardation, lower mortality, and normal radial growth. Thus, taking phenology-dependent variation in NSCs into consideration, defoliation and insect pest outbreaks more negatively impacted S. superba than E. roxburghiana.

Epidemics of Ray Blight on Pyrethrum are Linked to Seed Contamination and Overwintering Inoculum of Phoma ligulicola var. inoxydabilis

Ray blight, caused by Phoma ligulicola var. inoxydabilis, is the most damaging disease of pyrethrum (Tanacetum cinerariifolium) in Australia. Data collected from 72 plots in commercial pyrethrum fields since 2001 to 2009 revealed substantial annual variations in isolation frequency of the pathogen during semidormancy of the crop in autumn and winter. Isolation frequency of the pathogen during this time and subsequent outbreaks of ray blight in spring were similar across the eight production regions where sampling was conducted, and isolation frequency of the pathogen was linearly correlated (r = 0.88; P < 0.0001) with subsequent defoliation severity when plants commenced growth in spring. Isolation frequency and defoliation severity also were correlated with the incidence of seed infested with P. ligulicola var. inoxydabilis (r = 0.71 and 0.44, respectively; P < 0.0001 in both correlations). Highly accurate risk algorithms for the occurrence of severe epidemics of ray blight were constructed using logistic regression. A model based solely on isolation frequency of the pathogen over autumn and winter correctly predicted epidemic development in 92% of fields. Another model utilizing the incidence of infested seed and rain-temperature interactions in early autumn (austral March and April) and late winter (austral June and July) had similar predictive ability (92% accuracy). Path analysis modeling was used to disentangle interrelationships among the explanatory variables used in the second logistic regression model. The analysis indicated that seedborne inoculum of P. ligulicola var. inoxydabilis contributes indirectly to ray blight defoliation severity through directly increasing overwintering frequency of the pathogen. Autumn and fall weather variables were modeled to have indirect effects on defoliation severity through increasing overwintering success of the pathogen but also direct effects on defoliation severity. Collectively, the analyses point to several critical stages in the disease cycle that can be targeted to minimize the probability of regional epidemics of ray blight in this perennial pathosystem.

First Report of Foliar Blight on Dendropanax morbifera Caused by Alternaria panax

Leaf spot and blight disease was observed on two-year-old seedlings of Dendropanax morbifera (Korean name: Hwangchil tree) during July of 2008 in Jindo Island, Korea. Symptoms included yellow-brown to dark brown irregularly enlarged spots frequently located along the veins of leaves. The lesions were often surrounded by chlorotic haloes. Severe leaf blight and subsequent defoliation occurred when conditions favored disease outbreak. The causal organism of the disease was identified as Alternaria panax based on morphological characteristics and sequence analysis of the internal transcribed spacer region of rDNA. A. panax isolates induced leaf spots and blight symptoms not only on D. morbifera but also on the other members of Araliaceae tested. This is the first report of foliar blight caused by A. panax on D. morbifera.

Insect defoliation of mixed-species eucalypts in East Gippsland

Summary Ground surveys were conducted in the coastal and inland mixed—species eucalypt forests of East Gippsland from 2003 to 2006, using ten permanent forest health assessment sites across the region, to determine the cause, extent and severity of extensive defoliation first observed in late 2003. The primary cause of defoliation in the 2003 and 2005 outbreaks were Doratifera spp. (cup moth) and Uraba lugens (gumleaf skeletoniser) respectively. Eucalyptus globoidea (white stringybark) and E. elata (river peppermint) appeared most susceptible while E. cypellocarpa (mountain grey gum), E. obliqua (messmate) and E. sieberi (silvertop) were generally more resistant to defoliation by these insect species. The initial assessment in November 2003 indicated high levels of defoliation with a mean of 71% (range: 30–85%) across all ten sites. Re-assessment of the sites in March 2004 indicated active defoliation had ceased and that foliage cover in the trees had improved with mean defoliation of 34% (range: 15–60%), an improvement of 37%. Subsequent defoliation late in 2005 was not as severe as the 2003 outbreak, with mean defoliation in November 2005 being 23% (range: 10–40%) across all ten sites. Re-assessment in March 2006 indicated that active defoliation had ceased and that levels of foliage cover in the trees had increased over the 2005–2006 summer, with mean defoliation of 17% (range: 10–30%) recorded, an improvement of 6%. Rather than being considered as one continuous outbreak by a single pest species, the two defoliation episodes should be regarded as separate events caused by separate insect species, although their cause(s) may have foundation in similar conditions. The U. lugens outbreak can be reliably linked to low rainfall in the region. The cause of the outbreaks by Doratifera spp. is uncertain because of insufficient knowledge concerning their lifecycle. While climatic factors are likely triggers, other factors such as eucalypt host susceptibility, foliage nutritional status, altitude, forest type, soils and geology may also influence the occurrence of Doratifera spp. outbreaks. Further, it still has to be determined whether the factors that trigger outbreaks affect Doratifera spp. directly or reduce parasitoid/predator populations that usually keep Doratifera spp. populations in check. As little is known of the predisposing factors for outbreaks (especially for Doratifera spp.), the appropriate nature and timing of any potential control measures are difficult to identify. Continued monitoring of all potential damaging insect pest populations and associated canopy cover is recommended as part of a structured forest health surveillance system in order to predict outbreaks and allow appropriate contingency plans to be made if required. However, as most native insect outbreaks in native forests are short term and part of the normal forest ecosystem, the implementation of control measures is usually not required. The potential for long-term effects of drought to increase outbreak frequency and subsequently affect tree growth and health should not be discounted, thus emphasising the need for regular monitoring.

Sampling strategies and density–defoliation relationships for the pale-winged gray moth, Iridopsis ephyraria, on mature eastern hemlock

The pale-winged gray moth, Iridopsis ephyraria (Walker), a native geometrid moth species found across eastern North America, has recently caused severe defoliation of eastern hemlock trees, Tsuga canadensis (L.) Carrière, in south-central Nova Scotia, Canada. Field studies were carried out to develop sampling techniques that could be used to predict subsequent defoliation of mature hemlocks, which are too large to sample by conventional methods. Densities of newly emerged, first-instar larvae, estimated by sticky tape traps, explained 77% of the subsequent current-year shoot defoliation by I. ephyraria. Egg densities from foam oviposition traps and mid-instar larval densities from beating sheets were weakly and usually non-significantly related to defoliation. Therefore, foam oviposition traps could be used to qualitatively estimate egg densities of I. ephyraria, but first-instar larvae must be sampled with sticky tape if accurate predictions of hemlock defoliation are desired.

Monitoring autumn gum moth (Mnesampela privata): relationships between pheromone and light trap catches and oviposition in eucalypt plantations

Summary Following the identification of a biologically-active compound from the sex pheromone gland of the autumn gum moth, Mnesampela privata (Guenée) (Lepidoptera: Geometridae), field studies were conducted to compare the potential efficacy of pheromone traps with light traps and to determine whether pheromone trap catches could forecast the future abundance of eggs and subsequent defoliation. Small to incipient populations of the adult moth were monitored over two moth flight seasons using pheromone traps in 12 plantations of either Eucalyptus globulus Labill. or E. nitens (Deane and Maiden) Maiden in Tasmania, Australia. In three of these plantations, light traps were also used to monitor adult moth numbers for one moth flight season. Pheromone trap catches from Tasmania were compared with those in a plantation of E. grandis W.Hill ex Maiden in Victoria where an outbreak of M. privata was ongoing. Early in the season (February—April), light traps caught five to six times more M. privata than pheromone traps per week but this situation reversed later in the season (May). Although small, total pheromone trap catches of male moths during March—April 2003 were positively correlated with the total numbers of eggs per tree recorded in June. Catches were substantially larger during March-July 2004 and again positively correlated with the total numbers of eggs per tree recorded in July. Sixty-nine percent of all eggs located in 2003 were parasitised compared with only 18% in 2004. Because pheromone trap catches could be positively correlated with oviposition, it is suggested they could forecast larval populations and, in the absence of high rates of egg parasitism, defoliation.

Defoliation and Plasmid Delivery with Layer‐by‐Layer Coated Colloids

The uptake of polyelectrolyte multilayer coated colloids into cells, subsequent defoliation and plasmid delivery was studied by means of confocal microscopy and flow cytometry. Silica particles coated layer-wise with protamine and dextran sulfate were given to HEK 293T cells. Optimum uptake was found with protamine as the top layer. The particle uptake likely follows an non-receptor-mediated endocytotic pathway. Defoliation of polyelectrolyte multilayer coated particles within cells was demonstrated by the release of incorporated plasmids as indicated by the expression of plasmid encoded proteins using the enhanced green fluorescence proteine (pEGFP-C1) plasmid and a red fluorescence protein (pDsRed1-N1) plasmid. This proves, together with the direct observation of fluorescent layer debris, the defoliation of coated particles and the release of layer components into the cytoplasm. Particle uptake and GFP expression.

Genetic variation in Eucalyptus globulus in relation to susceptibility from attack by the southern eucalypt leaf beetle, Chrysophtharta agricola

The southern eucalypt leaf beetle, Chrysophtharta agricola (Chapuis), is an outbreak insect pest of commercial Eucalyptus globulus Labill. plantations in south-eastern Australia. We surveyed a young E. globulus family trial in southern Tasmania to determine whether genetic variation existed in the susceptibility of trees to C. agricola field oviposition. The family trial consisted of 225 families, derived from open-pollinated seed collected from native stands at 24 different localities, representing nine geographic subraces. The survey showed that E. globulus subraces from Victoria were significantly more susceptible to C. agricola oviposition than Tasmanian subraces. Significant additive genetic variation within subraces was evident for the number of egg batches, larval clutches and their combination (infestation level), although these heritability scores were all low (egg batches h2op = 0.09; larval clutches h2op = 0.14 and infestation level h2op = 0.11). Subsequent tree defoliation was significantly positively correlated with infestation at a phenotypic, genetic and environmental level. No significant differences in C. agricola oviposition on foliage sprigs was detected among subraces in an ex situ caged oviposition experiment. However, the cage experiment proved to be a good predictor of field oviposition, accounting for 70 and 88% of variation in field oviposition among localities and subraces, respectively.

Stomatal regulation in Douglas fir following a fungal-mediated chronic reduction in leaf area

Pathogens can cause chronic premature needle abscission in coniferous species. To assess the potential impacts on tree productivity, stomatal regulation was investigated in Douglas fir with chronic stomatal occlusion and defoliation from varying levels of the Swiss needle cast (SNC) fungus, Phaeocryptopus gaeumannii. Levels of SNC disease and subsequent defoliation were manipulated by choosing six sites with varying levels of disease and by foliar applications of fungicides on six trees per site. Diurnal measurements of leaf water potential (Ψleaf), stomatal conductance (gs) and vapor pressure deficit (D) were made on six fungicide treated and six control trees per site. In addition, leaf specific hydraulic conductance was calculated on a single branch (KL_B) from three trees per treatment per site. Stomatal conductance at D=1 kPa (gsref) was negatively correlated with fungal colonization (number of fruiting bodies present in needle stomata) and positively correlated with KL_B. Despite reduced needle retention in diseased trees, KL declined due to a reduction in sapwood area and permeability (i.e., increasing presence of latewood in functional sapwood). In general, stomatal sensitivity to D for all foliage was consistent with stomatal regulation based on a simple hydraulic model [gs=KL(Ψsoil−Ψleaf)/ D], which assumes strict stomatal regulation of Ψleaf. However, when fungal presence reduced maximum gs below the potential maximum supported by hydraulic architecture, stomatal sensitivity was lower than expected based on the theoretical relationship: dgs/dlnD=0.6·gsref. The results indicate that losses in productivity associated with physical blockage of stomata and defoliation are compounded by additional losses in KL and a reduction in gs in remaining functional stomata.

Rough fescue (Festuca campestris Rydb.) response to heat injury

Rough fescue (Festuca campestris Rydb.) is an ecologically and economically important native plant species within grasslands of southwest Alberta. This is also a region where wildfires have become prevalent over the last decade. While the risk of long-term damage from fire may be determined by the susceptibility of rough fescue to heat injury, understanding the additive stress imposed by defoliation may assist in the development of grazing strategies facilitating rangeland recovery. Three laboratory studies were conducted to assess rough fescue sensitivity to heat stress, including the added impact of subsequent defoliation. Results indicated that fescue tillers were capable of withstanding temperatures of 60°C, but only for short periods (e.g., 16 s or less). At lower temperatures, a distinct interaction between exposure time and temperature was evident, with shorter times at greater temperatures causing similar reductions in growth as long exposure times at low temperatures. Decreased plant vigour, as evidenced by lower tiller numbers, resulted from defoliation coinciding with active regrowth, reinforcing the notion that rough fescue is sensitive to defoliation following heat stress. The greatest detrimental impact occurred with relatively longer periods of deferment (8 weeks) until defoliation following exposure to heat treatment. These results have implications for the recovery and conservation of burned rough fescue rangeland. Key words: Defoliation, Festuca campestris Rydb., heat stress, mortality, tillers, water bath

Comparison of Three Egg Mass Survey Methods in Relation to Gypsy Moth (Lepidoptera: Lymantriidae) Defoliation in Michigan

We evaluated 3 egg mass survey methods used to predict gypsy moth, Lymantria dispar (L.), defoliation in 32 oak stands in northwestern lower Michigan. Fixed-radius plots, timed walks, and a recently developed method, the 100-tree plot, were used to assess egg mass density in each stand. Defoliation in each stand was estimated visually the following summer, and associations among defoliation levels and the 3 survey methods were evaluated. Larval cadavers were collected in each stand to determine if the gypsy moth pathogens Entomophaga maimaiga and nuclear polyhedrosis virus (NPV) were present. Egg mass counts from the fixed-radius plot and 100-tree plot methods were significantly associated with subsequent defoliation, but timed walk counts were not. We used common egg mass density thresholds and results of the 3 survey methods to determine if the stands would require treatment in a hypothetical suppression program. Treatment decisions based on results of the fixed-radius plots and timed walks were similar. The 100-tree plot method, however, yielded fewer erroneous decisions to treat stands when suppression was not needed. All stands that sustained >30% defoliation had at least 84% new egg masses and a new egg mass density of at least 6,563 egg masses per hectare as determined by fixed-radius plots. Surveys conducted using fixed-radius plots and 100-tree plots took 2–3 times longer than surveys using timed walks. Infection of cadavers by NPV was higher in stands with high egg mass density and defoliation, whereas infection by E. maimaiga was more prevalent in stands with low egg mass density and defoliation.

Tree Mortality Following Defoliation by the European Gypsy Moth (Lymantria dispar L.) in the United States: A Review

Abstract This review presents information related to defoliation by the European gypsy moth (Lymantria dispar L.) and subsequent tree mortality in the eastern United States. The literature describing defoliation-induced tree mortality is extensive, yet questions still remain concerning (1) the association between initial stand composition and subsequent tree mortality, (2) the influence of site quality on tree mortality, and (3) observed differences between mortality rates in initial and subsequent outbreaks. Our review and analysis of the available literature indicates that initial species composition affects subsequent defoliation. Stands with predominantly susceptible host species have higher levels of species-specific and total mortality than mixed stands of susceptible, resistant, and immune host species. Differences in mortality on sites of varying productivity do not appear to be a direct result of site quality; rather, site quality indirectly influences mortality rates through its effect on species composition and therefore defoliation. Differences between initial and subsequent outbreaks appear to be due primarily to losses of vulnerable oaks and lower canopy species during the initial outbreak; oak mortality in initial outbreaks was found to be significantly greater (P = 0.0727) than oak mortality in subsequent outbreaks. For. Sci. 45(1):74-84.

Role of leaf development and colour change in differential defoliation of Eucalyptus regnans families by the leaf eating beetle Chrysophtharta bimaculata (Olivier)

Open-pollinated families of Eucalyptus regnans, selected from a single provenance on their susceptibility to defoliation by the chrysomelid, Chrysophtharta bimaculata, were used to determine whether spring growth phenology (leaf numbers and leaf colour) was related to previously observed levels of defoliation. Families did not differ in numbers of leaves or leaf area produced per shoot. However, more susceptible families carried over 29% of their new foliage as red leaves during the period of maximum beetle activity; less susceptible families carried less than 20% of red foliage during the same period. Results were consistent across sites assessed in different years. The percentage of red leaves was strongly correlated with numbers of egg batches deposited and degree of subsequent defoliation. However as the egg lay did not occur when colour differences were evident, red foliage colour per se could not directly affect C. bimaculata host selection for oviposition.

Seeds of Civilization: Bronze Age Rural Economy and Ecology in the Southern Levant

This paper considers the economic and environmental impacts of emerging regional commerce that accompanied the rise and collapse of early Near Eastern urbanism. We integrate regional data on settlement and vegetation with detailed evidence of rural agriculture from two Bronze Age villages in the Jordan Valley. This approach is explicitly rural, in light of the largely rural character of Levantine civilization, and in response to more orthodox analytical perspectives focused on the first cities. Long-standing interest in the advent of agriculture now reveals that intensive localized depletion of woodland resources followed the aggregation of sedentary agrarian communities in the eighth through sixth millennia B.C., while the development of specialized pastoralism established one potential source of more extensive, subsequent defoliation. We argue, however, that regional human impacts on Levantine vegetation were triggered only with the genesis of Bronze Age cities and urbanized economies in the third and second millennia B.C. Thereafter, these regional impacts molded an ever-shifting mosaic of anthropogenic and natural landscapes. Rank-size analysis illustrates the modestly integrated, largely rural nature of Bronze Age settlement in the southern Levant. In this context, Tell Abu en-Ni‘aj and Tell el-Hayyat provide appropriate examples of the resilient agrarian villages that persisted through the dramatic collapse and rebirth of early Levantine cities. Excavated plant remains and animal bones show that their inhabitants responded to the development of Bronze Age urbanism with a shift toward increased management of taxa with greater market potential, tempered by some retention of local economic autonomy. Shifts to greater sheep husbandry and, most significantly, cultivation of orchard crops like olives, figs, and grapes, signal a second wave of economic innovation that fundamentally altered the agricultural strategies of village farmers and their exploitation of the surrounding countryside. Thus the mixed cultural and natural landscapes that have supported long-term agriculture in the Levant reflect a legacy of discontinuous changes in rural economy and ecology in response to the waxing and waning of urbanized society and regional mercantile exchange.

Length and Timing of Grazing on Postburn Productivity of Two Bunchgrasses in an Idaho Experimental Range

Plant mortality and productivity in semiarid grasslands may be affected by the length of time grazing is excluded during the postfire regeneration period. The degree of grazing tolerance for the semiarid bunchgrass species, Festuca idahoensis and Agropyron spicatum, exposed to fire, and how the variation in grazing tolerance was affected by the length of time allowed for undisturbed plant regeneration after fire, were central questions addressed in this study. We examined the degree of plant mortality and productivity that resulted from the interaction of fire and grazing. Plants exposed to fire alone, i.e., without subsequent defoliation, exhibited low plant mortality, although culm production was reduced relative to unburned plants. An early-season-defoliation treatment after fire resulted in the plant mortality as high as 50% for Festuca and 70% for Agropyron bunchgrasses. Plant height and the number of vegetative and reproductive culms were also most affected by this defoliation treatment. These detrimental effects were lessened when defoliation was delayed by one growing season after the fire. Although our results suggest that one growing season seems to be enough for both species to recover after the fire, more studies will be necessary to confirm these trends, and induce changes in current grazing management policies.

Comparative Morphology and Pathology of Calonectria theae and C. colhounii in Hawaii.

Calonectria theae is distinguished from C. colhounii by perithecial color, number of ascospores in an ascus, longer stipes, longer conidia, and the formation of a second conidial type that is extraordinarily long, angular, and borne on simple, submerged, dichotomously branching conidiophores. Both species were isolated from ohia (Metrosideros collinus), M. excelsus, and sentry palm (Howea forsteriana). C. theae was also isolated from leather leaf fern (Rumohra adiantiformis) and Strelitzia, while C. colhounii isolates were obtained from Eucalyptus, Leucospermum, and Chrysalidocarpus lutescens. All tested isolates of both Calonectria spp. were pathogenic to ohia, an important native tree species in Hawaiian forests. Both species killed apical shoots, and caused leaf spotting, blighting, and subsequent defoliation. Symptomatically, the diseases caused by these species are indistinguishable on ohia. This disease poses a potential threat to native forests.