Effect of temperature,relative humidity,leaf wetness and leaf age on <Emphasis Type="Italic">Spilocaea oleagina</Emphasis> conidium germination on olive leaves

The effects of temperature, relative humidity (RH), leaf wetness and leaf age on conidium germination were investigated for Spilocaea oleagina, the causal organism of olive leaf spot. Detached leaves of five ages (2, 4, 6, 8 and 10 weeks after emergence), six different temperatures (5, 10, 15, 20, 25 and 30°C), eight wetness periods (0, 6, 9, 12, 18, 24, 36 and 48 h), and three RH levels (60, 80 and 100%) were tested. Results showed that percentage germination decreased linearly in proportion to leaf age (P < 0.001), being 58% at 2 weeks and 35% at 10 weeks. A polynomial equation with linear term of leaf age was developed to describe the effect of leaf age on conidium germination. Temperature significantly (P < 0.001) affected frequencies of conidium germination on wet leaves held at 100% RH, with the effective range being 5 to 25°C. The percent germination was 16.1, 23.9, 38.8, 47.8 and 35.5% germination at 5, 10, 15, 20 and 25°C, respectively, after 24 h. Polynomial models adequately described the frequencies of conidium germination at these conditions over the wetness periods. The rate of germ tube elongation followed a similar trend, except that the optimum was 15°C, with final mean lengths of 175, 228, 248, 215 and 135 μm at 5, 10, 15, 20 and 25°C, respectively after 168 h. Polynomial models satisfactorily described the relationships between temperature and germ tube elongation. Formation of appressoria, when found, occurred 6 h after the first signs of germination. The percentage of germlings with appressoria increased with increasing temperature to a maximum of 43% at 15°C, with no appressoria formed at 25°C after 48 h of incubation. Increasing wetness duration caused increasing numbers of conidia to germinate at all temperatures tested (5–25°C). The minimum leaf wetness periods required for germination at 5, 10, 15, 20 and 25°C were 24, 12, 9, 9 and 12 h, respectively. At 20°C, a shorter wetness period (6 h) was sufficient if germinating conidia were then placed in 100% RH, but not at 80 or 60%. However, no conidia germinated without free water even after 48 h of incubation at 20°C and 100% RH. The models developed in this study should be validated under field conditions. They could be developed into a forecasting component of an integrated system for the control of olive leaf spot.     

The Epidemiology of Purple Leaf Blotch on Leeks in Victoria, Australia

The incidence of purple leaf blotch disease was investigated on seven successive commercial leek crops grown at Cranbourne, Victoria between 1996 and 1997. First symptoms occurred on older leaves, 54–69 days after transplanting. Lesions with typical symptoms were colonised by either Alternaria porri (6%), Stemphylium vesicarium (42%) or mixtures of both pathogens (52%). Purple leaf blotch was caused by a disease complex and was endemic at nobreak Cranbourne due to the continuous cropping of leeks. Disease incidence in all monitored crops increased as plants matured (123–158 days after transplanting) until harvest but never exceeded 11% due to fortnightly applications of mancozeb. Disease levels showed no significant correlation with weekly temperature, precipitation, relative humidity or leaf wetness duration. Disease levels were significantly (P < 0.05) higher on autumn/winter (May/June) 1997 crops when 38 periods of leaf wetness 8 h because of dew and low temperatures (10–13 °C). The weekly rate of increase of disease incidence was significantly (P < 0.01) correlated with days after transplantation. nobreak Concentrations of airborne A. porri and S. vesicarium conidia within leek crops showed a diurnal periodicity and maximum numbers were trapped between 11:00 and 15:00 h. The concentration of airborne S. vesicarium conidia was three to six times the concentration of airborne A. porri conidia. Conidia were more abundant during spring/summer (September–February). Ascospores of Pleospora allii were found during May–September. The greater concentrations of airborne S. vesicarium conidia suggest that it may be the dominant pathogen in the purple leaf blight complex. Fungicide sprays were unnecessary until 8–10 weeks after transplanting, and regular protectant sprays curtailed but did not eradicate purple leaf blight. The results indicated that predictive models, based on temperature and the frequency of leaf wetness periods 8 h, will assist in reducing fungicide inputs as plants mature and, in southern Victoria, fungicide applications on leeks should be timed for autumn/winter when infection periods occur.     

Effects of inoculum density,leaf wetness duration and nitrate concentration on the occurrence of lettuce leaf spot

In Ehime Prefecture, Japan, lettuce leaf spot (Septoria lactucae) caused huge losses in marketable lettuce yields. To explore potential measures to control disease outbreaks, the effects of inoculum density, leaf wetness duration and nitrate concentration on the development of leaf spot on lettuce (Lactuca sativa) were evaluated. Conidia were collected from diseased plants in an infested field by single-spore isolation and were used to inoculate potted lettuce plants with different conidial concentrations. Lesions developed on inoculated lettuce plants at inoculum concentrations from 10⁰ to 10⁶ conidia/ml. The disease was more severe when the inoculum exceeded 10² conidia/ml, and severity increased with increasing concentrations. Assessment of the relationship between disease development and the duration of postinoculation leaf wetness revealed that symptoms appeared when the inoculated plants remained wet for 12 h or longer. The number of lesions and total nitrogen content in the lettuce leaves both increased when nitrate was applied.     

Black Streak of Edible Burdock Caused by Itersonilia perplexans in Japan

Black streak disease of edible burdock (Arctium lappa L.) has been observed periodically in Hokkaido Prefecture, Japan since 1988. Symptoms appeared initially as small, dark brown to black spots on the leaf veins and petioles. The necrotic spots developed longitudinally along the leaf veins or petioles. Diseased leaf veins or petioles occasionally snapped off at the necrotic lesions. An Itersonilia sp. was isolated from rotting leaf veins and petioles. Laboratory inoculations of edible burdock seedlings using ballistospore suspensions produced typical symptoms observed in nature. The fungus had a feathery mycelium and developed a white to pale cream colony color. The mycelium was composed primarily of branched hyphae with clamp connections at the septa. Ballistospores, formed at the apex of inflated cells, were lunate, ovoid to pyriform. The fungus occasionally produced appressoria, chlamydospores and yeast cells. Based on the morphological characteristics, the causal agent was identified as Itersonilia perplexans Derx. Edible burdock strains were also pathogenic to chrysanthemum and caused petal blight. This report is the first of a foliar disease of edible burdock caused by I. perplexans in Japan. Received 8 April 2002/ Accepted in revised form 26 June 2002     

Effect of interrupted leaf wetness periods on suppression of sporulation ofBotrytis allii andB. cinerea by antagonists on dead onion leaves

Saprophytic antagonists were evaluated for suppression of sporulation ofBotrytis allii andB. cinerea on artificially killed segments of onion leaves that were pre-inoculated with the pathogens. During incubation of the antagonisttreated leaf segments in moist chambers, periods of leaf wetness and leaf dryness were alternated to simulate conditions in the field. Interruption of humid conditions with dry periods had a differential effect on antagonists.Alternaria alternata, Chaetomium globosum, Ulocladium atrum andU. chartarum suppressed sporulation ofB. allii almost completely under continuously wet conditions, and when the leaf wetness periods were interrupted with drying periods of 9h imposed 16, 40, and 64 h after the antagonists were applied. When leaf wetness was interrupted 16 h after antagonist application, the number of conidia ofB. allii produced cm^–2 leaf surface after eight days was under the detection limit of 5.2 × 10³ conidia on leaves treated with these antagonists compared to 3.7 × 10⁵ conidia on leaves that were not treated. On the other hand,Gliocladium roseum, G. catenulatum andSesquicillium candelabrum, all highly efficient under continuously wet conditions, were of low to moderate efficiency when leaf wetness periods had been interrupted 16 h after application of the antagonists. The antagonists showed the same differentiation and sensitivity to interrupted wetness periods when tested withB. cinerea.     

Pathogenicity of <Emphasis Type="Italic">Mycochaetophora gentianae</Emphasis>, causal fungus of gentian brown leaf spot,as affected by host species,inoculum density,temperature, leaf wetness duration,and leaf position

When the influence of host species, inoculum density, temperature, leaf wetness duration, and leaf position on the incidence of gentian brown leaf spot caused by Mycochaetophora gentianae, was examined, the fungus severely infected all seven Gentiana triflora cultivars, but failed to infect two cultivars of G. scabra and an interspecific hybrid cultivar. Inoculum density correlated closely with disease incidence, and a minimum of 10² conidia/mL was enough to cause infection. In an analysis of variance, temperature and leaf wetness duration had a significant effect upon disease incidence, which increased with higher temperature (15–25°C) and longer duration of leaf wetness (36–72 h). No disease developed at temperatures lower than 10°C or when leaf wetness lasted <24 h. At 48-h leaf wetness, disease incidence was 0, 28, 77, and 85% at 10, 15, 20, and 25°C, respectively. Middle and lower leaves on the plant were more susceptible than upper leaves. In microscopic observations of inoculated leaves, >50% of conidia germinated at temperatures >15°C after 24-h leaf wetness. More appressoria formed at higher temperatures (15–25°C) with extended duration of leaf wetness (24–72 h). At 48-h leaf wetness, appressorium formation was 0, 8, 26, and 73% at 10, 15, 20, and 25°C, respectively. These results suggest that temperature and leaf wetness duration were important factors for infection of gentian leaves.     

Effects of temperature,inoculum concentration,leaf age,and continuous and interrupted wetness on infection of olive plants by Spilocaea oleagina

Experiments were conducted on olive plants in controlled environments to determine the effect of conidial concentration, leaf age, temperature, continuous and interrupted leaf wetness periods, and relative humidity (RH) during the drier periods that interrupted wet periods, on olive leaf spot (OLS) severity. As inoculum concentration increased from 1·0 × 10² to 2·5 × 10⁵ conidia mL^?1, the severity of OLS increased at all five temperatures (5, 10, 15, 20 and 25°C). A simple polynomial model satisfactorily described the relationship between the inoculum concentration at the upper asymptote (maximum number of lesions) and temperature. The results showed that for the three leaf age groups tested (2–4, 6–8 and 10–12 weeks old) OLS severity decreased significantly (P < 0·001) with increasing leaf age at the time of inoculation. Overall, temperature also affected (P < 0·001) OLS severity, with the lesion numbers increasing gradually from 5°C to a maximum at 15°C, and then declining to a minimum at 25°C. When nine leaf wetness periods (0, 6, 12, 18, 24, 36, 48, 72 and 96 h) were tested at the same temperatures, the numbers of lesions increased with increasing leaf wetness period at all temperatures tested. The minimum leaf wetness periods for infection at 5, 10, 15, 20 and 25°C were 18, 12, 12, 12 and 24 h, respectively. The wet periods during early infection processes were interrupted with drying periods (0, 3, 6, 12, 18 and 24 h) at two levels of RH (70 and 100%). The length of drying period had a significant (P < 0·001) effect on disease severity, the effect depending on the RH during the interruption. High RH (100%) resulted in greater disease severity than low RH (70%). A polynomial equation with linear and quadratic terms of temperature, wetness and leaf age was developed to describe the effects of temperature, wetness and leaf age on OLS infection, which could be incorporated as a forecasting component of an integrated system for the control of OLS.     

Infection of Linseed by Alternaria linicola; Effects of Inoculum Density, Temperature, Leaf Wetness and Light Regime

Controlled environment studies were conducted to determine the effects of inoculum density, temperature, leaf wetness and light regime on the infection of linseed by Alternaria linicola. The % cotyledons and leaves with symptoms, and the disease severity (% leaf area with symptoms) increased linearly when the inoculum density increased from 1×10³ to 1×10⁵ conidiaml^–1. The first symptoms appeared on cotyledons and leaves 4 and 6 days after inoculation, respectively. Eight hours of leaf wetness were sufficient to initiate the disease at 25°C but not at 15°C, when 10-h periods of leaf wetness were required. % leaf area with symptoms was lower at 15°C than that at 25°C irrespective of the leaf wetness periods tested. Interruption of a continuous leaf wetness period by a 12-h dry period, occurring at any time between 1 and 18h after inoculation, decreased the % cotyledons with symptoms and the disease severity, with the greatest reductions (60% and 100%, respectively) being observed when the dry period began 6h after inoculation. A. linicola conidia were able to exploit successive 12-h periods of leaf wetness cumulatively to infect linseed plants. Disease incidence and severity were positively correlated with the dark period following inoculation, but they were negatively related to the length of the initial light period. Our findings suggest that infection of linseed by A. linicola and further development of symptoms can occur under unfavourable environmental conditions.     

Germination of <Emphasis Type="Italic">Gibberella zeae</Emphasis> ascospores as affected by age of spores after discharge and environmental factors

The effects of age of ascospores (0–18 days after discharge), photon flux density (0–494 mol m^–2 s^–1 PAR), temperature (4–30 °C), frost (–15 °C for 30 min), relative humidity (RH; 0–100%), pH (2.5–6.5) and dryness (0 and 53% RH for up to 40 min) on the germination of the ascospores of the mycotoxin-producing fungus Gibberella zeae (anamorph Fusarium graminearum) were studied. Freshly discharged ascospores germinated within 4 h at 20 °C and 100% RH. The rate of germination and the percentage of viable ascospores decreased over time after the spores were discharged from perithecia. The time course of ascospore germination was not significantly affected by photon flux density. The period of time required to obtain 50% germinated ascospores at 100% RH was 26.90 h at 4 °C, 10.40 h at 14 °C, 3.44 h at 20 °C and 3.31 h at 30 °C. There was no significant effect of frost on the percentage of viable ascospores. A small percentage (6.6 ± 3.8%) of the ascospores germinated at 53% RH. At RH 84% and 20 °C almost 100% of the freshly discharged ascospores germinated. The time course of ascospore germination was affected by pH. The maximum rate of ascospore germination was estimated to be at pH 3.76. Ascospores lost their ability to germinate following exposure to 0% RH almost instantaneously. No germinating spores were detected after an incubation period of 1 min at 0% RH. Incubating the ascospores at 53% RH decreased the percentage of viable spores from 93 to 6% within 10 min. The data demonstrate that age of spores, relative humidity, temperature and pH, but not photon flux density, are key factors in germination of G. zeae ascospores.     

Factors affecting the incubation period of dark leaf and pod spot (Alternaria brassicae) on oilseed rape (Brassica napus)

Experiments to investigate the factors affecting the incubation period of dark leaf and pod spot (Alternaria brassicae) on leaves and pods of oilseed rape (Brassica napus) were done in controlled environment (constant temperatures) and glasshouse conditions (fluctuating temperatures). The length of the incubation period of dark leaf and pod spot decreased as infection and incubation temperatures increased from 6 to 20 °C. The incubation period decreased as wetness period increased from 2 to 12 h, as inoculum concentration increased from 80 to 2 × 10³ spores ml^–1 and as leaf age increased from 4 to 10 days. Asymptotes of leaf age and inoculum concentration, above which the length of the incubation period did not decrease, were 10 days and 2 × 10³ spores ml^–1, respectively. The shortest and longest incubation periods were 1 and 11 days. The mechanism by which the infection conditions influenced the incubation period of dark leaf and pod spot on oilseed rape seemed to be linked to lesion density. Usually, the length of the incubation period decreased greatly with increasing lesion density.     

Modelling the progress of Asiatic citrus canker on Tahiti lime in relation to temperature and leaf wetness

The combined effect of temperature (15°C, 20°C, 25°C, 30°C, 35°C, 40°C and 42°C) and leaf wetness duration (0, 4, 8 12, 16, 20 and 24 h) on infection and development of Asiatic citrus canker (Xanthomonas citri subsp. citri) on Tahiti lime plant was examined in growth chambers. No disease developed at 42°C and zero hours of leaf wetness. Periods of leaf wetness as short as 4 h were sufficient for citrus canker infection. However, a longer leaf duration wetness (24 h) did not result in much increase in the incidence of citrus canker, but led to twice the number of lesions and four times the disease severity. Temperature was the greatest factor influencing disease development. At optimum temperatures (25–35°C), there was 100% disease incidence. Maximum disease development was observed at 30–35°C, with up to a 12-fold increase in lesion density, a 10-fold increase in lesion size and a 60-fold increase in disease severity.     

Axenic culture and influence of wetness period and inoculum concentration on infection and development of cercospora blight ofHeliotropium europaeum

Cercospora heliotropii-bocconii is a fungal pathogen of the ephemeral annual weedHeliotropium europaeum. The effects of wetness period and inoculum concentration on disease severity were studied under controlled conditions. The fungus was grown on different artificial culture media and carrot juice agar with 5 g l^–1 yeast extract was found to be the most suitable medium for conidial production under artificial conditions. Abundant disease symptoms only occurred after 8 h of wetness at 20°C. The minimum incubation period before disease symptoms appeared was 8 days following a wetness period of at least 40 h. Inoculum concentration of 1×10⁴ conidia per ml killed plants in less than one month and reduced seed production by two thirds. These results suggest that this pathogen has the potential to reduce plant survival and seed bank replenishment of this annual weed species.     

Phyllosphere yeasts antagonize penetration from appressoria and subsequent infection of maize leaves by Colletotrichum graminicola

In growth cabinet experiments, the common phyllosphere yeastsSporobolomyces roseus andCryptococcus laurentii var.flavescens were sprayed as a mixture (11) onto the fourth leaves of maize plants (Zea mays) two-three days prior to inoculation withColletotrichum graminicola. In four experiments the average yeast population of the treated leaves at the time of pathogen inoculation varied between 5× 10⁴ and 8× 10⁵ cells cm^–2 leaf, whereas on the untreated leaves the yeast population varied from <10³ to 10⁴ cells cm^–2 leaf. The yeasts reduced lesion density and necrosis fromC. graminicola infection by approximately 50%. Contrary to findings with other necrotrophic pathogens, conidial germination, superficial mycelial growth and appressorium formation were not affected. Instead, the reduction of infection could only be explained by a reduced number of penetrations from the normally formed appressoria, a site of interaction not previously recorded.Samenvatting In klimaatkastexperimenten werden maisbladeren (4e blad) twee-drie dagen voor inoculatie metColletotrichum graminicola bespoten met een mengsel (11) van de algemeen voorkomende fyllosfeergistenSporobolomyces roseus enCryptococcus laurentii var.flavescens. In vier experimenten varieerde de gemiddelde gistpopulatie op de behandelde bladeren, op het moment van inoculatie met het pathogen, van 5× 10⁴ tot 8× 10⁵ cellen cm^–2 blad, op de onbehandelde bladeren van <10³ tot 10⁴ cellen cm^–2 blad. De gisten reduceerden de lesiedichtheid en het necrotisch bladoppervlak tengevolge van deC. graminicola infectie voor ongeveer 50%. De stadia in de ontwikkeling van andere necrotrofe pathogenen, die gewoonlijk gevoelig zijn voor antagonisme door gisten, zoals sporekieming, oppervlakkige myceliumgroei en vorming van appressoria, werden bijC. graminicola niet beïnvloed. De waargenomen reductie van infectie kon alleen verklaard worden door een remming van de penetratie vanuit normaal gevormde appressoria. Interactie in dit stadium van het infectieproces is nog niet eerder waargenomen.     

The relationship of leaf wetness duration and disease progress of glume blotch,caused byStagonospora nodorum,in winter wheat to standard weather data

Almost 50% of the variation in leaf wetness duration can be explained by maximum and minimum temperatures, rainfall and hours with relative humidity above 90% on a daily basis. All of these parameters can be estimated from a standard weather station. If variables related to wind are added the level of explanation increases to 69–76%. Leaf wetness duration explained up to 42% of the rate of disease increase (RDI) forS. nodorum. Leaf wetness duration was accumulated over a 5-day window period and correlated with rate of disease increase after a 7-day lag period. Standard weather variables could explain 20–34% of the disease increase. The relevance of these statistical models to disease prediction is discussed.     

Biocontrol agents in combination with Moringa oleifera extract for integrated control of Sclerotium-caused cowpea damping-off and stem rot

Damping-off and stem rot disease-causing Sclerotium rolfsii has been reported as a destructive soil-borne pathogen of numerous crops, especially in the tropics and subtropics. Trials were conducted to test the efficacy of biocontrol agents alone or combined with Moringa oleifera leaf extracts for the control of the disease. In the laboratory, PDA was amended with Moringa leaf extract, and mycelial growth of S. rolfsii was measured. In the greenhouse and field, Trichoderma Kd 63, Trichoderma IITA 508 and Bacillus subtilis were evaluated as seed treatments, soil drench or sprinkle, separately or combined with Moringa leaf extracts. Percentage disease incidence, severity and control were recorded. In the laboratory, the higher the extract concentration the less the mycelial growth and no mycelial growth occurred on extract at 15 or 20 g leaves 10 ml⁻¹ water. In the greenhouse, the highest disease control was observed at a Moringa extract concentration of 15 kg leaves 10 l⁻¹ water (w/v). Seed treatments using Trichoderma Kd 63, and soil sprinkle using Trichoderma IITA 508 had a significantly (P = 0.05) higher effect on a disease incidence than Bacillus. Disease severity followed the same pattern. Moringa seed treatment combined with Trichoderma soil sprinkle resulted in significantly more than 94% and 70% disease control in the greenhouse and field, respectively, with significant yield increase in the field. This is the first report of Moringa leaf extract combined with Trichoderma as an integrated control for Sclerotium damping-off and stem rot of cowpea in the field.     

Effects of temperature increase on the epidemiology of three major vector-borne viruses

The epidemiologies of Maize streak virus (MSV), Maize stripe virus (MSpV), and Maize mosaic virus (MMV) were compared in La Réunion over a three year-period. Disease incidence caused by each virus was assessed, and the leaf and planthopper vector populations (Cicadulina mbila and Peregrinus maidis) were estimated in weekly sowings of the temperate, virus-susceptible maize hybrid INRA 508 and of the composite resistant cv. IRAT 297. MSV caused the most prevalent disease and MMV the least, with lower incidences in cv. IRAT 297 than in INRA 508. For each plant–virus–vector combination, (a) disease incidence was positively correlated to vector abundance, often with 1 month of time lag; (b) annual periodicity of disease incidence and of vector numbers was consistent with highest autocorrelations and a time lag of 12 months, (c) vector numbers and disease incidence were closely associated with temperature fluctuations, both remaining relatively constant below 24°C and increasing rapidly above this threshold temperature. By contrast, relationships with rainfall and relative humidity (RH) were less consistent. Overall, 63 to 80% of the variance of disease incidence was explained through stepwise regression with vector number, temperature, and sometimes also rainfall or RH. The simple epidemiological model proposed underlines the close link between increased temperature and possible (re-) emergence of these three diseases in a maize cropping area.     

Method to diagnose latent infection by <Emphasis Type="Italic">Glomerella cingulata</Emphasis> in strawberry plants using ethanol

Signs on strawberry leaves with latent infection by Glomerella cingulata became visible by a simple diagnostic method using ethanol immersion treatment (SDEI). Leaves treated with SDEI changed to dark brown or nearly black, and salmon-pink conidial masses were subsequently produced in the acervuli 5–10 days after incubation in moist petri dishes. The formation rate of conidial masses through SDEI was higher as the position of the leaves became lower. Conidial masses were produced more readily and abundantly when SDEI was performed at 28°C than at 22°, 25°, or 31°C. Latent infection was found to last 1–180 days. There was no difference in the time required for conidial production or in the rate of conidial formation regardless of isolate, cultivar, or leaf position. The varietal difference in resistance to strawberry anthracnose did not influence the rate of conidial mass formation after SDEI. SDEI is thus useful for detecting latent infections during the process of selecting disease-free plants.     

Temperature Dependent Seed Transmission of Stagonospora nodorum in Wheat

The transmission of Stagonospora nodorum from four naturally infected winter wheat seedlots was quantified in controlled environment germination chambers at 9, 13, 17, 21, and 25 °C. Seedlings were harvested when the second leaf began to emerge. Coleoptiles and first seedling leaves were examined for the presence of lesions caused by S. nodorum. First leaves were incubated on Bannon's medium for 2 weeks, after which they were examined for pycnidia of S. nodorum. Transmission to the coleoptile occurred at all temperatures, but decreased from 100% to 72% as temperature increased from 9 to 25 °C. Transmission to the first leaf was less, dropping from 37% to 2% as temperature increased from 9 to 25 °C. At least 44% of infected first leaves were symptomless at all temperatures, with 96% of infected leaves showing no symptoms at 25 °C. Transmission to seedling leaves occurred over a broad temperature range. Under the high densities at which wheat is sown, a significant number of infected seedlings per unit area may originate from relatively low initial seed infection levels and transmission efficiencies.     

Conidial production and viability of Calonectria pseudonaviculata on infected boxwood leaves as affected by temperature,wetness, and dryness periods

Calonectria pseudonaviculata causes lesions on boxwood leaves and twigs. Controlled-environment experiments were conducted to determine the effects of temperature and leaf wetness period on C. pseudonaviculata sporulation on diseased (cv. Suffruticosa) leaves and of dryness periods and high temperature on conidial survival. Infected leaves were incubated in moist chambers and subjected to six temperatures (9, 13, 17, 21, 25, and 29°C) and six leaf wetness periods (0, 12, 24, 40, 48, and 72 h). Spore production was influenced significantly by wetness period, temperature, and their interaction. Increasing duration of leaf wetness and increasing temperature generally increased sporulation, with no sporulation occurring at 29°C or 9 and 13°C, except at 72 h of wetness exposure, while it was optimal at 21°C. Detached leaves with profuse conidia were subjected to a range of drying (relative humidity at 65%) times (0, 2, 4, 6, and 8 h) at two temperatures of 21 and 29°C. Conidia were then harvested and plated on water agar. Germinating conidia were counted to measure the spore viability. Spore mortality increased with increasing dryness duration at both temperatures but occurred more quickly and severely at 29 than 21°C. Overall, this study extended biological knowledge of conditions required for crucial stages of the C. pseudonaviculata disease cycle and the obtained results will be vital for developing boxwood blight forecasting and management tools.