scholarly journals Temporal Progress of Septoria Leaf Spot on Rabbiteye Blueberry (Vaccinium ashei)

Plant Disease ◽  
2005 ◽  
Vol 89 (10) ◽  
pp. 1090-1096 ◽  
Author(s):  
P. S. Ojiambo ◽  
H. Scherm
Keyword(s):  
Disease Severity ◽  
Leaf Spot ◽  
Developmental Stages ◽  
Disease Incidence ◽  
Disease Onset ◽  
Parameter Estimates ◽  
Vaccinium Ashei ◽  
Leaf Emergence ◽  
Temporal Progress ◽  
Septoria Leaf Spot

Septoria leaf spot, caused by Septoria albopunctata, is an important disease on blueberry in the southeastern United States, yet its epidemiology is largely unknown. Disease severity and dissemination of pycnidiospores were monitored from 2002 to 2004 in a planting of susceptible Premier rabbiteye blueberry to characterize the temporal progress of the disease and determine the effect of inoculum dynamics and selected leaf attributes on disease development. Disease onset was observed between late April and mid-June, followed by a rapid increase in disease severity until mid- to late September; thereafter, disease severity decreased until the end of the season due to abscission of severely infected leaves. A logistic model was fitted to disease severity data using nonlinear regression, and parameter estimates were used to compare the effects of leaf position on the shoot and shoot location in the canopy on disease progress. Based on this model, the highest absolute rate of disease increase and the highest upper asymptote of disease severity were predicted for leaves in intermediate positions on the shoot and for shoots in the lower canopy. Data collected with funnel spore samplers showed that splash-dispersed pycnidiospores of S. albopunctata were available throughout most of the period from April through late October. Final disease severity on individual leaves was more strongly correlated with cumulative spore numbers throughout the entire season (from leaf emergence to the end of the assessment period in November) than with cumulative spore numbers during shorter periods around the time of leaf emergence; this suggests that infection is not limited to young, expanding leaves, but rather that leaves at all developmental stages can become infected by S. albopunctata seasonlong. Disease incidence on leaves of potted trap plants exposed to natural inoculum in the field during rain events in 2003 and 2004 was >70.0% irrespective of leaf developmental stage at the time of exposure. Taken together, the results of this study indicate that inoculum of S. albopunctata is present throughout most of the growing season and that infection can occur season-long on leaves of any age, giving rise to a polycyclic epidemic.

scholarly journals Survival Analysis of Time to Abscission of Blueberry Leaves Affected by Septoria Leaf Spot

2005 ◽  
Vol 95 (1) ◽  
pp. 108-113 ◽  
Author(s):  
P. S. Ojiambo ◽  
H. Scherm
Keyword(s):  
Survival Analysis ◽  
Disease Severity ◽  
Leaf Spot ◽  
Accelerated Failure Time Model ◽  
Yield Potential ◽  
Parameter Estimates ◽  
Disease Progress ◽  
Assessment Period ◽  
Starting Point ◽  
Septoria Leaf Spot

In the southeastern United States, Septoria leaf spot, caused by Septoria albopunctata, can result in premature defoliation of blueberry plants during summer and fall, thereby reducing yield potential for the following year. The effects of disease severity and leaf attributes (leaf age and leaf location in the canopy) on the dynamics (timing and extent) of defoliation were quantified in field plots of Premier rabbiteye blueberry (Vaccinium ashei) in 2002 and 2003. In each year, 50 shoots were selected for assessment in early spring, and all leaves on these shoots (n = 410 and 542 in 2002 and 2003, respectively) were monitored individually for disease progress and time of abscission at 3- to 10-day intervals throughout the season. In both years, disease progress was characterized by an exponential increase in disease severity up to late September, followed by a decline toward the end of the assessment period in late November. Defoliation was sporadic up to late August, followed by more rapid and sustained levels of leaf loss. Abscission of severely infected leaves could explain the decline in disease severity toward the end of the season. Final disease severity (i.e., disease severity on the last assessment date before leaf drop) was highest for leaves that abscised early and lowest for leaves that had not abscised by the end of the assessment period. Survival analysis revealed that older leaves (located on the lower halves of shoots) and leaves with high levels of disease (≥5 spots/leaf at the time of fruit harvest in mid-June) abscised significantly (P < 0.0001) earlier than younger leaves and leaves with lower disease severity. Relative to their respective reference groups, mean times to abscission were ≈2 weeks shorter for the older leaf group and ≈3 weeks shorter in the leaf group afflicted by high disease severity. When an accelerated failure time model was fitted to the data, the resulting parameter estimates indicated that each additional leaf spot present at harvest accelerated time to leaf abscission (expressed using late August as a starting point) by 1.9 and 4.5% in 2002 and 2003, respectively. Leaf location in upper or lower portions of the canopy had no significant effect on time to abscission (P > 0.05).

scholarly journals Photosynthesis of Blueberry Leaves as Affected by Septoria Leaf Spot and Abiotic Leaf Damage

Plant Disease ◽  
2004 ◽  
Vol 88 (4) ◽  
pp. 397-401 ◽  
Author(s):  
I. Roloff ◽  
H. Scherm ◽  
M. W. van Iersel
Keyword(s):  
Leaf Area ◽  
Disease Severity ◽  
Leaf Spot ◽  
Abiotic Factors ◽  
Lesion Size ◽  
Leaf Conductance ◽  
Yield Potential ◽  
Leaf Spots ◽  
Virtual Lesion ◽  
Septoria Leaf Spot

Leaf spots caused by fungal pathogens or abiotic factors can be prevalent on southern blueberries after harvest during the summer and fall, yet little is known about how they affect physiological processes that determine yield potential for the following year. In this study, we measured CO2 assimilation and leaf conductance on field-grown blueberry plants affected by Septoria leaf spot (caused by Septoria albopunctata) or by edema-like abiotic leaf blotching. Net assimilation rate (NAR) on healthy leaves varied between 6.9 and 12.4 μmol m-2 s-1 across cultivars and measurement dates. Infection by S. albopunctata had a significant negative effect on photosynthesis, with NAR decreasing exponentially as disease severity increased (R2 ≥0.726, P < 0.0001). NAR was reduced by approximately one-half at 20% disease severity, and values approached zero for leaves with >50% necrotic leaf area. There was a positive, linear correlation between NAR and leaf conductance (R2 ≥ 0.622, P < 0.0001), suggesting that the disease may have reduced photosynthesis via decreased CO2 diffusion into affected leaves. Estimates of virtual lesion size associated with infection by S. albopunctata ranged from 2.8 to 3.1, indicating that the leaf area in which photosynthesis was impaired was about three times as large as the area covered by necrosis. For leaves afflicted by edema-like damage, there also was a significant negative relationship between NAR and affected leaf area, but the scatter about the regression was more pronounced than in the NAR-disease severity relationships for S. albopunctata (R2 = 0.548, P < 0.0001). No significant correlation was observed between leaf conductance and affected area on these leaves (P = 0.145), and the virtual lesion size associated with abiotic damage was significantly smaller than that caused by S. albopunctata. Adequate carbohydrate supply during the fall is critical for optimal flower bud set in blueberry; therefore, these results document the potential for marked yield losses due to biotic and abiotic leaf spots.

scholarly journals Effective Biomass Reduction of the Invasive Weed Species Banana Poka by Septoria Leaf Spot

Plant Disease ◽  
2001 ◽  
Vol 85 (4) ◽  
pp. 357-361 ◽  
Author(s):  
Eduardo E. Trujillo ◽  
Chris Kadooka ◽  
Victor Tanimoto ◽  
Steve Bergfeld ◽  
Glenn Shishido ◽  
...  
Keyword(s):  
Leaf Spot ◽  
Disease Incidence ◽  
Severe Disease ◽  
Disease Spread ◽  
Leaf Spot Disease ◽  
Native Forest ◽  
Invasive Weed ◽  
Disease Epidemics ◽  
Biomass Reduction ◽  
Septoria Leaf Spot

Inoculations of Septoria passiflorae for biological control of banana poka (Passiflora tripartita var. tripartita) at different forest sites in Hawaii, Kauai, and Maui resulted in successful establishment of the Septoria leaf spot disease at all sites during 1996. Semi-annual monitoring of sites in 1997 revealed low disease incidence and no disease spread to adjacent non-inoculated plants. Site inspections in March 1998 revealed light disease epidemics causing visible defoliation at inoculated sites on Kauai and Maui. Banana poka biomass reduction at sites with light epidemics of the disease in Kauai and Maui were estimated to be less than 10% in 1998, whereas in 1999 biomass reduction ranged from 50 to 95%. Five of 11 inoculation sites in 1996 on the island of Hawaii showed no disease. These five sites on Kaloko had frequent acid rainfall averaging 3.2 pH, which inhibited spore germination and infection. Six sites, free of acid rain, three at Hilo Forest Reserve and three at Puuwaawaa Wildlife Sanctuary, had severe disease epidemics by 1998, and vine defoliation was >90%. Widespread epidemics of the disease occurred in 1999, resulting in estimated 80 to 95% biomass reductions in more than 2,000 hectares of native forest infested with banana poka.

scholarly journals SUSCEPTIBILITY OF LEMON BALM (Melissa officinalis L.) VARIETIES TO SEPTORIA LEAF SPOT (Septoria melissae Desm.) IN HUNGARY

2019 ◽  
Vol 18 (1) ◽  
pp. 47-56
Author(s):  
Gergő Kovács ◽  
Éva Zámbori-Németh ◽  
Géza Nagy
Keyword(s):  
Leaf Spot ◽  
Plant Protection ◽  
Disease Incidence ◽  
Weather Conditions ◽  
The Other ◽  
Melissa Officinalis ◽  
Lemon Balm ◽  
Protection Method ◽  
Cultivated Plant ◽  
Septoria Leaf Spot

Lemon balm (Melissa officinalis L.) is a widely cultivated plant in Europe. Septoria melissae Desm. is the most important pathogen of lemon balm crops, which may cause serious yield loss by the severe leaf fall. As chemical control of the pathogen is restricted, alternative plant protection methods, like the use of tolerant varieties, should be taken under consideration. The goal of our work was to evaluate the susceptibility of three lemon balm varieties to Septoria leaf spot in field. The trials were carried out in 2016 and 2017 in Budapest-Soroksár, Hungary. Dynamics of infection showed characteristic sharp increase from the beginning of August in both years. The lowest infection levels were observed in cultivar ‘Lemona’. The disease incidence in the middle of August was 19% in the first year and 59% in the second year, while these values were over 40% and 70% in the other cultivars ‘Soroksári’ and ‘Quedlinburger Niederliegende’, respectively. The manifestation of symptomps was also significantly lighter on the ‘Lemona’ plants and they had the highest ratio of healthy leaves (81%) compared to the other cultivars. According to the data, weather conditions might modify the range of the differences among the cultivars. It was concluded that appropriate selection of varieties could be an effective and enviromental friendly plant protection method in the practice of lemon balm cultivation.

scholarly journals Temperature and incubation period affect Septoria pistaciarum conidium germination: disease forecasting and validation

2021 ◽  
Vol 60 (1) ◽  
pp. 113-117
Author(s):  
Thomas THOMIDIS ◽  
Konstantinos MICHOS ◽  
Fotis CHATZIPAPADOPOULOS ◽  
Amalia TAMPAKI
Keyword(s):  
Incubation Period ◽  
Disease Severity ◽  
Leaf Spot ◽  
Disease Risk ◽  
Generic Model ◽  
High Disease Severity ◽  
Conidium Germination ◽  
Effects Of Temperature ◽  
Important Disease ◽  
Septoria Leaf Spot

Septoria leaf spot is an important disease of pistachio trees in Greece. This study aimed to determine effects of temperature and the incubation period on germination of conidia of Septoria pistaciarum, and to evaluate a generic model to forecast pistachio leaf spot under the field conditions of Aegina Island, Greece. The optimum temperature for conidium germination was 23°C, and germination was inhibited at 35 and 4°C. At constant temperature of 23°C, conidia commenced germination after 9 h. The predictive model indexed disease risk close to 100 at 10 May at two locations (Rachi Moschona and Vigla) in 2017, and first leaf spot symptoms were observed on 17 May. Moderate to high disease severity (>25% leaves infected) were observed in unsprayed trees at the end of May. In 2018, the model indexed risk close to 100 on 9 May at Rachi Moschona, and first symptoms were observed on 18 May. Moderate to high disease severity (>25% leaves infected) were observed in unsprayed trees on 25th of May. This study has shown that the forecasting model can be used in Aegina Island, Greece, to predict the severity of Septoria leaf spot of pistachio.

Directional Spread of Septoria Leaf Spot in Tomato Rows

Plant Disease ◽  
1997 ◽  
Vol 81 (3) ◽  
pp. 272-276 ◽  
Author(s):  
S. K. Parker ◽  
F. W. Nutter ◽  
M. L. Gleason
Keyword(s):  
Disease Severity ◽  
Leaf Spot ◽  
Logistic Model ◽  
Disease Spread ◽  
Infection Rates ◽  
Fresh Market ◽  
Tomato Plants ◽  
Septoria Leaf Spot

Disease severity of Septoria leaf spot in rows of fresh-market tomato plants that were not staked was assessed in 1992 and 1993 following inoculation of the center plant in each row. Both temporal disease increase and spatial disease gradients were best described by the logistic model. Apparent infection rates for Septoria leaf spot epidemics averaged 0.282 day-1 (SE = 0.015, r2 = 0.96, P < 0.0001) in 1992 and 0.260 day-1 (SE = 0.011, r2 = 0.96, P < 0.0001) in 1993. Apparent infection rates remained relatively constant at increasing distances from initial foci. Estimated values for disease gradient slopes 3 to 5 weeks after inoculation ranged from -0.26 to -1.05 m-1. Velocities of disease spread ranged from 0.3 to 1.3 m/day. Results of analysis of disease severity data for these 2 years suggest that Septoria leaf spot epidemics can develop at rapid rates, but steep disease gradients limit the velocity of spread.

scholarly journals SEVERITY AND INTENSITY OF FUNGAL DISEASES OF CUCURBIT CROPS OF HAMIRPUR REGION, HP, INDIA

2021 ◽  
Vol 21 (2) ◽  
Author(s):  
Manu Vineet Sharma ◽  
Hem Chander
Keyword(s):  
Cucumis Sativus ◽  
Disease Severity ◽  
Leaf Spot ◽  
Fungal Pathogens ◽  
Disease Incidence ◽  
Fungal Diseases ◽  
Lagenaria Siceraria ◽  
Coccinia Grandis ◽  
Downy Mildews ◽  
Powdery Mildews

Cucurbitaceae is the vegetable family enriched with numerous vitamins and minerals. In early rainy season cucurbits are the host of different fungal pathogens. In present study, four fungal diseases dominant on three members of cucurbitaceae family are observed in Bhoranj block of District Hamirpur, lie in lower foot hills of Himachal Pradesh. Four fungal diseases along with host plants are leaf spot of Lagenaria siceraria, downy mildews of Cucumis sativus, powdery mildews of Coccinia grandis and powdery mildews of Cucumis sativus. Among all these diseases, Disease Incidence and Disease Severity of Powdery mildews of Coccinia grandis are most dominant i.e. 40.3±1 and 51.2±1 respectively. Disease Incidence and Disease Severity of Leaf spot of Lagenaria siceraria is least i.e. 12.5±1 and 1.1±1, respectively.

scholarly journals Planting Technique Matters in Reducing Vinca Disease in Landscapes

HortScience ◽  
2006 ◽  
Vol 41 (4) ◽  
pp. 1004D-1004
Author(s):  
Yan Chen ◽  
Regina Bracy ◽  
Allen Owings
Keyword(s):  
Plant Growth ◽  
Disease Severity ◽  
Leaf Spot ◽  
Sandy Loam ◽  
Disease Incidence ◽  
Growth Index ◽  
Fertilization Rate ◽  
Negative Effects ◽  
Alternaria Leaf Spot ◽  
Quality Ratings

Annual vinca, Catharanthus roseus, is exceptionally adaptive to the summer heat and the sandy loam or clay soil in the southeastern region and provides season-long blooms once established in landscape plantings. A wide variety of colors, sizes, and applications are available for landscape use. However, diseases such as alternaria leaf spot and phytophthora leaf blight are prevalent in this region in vinca plantings. Effective disease control requires frequent fungicide application that is expensive and may pose negative effects on the environment. Proper planting techniques including date of planting, fertilization rate at planting, and variety selection may improve plant growth, reduce disease severity, and save landscape service business labor in disease management. Plants of three varieties: open-pollinated `Cooler Hot Rose', F1 hybrid `Titan Rose', and trailing variety `Mediterranean Lilac' were planted on 1 Apr. or 1 May in landscape plots. Plants were at the same growth stage at the time of planting and were fertilized with Osmocote 14–14–14 (3 months) at 0, 35, 70, or 140 g·m2. Plant growth index indicates that plant growth increased significantly at increasing fertilization rates; however, plant overall quality ratings were not significantly different among fertilized plants. Disease incidence in July suggests that late planting may reduce alternaria leaf spot in open-pollinated and hybrid upright type vinca. Disease severity in August was more pronounced on trailing vinca and more severe when plants were not fertilized or fertilized with the highest fertilization rate. Tissue analysis indicates that trailing vinca `Mediterranean Lilac' may require less fertilization than upright type.

scholarly journals Outbreaks of Soybean Frogeye Leaf Spot in Iowa

Plant Disease ◽  
2001 ◽  
Vol 85 (4) ◽  
pp. 443-443 ◽  
Author(s):  
X. B. Yang ◽  
M. D. Uphoff ◽  
S. Sanogo
Keyword(s):  
Disease Severity ◽  
Leaf Spot ◽  
Performance Test ◽  
Disease Incidence ◽  
Central City ◽  
Cercospora Sojina ◽  
East Central ◽  
Production Region ◽  
Frogeye Leaf Spot ◽  
Winter Temperatures

Frogeye leaf spot of soybean, caused by Cercospora sojina, is typically a disease of warm and humid regions (2). Although the disease was reported in the Midwest in the 1920s (1), no outbreaks have been recorded in Iowa. Outbreaks of frogeye leaf spot occurred during 1999 in soybean fields in Ames and Grand Junction in central Iowa. During the 2000 growing season, the disease occurred in southwestern, southcentral, central, southeastern, and east-central Iowa. Occurrences of the disease with severity (reduction of green leaf area) greater than 50% were observed in production soybean fields at Grand Junction in central Iowa and Central City in eastern Iowa. In a 12-ha no-till field planted with cv. Asgrow 2501, the disease was noticeable and uniformly distributed in the entire field in mid July. Disease severity in this field was greater than 70% by the end of August. Disease incidence, however, was less than 10% in three adjacent soybean fields. In a soybean performance test at a central Iowa location where the disease occurred in 1999 and 2000, the disease was observed on all 80 varieties, with four having a severity equal to or greater than 40%. Fourteen entries had less than a 10% disease severity and 19 entries had a disease severity equal to or greater than 30%. Infected leaves in these locations had typical lesions of frogeye leaf spot, which appeared as reddish brown margins surrounding light brown or ash gray centers. On the infected tissues, hyaline, straight, and multiseptate conidia from clustered conidiophores were found, isolated, and identified to C. sojina. The relatively warm winter temperatures in 1998 to 1999 and 1999 to 2000 were associated with frogeye leaf spot epidemics. Because of the seedborne nature of C. sojina, efforts are warranted to monitor and survey the occurrence of frogeye leaf spot in Iowa, an important seed production state in the northern soybean production region. References: (1) K. Athow and A. H. Probst. Phytopathology 42:660–662, 1952. (2) D. V. Phillips. 1999. Pages 20–21 in: Soybean Disease Compendium. Hartman et al. eds, American Phytopathological Society. St. Paul, MN.

scholarly journals Variability of Alternaria Leaf Spot Resistance in Jerusalem Artichoke (Helianthus Tuberosus L.) Accessions Grown in a Humid Tropical Region

Agronomy ◽  
2019 ◽  
Vol 9 (6) ◽  
pp. 268 ◽  
Author(s):  
Viriyasuthee ◽  
Saksirirat ◽  
Saepaisan ◽  
Gleason ◽  
Jogloy
Keyword(s):  
Disease Severity ◽  
Leaf Spot ◽  
Disease Incidence ◽  
Jerusalem Artichoke ◽  
Severity Index ◽  
Field Conditions ◽  
Helianthus Tuberosus ◽  
Disease Severity Index ◽  
Alternaria Leaf Spot ◽  
Progress Curve

Alternaria leaf spot is an emerging disease of Jerusalem artichoke (Helianthus tuberosus L.) in tropical regions. The lack of known resistant germplasm sources is an important constraint to development of Jerusalem artichoke varieties with resistance to Alternaria leaf spot. The objectives of this study were to identify variability of Jerusalem artichoke genotypes for resistance to Alternaria leaf spot under field conditions and to investigate the relationships among resistance characters, yield, and yield components for selection of resistant varieties. Ninety six accessions of Jerusalem artichoke were evaluated in replicated trials under field conditions in early rainy and late rainy seasons in Khon Kaen, Thailand during 2014. Parameters evaluated included disease incidence, disease score, disease severity index, area under disease progress curve of disease incidence, area under disease progress curve of disease severity index, number of tubers/plants, tuber size, and fresh tuber yield. The genotypes HEL 335, HEL 256, HEL 317, HEL 308, and JA 86 were identified as sources of leaf spot resistance in both seasons. These genotypes can be used as sources of leaf spot resistance for Jerusalem artichoke breeding programs. HEL 293 and HEL 246 showed susceptibility to leaf spot disease in both seasons and should be used as standard susceptible checks.

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