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L W Timmer - One of the best experts on this subject based on the ideXlab platform.
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effect of temperature Leaf Wetness and rainfall on the production of guignardia citricarpa ascospores and on back spot severity on sweet orange
Fitopatologia Brasileira, 2006Co-Authors: R F Reis, L W Timmer, Antonio De GoesAbstract:A pinta preta dos frutos citricos (Citrus sp.)e causada por Guignardia citricarpa e a producao de ascosporos depende da temperatura, molhamento foliar e chuva. O numero de ascosporos foi monitorado usando uma armadilha de esporos e os fatores climaticos foram avaliados usando uma estacao automotizada em pomares de laranja (Citrus sinensis) Natal e Valencia, no periodo de novembro de 2000 a marco de 2001 no municipio de Mogi-Guacu/SP, Brasil. Em ambos os pomares, os frutos foram ensacados para prevenir a infeccao natural, e os sacos foram removidos semanalmente em diferentes estadios de desenvolvimento dos frutos durante 18 semanas. Ascosporos foram produzidos durante todo o periodo do experimento especialmente primeiramente depois da ocorrencia de chuvas. Em ambos os pomares o pico de producao de ascosporos ocorreu em janeiro e fevereiro. A producao de ascosporos foi correlacionada com o molhamento foliar apenas para o pomar de laranja Natal, mas nao foi correlacionada com o total de chuva ou temperatura para as duas variedades. A doenca foi mais severa em frutos expostos na 7a, 8a e 13a semana, apos o inicio do experimento para ambas variedades e, na 16a semana para a variedade Natal. Verificou-se uma forte correlacao entre severidade da doenca e quantidade total de chuva para ambas variedades e uma fraca correlacao entre temperatura e severidade para o pomar de laranja Natal. Nao houve correlacao entre severidade e molhamento foliar ou com o numero de ascosporos.
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evaluation of the alter rater model for timing of fungicide applications for control of alternaria brown spot of citrus
Plant Disease, 2003Co-Authors: Alka Bhatia, Pamela D Roberts, L W TimmerAbstract:ABSTRACT Alternaria brown spot, caused by Alternaria alternata, results in serious yield losses of tangerines and their hybrids in Florida. The Alter-Rater model predicts the need for fungicide applications based on daily cumulative points that are assigned on the basis of rainfall, Leaf Wetness, and temperature. Previously, Alter-Rater threshold or trigger values of 50, 75, 100, and 150 points for application of copper fungicides were suggested for groves with different cultivars and disease histories. In this study, we evaluated thresholds of 50, 100, and 150 points in four Minneola tangelo and Murcott tangor groves in 2000 and 2001. For comparison, copper fungicides were applied according to the DISC Copper Model in 2000 and according to calendar sprays in 2001. Use of the Alter-Rater model resulted in fewer sprays in three of the four groves in 2000 and better fruit quality in the other grove than the Copper Model. Compared to a calendar spray schedule in 2001, use of the Alter-Rater model resulted in...
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a fungicide application decision fad support system for postbloom fruit drop of citrus pfd
Plant Health Progress, 2002Co-Authors: Natalia A Peres, Soonho Kim, Howard W Beck, Nilton Luiz De Souza, L W TimmerAbstract:Postbloom fruit drop (PFD) caused by Colletotrichum acutatum, affects citrus flowers and produces abscission of young fruitlets. PFD is a serious problem in most humid citrus production areas of the Americas. Because a predictive model previously developed in Florida to time fungicide applications was inadequate for use in many other regions, an expert system (PFD-FAD) with broader applicability was developed and implemented in Java Servlet. The PFD-FAD system considers previous history of PFD in the grove, susceptibility of the citrus species, the stage of the bloom as well as rainfall, duration of Leaf Wetness following the rain, and the current inoculum levels in the grove. It predicts the need for a fungicide application based on these factors and the time since the last application. The PFD-FAD system is easy to use and minimizes the need for scouting of groves and acquisition of exact weather information, and is more widely applicable to other regions. The PFD-FAD system was compared to the PFD model, the grower’s program, and to a nonsprayed control in Brazil in 2001. The PFD model indicated 2 sprays were needed, PFD-FAD indicated one spray, and the grower made 3 applications. All programs reduced counts of persistent calyces by about 50% and increased fruit counts by about 20%. Cost savings with the use of PFD-FAD was about $47/ha.
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environmental factors affecting the severity of alternaria brown spot of citrus and their potential use in timing fungicide applications
Plant Disease, 2000Co-Authors: L W Timmer, Tobin L Peever, A M Ibanez, H M Darhower, S E Zitko, P M BushongAbstract:Alternaria brown spot affects many tangerines and their hybrids, causing lesions on leaves, twigs, and fruit resulting in reduced yield and fruit quality. Field studies were conducted in a severely affected Minneola tangelo grove in central Florida from 1996 to 1998 to determine the environmental factors associated with infection of field trees and potted trap plants. Conidial production peaked following large flushes of new leaves, which were heavily infected. Most infections occurred during the summer rainy season, but trap plants became infected nearly every week of the year. When plants were exposed for 1-week periods, linear regression analysis indicated that disease severity on trap plants was positively related to the amount of rainfall, duration of Leaf Wetness, and average daily temperatures, and negatively related to the number of conidia trapped. Similar relationships occurred with trap plants exposed for 24-h periods on 141 different dates, except that temperature was not a significant factor. Nevertheless, these factors individually or combined in stepwise multiple regressions explained only a low percentage of the variability in disease severity with both weekly and daily trap plant sampling. When daily environmental data were categorized as: (i) rain versus no rain, (ii) 10 h Leaf Wetness duration, and (iii) average temperature 28°C, relationships to disease severity on trap plants were clearer. Disease severity on days with rain was nearly double that of days without rain, but considerable infection occurred on days with >10 h Leaf Wetness duration and no rain. Infection was greatest on days with temperatures of 20 to 28°C and slightly less at lower or higher temperatures. A point system, called the ALTER-RATER, was designed whereby each day would be assigned a severity value according to the prevailing environmental conditions. A fungicide application would be made after a predetermined number of points had accumulated. Simulated spray programs based on accumulation of 50, 75, 100, and 150 points from historical weather data at several locations indicated that from 8 to 15, 6 to 8, 5 to 6, or 3 to 4 sprays, respectively, would be needed depending on year and location in Florida. Such a weather-based control system could reduce the number of fungicide applications and improve control of Alternaria brown spot of tangerine.
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a computer controlled environmental chamber for the study of aerial fungal spore release
Phytopathology, 1997Co-Authors: Tim R Gottwald, T M Trocine, L W TimmerAbstract:ABSTRACT An environmental chamber was designed to study aerial release of spores of ascomycetes and hyphomycetes, based on a device developed by C. M. Leach. Relative humidity (RH), temperature, red (660 nm) and infrared (880 nm) light, Leaf Wetness, wind speed, vibration, and rain events are controlled and monitored within the chamber via an RTC-HC11 real-time controller and data-acquisition system. A BASIC11 computer program is uploaded to and controls the system. The program requests values for environmental parameters that change through time according to user specifications. The controller interacts with a stepper motor, solenoids, and relay switches via a feedback system based on data received from solid-state RH, temperature, and Leaf-Wetness sensors. The data-acquisition system records environmental data from the chamber in RAM (random access memory) that can be downloaded to a personal computer for correlation with spore-release data. Spores released from fungal specimens on plant tissues and cul...
Bruce D L Fitt - One of the best experts on this subject based on the ideXlab platform.
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temperature and Leaf Wetness duration affect phenotypic expression of rlm6 mediated resistance to leptosphaeria maculans in brassica napus
New Phytologist, 2006Co-Authors: Yongju Huang, N Evans, Ziqin Li, M R Eckert, Annemarie Chevre, M Renard, Bruce D L FittAbstract:Near-isogenic Brassica napus lines carrying/lacking resistance gene Rlm6 were used to investigate the effects of temperature and Leaf Wetness duration on phenotypic expression of Rlm6-mediated resistance. Leaves were inoculated with ascospores or conidia of Leptosphaeria maculans carrying the effector gene AvrLm6. Incubation period to the onset of lesion development, number of lesions and lesion diameter were assessed. Symptomless growth of L. maculans from Leaf lesions to stems was investigated using a green fluorescent protein (GFP) expressing isolate carrying AvrLm6. L. maculans produced large grey lesions on Darmor (lacking Rlm6) at 5-25 degrees C and DarmorMX (carrying Rlm6) at 25 degrees C, but small dark spots and 'green islands' on DarmorMX at 5-20 degrees C. With increasing temperature/Wetness duration, numbers of lesions/spots generally increased. GFP-expressing L. maculans grew from Leaf lesions down Leaf petioles to stems on DarmorMX at 25 degrees C but not at 15 degrees C. We conclude that temperature and Leaf Wetness duration affect the phenotypic expression of Rlm6-mediated resistance in leaves and subsequent L. maculans spread down petioles to produce stem cankers.
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development of phoma lesions on oilseed rape leaves inoculated with ascospores of a group or b group leptosphaeria maculans stem canker at different temperatures and Wetness durations
Plant Pathology, 2001Co-Authors: C Toscanounderwood, Bruce D L Fitt, J S West, A D Todd, M JedryczkaAbstract:In controlled-environment experiments, ascospores of both A-group and B-group Leptosphaeria maculans were able to infect leaves of oilseed rape and produce phoma Leaf spot lesions at temperatures from 5 to 20°C and Wetness durations from 8 to 72 h after inoculation. Lesions formed on leaves inoculated with B-group ascospores had few pycnidia and were darker, smaller and less noticable than the larger, pale grey lesions with many pycnidia produced by A-group ascospores. Lesions formed by A-group or B-group L. maculans on naturally infected winter oilseed rape experimental crops were similar to lesions produced by the two groups on inoculated plants. The greatest numbers of lesions were produced with a Leaf Wetness duration of 48 h and at temperatures of 15–20°C for both A-group and B-group ascospores. As Leaf Wetness duration and temperature decreased below the optimal values, the number of lesions decreased. The incubation period, estimated as the time from inoculation to the appearance of the first lesions (t1), or the time to the appearance of 50% of the lesions (t50), of B-group was often shorter than that of A-group L. maculans. As temperature decreased below 20°C, the length of the incubation period of both A-group and B-group L. maculans increased.
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effects of temperature and Wetness duration on conidial infection latent period and asexual sporulation of pyrenopeziza brassicae on leaves of oilseed rape
Plant Pathology, 2000Co-Authors: T Gilles, Roy Kennedy, Bruce D L Fitt, S J Welham, M J JegerAbstract:Experiments in controlled environments were carried out to determine the effects of temperature and Leaf Wetness duration on infection of oilseed rape leaves by conidia of the light Leaf spot pathogen, Pyrenopeziza brassicae. Visible spore pustules developed on leaves of cv. Bristol inoculated with P. brassicae conidia at temperatures from 4 to 20 degrees C, but not at 24 degrees C; spore pustules developed when the Leaf Wetness duration after inoculation was longer than or equal to approximately 6 h at 12-20 degrees C, 10 h at 8 degrees C, 16 h at 6 degrees C or 24 h at 4 degrees C. On leaves of cvs. Capricorn or Cobra, light Leaf spot symptoms developed at 8 and 16 degrees C when the Leaf Wetness duration after inoculation was greater than 3 or 24 h, respectively. The latent period (the time period from inoculation to first spore pustules) of P. brassicae on cv. Bristol was, on average, approximately 10 days at 16 degrees C when Leaf Wetness duration was 24 h, and increased to approximately 12 days as temperature increased to 20 degrees C and to 26 days as temperature decreased to 4 degrees C. At 8 degrees C, an increase in Leaf Wetness duration from 10 to 72 h decreased the latent period from approximately 25 to 16 days; at 6 degrees C, an increase in Leaf Wetness duration from 16 to 72 h decreased the latent period from approximately 23 to 17 days. The numbers of conidia produced were greatest at 12-16 degrees C, and decreased as temperature decreased to 8 degrees C or increased to 20 degrees C. At temperatures from 8 to 20 degrees C, an increase in Leaf Wetness duration from 6 to 24 h increased the production of conidia. There were linear relationships between the number of conidia produced on a Leaf and the proportion of the Leaf area covered by 'lesions' (both log(10)-transformed) at different temperatures.
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effects of temperature and Wetness duration on infection of oilseed rape leaves by ascospores of leptosphaeria maculans stem canker
European Journal of Plant Pathology, 1999Co-Authors: J E Biddulph, Bruce D L Fitt, S J Welham, P K Leech, P GladdersAbstract:In controlled environment experiments, ascospores of Leptosphaeria maculans(stem canker) infected oilseed rape (cv. Nickel) leaves and caused phoma Leaf spots at temperatures from 8 Ct o 24C and Leaf Wetness durations from 8 h to 72 h. The conditions that produced the greatest numbers of Leaf spot lesions were a Leaf Wetness duration of 48 h at 20C; numbers of lesions decreased with decreasing Leaf Wetness duration and increasing or decreasing temperature. At 20C with 48 h of Leaf Wetness, it was estimated that one out of four spores infected leaves to cause a lesion whereas with 8 h of Leaf Wetness only one out of 300 spores caused a lesion. As temperature increased from 8 Ct o 20C, the time from inoculation to the appearance of the first lesions (a measure of the incubation period) decreased from 15 to 5 days but Leaf Wetness duration affected the length of the incubation period only at sub-optimal temperatures. Analyses suggested that, within the optimal ranges, there was little effect of temperature or Wetness duration on incubation period expressed as degree-days; the time until appearance of 50% of the lesions was ca. 145 degree-days. A linear regression of % leaves with lesions (Pl) (square-root transformed) on % plants with lesions (Pp) accounted for 93% of the variance: p PlD 1:31C 0:061Pp. This relationship was also investigated in winter oilseed rape field experiments in unsprayed plots from October to April in 1995/96 (cv. Envol), 1996/97 (cv. Envol), 1997/98 (cvs Bristol and Capitol) and 1998/99 (cvs Apex, Bristol and Capitol) seasons. The linear regression of % leaves with lesions (square-root transformed) on % plants with lesions accounted for 90% of the variance and had a similar slope to the controlled environment relationship: p PlD 0:81C 0:051Pp. These results were used to examine relationships between the development of phoma Leaf spot on plants in winter oilseed rape crops, the incubation period of L. maculans and the occurrence of infection criteria (temperature, rainfall) in the autumns of 1996, 1997 and 1998.
Natalia A Peres - One of the best experts on this subject based on the ideXlab platform.
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use of Leaf Wetness and temperature to time fungicide applications to control anthracnose fruit rot of strawberry in florida
Plant Disease, 2012Co-Authors: S J Mackenzie, Natalia A PeresAbstract:Anthracnose fruit rot (AFR), caused by Colletotrichum acutatum, is a major disease of strawberry in Florida and is generally controlled by weekly fungicide applications. More than 20 applications may be made during the growing season, most commonly using captan and the quinone-outside inhibitors. Field experiments were conducted for three seasons on a susceptible and a partially resistant cultivar to evaluate the effectiveness of timing fungicide applications for managing AFR based on a previously published model by Wilson and associates that uses Leaf Wetness duration and temperature to predict fruit infection by C. acutatum under controlled conditions. For most treatments, rules were established where captan was applied when the predicted proportion of fruit infected (INF) from the model exceeded 0.15 and pyraclostrobin was applied when INF exceeded 0.5. For one model-timed treatment where captan and pyraclostrobin were applied before symptoms first appeared in the field, disease control was as good as the treatment where calendar weekly applications were made and the model-timed treatment utilized 47% fewer sprays. In treatments where fungicide application began after symptom appearance, the number of applications was reduced further but disease control was 40% less effective. Model-timed fungicide treatments that included pyraclostrobin gave better control than the treatments using captan alone. The model relating Leaf Wetness and temperature to predict AFR infection can be used effectively in a disease-forecasting system to time fungicide treatments and greatly reduce the number of applications without loss of disease control or yield.
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original paper development of a web based disease forecasting system for strawberries
Computers and Electronics in Agriculture, 2011Co-Authors: Willingthon Pavan, Clyde W Fraisse, Natalia A PeresAbstract:Abstract: Florida produces about 16 million flats of strawberries every year, 15% of berries produced in the U.S. and virtually all the berries grown in the winter. Fungicides are applied on a weekly schedule to control Anthracnose and Botrytis fruit rot from December through March. Different predictive models for these diseases were evaluated and systems developed to time fungicide applications that reduced the number of sprays by about 50%. The models utilized Leaf Wetness and temperature during the wet period to predict disease outbreaks. The most effective models were embedded in a web-based tool developed for use by growers to schedule their fungicide applications. This internet-based forecasting system to predict these diseases, the Strawberry Advisory System (SAS), was implemented on the AgroClimate website using weather data from the Florida Agricultural Weather Network. Growers can select the location closest to their plantings and SAS will provide a prediction of disease incidence and recommendations for fungicide applications. Users can also be provided warnings of the need to spray via email or text messages. In preliminary trials, SAS has been successful in eliminating many unnecessary fungicide applications and has proven user friendly.
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a fungicide application decision fad support system for postbloom fruit drop of citrus pfd
Plant Health Progress, 2002Co-Authors: Natalia A Peres, Soonho Kim, Howard W Beck, Nilton Luiz De Souza, L W TimmerAbstract:Postbloom fruit drop (PFD) caused by Colletotrichum acutatum, affects citrus flowers and produces abscission of young fruitlets. PFD is a serious problem in most humid citrus production areas of the Americas. Because a predictive model previously developed in Florida to time fungicide applications was inadequate for use in many other regions, an expert system (PFD-FAD) with broader applicability was developed and implemented in Java Servlet. The PFD-FAD system considers previous history of PFD in the grove, susceptibility of the citrus species, the stage of the bloom as well as rainfall, duration of Leaf Wetness following the rain, and the current inoculum levels in the grove. It predicts the need for a fungicide application based on these factors and the time since the last application. The PFD-FAD system is easy to use and minimizes the need for scouting of groves and acquisition of exact weather information, and is more widely applicable to other regions. The PFD-FAD system was compared to the PFD model, the grower’s program, and to a nonsprayed control in Brazil in 2001. The PFD model indicated 2 sprays were needed, PFD-FAD indicated one spray, and the grower made 3 applications. All programs reduced counts of persistent calyces by about 50% and increased fruit counts by about 20%. Cost savings with the use of PFD-FAD was about $47/ha.
P M Bushong - One of the best experts on this subject based on the ideXlab platform.
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environmental factors affecting the severity of alternaria brown spot of citrus and their potential use in timing fungicide applications
Plant Disease, 2000Co-Authors: L W Timmer, Tobin L Peever, A M Ibanez, H M Darhower, S E Zitko, P M BushongAbstract:Alternaria brown spot affects many tangerines and their hybrids, causing lesions on leaves, twigs, and fruit resulting in reduced yield and fruit quality. Field studies were conducted in a severely affected Minneola tangelo grove in central Florida from 1996 to 1998 to determine the environmental factors associated with infection of field trees and potted trap plants. Conidial production peaked following large flushes of new leaves, which were heavily infected. Most infections occurred during the summer rainy season, but trap plants became infected nearly every week of the year. When plants were exposed for 1-week periods, linear regression analysis indicated that disease severity on trap plants was positively related to the amount of rainfall, duration of Leaf Wetness, and average daily temperatures, and negatively related to the number of conidia trapped. Similar relationships occurred with trap plants exposed for 24-h periods on 141 different dates, except that temperature was not a significant factor. Nevertheless, these factors individually or combined in stepwise multiple regressions explained only a low percentage of the variability in disease severity with both weekly and daily trap plant sampling. When daily environmental data were categorized as: (i) rain versus no rain, (ii) 10 h Leaf Wetness duration, and (iii) average temperature 28°C, relationships to disease severity on trap plants were clearer. Disease severity on days with rain was nearly double that of days without rain, but considerable infection occurred on days with >10 h Leaf Wetness duration and no rain. Infection was greatest on days with temperatures of 20 to 28°C and slightly less at lower or higher temperatures. A point system, called the ALTER-RATER, was designed whereby each day would be assigned a severity value according to the prevailing environmental conditions. A fungicide application would be made after a predetermined number of points had accumulated. Simulated spray programs based on accumulation of 50, 75, 100, and 150 points from historical weather data at several locations indicated that from 8 to 15, 6 to 8, 5 to 6, or 3 to 4 sprays, respectively, would be needed depending on year and location in Florida. Such a weather-based control system could reduce the number of fungicide applications and improve control of Alternaria brown spot of tangerine.
F W Nutter - One of the best experts on this subject based on the ideXlab platform.
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effects of Leaf Wetness duration and temperature on infection efficiency latent period and rate of pustule appearance of rust in alfalfa
Phytopathology, 1997Co-Authors: D H Webb, F W NutterAbstract:ABSTRACT Dew and growth chamber tests were conducted on the alfalfa cultivar Ranger to determine the effect of duration of Leaf Wetness and temperature on several components of the alfalfa rust (Uromyces striatus) monocycle. Duration of Leaf Wetness and temperature both had significant effects on pustule development. Infection efficiency (number of alfalfa rust pustules per Leaf) increased linearly as duration of Leaf Wetness was increased from 4 to 24 h after inoculation. There was an inverse linear relationship between temperature and infection efficiency as indicated by the slope (-5.73) of the regression line relating the number of pustules per Leaf to increasing temperatures between 17.5 and 28°C. Infection efficiency was approximately 20 times greater at 17.5°C than at 28°C. Inoculated alfalfa plants exposed to constant temperatures of 15, 18, 21, 24, 27, or 30°C after an initial 24-h Leaf Wetness period (19°C) did not significantly affect infection efficiency (P ≤ 0.05), but did affect the time (fr...