Hours Of Relative Humidity Research Articles

Evaluation of a Model for Predicting the Infection Risk of Squash and Cantaloupe by Pseudoperonospora cubensis.

Infection risk models of downy mildew of cucumber caused by Pseudoperonospora cubensis were evaluated for their performance in predicting the infection risk of squash and cantaloupe plants under field conditions. Experiments were conducted from 2012 to 2014 in Clayton, NC and Charleston, SC, where disease-free potted plants were exposed to weather conditions during a 24- and 48-h period (hereafter 24- and 48-h models, respectively) within a plot with naturally occurring inoculum. Exposed plants were subsequently placed in a growth chamber where they were monitored for disease symptoms, which was indicative of a successful infection. Disease severity was assessed after 7 days as the proportion of leaf area with disease symptoms. Two predictor variables, day temperature and hours of relative humidity >80% during each exposure were used as inputs to generate model predictions that were compared with observed data. The threshold probability on the receiver operating characteristic (ROC) curve that minimized the overall error rate for the 24-h model was 0.85 for both squash and cantaloupe. The 24-h model was consistently more accurate than the 48-h model in predicting the infection risk for the two hosts. The accuracy of the 24-h model as estimated using area under ROC curve ranged from 0.75 to 0.81, with a correct classification rate ranging from 0.69 to 0.74 across the two hosts. Specificity rates for the model ranged from 0.81 to 0.84, while the sensitivity rates ranged from 0.58 to 0.67. Optimal decisions thresholds (POT) developed based on estimates of economic damage and costs of management showed that POT was dependent on the probability of disease occurrence, with the benefit of using the 24-h model for making management decisions being greatest at low levels of probability of disease occurrence. This 24-h model, previously developed using cucumber as the host, resulted in accurate estimates of the daily infection risk of squash and cantaloupe and could potentially be useful when incorporated into a decision support tool to guide fungicide applications to manage downy mildew in these other cucurbit host types.

A model to predict the risk of infection of cucumber by Pseudoperonospora cubensis

Infection of cucurbits by Pseudoperonospora cubensis and subsequent development of cucurbit downy mildew (CDM) is primarily driven by prevailing weather factors. However, weather factors that influence the daily infection risk of cucurbits by P. cubensis have not been determined. Field experiments were conducted from 2012 to 2014 in Clayton, North Carolina and Charleston, South Carolina under naturally occurring inoculum. Weather factors were monitored during the study during which bioassay cucumber plants were exposed to prevailing weather conditions over a 24- and 48-h period. Disease severity was assessed 7 days after exposure and logistic regression models were developed to predict the probability of disease development on the bioassay plants. Hours of relative humidity >80% and day temperature were identified to be important predictors of the risk of infection for both the 24-h and 48-h cases. Threshold probability (PT) on the receiver operating characteristic curve (ROC) that minimized the overall error rate for the 24-h and 48-h model was 0.54 and 0.62, respectively. Model accuracy as estimated using area under ROC (AUC) ranged from 0.82 to 0.86, with a correct classification rate ranging from 0.73 to 0.80. Specificity rates of the models ranged from 0.72 to 0.86, while the sensitivity rates ranged from 0.71 to 0.76. External validation of the models using an independent dataset collected in South Carolina, showed good performance of the models with an AUC >0.91. Using estimates of economic damage and costs of management, optimal decision thresholds that minimized the average costs due to disease control and crop loss were determined. Optimal decision thresholds were dependent on disease prevalence and management decisions informed by the models reduced average costs when disease prevalence was ≤0.50 and ≤0.90 for the 24- and 48-h models, respectively. However, the value of using these models for making disease management decisions was greatest at low levels of disease prevalence. The PT for the validation models was 0.2 and under this threshold, the 24-h model had a correct classification, sensitivity and specificity rates of 0.88, 0.91 and 0.71, respectively, and the corresponding values for the 48-h model were 0.98, 0.97 and 1.0, respectively. These models provide accurate estimates of the daily infection risk of cucumber by P. cubensis and could serve as a useful decision support tool to guide fungicide applications to manage CDM during the growing season.

Influence of meteorological parameters during the preceding fall and winter on the questing activity of nymphal Ixodes ricinus ticks.

Wood ticks, Ixodes ricinus L., serve as vectors for various pathogens and are ubiquitous throughout Central Europe. Survival and development of I. ricinus depend on biotic and abiotic factors. We examined whether relative humidity (RH), air (T a ) and soil temperatures (T s ), or snow depth during November through February affect the questing activity of ticks during their subsequent season of activity. We related the number of host-seeking nymphs to meteorological parameters measured in close proximity at minutely intervals over the period of 6years (2010-2015) in an urban park in Berlin. We defined thresholds at which associations appeared strongest. Although the annual variations in RH, T a , and snow depth were typical of the mid-latitudes, the questing activity of nymphs during their first peak of activity (March through July) varied among the 6years more than threefold. The accumulated hours of RH below 77% in 2m height during November through February affected the questing activity of nymphs during the following activity peak. In contrast to T a , accumulated hours of T s below -1°C in 0.02m depth or below -4°C in 0.05m depth during the preceding period significantly influenced the average number of nymphs questing during spring. Our observations suggest that RH, T s , and snow cover during the preceding months affect the questing activity of nymphal I. ricinus during their first peak of activity. Snow cover serves as an insulator between the atmosphere and soil, which not only stabilizes T s but also appears to protect ticks from exposure to frost and frequent temperature shifts.

Impact Analysis of Genetically Modified (<i>Bt</i>) Cotton Genotypes on Economically Important Natural Enemies under Field Conditions

Field studies were conducted at Hisar during Kharif, 2009-2010 and 2010-2011 under natural and unsprayed condition. RCH 134 Bt, HS 6 (non Bt), H 1117 and Ganganagar Ageti (non Bt) were selected for the studies. The experiment was laid down in Randomized Block Design replicated thrice having plant spacing 67.5 × 60 cm. Among the bollworms, Erias spp. exhibited positive correlation with rainfall, minimum temperature and relative humidity morning hours significantly at 5 percent level whereas Helicoverpa and Pectinophora displayed positive relations only with evening hours relative humidity significantly while Spodoptera were significantly positive correlated with relative humidity of morning and evening hours. Bollworm complex was negatively correlated with all the weather parameters employed to study although being non-significant in case of rainfall, maximum and minimum of temperature, morning and evening hours of relative humidity. Among the sucking pests, leafhoppers, whitefly, thrips and aphids population showed significantly negative correlation with weather parameters. The comparison of natural bio-agents in cotton hybrids under study revealed that overall mean population of natural enemies were higher in Bt cotton hybrid as compared to non-Bt. These results confirm that use of genetically modified (Bt) cotton in lieu of conventional genotypes could positively impact non-target and beneficial insect species by preserving their host populations.

Modeling temporal and spatial variability of leaf wetness duration in Brazil

Leaf wetness duration (LWD) is recognized as a very important conditioner of crops and forests diseases, but clearly, there is a considerable gap in literature on temporal models for prediction of LWD in broad regions from standard meteorological data. The objective of this study was to develop monthly LWD models based on the relationship between hours of relative humidity (RH) ≥ 90 % and average RH for Brazil and based on these models to characterize the temporal and spatial LWD variability across the country. Two different relative humidity databases, being one in an hourly basis (RHh) and another in a monthly basis (RHm), were used. To elaborate the LWD models, 58 automatic weather stations distributed across the country were selected. Monthly LWD maps for the entire country were prepared, and for that, the RHm from the 358 conventional weather stations were interpolated using geostatistical techniques. RHm and LWD showed sigmoidal relationship with determination coefficient above 0.84 and were highly significant (p < 0.0001). In relation to the validation of the LWD monthly models, a very good performance for all months was obtained, with very high precision with r between 0.92 and 0.96. Regarding the errors, mean error showed a slight tendency of overestimation during February (0.29 h day−1), May (0.31 h day−1), July (0.14 h day−1), and August (0.34 h day−1), whereas for the other months, the tendency was of underestimation like January (−0.27 h day−1) and March (−0.25 h day−1). Even as a first approach, the results presented here represent a great advance in the climatology of LWD for Brazil and will allow the development of studies related to crop and forest diseases control plans.

Quantification of the relationship between the environment and Fusarium head blight, Fusarium pathogen density, and mycotoxins in winter wheat in Europe

Measurements of local environmental conditions, intensity of Fusarium head blight (FHB) in wheat spikes, biomass of Fusarium graminearum, F. culmorum, and F. poae (pathogens causing FHB) and concentration of the mycotoxins deoxynivalenol (DON) and nivalenol (NIV) in harvested wheat grain were obtained in a total of 150 location-years, originating in three European countries (Hungary, Ireland, United Kingdom) from 2001 to 2004. Through window-pane methodology, the length and starting time of temporal windows where the environmental variables were significantly associated with the biological variables were identified. Window lengths of 5 to 30 days were evaluated, with starting times from 18 days before anthesis to harvest. Associations were quantified with nonparametric Spearman correlation coefficients. All biological variables were significantly associated with at least one evaluated environmental variable (P ≤ 0.05). Moisture-related variables (e.g., average relative humidity, hours of relative humidity above 80%) had the highest positive correlations with the biological variables, but there also was a significant negative correlation between average temperature and several biological variables. When significant correlations were found, they were generally for all window lengths, but for a limited number of window start times (generally before anthesis for disease index and after anthesis for the toxins and late-season fungal biomasses). Semi-partial Spearman correlation coefficients were used to evaluate the relationship between the environmental variables and the concentration of DON and NIV after the effects of FHB intensity and fungal biomass on the mycotoxins were removed. Significant semi-partial correlations were found between relative humidity variables and DON, and between temperature and relative humidity variables and NIV for time windows that started after anthesis (and not for any earlier time windows). Results confirm that the environment influences disease, fungal biomass, and mycotoxin production, and help refine the time windows where the association is greatest. However, variability in the relationships was high, indicating that no single environmental variable is sufficient for prediction of disease or mycotoxin contamination.

Predicting Infection Risk of Hop by Pseudoperonspora humuli

ABSTRACT Downy mildew, caused by Pseudoperonospora humuli, is one of the most destructive diseases of hop. Weather factors associated with infection risk by P. humuli in the maritime region of western Oregon were examined for 24- and 48-h periods and quadratic discriminant function models were developed to classify periods as favorable for disease development on leaves. For the 24-h data sets, the model with superior predictive ability included variables for hours of relative humidity>80%, degree-hours of wetness, and mean night temperature. The same variables were selected for the 48-h data sets, with the addition of a product variable for mean night temperature and hours of relative humidity>80%. Cut-points (pT) on receiver operating characteristic curves that minimized the overall error rate were identified by selecting the cut-point with the highest value of Youden's index. For the 24- and 48-h models these were pT=0.49 and 0.39, respectively. With these thresholds, the sensitivity and specificity of the models in cross validation by jackknife exclusion were 83.3 and 88.8% for the 24-h model and 87.5 and 84.4% for the 48-h model, respectively. Cut-points that minimized the average costs associated with disease control and crop loss due to classification errors were determined using estimates of economic damage during vegetative development and on cones near harvest. Use of the 24- and 48-h models was estimated to reduce average management costs during vegetative development when disease prevalence was <0.31 and 0.16, respectively. Using economic assumptions near harvest, management decisions informed by the models reduced average costs when disease prevalence was <0.21 and 0.1 for the 24- and 48-h models, respectively. The value of the models in management decisions was greatest when disease prevalence was relatively low during vegetative development, which generally corresponds to the normally drier period from late spring to midsummer in the Pacific Northwest of the United States.

Adaptation of an Apple Sooty Blotch and Flyspeck Warning System for the Upper Midwest United States.

A warning system for sooty blotch and flyspeck (SBFS) of apple, developed in the southeastern United States, uses cumulative hours of leaf wetness duration (LWD) to predict the timing of the first appearance of signs. In the Upper Midwest United States, however, this warning system has resulted in sporadic disease control failures. The purpose of the present study was to determine whether the warning system's algorithm could be modified to provide more reliable assessment of SBFS risk. Hourly LWD, rainfall, relative humidity (RH), and temperature data were collected from orchards in Iowa, North Carolina, and Wisconsin in 2005 and 2006. Timing of the first appearance of SBFS signs was determined by weekly scouting. Preliminary analysis using scatterplots and boxplots suggested that cumulative hours of RH ≥ 97% could be a useful predictor of SBFS appearance. Receiver operating characteristic curve analysis was used to compare the predictive performance of cumulative LWD and cumulative hours of RH ≥ 97%. Cumulative hours of RH ≥ 97% was a more conservative and accurate predictor than cumulative LWD for 15 site years in the Upper Midwest, but not for four site years in North Carolina. Performance of the SBFS warning system in the Upper Midwest and climatically similar regions may be improved if cumulative hours of RH ≥ 97% were substituted for cumulative LWD to predict the first appearance of SBFS.

Temporal progress of southern rust in maize under different environmental conditions

The progress of the severity of southern rust in maize (Zea mays) caused by Puccinia polysora was quantified in staggered plantings in different geographical areas in Brazil, from October to May, over two years (1995-1996 and 1996-1997). The logistic model, fitted to the data, better described the disease progress curves than the Gompertz model. Four components of the disease progress curves (maximum disease severity; area under the disease progress curve, AUDPC; area under the disease progress curve around the inflection point, AUDPCi; and epidemic rate) were used to compare the epidemics in different areas and at different times of planting. The AUDPC, AUDPCi, and the epidemic rate were analyzed in relation to the weather (temperature, relative humidity, hours of relative humidity &gt;90%, and rainfall) and recorded during the trials. Disease severity reached levels greater than 30% in Piracicaba and Guaíra in the plantings between December and January. Lower values of AUDPC occurred in later plantings at both locations. The epidemic rate was positively correlated (P &lt; 0.05) with the mean daily temperatures and negatively correlated with hours of relative humidity &gt;90%. The AUDPC was not correlated with any weather variable. The AUDPCi was negatively related to both variables connected to humidity, but not to rain. Long periods (mostly &gt;13 h day-1) of relative humidity &gt;90% (that corresponded to leaf wetness) occurred in Castro. Severity of southern rust in maize has always been low in Castro, thus the negative correlations between disease and the two humidity variables.

Meteorological factors affecting periodicity and concentration of airborne spores of Bremia lactucae

Several systems for forecasting downy mildew of lettuce are based on the assumption that spores infect leaves in the early morning. However, there is no clear indication that spores are present in sufficient amounts at that time. Spores of Bremia lactucae were trapped using a 7-day volumetric spore trap for about 35 days in each of 1997 and 1998. Three periodicity patterns were observed. The most frequent pattern had a peak, representing more than 75% of the daily catch, near 10:00 a.m. The second pattern was similar except that the peak occurred later. The third pattern was observed on days with low numbers of spores and was characterized by a random distribution, though most spores were trapped during daylight hours. Spore release was associated with a drop in relative humidity (RH) and increases in temperature and wind speed. The fluctuations in numbers of airborne spores followed fluctuations in disease severity. Overall, daily spore concentrations and number of spores per lesion were not correlated with daily weather variables. However, when spore concentrations were grouped into three categories (low: <10 spores/L; intermediate: ≤10 to < 100 spores/L; high: ≥100 spores/L), a good correlation (r = 0.79) was obtained with night hours of high RH (>95%). For both years, the first significant spore catch was observed when about 200 degree-night hours of RH > 95% (base 0°C) (DNRH) had accumulated. The relative spore concentration (RSC) was modeled as a function of DNRH and the model that best explained (R 2= 0.97) this relationship was RSC = 1×(1 + e–0.0183×DNRH)1/1−1.005.

Summer Pruning as a Method for Reducing Flyspeck Disease on Apple Fruit.

Summer pruning of apples, as opposed to the conventional commercial practice of dormant pruning, consistently reduced the incidence of flyspeck on apple fruit by approximately 50% in each of 2 years in trees where no fungicides were applied. In commercial orchard blocks using fungicides, summer pruning also produced a slight but significant decrease in disease severity. There appear to be at least two mechanisms contributing to decreased flyspeck incidence and severity in summer-pruned apple trees. Summer pruning resulted in a small change in the apple canopy microclimate, decreasing the hours of relative humidity >95% in the canopy by 63% and increasing the evaporative potential. Summer pruning also resulted in improved spray deposition in the upper two-thirds of the tree canopy when applications were made with an airblast sprayer.

Studies on the Concentration of Ramularia beticola Conidia in the Air Above Sugar Beet fields in Denmark

AbstractConcentrations of Ramularia beticola Faut. &amp; Lamb. conidia in the air above 3 sugar beet (Beta vulgaris L.) field were registered for a period of 41 days altogether. A significant diurnal periodicity was revealed. Two periods of 3 and 5 days, respectively, included peaks of several thousands of conidia per m3 of air. The conidial concentrations were related to temperature, relative humidity (RH) and vapour pressure of the air, and to wind speed, dew point, rainfall and hours of sunshine. A significant effect of vapour pressure was observed for 2 fields. In one field with very low conidial concentrations, vapour pressure was nearly significant. In this field only wind speed significantly influenced dispersal of conidia. In an analysis of covariance including all data, 50% of the variation was explained by field, time of day, vapour pressure and number of hours of RH above 95% in the preceding 24h.

Effect of Temperature and Relative Humidity on Development ofCercosporidium personatumon Peanut in Georgia

In controlled environment experiments, a minimum of 4 hr of relative humidity ?95% per day was required for conidial production by Cercosporidium personatum, and the highest numbers of conidia were produced when lesions were subjected to daily periods of 16 or more hours of relative humidity ≥ 95%. The optimum temperature for spore production was near 20°C. In field studies, numbers of airborne conidia of C. personatum, the causal agent of peanut late leaf spot, were monitored with Burkard 7-day recording volumetric spore traps at Athens, Plains, and Tifton, Georgia, in 1986-1988. Trapping of conidia was initiated in mid-July to early August, when late leaf spot lesions were first detected. A diurnal periodicity in spore release was observed, with peak spore catches occurring between 10 a.m. and 6 p.m. Conidia were detected on most days during the trapping period. For the years and locations examined, duration of relative humidity ≥ 95% generally exceeded 5-hr duration each day and temperatures seldom dropped below 20°C, indicating that conditions in Georgia were generally favorable for spore production.

Effect of Relative Humidity During Mango Growth on the Incidence of Quiescent Infections ofAlternaria alternata

The quiescent infected area of Alternaria alternata on mango fruit at harvest was closely related to the number of hours of relative humidity (RH)≥80% during a 52-day period of fruit development. At least 350 hr of RH≥80% were needed for a significant quiescent infected area in fruits at harvest. Disease incidence increased as the number of hours of RH≥80% over 320 increased. In some groves climatic parameters other than RH appeared to affect disease incidence. A map of average daily maximum RH during fruit growth can be used as a basis for predicting the incidence of black spot in Israel

Temporal Dynamics of Entomophaga maimaiga After Death of Gypsy Moth (Lepidoptera: Lymantriidae) Larval Hosts

Conidial discharge by a 1984 Japanese isolate of Entomophaga maimaiga Humber, Shimazu & Soper infecting gypsy moth, Lymantria dispar (L.), larvae was investigated under field conditions. On an hourly basis, levels of conidia discharged were correlated with relative humidity (RH) for the previous 2 h and with leaf wetness for the previous 3 h. Greater than 90% of cadavers discharged maximum numbers of conidia between 2000 and 0800. Increased hours of RH ≥70 or ≥90% after larval death and before sporulation began resulted in increased numbers of conidia released during the first day of sporulation. One-day-old cadavers usually sporulated within an average of 1.5–2.2 d of being placed in the field and 71.6% of cadavers produced conidia for ≤2 d during the average of 5.4 d they were monitored. Cadavers of larvae infected with E. maimaiga demonstrated the ability to sporulate, cease sporulation, and later sporulate again; however, the numbers of conidia discharged after conidial discharge resumed were much lower. Of 40 larvae infected with E. maimaiga that produced only resting spores after death, 50% persisted on tree trunks for only 2 d, although 19.7% still remained attached to tree trunks after 9 d.

The relation of late blight development on potato foliage to temperature and humidity

During four seasons, late blight on the foliage of potato plants spread to nearby plants during periods described by Wallin and his coworkers as “favorable,”i.e. 10 or more hours of relative humidity above 90 per cent and temperatures between 60° and 77° F.

Observations on the Life-history of the Red Locust, Nomadacris septemfasciata (Serv.) in the solitary Phase

The populations of Nomadacris septemfasciata described in this paper were all of solitaria or neai-solitaria phase.Sexual maturation as measured by the developing ovaries took place rapidly though irregularly through the population. Its onset coincided with an increase in the daily number of hours of relative humidity at or above 75 per cent., and abundance of green food; Copulation, which started after the first wide-spread rain, took place before the ovaries of many females were completely mature.Caged locusts gave a mean fecundity of 183 eggs contained in 2·4 pods which is probably a minimum figure. Pods were laid at intervals of about two weeks and each was laid before the next batch had visibly developed.The period spent in the egg was at least 39 days, at most 46 days and probably 42 days. Adults appeared 67 days after the first hatchings. Both these periods are greater than those recorded in phase transiens or gregaria.Solitaria locusts were found to pass through seven instead of six nymphal instars as do gregaria. This difference seemed to be constant. The extra instar was probably interpolated between the second and third of gregaria but was not an exact duplicate of any other instar.The number of vertical dark eye-stripes is a convenient and fairly constant indicator of the instar. The number of antennal segments in the later instars and in the adult, and also the number of adult eye-stripes, is greater in the solitaria phase.Amongst the hoppers three main types of coloration were encountered and are briefly described but they could not be closely related to phase. The amount of dark pigment present in late stage nymphs was reflected in the young adult, the appearance of which is described in some detail. Subsequent changes during the dry season are briefly noted, in particular the pink of the hind wing, which becomes faintly visible within a month of the last moult.The changes in pigmentation which take place during sexual maturation are described in detail. In addition to pronounced darkening of the tegmina which completely changes the appearance of the solitaria locust, certain bright pigments are laid down which are later obscured by a general blackening. It is unsafe to classify Nomadacris septemfasciata as to phase on colour alone unless the date of capture and its relation to the breeding season in the locality is taken into consideration. Solitaria do not normally develop the general reddening of the body which is shown by migrating swarms, even when these are only transiens in phase.