Cercospora Leaf Spot Severity Research Articles

Cercospora leaf spot impacts on postharvest disease and respiration of affected sugarbeet roots.

In Michigan, sugarbeets (Beta vulgaris) are stored for up to 200 days post-harvest, during which sugar loss may occur due to energy use from respiration and factors like rot. Cercospora leaf spot (CLS) has been considered a potential predisposing factor for increased storage rot. To investigate these impacts, field and postharvest studies evaluated storage rot symptom development in sugarbeets with designated 'high' or 'low' in-season CLS severity. Root slices of sugarbeets from each CLS level were inoculated with Fusarium graminearum, Botrytis cinerea, or Penicillium vulpinum and symptoms assessed after seven days. Across three CLS-susceptible commercial varieties, there were no significant differences between storage rot susceptibility to any of the tested pathogens in hand-harvested sugarbeets, regardless of CLS level, at any storage timepoint in 2020 or 2021 (P > 0.05). In studies using CLS-susceptible and -resistant germplasm and varieties, CLS effects were inconsistent and only significant in one parameter at two of six storage timepoints across years (P < 0.05). Across storage pathogens, prior CLS level also did not impact root respiration or the change in respiration rate from initial to final storage timepoint in either 2021 or 2023 (P > 0.05). Of note, B. cinerea caused more severe symptoms than other pathogens in these studies (P < 0.05). Finally, varietal responses differed significantly to storage pathogens (P < 0.05) and may be of interest to future cultivar development efforts. This research increases our understanding of factors contributing to potential storage losses, which will improve yield and profit for sugar growers.

Nighttime Applications of Germicidal UV Light to Suppress Cercospora Leaf Spot in Table Beet.

Cercospora leaf spot (CLS), caused by the hemibiotrophic fungus Cercospora beticola, is a destructive disease affecting table beet. Multiple applications of fungicides are needed to reduce epidemic progress to maintain foliar health and enable mechanized harvest. The sustainability of CLS control is threatened by the rapid development of fungicide resistance, the need to grow commercially acceptable yet CLS-susceptible cultivars, and the inability to manipulate agronomic conditions to mitigate disease risk. Nighttime applications of germicidal UV light (UV-C) have recently been used to suppress several plant diseases, notably those caused by ectoparasitic biotrophs such as powdery mildews. We evaluated the efficacy of nighttime applications of UV-C for suppression of CLS in table beet. In vitro lethality of UV-C to germinating conidia increased with increasing dose, with complete suppression at 1,000 J/m2. Greenhouse-grown table beet tolerated relatively high doses of UV-C without lethal effects despite some bronzing on the leaf blade. A UV-C dose >1,500 J/m2 resulted in phytotoxicity severities greater than 50%. UV-C exposure to ≤750 J/m2 resulted in negligible phytotoxicity. Older (6-week-old) greenhouse-grown plants were more susceptible to UV-C damage than younger (2- and 4-week-old) plants. Suppression of CLS by UV-C was greater when applied within 6 days of C. beticola inoculation than if delayed until 13 days after infection in greenhouse-grown plants. In field trials, there were significant linear relationships between UV-C dose and CLS control and phytotoxicity severity, and a significant negative linear relationship between phytotoxicity and CLS severity at the final assessment. Significant differences between UV-C doses on the severity of CLS and phytotoxicity indicated an efficacious dose near 800 J/m2. Collectively, these findings illustrate significant and substantial suppression by nighttime applications of UV-C for CLS control on table beet, with potential for incorporation in both conventional and organic table beet broadacre production systems.

Cultivar and Fungicide Evaluations for Cercospora Leaf Spot Control in Organic and Conventional Table Beet Production

Cercospora leaf spot (CLS), caused by the fungal pathogen Cercospora beticola, is the most destructive foliar disease of table beet (Beta vulgaris ssp. vulgaris) in Wisconsin, USA, and globally. Under conducive conditions, symptomatic lesions on the leaf expand and coalesce forming large necrotic areas that can ultimately lead to complete defoliation. This damage reduces productivity and threatens the ability to mechanically harvest. CLS damage also detracts from the visual appeal of fresh market bunched beets to such an extent that growers risk buyer rejection if CLS severity is observed to be greater than 5%. Fungicide use for CLS control is threatened by the emergence of resistant C. beticola strains, and the application of host resistance is constrained by limited knowledge of cultivar reaction to CLS in table beet. This study aimed to address the knowledge gaps of fungicide efficacy and cultivar reaction by conducting replicated field trials in multiple table beet growing environments across Wisconsin. Broad variation for resistance to CLS was observed among the 10 included cultivars. The mean area under disease progress curve (AUDPC) across environments for the most susceptible cultivar was 267% greater than the most resistant cultivar. Spearman correlations between environments for mean cultivar AUDPC value ranged from 0.71 to 0.99, revealing consistent cultivar CLS reactions across environments. Although susceptible cultivars surpassed 5% severity in all environments, the resistant cultivars remained below this threshold in six of the 10 environments. By comparison with resistant sugar beet (Beta vulgaris ssp. vulgaris) cultivars, however, all tested table beets appeared susceptible to CLS, highlighting the potential for a CLS breeding effort in table beet. Neither of the evaluated Organic Materials Review Institute–listed treatments were effective at limiting CLS disease progress, whereas both tested conventional fungicides significantly reduced disease severity over the nontreated plots. These findings may provide helpful guidance to table beet growers affected by CLS in Wisconsin and beyond.

Insights into Antifungal Mechanisms of &lt;i&gt;Bacillus velezensis&lt;/i&gt; S141 against &lt;i&gt;Cercospora&lt;/i&gt; Leaf Spot in Mungbean (&lt;i&gt;V. radiata&lt;/i&gt;)

Cercospora leaf spot (CLS) is caused by Cercospora canescens and is one of the most important diseases of mungbean (Vigna radiata). Cercospora leaf spot may result in economic loss in production areas. The present study investigated the potential of Bacillus velezensis S141 as a biocontrol agent for C. canescens PAK1 growth on culture plates. Cell-free secretions from a dual culture of S141+PAK1 inhibited fungal growth more than those from a single culture of S141. The biocontrol efficiency of S141 against Cercospora leaf spot on mungbean was then evaluated by spraying. The disease severity of Cercospora leaf spot was significantly reduced in plants treated with S141, with a control efficiency of 83% after 2 days of infection. Comparative transcriptomics and qRT-PCR ana-lyses of S141 during C. canescens inhibition were performed to elucidate the antifungal mechanisms underlying its antifungal activity against Cercospora leaf spot. According to the differentially expressed genes, most up-regulated genes involved in the biosynthetic genes encoding enzymatic hydrolases, including protease, β-glucanase, and N-acyl glucosaminase, were detected in strain S141 following its interaction. Moreover, genes related to secondary metabolites (surfactin, bacilysin, and bacillomycin D) were up-regulated. Collectively, these results suggest that S141 exhibited strong antifungal activity against C. canescens due to multiple enzymatic hydrolases and secondary metabolites. Therefore, the present study provides insights into the biological network responsible for the antifungal activity of B. velezensis S141 against C. canescens.

Disease incidence and severity of Cercospora leaf spot in sugar beet assessed by multispectral unmanned aerial images and machine learning.

Disease incidence and metrics of disease severity are relevant parameters for decision making in plant protection and plant breeding. To develop automated and sensor-based routines, a sugar beet variety trial was inoculated with Cercospora beticola and monitored with a multispectral camera system mounted to an unmanned aerial vehicle (UAV) over the vegetation period. A pipeline based on machine learning methods was established for image data analysis and extraction of disease-relevant parameters. Features based on the digital surface model (DSM), vegetation indices, shadow condition and image resolution improved classification performance in comparison to using single multispectral channels in 12% and 6% of diseased and soil regions, respectively. With a post-processing step, area-related parameters were computed after classification. Results of this pipeline also included extraction of disease incidence (DI) and disease severity (DS) from UAV data. The calculated area under disease progress curve (AUDPC) of DS was 2810.4 to 7058.8 %.days for human visual scoring and 1400.5 to 4343.2 %.days for UAV-based scoring. Moreover, a sharper differentiation of varieties compared to visual scoring was observed in area-related parameters, like area of complete foliage (AF), area of healthy foliage (AH) and mean area of CLS lesion by unit of foliage (Ac/F). These advantages provide the option to replace the laborious work of visual disease assessments in the field with a more precise non-destructive assessment via multispectral data acquired by UAV flights.

Efficacy of Selected Bio-Agents and Neem Cake on Cercospora Leaf Spot and Growth of Black Gram (Vigna mungo L.)

Black gram (Vigna mungo L.) is a vital pulse crop globally and one of the most vital pulse in India. It is understood to be affected by many varieties of diseases, Cercospora leaf spot is certainly considered one among them. Cercospora leaf spot due to Cercospora canescens causes much damage to the production of black gram. The neem cake, Trichoderma viride, Pseudomonas fluorescens, Paecilomyces lilacinus, Carbendazim were tested under field conditions during Rabi 2020-2021 for their efficacy against the disease and growth and yield parameters. A survey was conducted during Rabi, 2020-2021 to know the severity of Cercospora leaf spot of black gram in farmer’s fields in Kurnool district of Andhra Pradesh. In-situ (field) experiment was carried out in randomized block design with five treatments and three replications. The highest plant height at 60 DAS (56.96 cm), fresh weight (35.59 gm), dry weight (14.98 gm), number of pods per plant (18.17 pods/plant), yield (7.96 q/ha) and Benefit Cost ratio (1:3.48) showing better result when treated with treatment neem cake @ 0.5 t/ha + Trichoderma viride @ 2.5 kg/ha. The treatment T1 – neem cake @ 0.5 t/ha + Trichoderma viride @ 2.5 kg/ha significantly decreased the disease intensity at 30, 45 and 60 DAS (10.02%), (12.02%) and (16.42%) respectively. It is concluded that T1 – neem cake @ 0.5 t/ha + Trichoderma viride @ 2.5 kg/ha found superior in all the growth and yield parameters.

Management of Cercospora Leaf Spot of Mungbean [Vigna radiata (L.) Wilczek] using Fungicides and Host Resistance in Bundelkhand Region of Uttar Pradesh, India

Background: The pulses are important crop of Bundelkhand region of Uttar Pradesh. Among the pulses, mungbean is an important. Despite the multifaceted importance of this crop, its production could not be stabilized in the Uttar Pradesh as well as in the country due to several biotic constraints like diseases and insect-pests leading to considerable yield losses. Among several diseases affecting mungbean, cercospora leaf spot (CLS) caused by Cercospora canescens Ellis and Martin is one of the most important fungal diseases occurring regularly in the mungbean growing areas during the warm and humid weather. Methods: Experiments were conducted during two cropping seasons i.e. Kharif 2019 and 2020 to find out an efficient management strategy for this disease. In first experiment, 9 fungicides were assessed against CLS during both the seasons. In second experiment, 200 germplasm of mungbean were evaluated for resistance against cercospora leaf spot. Result: Among nine different fungicide treatments evaluated individually and as well as in combinations, spraying Carbendazim twice after first appearance of symptoms and second at 15 days’ interval, gave maximum reduction in the incidence and severity of Cercospora leaf spot i.e. 45.57% and 58.45%, respectively along with significant enhancement (53.39%) in grain yield over the unprotected crop followed by treatment with Carbendazim + Mancozeb which resulted in 35.44% and 52.65% reduction in incidence and severity respectively and 44.88% enhancement in yield. Treatment with Captan + Hexaconazole was found to be least effective to reduce the disease incidence/ severity as well as to increase the crop yield. In second field experiment out of 200 mungbean genotypes evaluated against cercospora leaf spot during two consecutive crop seasons, four genotypes viz., PDM 04-123, PDM 54, EC520034-1 and EC 520022 were found to be resistant against cercospora leaf spot disease.

Field Performance Evaluation of Different Fenugreek (Trigonella foenum-graecum L.) genotypes in Northern Ethiopia of Southern Tigray

This research was conducted in 2019 during the rain feed cropping season. It was conducted in Northern Ethiopia of Ofla Woreda at the specific site of Awuligara testing site. Sixteen fenugreek genotypes and one standard check (Jamma) were tested. It was undertaken to evaluate the yield performance of the different fenugreek genotypes in the study area. The trial was laid out in Randomized Complete Block Design with three replications with a plot size of 1.2mx1.5m. The phenology (flowering and maturity days), growth performance, and yield, as well as yield component parameters, did not show significant variation. However, the two fenugreek accessions (Acc#234031 and Acc#234032) and one genotype collected fromLesalso were characterized under resistant for cercospora leaf spot severity. The standard check variety (Jamma) was also categorized in susceptible cercospora leaf spot severity scale. The minimum and maximum seed yield obtained from Acc#234027 (17.19Qt/ha) and the improved variety Jamma (33.97 Qt/ha) were not significantly influenced in the trail. To come in strong recommendation, further studies on the disease prevalence effect on yield and yield parameters performance should be conducted .

English

English

Progresso da cercosporiose da beterraba sob diferentes regimes de pulverização

A cercosporiose da beterraba, causada por Cercospora beticola Sacc. é controlada por meio de pulverizações foliares com fungicidas seguindo um calendário fixo, sem considerar o progresso da doença. Um sistema de previsão pode predizer o progresso da doença e direcionar o regime de pulverizações, reduzindo o número de aplicações e otimizando o manejo da doença. Com o objetivo de avaliar o progresso da cercosporiose sob os diferentes regimes de pulverização foi aplicada a técnica de modelagem estatística conhecida por modelos mistos. Estes modelos não incluem apenas os efeitos fixos, mas também os efeitos aleatórios para cada um dos indivíduos da população em estudo. Nas safras agrícolas de 2018 e 2019, os regimes de pulverização utilizados foram baseados em sistemas com valores de severidade estimada (SE) acumulada de 0,15; 0,25, e 0,35, além dos controles padrões com intervalos de pulverizações de cinco e sete dias. A severidade acumulada da cercosporiose em função do tempo, nos cinco regimes de pulverização, foi calibrada com um modelo Gompertz ajustado pelo modelo misto e o efeito aleatório ajustado à assíntota superior. Como resultado da calibração do modelo, o tratamento com regime de pulverização com SE=0,35 não diferiu dos controles padrões com relação à área abaixo da curva de progresso da doença (AACPD), severidade final e produtividade. Os dados apresentados nesse trabalho demonstram a eficiência do sistema de previsão no manejo da cercosporiose em beterraba, com a vantagem de reduzir o número de pulverizações com fungicidas e o impacto sobre o ambiente.

Integrated management of foliar diseases of sesame (Sesamum indicum L.)

In sesame, minimum incidence of Alternaria leaf spot with severity of 10.6 and 7.8% with higher seed yield of514 and 612 kg/ha, respectively were recorded in summer, 2018 and 2019 with spray of carbendazim 12% + mancozeb 63% 75WP @ 2 g/l. Low severity of Cercospora leaf spot 5 and 6.7% with higher seed yield of 509 and 565 kg/ha, respectively were recorded in summer 2018 and 2019 with spray of myclobutanil 10% WP @ 1 g/l.

Scoring Cercospora Leaf Spot on Sugar Beet: Comparison of UGV and UAV Phenotyping Systems.

Selection of sugar beet (Beta vulgaris L.) cultivars that are resistant to Cercospora Leaf Spot (CLS) disease is critical to increase yield. Such selection requires an automatic, fast, and objective method to assess CLS severity on thousands of cultivars in the field. For this purpose, we compare the use of submillimeter scale RGB imagery acquired from an Unmanned Ground Vehicle (UGV) under active illumination and centimeter scale multispectral imagery acquired from an Unmanned Aerial Vehicle (UAV) under passive illumination. Several variables are extracted from the images (spot density and spot size for UGV, green fraction for UGV and UAV) and related to visual scores assessed by an expert. Results show that spot density and green fraction are critical variables to assess low and high CLS severities, respectively, which emphasizes the importance of having submillimeter images to early detect CLS in field conditions. Genotype sensitivity to CLS can then be accurately retrieved based on time integrals of UGV- and UAV-derived scores. While UGV shows the best estimation performance, UAV can show accurate estimates of cultivar sensitivity if the data are properly acquired. Advantages and limitations of UGV, UAV, and visual scoring methods are finally discussed in the perspective of high-throughput phenotyping.

Improving fungicide-based management of Cercospora leaf spot in table beet in New York, USA

Cercospora leaf spot (CLS), caused by Cercospora beticola Sacc., is the dominant foliar disease affecting the profitability of table beet production in New York, USA. The disease is controlled primarily with fungicides, but sustainability is critically threatened by strobilurin resistance within the C. beticola population and a limited suite of alternatives. This study evaluated the temporal dynamics of strobilurin resistance within the C. beticola population over three years, and quantified sensitivity to selected demethylation inhibitors (DMIs; propiconazole and difenoconazole) and succinate dehydrogenase inhibitors (SDHIs; fluopyram, penthiopyrad, boscalid and benzovindiflupyr). Resistance to azoxystrobin (EC50 > 0.2 µg mL−1) was prevalent and detected in all fields sampled in 2015 and 2016, and six of 10 fields in 2017. Within fields, the incidence of azoxystrobin-resistant isolates ranged between 4.8% and 70%. No significant differences were detected in the frequency of azoxystrobin-resistant isolates within populations from fields with conventional and organic practices in 2016 and 2017. Reduced sensitivity to propiconazole and difenoconazole was detected in less than 1% of isolates. The EC50 values for the SDHIs were higher than the maximum concentrations (≥ 20 µg mL−1) evaluated. Two small-plot replicated field trials were also conducted over two years to evaluate alternatives to the commercial standards, propiconazole and azoxystrobin. Two applications of benzovindiflupyr + difenoconazole and pydiflumetofen + difenoconazole significantly reduced CLS severity and epidemic progress compared with plots that received propiconazole and non-treated controls.

Sensory assessment of Cercospora beticola sporulation for phenotyping the partial disease resistance of sugar beet genotypes

BackgroundDue to its high damaging potential, Cercospora leaf spot (CLS) caused by Cercospora beticola is a continuous threat to sugar beet production worldwide. Breeding for disease resistance is hampered by the quantitative nature of resistance which may result from differences in penetration, colonization, and sporulation of the pathogen on sugar beet genotypes. In particular, problems in the quantitative assessment of C. beticola sporulation have resulted in the common practice to assess field resistance late in the growth period as quantitative resistance parameter. Recently, hyperspectral sensors have shown potential to assess differences in CLS severity. Hyperspectral microscopy was used for the quantification of C. beticola sporulation on sugar beet leaves in order to characterize the host plant suitability / resistance of genotypes for decision-making in breeding for CLS resistance.ResultsAssays with attached and detached leaves demonstrated that vital plant tissue is essential for the full potential of genotypic mechanisms of disease resistance and susceptibility. Spectral information (400 to 900 nm, 160 wavebands) of CLSs recorded before and after induction of C. beticola sporulation allowed the identification of sporulating leaf spot sub-areas. A supervised classification and quantification of sporulation structures was possible, but the necessity of genotype-specific reference spectra restricts the general applicability of this approach. Fungal sporulation could be quantified independent of the host plant genotype by calculating the area under the difference reflection spectrum from hyperspectral imaging before and with sporulation. The overall relationship between sensor-based and visual quantification of C. beticola sporulation on five genotypes differing in CLS resistance was R2 = 0.81; count-based differences among genotypes could be reproduced spectrally.ConclusionsFor the first time, hyperspectral imaging was successfully tested for the quantification of sporulation as a fungal activity depending on host plant suitability. The potential of this non-invasive and non-destructive approach for the quantification of fungal sporulation in other host–pathogen systems and for the phenotyping of crop traits complex as sporulation resistance is discussed.

Interactions between Ascochyta fabae and Cercospora zonata, fungal pathogens of faba bean

Ascochyta blight (Ascochyta fabae) and cercospora leaf spot (Cercospora zonata) have been observed on the same faba bean plants, even on the same leaf, in southern Australia. Ascochyta blight has long been prevalent and cercospora leaf spot has become more common in recent years, but their interactions have not been studied. Potential mechanisms of interactions between A. fabae and C. zonata in vitro and on faba bean plants were investigated. The interactions between isolates of each of the two pathogens varied within species. Ascochyta fabae isolate 55/01 and Cercospora zonata 69/04 inhibited the opposing fungus when exposed to volatile metabolites. In dual culture on agar medium, interactions between the species ranged from neutral to antagonistic. In dual inoculation experiments on faba bean plants in a greenhouse, the severity of cercospora leaf spot decreased in the presence of ascochyta blight, however, the severity of ascochyta blight increased on plants showing symptoms of cercospora leaf spot. These findings suggest that the widespread adoption of ascochyta blight-resistant cultivars and, therefore, reduced competition from A. fabae, may have contributed to the increased prevalence of cercospora leaf spot.

Optimizing management of cercospora leaf spot (Cercospora beticola) of sugarbeet in the wake of fungicide resistance

Cercospora leaf spot (CLS), caused by Cercospora beticola, is the most detrimental disease of sugar beet in temperate climates. In the Great Lakes region, CLS was well managed by pyraclostrobin-based programmes using the decision support tool BEETcast™. Due to C. beticola resistance to pyraclostrobin in the region, other groups of fungicides were evaluated. Field experiments were conducted at six sites from 2013 to 2015 in Pain Court (PC) and Ridgetown (RT), Ontario. BEETcast™ application schedules for prothioconazole and mancozeb as well as carrier volume (115 and 235 L ha−1) were compared with label-based (calendar) applications. When disease intensity was high, the conservative calendar application schedule reduced the standardized area under the disease progress curve (sAUDPC) by an average of 84% compared with all BEETcast™ schedules, and the BEETcast™ 50/35 schedule (235 L ha−1) reduced sAUDPC by 48% compared with the 55/50 schedules. However, there were fewer differences among application schedules at sites with low or moderate disease intensity. BEETcast™ application schedules reduced the number of fungicide applications by 34–55%. All application schedules increased sucrose (%) and recoverable white sugar (RWS) to an equivalent level, but none of the schedules increased profit margin compared with the non-treated control. Using a carrier volume of 235 L ha−1 reduced sAUDPC by 28% compared with 115 L ha−1 at one site when disease severity exceeded 95% in non-treated control plots. Thus, management recommendations should consider that CLS severity is reduced by application schedules using a shortened interval and appropriate carrier volume, but this does not necessarily result in higher beet or sucrose yield or increases in profit margin.

Inhibitory Effect of Certain Chemical Food Preservatives against Cercospora Leaf Spot Disease of Sugar Beet

The antifungal activity of citric acidand its salt (sodium citrate) as chemical food preservatives was evaluated against Cercospora beticola in vitro and in vivo. The inhibitory effect of both compounds was studied against mycelial growth of the pathogen in vitro at concentrations, i.e. 0, 10, 20, 30, 40 and 50 mM. Both of citric acid and sodium citrate were able to inhibit the mycelial growth of the pathogen when they were added to the medium at the tested concentrations. Citric acid at 50 mM had the highest effect on the inhibition growth of the pathogen being 83.70% and also had antifungal activity. The percentage of inhibition growth increased as the tested compounds concentration increased. Data also indicate that microscopic examination of treated plates with citrate shows that this treatment reduced the numbers of C. beticola spores on the medium at all tested concentrations and reached its maximum reducing at concentration 50 mM of citric acid compared to untreated plates. The results revealed that spraying of diseased plants with citric acid and sodium citrate either alone or in combination at concentration 50 mM was effective in decreasing disease severity of Cercospora leaf spot compared to untreated plants. The highest reduction in disease severity was observed in case of citric acid treatment. The results revealed that foliar application of these compounds enhanced significantly root yield and sugar percentage as compared to the control.

Relationships among airborne Cercospora beticola conidia concentration, weather variables and cercospora leaf spot severity in sugar beet (Beta vulgaris L.)

: Cercospora beticola is the most important pathogen of sugar beet in temperate climates and is the causal agent of Cercospora leaf spot (CLS). The relationships among weather variables, disease severity and the aerial concentration of C. beticola conidia were assessed in 2014 and 2015. Volumetric spore traps were deployed to quantify conidia concentration every 6 h in Pain Court (PC) and Ridgetown (RT), Ontario. Mean daily air temperature (AT) and relative humidity (RH) were rarely at optimal levels for CLS development. Conidia were first detected in early May in RT both years and PC in 2015, and in mid-June in PC 2014. CLS symptoms were not observed until 75–91 days after the first detection of conidia. Thus, the presence of conidia was not a limiting factor for disease development. Daily conidia concentration peaked (0.83 spores m−3) between 12 pm and 6 pm and was lowest (0.34 spores m−3) between 12 am and 6 am at all sites, providing evidence of a diurnal effect for airborne C. beticola conidia. A logistic curve explained the relationship between cumulative weekly conidia concentration and CLS severity (R2 ≥ 0.93, P < 0.0001), but CLS severity associated with levels of conidia accumulation was variable among sites. Mean AT 0 h before conidia capture was most influential on aerial conidia concentration compared with other weather variables (R2 = 0.11, P < 0.0001). Additional research is required to validate the relationship among mean daily AT, airborne C. beticola conidia and CLS epidemics.

Efficiency of Some Biocides as Safe Alternatives to Fungicides on Cercospora Leaf Spot Control, their Effect on Biochemical Constituent and Yield of Sugar Beet

Cercospora leaf spot incited by Cercospora beticola Sacc. is a very detrimental fungal disease affecting sugar beet crop production in Egypt as well as sugar yield. The efficacy of four selected commercial biocides i.e., Biobac, Bio-Arc, Bio-Zeid and Plant Guard, was investigated to control Cercospora leaf spot on sugar beet plants in comparison with the recommended fungicide Score as a check difenoconazole fungicide as well as untreated control under field conditions at Sakha Agricultural Research Station, Kafr El-Sheikh Governorate, Egypt. The biocides and fungicide were sprayed at different three spray regimes as two sprays, four sprays or six sprays with 15 days intervals between sprays for such treatment. All tested biocides and Score fungicide led to significant decrease in Cercospora leaf spot disease severity of the treated sugar beet plants in comparison with control treatment. Increasing spraying numbers of the tested biocides or Score fungicide from two times to six sprays per season caused increasing reduction of Cercospora leaf spot severity. Spraying Plant guard, Bio-Zeid and Biobac biocides six times achieved very comparable effectiveness to Score treatment at the same spray regime in the two growing seasons 2015/2016 and 2016/2017, whereas, Bio-Arc was the less effective biocide treatment particularly when sprayed two times per season. All tested biocides at different spraying regimes led to significant increase in values of phenolic compounds, total chlorophyll, (achieved higher quality traits at the end of the season), sucrose (%) and purity (%) and top, root as well as sugar yield quality of sugar beet were significantly increased. The impurities of produced sugar as sodium, potassium and α-amino nitrogen in the juice were significantly decreased in comparison with untreated control during the two growing seasons. Overall results clarified that spraying Score fungicide or Bio- Zeid, Plant guard and Biobac, respectively six times resulted the highest increase of quality traits as sucrose (%) and purity %) and top, root and sugar yields of sugar beet and significant decrease in total amino acid, juice impurities (Na, K and α-a N %), whereas Bio- Arc when applied two times recorded the least effective treatment close to the control during the two growing seasons 2015/2016 and 2016/2017. It was concluded that biocides, Bio-Zeid, Plant guard and Biobac could be sprayed six times/season at 15 days intervals as alternatives to fungicide applications to control Cercospora leaf spot of sugar beet and to produce higher yields of root and sugar with better quality.

Estimate, a New iPad Application for Assessment of Plant Disease Severity Using Photographic Standard Area Diagrams.

Assessment of disease severity is a foundational component of plant pathology and essential for robust disease management. Researchers often estimate disease severity using standard area diagrams (SADs) that are reference images representing disease severity in percentage increments. SADs provide assessments of disease severity that are more accurate, precise, and reliable than other methods. Although specific SADs have been constructed for many plant diseases, they often depict severity in unrealistic black-and-white or grayscale illustrations. SADs are also usually printed, static references that can burden data collection in the field and require data to be transferred manually to a computer spreadsheet for manipulation. This data entry process and verification are prone to errors and require additional inputs of time and labor. We developed a new iPad application (app) called Estimate for researchers and crop managers for their use on a mobile device at the field-level for assessing plant disease severity in order to collect data or aid in treatment decisions. The app is a repository for digital, photographic SADs and offers savings in time for data collection and processing. Estimate allows users to select a disease from a prepopulated list and specify the reference disease images in either logarithmic or linear intervals. Data may be collected as the midpoint of an interval (ordinal) or as 1% increments (continuous). Users then select among photographic images by touching those that best match the observed disease severity on successive samples. Estimate allows data entry at the plant and leaf hierarchical levels within plots and subplots. Alternatively, data may be collected on single sampling units with an undefined experimental design (i.e., 1 to x leaves). The user may inspect and e-mail the final data in comma-separated values format for analysis using conventional spreadsheet software. Estimate was released with SADs for assessing the severity of Cercospora leaf spot in red and yellow table beet cultivars. A list of collaborators and up-to-date list of SADs included in Estimate is available at http://evade.pppmb.cals.cornell.edu/estimate/ . SADs for other diseases will be added to Estimate as they become available. Estimate is available for free download from iTunes ( https://itunes.apple.com/WebObjects/MZStore.woa/wa/viewSoftware?id=1193605571&mt=8 ) and is compatible with an iPad Air 2 or equivalent using iOS 9.0 or greater.