Effect of carbendazim and mancozeb combinationon Alternaria leaf blight and seed yield in sunflower (Helianthus annus L.)

Abstract

Leaf blight caused by Alternaria helianthi (Hansf.) Tubaki & Nishihara, is the major disease of sunflower affecting the successful cultivation across India. Five individual fungicides and two combination fungicides were evaluated against this pathogen in laboratory and in field experiments. Among them, the combination of carbendazim + mancozeb completely (100%) inhibited the mycelial growth of A. helianthi, irrespective of the concentrations tested followed by carbendazim alone and metalaxyl + mancozeb under in vitro condition. In field conditions, the combination of carbendazim + mancozeb was found to be highly effective in reducing the leaf blight disease of sunflower in all the three experiments as compared to other fungicides and unsprayed control. The reduction of Alternaria leaf blight was also directly associated with an increase in seed yield. The economics of the fungicides spray has been worked out and the benefit cost ratio for the combination of carbendazim + mancozeb at 2.0 g/l was 7.1 as compared to unsprayed control. The overall analysis of the results revealed that the combination of carbendazim + mancozeb at 2.0 g/l can be used for the management of foliar diseases such as Alternaria leaf spot/blight in agricultural crops.     

Effects of light leaf spot (Pyrenopeziza brassicae) on yield of winter oilseed rape (Brassica napus)

The relationship between development of light leaf spot and yield loss in winter oilseed rape was analysed, initially using data from three experiments at sites near Aberdeen in Scotland in the seasons 1991/92, 1992/93 and 1993/94, respectively. Over the three seasons, single-point models relating yield to light leaf spot incidence (% plants with leaves with light leaf spot) at GS 3.3 (flower buds visible) generally accounted for more of the variance than single-point models at earlier or later growth stages. Only in 1992/93, when a severe light leaf spot epidemic developed on leaves early in the season, did the single-point model for disease severity on leaves at GS 3.5/4.0 account for more of the variance than that for disease incidence at GS 3.3. In 1991/92 and 1992/3, when reasonably severe epidemics developed on stems, the single-point model for light leaf spot incidence (stems) at GS 6.3 accounted for as much of the variance. Two-point (disease severity at GS 3.3 and GS 4.0) and AUDPC models (disease incidence/severity) accounted for more of the variance than the single-point model based on disease incidence at GS 3.3 in 1992/93 but not in the other two seasons. Therefore, a simple model using the light leaf spot incidence at GS 3.3 (x) as the explanatory variable was selected as a predictive model to estimate % yield loss (y_r): y_r= 0.32x– 0.57. This model fitted all three data sets from Scotland, When data sets from Rothamsted, Rosemaund and Thurloxton in England were used to test it, this single-point predictive model generally fitted the data well, except when yield loss was clearly not related to occurrence of light leaf spot. However, the regression lines relating observed yield loss to light leaf spot incidence at GS 3.3 often had smaller slopes than the line produce, by the model based on Scottish data.     

Comparison of fungicides for control of leaf spot (Septoria apiicola) of celery

Of twenty-one fungicides tested at recommended rates of application for their effectiveness in controlling leaf spot of celery grown in Ireland on peat and on a clay-loam soil, three formulations containing fentin acetate with maneb and formulations of fentin hydroxide and fentin chloride were most effective. Benomyl was superior to the other non-tin fungicides tested and, at moderate disease levels, it resulted in marketable yields of celery equal to those recorded after treatment with the organotin compounds. Generally, the organotin compounds and benomyl were followed in descending order of effectiveness by copper oxychloride, captafol, Daconil 2787 and maneb. None of the fungicides tested in the three seasons caused visible symptoms of phytotoxicity and, on disease-free celery in 1969, none had a significant effect on yield.     

Studies on plant growth-regulating substances. XLII. Abscisic acid as a genetic character related to drought tolerance

A single fentinhydroxide spray at the end of May controlled Ramularia leaf spot in in-situ sugar-beet seed crops and increased seed yield on average by 4%. Sprays controlled leaf spots most effectively in the Cotswolds, but yield increases were larger in Lincolnshire. Benomyl controlled leaf spot as well as did fentinhydroxide; thiabendazole was less effective, and maneb and cuprous oxide gave poor control.     

The effect of treating seed potato tubers with benzimidazole, imidazole and phenylpyrrole fungicides on the control of rot and skin blemish diseases

Over 6 yr the effectiveness of imazalil, prochloraz and fenpiclonil, applied either alone or in a mixture, in controlling gangrene, dry rot, skin spot and silver scurf on potato tubers in store was compared with that of 2-aminobutane and thiabendazole. An assessment was also made of their efficiency in controlling the development of these diseases on the daughter tubers of seed tubers treated at harvest or before planting. Overall, 2-aminobutane was more effective in controlling gangrene (Phoma foveata) in store than the spray-applied fungicides. Deposits of imazalil, thiabendazole and fenpiclonil were greater when sprays were applied with an electrostatic sprayer than with a hydraulic sprayer. The opposite was found with the mixture of prochloraz Mn and tolclofos-methyl. More effective gangrene control was associated with the highest deposits. Fenpiclonil and the mixture of thiabendazole and imazalil were more effective in controlling dry rot (Fusarium solani var. coeruleum) than imazalil alone. The development of dry rot was, however, increased by 2-aminobutane treatment on eight out of 14 stocks. 2-aminobutane gave the greatest reduction (83%) in the severity of skin spot during storage whereas thiabendazole alone, and the mixture of thiabendazole and imazalil, gave mean reductions of 70% and 65% respectively. This mixture and fenpiclonil gave the greatest reduction in the severity of silver scurf although, in general, reductions in silver scurf with fungicide treatment were less than with skin spot. The type of sprayer used to apply a fungicide did not affect the effectiveness of the fungicides in controlling either skin spot or silver scurf on tubers in store, or on the daughter tubers. The incidence of gangrene and dry rot on daughter tubers was not reduced consistently by fungicide treatment of seed tubers of the six stocks tested. However, the severity of skin spot and silver scurf was reduced by fungicide treatments of all eight stocks but the reduction in disease was greater for skin spot than for silver scurf. All fungicides gave reductions in the severity of skin spot, and fenpiclonil and the mixture of thiabendazole and imazalil were the most effective for silver scurf. The effectiveness of the fungicides in controlling these diseases was similar for seed treated at harvest and that treated before planting.     

Methodology to Improve the Efficiency of Evaluation of the Severity of Angular Leaf Spot in Common Bean

Disease severity assessment by means of a scoring scale, especially for angular leaf spot (Pseudocercospora griseola) in common bean, is hindered in experiments for assessment of progenies and/or breeding lines due to lack of uniformity of occurrence of the pathogens and segregation within progenies. The purpose of this study was to estimate the efficiency of the use of one plant per plot in assessing the severity of angular leaf spot in experiments for assessment of progenies and/or breeding lines in the common bean crop. To that end, two experimental strategies were used – one of them using one plant per plot and another using a standard size plot (SPP) (2–4‐m length rows). The experiments were conducted in the period from November 2011 to May 2012 in the municipalities of Lavras and Lambari, state of Minas Gerais, Brazil. Forty‐one lines from the breeding programme of the Universidade Federal de Lavras (UFLA) and from other research institutions were assessed, which differed in regard to their degree of susceptibility to P. griseola. The lines were assessed in regard to the severity of said disease using a five‐degree diagrammatic scale. In all the one plant per plot experiments, severity scores of angular leaf spot from the beginning of its occurrence, and later in intervals ranging from 7 to 12 days, were obtained. In the experiment with the SPP, assessment was made a few days prior to grain harvest. Estimates of the correlations between severity scores and grain yield (GY) were mostly of small magnitude. There was good coincidence between the lines classified as more resistant or more susceptible to the pathogen under the two conditions.     

A Cucumber Disease Caused by Alternaria alternata and its Control

A severe leaf spot disease of cucumber caused by a pathotype of Alternaria alternata (Fr.) Keissler was recorded recently in plastic houses in Crete. Lesions ranged in size of a pin point to over 5 cm in diameter, with necrotic tissue on most of their area and a surrounding yellow zone. The pathogen grew satisfactorily on PDA at temperatures between 5 °C–40 °C and spore germination occurred in the range less than 10 °C to over 37 °C. Optimum temperature in both cases was near 26 °C. Of,13 fungicides tested in vitro, sodium omadine, etem, dichlofluanid, captan and folpet were the most inhibitory on spore germination, and iprodione, sodium omadine and dichlofluanid on mycelial growth. Of 25 fungicides applied on two leaf cucumber plants 24 h before inoculation, maneb, etem, dichlofluanid and chlorothalonil were the most effective. When the last fungicides, plus mancozeb, were applied 24 h after inoculation only maneb was effective. In greenhouse experiments, iprodione, prochloraz-manganese-complex, chlorothalonil, dichlofluanid, guazatine, maneb and etem were the most effective for disease control, while mancozeb was less effective. The local cucumber cv. Knossos and the Dutch F₁ hybrids Evadan, Frella, Herta, Malfa, Mazourka, Pepinex 69 and Renova were all susceptible to infection.     

First report of Bipolaris bicolor causing a leaf spot disease on rubber tree

The rubber tree (Hevea brasiliensis) is the only resource for commercial natural rubber production and thus has economic importance in Southeast Asia. A spot disease on the leaves of a rubber tree was first discovered in 2017 in Hainan, China. In this study, the fungal isolate MA1 from the infected tissues was determined to be a pathogen of the spot disease by satisfying Koch's postulates. The isolate MA1 was identified as Bipolaris bicolor based on the morphological characteristics and multigene phylogenetic analysis. Among fungicides, prochloraz, iprodione and pyraclostrobin significantly inhibited hyphal growth of B. bicolor under in vitro conditions. This study constitutes the first report on the association of B. bicolor with leaf spot disease of rubber trees worldwide.     

Resistance risk assessment for fludioxonil in Stemphylium solani

An outbreak of grey leaf spot caused by Stemphylium solani was observed on tomato in Shandong Province of China in recent years and brought huge economical losses. Fludioxonil is a phenylpyrrole fungicide with strong antifungal activity against S. solani. To evaluate the risk of S. solani developing fludioxonil resistance, a total of 145 field isolates were examined for sensitivity to fludioxonil by measuring mycelial growth. The baseline sensitivity was distributed as a unimodal curve with a mean EC₅₀ value of 0.0659 (±0.0170) µg mL^?1. Five mutants with high resistance to fludioxonil (RF > 1000) were obtained by successively selecting on fludioxonil‐amended plates in the laboratory. All the resistant mutants associated with strongly reduced fitness in mycelial growth, sporulation and pathogenicity. Fludioxonil had positive cross‐resistance with procymidone and iprodione, but there was no cross‐resistance with other fungicides including boscalid, fluazinam, azoxystrobin and flusilazole. Based on the current results, resistance risk of S. solani to fludioxonil could be moderate. This is the first report of baseline sensitivity of S. solani to fludioxonil and its risk assessment. In order to delay the resistance development, it is recommended that fludioxonil can be used as one component of the mixture or fungicides with different modes of action should be alternatively used for this disease management.     

Variety‐specific Epidemiology of Cercospora beticola Sacc. and Consequences for Threshold‐based Timing of Fungicide Application in Sugar Beet

In Central Europe, fungicides to control leaf spot disease in sugar beet caused by Cercospora beticola are applied based on thresholds of disease incidence (DI, per cent of infected plants). As variety‐specific fungicide application was not analyzed to date, the epidemiology of C. beticola and its effect on white sugar yield (WSY) in varieties with different susceptibility were investigated at seven sites in Germany and Austria in 2004 and 2005. All varieties reached the summary thresholds 5 / 15 / 45% DI in all environments. Fitting a logistic growth curve to DI revealed significant differences among varieties. At high disease pressure, susceptible varieties reached a considerably higher disease severity (DS, per cent of infected leaf area) at harvest and a larger area under disease progress curve (AUDPC) than resistant varieties. Fitting a logistic growth curve to DS showed an increasing differentiation among varieties with time. The growth rate estimated based on the logistic growth curve was the only variable that performed equally well in differentiating varieties under low and high disease pressure. With increasing disease pressure, varieties differed considerably in WSY, but differences between susceptible and resistant varieties were significant only in some environments. The disease‐loss relation between AUDPC and relative WSY was variety‐specific. Resistant varieties had an approximately identical WSY with and without infection and compensated for negative infection effects even at higher AUDPC. Therefore, at high disease pressure, resistant varieties had a higher relative yield compared to susceptible ones. However, our results indicate that there is no need to develop variety‐specific thresholds, but resistant varieties reach the established thresholds later than susceptible ones. Consequently, the time of fungicide application can be delayed in resistant varieties. This will help to reduce the use of fungicides to the bare essentials as requested for the integrated crop protection management.     

Effects of previous cropping and fungicide timing on the development of light leaf spot (Pyrenopeziza brassicae), seed yield and quality of winter oilseed rape (Brassica napus)

Light leaf spot, caused by Pyrenopeziza brassicae, was assessed regularly on double-low cultivars of winter oilseed rape during field experiments at Rothamsted in 1990-91 and 1991-92. Previous cropping and fungicide applications differed; seed yield and seed quality were measured at harvest. In each season, both the initial incidence of light leaf spot and the rate of disease increase were greater in oilseed rape crops sown after rape than those sown after cereals. The incidence of diseases caused by Phoma lingam or Alternaria spp. was also greater in second oilseed rape crops. In 1991-92 there was 42% less rainfall between September and March than in 1990-91, and much less light leaf spot developed. However, P. lingam and Alternaria spp. were more common. Only fungicide application schedules including an autumn spray decreased the incidence of light leaf spot on leaves, stems and pods, as indicated by decreased areas under the disease progress curves (AUDPC) and slower rates of disease increase. Summer sprays decreased incidence and severity of light leaf spot on pods only. In 1990-91, all fungicide treatments which included an autumn spray increased seed and oil yields of cv. Capricorn but only the treatment which included autumn, spring and summer sprays increased yields of cv. Falcon. No treatment increased the yields of cv. Capricorn or cv. Falcon in 1991-92. Fungicide applications decreased glucosinolate concentrations in the seed from a crop of cv. Cobra severely infected by P. brassicae in 1990-91, but did not increase yield.     

Tomato leaf mould: its assessment and effects on yield

When the natural incidence of Cladosporium fulvum Cooke, occurring at a relatively late stage of cropping, was controlled with fungicides, comparisons with unsprayed control plants showed that there was an interval of c. 6 weeks between the incidence of severe infection, when the fungus was colonizing at least 50 % of the host's leaf area, and fruit yield decreases. Eye estimates made on separate leaves usually over-estimated the percentage of infection. Correction factors were derived from the regression of eye estimates on infected areas calculated from leaf tracings. Whole-plant infection indices were obtained by averaging corrected values of percentage infection separately assessed on leaves immediately above each fruit truss. Although dichlofluanid and tank-mixed zineb decreased the incidence of C. fulvum more than captan sprays, tomato yields (including green fruit) were increased similarly by all three fungicides from 2·99 to an average of 3·51 kg/plant during c. 3 months' picking. Decreasing the intervals between successive sprays from 21 to 7 days greatly decreased leaf mould infection but did not significantly affect yields. Restricting applications to plant tops (namely foliage from the fourth-youngest truss to the mainstem apex) gave yield benefits equal to those gained from sprays applied to whole plants.     

Effectiveness of acibenzolar-S-methyl, fungicides and antibiotics for the control of brown eye spot, bacterial blight, brown leaf spot and coffee rust in coffee

This study was carried out to evaluate the potential of acibenzolar‐S‐methyl (ASM), combined or not combined with fungicides and antibiotics for the control of brown eye spot (Cercospora coffeicola) and bacterial blight (Pseudomonas syringae pv. garcae) in coffee seedlings, and ASM combined with conventional fungicide application schedules for the control of coffee rust (Hemileia vastatrix) and brown leaf spot (Phoma costarricencis) under field conditions in two coffee crops in the State of São Paulo, Brazil. ASM protected coffee seedlings against C. coffeicola when applied at the rates of 2.5 and 5 g of active ingredient per hectolitre of water (g a.i. hL^?1), providing 34–55% of disease control, and against bacterial blight, when applied at the rates of 2.5, 10 and 20 g a.i. hL^?1, with 38–57% of disease control. Tebuconazole (100 g a.i. hL^?1) and azoxystrobin (10 g a.i. hL^?1) showed the best results for brown eye spot control. Oxytetracycline + streptomycin, kasugamycin hydrochloride, oxytetracycline + metallic copper, copper oxychloride and mancozeb + copper oxychloride also controlled bacterial blight in levels similar to those shown by ASM. In the field experiments, all fungicide application schedules tested, cyproconazole (December, February, April), epoxiconazole (December, March), tetraconazole (December, February, April), cyproconazole (December, February) and azoxystrobin (January, March) were effective for coffee rust control and provided partial control of brown leaf spot. The results also showed that for all experiments, there was no synergistic effect of the combination of ASM with azoxystrobin, cyproconazole or cupric fungicides.     

Effect of numbers of fungicidal sprays and dates of application on control of celery leaf spot (Septoria apiicola) and on chemical residues

Experiments at two sites in each of three seasons showed that successful control of celery leaf spot depended more on the choice of fungicide than on the number of sprays and the dates of application. Organotin fungicides gave best control of celery leaf spot and with one exception residues were not detected even when the last application was given 4 weeks before harvest rather than 6 weeks.     

Some problems of evaluating fungicides for use on coffee in Kenya

As part of a programme testing fungicides for control of coffee berry disease (CBD) promising materials were also tested in the field against leaf rust of coffee. In all, fourteen fungicides were tested, five of which have been recommended for control of CBD. Only Perenox (representative of 50% copper fungicides) and Du-Ter (not highly effective against CBD and no longer recommended) gave good control of rust; Difolatan gave some control but Benlate and Daconil were virtually ineffective.
Where only CBD is present there is generally a good relationship between disease control and yield, but in these experiments where leaf rust was also present, this relationship was seriously disturbed. The implications of this for testing fungicides for use on coffee in Kenya are discussed.     

Analysis of β-tubulin Gene Fragments from Benzimidazole-sensitive and -tolerant Cercospora beticola

Cercospora leaf spot of sugar beet, caused by the fungus Cercospora beticola, is a major foliar pathogen on sugar beet. Fungicide sprays have been used extensively to manage Cercospora leaf spot, including the benzimidazole fungicides. Resistance to benzimidazoles has been observed in isolates of C. beticola. The precise genetics of this resistance is not known in this fungus. We tested benzimidazole‐tolerant and ‐sensitive isolates and found a single mutation in the β‐tubulin gene of benzimidazole‐tolerant isolates that corresponds to a mutation known to confer benzimidazole tolerance in other ascomycetes. This mutation is predicted to cause a change from glutamic acid to alanine in the protein product. Isolates containing this mutation further show an increased sensitivity to an N‐phenylcarbamate, as would be predicted based on the mutant phenotype found in other filamentous fungi. Only a single mutation was found in isolates from different regions of the United States, isolated in different growing seasons.     

Splash dispersal of fungus spores and fungicides in the laboratory and greenhouse

A laboratory technique is described for the production of drops of simulated rain in which fungal spores were suspended. When such drops containing conidia of Botrytis fabae impacted on a target leaf the secondary droplets produced infections on receptor broad bean leaves. The capacity of fungicides applied to the target leaf to redistribute in secondary splash droplets was examined in terms of the infectivity of the spores in the droplets. The extent to which a copper fungicide reduced infection on the receptor leaves was related to the level and tenacity of the fungicide deposit on the target leaf. The effect of wetting agents on the redistribution of this fungicide could probably be explained by their influence on the tenacity of the initial deposit. In general the capacity of different fungicides to inhibit infection by the secondary droplets was related to the inherent toxicity of the fungicides to B. fabae. Implications of the dispersal of spores and fungicides by rain splash are briefly considered with reference to field conditions.     

Effects of diseases on the growth and yield of spring linseed (Linum usitatissimum), 1988–1998

In spring linseed field experiments with fungicides at Rothamsted from 1988 to 1998, substantial yield losses assoeiated with diseases occurred in three years and slight losses could be associated with diseases in other years. These yield losses were related to decreases in yield components (thousand grain weights and number of capsules). Leaf browning was observed each year and percentage leaf area with browning was the disease factor most consistently related to yield losses (in five years). Yield loss relationships for these five years suggested that for each 10% increase in percentage leaf area with browning there was a yield loss of 0.10 to 0.18 t ha^?1. Stem browning, lesions on capsules and powdery mildew were associated with yield losses in two years, three years and one year, respectively. Yield losses were greatest in years when the period of flowering and early capsule development in June and July was wetter than average; the predominant disease was grey mould (Botrytis cinerea) in wet years up to 1996, whereas pasmo (Mycosphaerella linicola) was most important in 1997 and 1998. Observed yield losses were small in hot, dry years when powdery mildew (Sphaerotheca lini) and verticillium (Verticillium dahliae) were the predominant diseases.     

积雪草漆斑病病原鉴定及室内药剂筛选

近年来,在广西各地积雪草种植基地,出现一种为害极重的病害,该病害病原菌主要为害积雪草叶片、叶柄,可致使叶片大面积枯死,该病害发生普遍、侵染期长,严重影响积雪草药材的品质和产量。该研究采用常规组织分离法从积雪草病叶上分离病原菌并根据柯赫氏法则验证其致病性;通过菌落特征、菌株形态及ITS序列分析鉴定病原菌;在室内利用生长速率法测定10种杀菌剂对该菌的抑制活性。结果表明：为害积雪草叶片的病原菌为泛生漆斑菌( Myrothecium inundatum);该菌侵染性强,接种至健康积雪草叶片后24 h即可发病,并迅速扩展引起叶片萎蔫;杀菌剂60％唑醚?代森联水分散粒剂、45％恶霉灵?甲霜可湿性粉剂、1.8％辛菌胺醋酸盐水剂、80％代森锰锌可湿性粉剂室内对积雪草漆斑病病原菌的抑菌率均在98％以上,抑菌效果极强,建议在生产中轮换应用防治积雪草漆斑病。15％咪鲜胺微乳剂、70％甲基硫菌灵可湿性粉剂和10％苯醚菌酯悬浮剂对该病原菌的抑菌率也均在92％以上,抑菌效果良好,在生产中可酌情考虑使用。     

Biology and Control of Entyloma eryngii (Cda.) de By., the Cause of a Leaf Spot Disease on the Blue Thistle (Eryngium alpinum L.)

The blue thistle (Eryngium alpinum L.), an indigenous perennial flower of the alps, is grown in mountainous regions of south-eastern Switzerland. The commercial value of the fresh cut flowers can be seriously reduced due to a leaf spot disease caused by the smut fungus Entyloma eryngii (Cda.) de By. The fungus produces thick walled chlamydospores and two types of conidia. The disease appears to be favoured by cool-rainy weather and a dense foilage resulting in long periods of leaf wetness. Control of the disease can be achieved with the protective fungicide mancozeb or even more efficiently with the systemic ergosterol-biosynthesis-inhibiting fungicides cyproconazole and difenoconazole.