The fungicide-resistance problem

Mutation to resistance is more likely to occur to systemic fungicides than to conventional fungicides. The possibilities to obtain systemic fungicides, to which fungi will not readily become resistant, are discussed. A high potential for development of fungicide resistance does, however, not always imply that problems will arise in practice. If fungicide resistance is accompanied with reduced pathogenicity and fitness, the build-up of a resistant population will be hampered or prevented. Of importance are also the type of disease and the selection pressure exerted by the fungicide. The latter may be influenced by the management of fungicide application.     

A test method based on microscopic assessments to determine curative and protectant fungicide properties against Septoria tritici

Glasshouse experiments to test the activity of commercial fungicides against Septoria tritici were carried out under controlled conditions. In addition to the parameter, % necrotic leaf area (NEC), used to estimate the pathogen-induced leaf damage, the number of pycnidia per leaf (PYC) was determined to quantify the pathogen itself. Curative fungicide treatments were applied 100–210 day degrees after inoculation. A high curative activity was achieved up to 170 day degrees after inoculation, whereas the treatments at 200–205 day degrees were less effective. The best curative activity was observed for epoxiconazole-based treatments, followed by slightly less active azoles in the ranking tebuconazole, cyproconazole, prochloraz and flusilazole. Greater differences between the fungicides were observed for the protectant fungicide properties, which were tested 50–350 day degrees prior to inoculation. The best persistency was observed for epoxiconazole, whereas tebuconazole, cyprocoazole, prochloraz and flusilazole showed declining activity with this ranking. Combinations of triazoles with the active ingredients kresoxim-methyl and chlorothalonil, which are known to inhibit spore germination, significantly improved the longevity of the remaining green leaf area in comparison with disease-free treatments with triazoles alone. The results obtained under glasshous conditions were compared with field studies on S. tritici development after treatments with tebuconazole to place the results in context. The comparison of the assessment parameter PYC and NEC between glasshouse and field trial showed that curative and protectant fungicide properties based on microscopic assessments of PYC in the glasshouse correlated well with results from field trials.     

水稻恶苗病菌田间抗咪鲜胺菌株的适合度及其交互抗性

恶苗病是水稻生产上较为严重的种传真菌病害,咪唑类广谱内吸性杀菌剂咪鲜胺是目前防治该病害的主要药剂。以对咪鲜胺抗性及敏感的田间水稻恶苗病菌为试材,研究了其适合度及对几种常用杀菌剂的交互抗性。结果显示:抗性菌株的抗药性可稳定遗传,其温度敏感性与敏感菌株无明显差异,部分抗性菌株在菌丝生长速率、产孢量、孢子萌发率和致病力方面显著高于田间敏感菌株;咪鲜胺与三唑类及2-氰基丙烯酸酯类杀菌剂之间均无交互抗性。研究表明,对咪鲜胺产生抗性的水稻恶苗病菌具有较强的适合度,在田间自然条件下有可能形成优势群体,因此需合理轮换使用不同作用机制的杀菌剂,以延缓其抗药性的发展。     

Nine years of practical experience with phenylamide resistance in Phytophthora infestans in the Netherlands

Resistance to phenylamide fungicides in thePhytophthora infestans population in the Netherlands decreased from a level of 77% of the samples containing resistant strains in 1980 to 0% in 1986 with decreasing use of metalaxyl, the only phenylamide fungicide registered for use against late blight in this country. Use of metalaxyl decreased because the fungicide alone and combinations of metalaxyl with preventive late blight fungicides were not commercially available from 1981 through the first part of the potato growing season of 1984. When metalaxyl was made available again in August 1984 in a mixture with mancozeb and from 1985 in a mixture with almost full rates of maneb and fentinacetate its use remained limited because growers were advised to apply the combination only two times per season in critical situations only to control the severe late blight epidemics of 1984 and 1985. Moreover application on seed potato crops was not allowed. In 1986 the combination was hardly used because the mild epidemic was easily controlled by preventive compounds only.In 1987 and 1988 phenylamide resistance increased to 16 and 42%, respectively, inherent to a general use of the combination in both years in most potato growing regions of up to two applications to combat a very severe epidemic.In lots of seed potatoes harvested in 1988 the percentage of blighted tubers yielding resistant isolates significantly differed from 13% for regions where seed potatoes are predominantly grown for table and processing crops to 41% for a region where predominantly starch potatoes are grown, both as seed and production crops. The more intensive use of metalaxyl combinations in the latter area through the years as compared to the other areas is assumed to be responsible for the higher incidence of resistance.In most years application of the combination induced a significant shift in the population to resistance as is indicated by the higher frequency at which resistant isolates were present in leaf samples taken from treated fields or tuber samples from the harvested crop.The strategy adopted by Dutch potato growers to combat phenylamide resistance in late blight, involving limited use of metalaxyl mixtures to a maximum of two times in critical situations only, has kept up to now resistance in the population at a level at which metalaxyl still significantly contributes to the efficacy of the combination in controlling the disease. Never-theless the observed increase in resistance in the population of 1988 after two consecutive late blight years indicates that this may change if severe epidemics occur each year.     

Quantitative PCR monitoring of the effect of azoxystrobin treatments on Mycosphaerella graminicola epidemics in the field

Quantitative PCR and visual monitoring of Mycosphaerella graminicola epidemics were performed to investigate the effect of curative and preventative applications of azoxystrobin in wheat field crops. A non-systemic protectant and a systemic curative fungicide, chlorothalonil and epoxiconazole, respectively, were used as references. PCR diagnosis detected leaf infection by M graminicola 3 weeks before symptom appearance, thereby allowing a clear distinction between curative and preventative treatments. When applied 1 week after the beginning of infection, azoxystrobin curative activity was intermediate between chlorothalonil (low effect) and epoxiconazole. When applied preventatively, none of the fungicides completely prevented leaf infection. There was some indication that azoxystrobin preventative treatments may delay fungal DNA increase more than epoxiconazole at the beginning of leaf infection. Both curative and preventative treatments increased the time lapse between the earliest PCR detection and the measurement of a 10% necrotic leaf area. Azoxystrobin only slightly decreased the speed of necrotic area increase compared with epoxiconazole. Hence, azoxystrobin activity toward M graminicola mainly resides in lengthening the time lapse between the earliest PCR detection and the measurement of a 10% necrotic leaf area. Information generated in this way is useful for optimal positioning of azoxystrobin treatments on M graminicola.     

Control of cucumber downy mildew with novel fungicidal mixtures of Oxathiapiprolin

The efficacy of four oxathiapiprolin (OXPT)-based, novel fungicidal mixtures against downy mildew in cucumber caused by Pseudoperonospora cubensis was examined in growth chambers. OXPT+chlorothalonil (CHT) mixed at weight ratio of 1?+?66.7; OXPT+ azoxystrobin (AZ) 1?+?10.3; OXPT+mandipropamid (MPD) 1?+?8.3; and OXPT+mefenoxam (MFX) 1?+?3, were compared with each other and with individual components. Mixtures performed better than all fungicides alone except for oxathiapiprolin. Of the four mixtures, OXPT+MFX outperformed the other treatments with the highest preventive, curative, translaminar, root treatment and seed treatment efficacies. Deployment in the field of such mixtures with reduced doses of oxathiapiprolin may lower the selection pressure imposed on P. cubensis and delay the buildup of subpopulations resistant to oxathiapiprolin.     

Sensitivity to Protectant Fungicides and Pathogenic Fitness of Clonal Lineages of Phytophthora infestans in the United States

ABSTRACT Since 1991, dramatic changes have occurred in the genetic composition of populations of Phytophthora infestans in the United States. Clonal lineages recently introduced into the United States (US-7 and US-8) are more common now than the previously dominant lineage (US-1). To help determine why these changes occurred, four clonal lineages of P. in-festans common during the early 1990s in the United States and Canada were evaluated for sensitivity to the protectant fungicides mancozeb and chlorothalonil using amended agar assays for isolates collected from 1990 to 1994. No isolate or lineage was resistant to either mancozeb or chlorothalonil. There were significant differences among isolates for degree of sensitivity to one fungicide individually, but there were no significant (P = 0.05) differences among the US-1, US-6, US-7, and US-8 clonal lineages for degree of sensitivity to both fungicides. Therefore, resistance to protectant fungicides cannot explain the rapid increase in frequency of the US-7 and US-8 clonal lineages. Three components of pathogenic fitness (latent period, lesion area, and sporulation after 96 h) were tested for the three clonal lineages that were detected most commonly during 1994 (US-1, US-7, and US-8). All but one of the isolates in this analysis were collected during 1994 and evaluated within 10 months of collection by inoculating detached leaflets of the susceptible potato cultivar Norchip. There were significant differences between the US-1 and US-8 clonal lineages for lesion area and sporulation, and between US-1 and US-7 for latent period. The US-6 clonal lineage was excluded from the pathogenic fitness experiments, because no isolates of this lineage were collected during 1994. Compared with US-7 and US-8, US-1 had the longest latent period and the smallest lesions with the least sporulation. Incorporation of the differences between US-1 and US-8 in computer simulation experiments revealed that significantly more protectant fungicide (e.g., 25%) would be required to suppress epidemics caused by the US-8 clonal lineage compared with US-1. These differences in pathogenic fitness components probably contribute to the general predominance of the "new" clonal lineages (especially US-8) relative to the "old" US-1 lineage.     

Application of fungicides to foliage through overhead sprinkler irrigation – a review

Articles on chemigation with fungicides targeting foliage have been reviewed. They included 23 fungicides tested on 10 crops. Many studies compared chemigation to a check treatment, while others also included conventional methods. Chlorothalonil, followed by mancozeb, fentin hydroxide and captafol were the most studied fungicides, while peanut (Arachis hypogaea), potato (Solanum tuberosum), tomato (Lycopersicon esculentum ), and dry beans (Phaseolus vulgaris) were the most studied crops. Center pivot, followed by solid set, were the irrigation systems most frequently used. The minimum volume of water applied by some center pivots (25 000 litre ha⁻¹ ) is 25 times the maximum volume of water used by conventional ground sprayers. The reduction of fungicide residue on foliage caused by the very large volume of water used by chemigation might be offset by the following factors: (1) fungicide application at the time of maximum leaf wetness when fungi are most active, (2) complete coverage of plants, (3) reducing greatly the inoculum on plant and soil surface, (4) better control of some soil pathogens, and (5) more uniform distribution of fungicides by center pivot. Furthermore, chemigation avoids mechanical damage and soil compaction. Additionally, some systemic fungicides seem to be absorbed rapidly by the leaves, by root uptake from the soil, or by both. In general, all fungicides applied through irrigation water can lessen disease severity. However, when compared to conventional methods, chemigation with fungicides can be less, equally or more effective depending on crop, pathogen, disease severity, fungicide and volume of water. For Cercosporidium personatum control on peanuts, application of protectant fungicides through irrigation water is less effective than conventional methods, but the results with some systemic fungicides mixed with non-emulsified oil and applied through a relatively low volume of water (2.5 mm) are encouraging. Important diseases of potato and tomato can be controlled nearly as well by chemigation as by conventional methods without impairing yield. The main advantage of chemigation for these crops is avoiding a large number of tractor trips through the field and reduced costs of fungicide application. Chemigation has also been shown to be a good option for control of white mold [ Sclerotinia sclerotiorum] on dry beans. © 1999 Society of Chemical Industry     

梨黑斑病菌抗药性检测及其对啶酰菌胺的敏感性基线

黑斑病是梨的主要病害之一,近年来不少地区反映多菌灵等传统常用杀菌剂对其防治效果已出现下降。作者从浙江、江苏和安徽3省分离了252株梨黑斑病菌Alternaria kikuchiana,采用菌丝生长速率法检测了其抗药性发生情况。结果发现:所检测的黑斑病菌群体(n=252)对苯并咪唑类杀菌剂多菌灵的抗性频率为57.1%,且全部为高水平抗性(HR);对二甲酰亚胺类杀菌剂异菌脲的抗性频率为46.8%,全部为低水平抗性(LR);对甾醇脱甲基抑制剂类杀菌剂苯醚甲环唑的抗性为低水平(LR)及中等水平(MR),抗性频率均为28.6%;表明梨黑斑病菌对常用杀菌剂已产生较为严重的抗性。供试252株梨黑斑病菌对琥珀酸脱氢酶抑制剂啶酰菌胺的EC50值分布在0.12~3.85μg/m L之间,平均EC50值为(1.21±0.12)μg/m L,且其分布呈近似正态的单峰曲线。研究表明,啶酰菌胺可作为潜在的梨黑斑病防治替代药剂,其平均EC50值(1.21±0.12)μg/m L可作为梨黑斑病菌对啶酰菌胺的敏感性基线。     

Rational Management of Didymella rabiei in Chickpea by Integration of Genotype Resistance and Postinfection Application of Fungicides

ABSTRACT Various aspects of the integration of genotype resistance and chemical control of Ascochyta blight (caused by Didymella rabiei) in chickpea were examined in field experiments from 1993 to 1999 and in greenhouse experiments. Four commercially available chickpea cultivars representing a range of resistance to D. rabiei were used. The efficacy of chemical control in a highly susceptible cultivar was significantly (P < 0.01) related to the conduciveness of the environment to the pathogen. Adequate disease suppression (>80% control) was achieved when weather supported mild epidemics, but insufficient control (<20%) was achieved when weather supported severe epidemics. The contribution of genotype resistance to disease suppression in a moderately susceptible cultivar varied from <10% when weather supported severe epidemics to approximately 60% when weather supported mild epidemics. Spraying a moderately resistant cultivar resulted in 95% control when weather supported mild epidemics, but only 65% control was achieved when weather supported severe epidemics. The existing level of resistance in a moderately resistant cultivar resulted in 70% control when weather supported severe epidemics; fungicides improved control efficacy significantly to >95%. Under mild epidemics, moderate resistance alone provided >95% control. The level of genotype resistance available in a highly resistant cultivar was sufficient to suppress the disease under all weather conditions, even without application of fungicides. The possibility of relying on postinfection rather than prophylactic application of fungicides was tested in the greenhouse and in four field experiments. Activity of the systemic fungicide tebuconazole was detected when the fungicide was applied up to 3 days postinfection, and application of tebuconazole or difenoconazole in the field as a postinfection treatment (i.e., after rain or overhead irrigation) suppressed the disease as effectively as preventive applications and required fewer sprays. In two experiments, the interaction between genotype resistance and chemical control at various amounts of irrigation applied via overhead sprinklers (as a simulation of rain) was tested. The results show that both the level of genotype resistance and the quantity of water should be taken into account in deciding whether to apply a postinfection spray.     

Genetic correlations in resistance to morpholine and piperidine fungicides inPyrenophora teres populations

Highly significant genetic variation (P<0.001) in resistance to the morpholine fungicides fenpropimorph, tridemorph and dodemorph and the piperidine fungicide, fenpropidin was found in different populations ofPyrenophore teres in North America and Europe which had not been previously exposed to these fungicides. Resistance phenotypes were continuously distributed for each fungicide in each population. Cross resistance relationships were determined by estimating genetic correlation coefficients in resistance to all pairwise combinations of fungicides. The majority of the correlation coefficients were highly positive for all fungicide combinations in all populations; eight of 36 (22%) coefficients were not significantly different from 1 (P>0.05). This result is consistent with the hypothesis that many of the same genes, or genes in gametic disequilibrium, control resistance to more than one fungicide in most populations ofP. teres and that these fungicides comprise a single cross resistance group. Three of 36 (8%) correlation coefficients were not significantly different from 0 (P>0.05) indicating that, in these populations, independent genes controlled resistance to these fungicides. The results of this study indicate that although most of the same genes control resistance to morpholine and piperidine fungicides inP. teres, differences in frequencies of these genes among populations can result in different cross resistance relationships from one population to another.     

Combinations of Fungicides with Phylloplane Yeasts for Improved Control of Botrytis cinerea on Geranium Seedlings

ABSTRACT Control of Botrytis cinerea on geranium seedlings was evaluated in treatments with phylloplane yeasts in combination with 10 fungicides used to manage Botrytis blight of ornamental plants. Rhodotorula glutinis PM4 significantly reduced the development of lesions caused by B. cinerea on geranium cotyledons; however, yeast biocontrol efficacy was highly variable between trials. Treatment with the yeast in combination with azoxystrobin or trifloxystrobin at one tenth the labeled rate (7.5 mug a.i. ml(-1)) or the full labeled rate (7.5 mug a.i. ml(-1)) reduced lesion development, compared to treatment with the yeast or the fungicide alone. Vinclozolin at half the labeled rate or the full labeled rate (250 or 500 mug a.i. ml(-1)), in combination with R. glutinis PM4, significantly reduced the development of lesions caused by an isolate of B. cinerea resistant to vinclozolin. Copper hydroxide and iprodione at one-tenth the labeled rates, with or without yeast, were highly effective in limiting lesion development. Mancozeb did not increase the biocontrol efficacy of the yeast, and thiophanate-methyl negatively affected the yeast efficacy. Improved disease control was observed in treatments with vinclozolin at the labeled rate and R. glutinis PM4 at cell densities of 5 x 10(5) and 1 x 10(6) cells ml(-1), but not 1 x 10(5) cells ml(-1), on seedlings co-inoculated with B. cinerea in a suspension containing 1 x 10(5) conidia ml(-1). Disease control improved in treatments with combinations of vinclozolin and eight other isolates of R. glutinis, two isolates of R. graminis, and two isolates of R. mucilaginosa. Biocontrol was not observed in treatments with two isolates of R. minuta. The combination of yeast and vinclozolin significantly reduced the germination of conidia of B. cinerea and the growth of R. glutinis PM4 in vitro. All combinations of R. glutinis PM4 with azoxystrobin, trifloxystrobin, or vinclozolin provided highly effective and consistent disease control not observed in treatments with the fungicides alone or the yeast alone.     

The benefits of combining elemental sulfur with a DMI fungicide to control Monilinia fructicola isolates resistant to propiconazole

BACKGROUND: Management of demethylation inhibitor (DMI) fungicide resistance in Monilinia fructicola (G. Winter) Honey is a priority in peach orchards of the southeastern United States, but DMI fungicides are still an important component of antiresistance strategies in view of the few effective alternatives. The goal of this study was to investigate potential benefits of a sulfur/propiconazole mixture for the control of propiconazole-resistant isolates.RESULTS: The mixture provided the best control for propiconazole-resistant isolates, regardless of protective or curative application timings, or the presence or absence of fruit injury. Propiconazole-resistant isolates developed disease on detached fruit after protective or curative applications of propiconazole or its mixture with sulfur, but protective applications of the mixture significantly reduced (P = 0.05) disease symptoms compared with the individual compounds. Additive to slightly synergistic effects were observed for the mixture in protective treatments of peaches inoculated with propiconazole-resistant isolates.CONCLUSION: The results suggest that the addition of elemental sulfur to a DMI fungicide is likely to be a relatively inexpensive means to improve brown rot control in peach production areas where reduced sensitivity to DMI fungicides is suspected but has not led to noticeable control failure.     

Bioassays using detached tobacco leaves to determine the sensitivity of Peronospora tabacina to fungicides

Two bioassay methods are described which use detached tobacco leaves to measure the sensitivity of Peronospora tabacina to systemic fungicides. Tobacco leaves (13–15 cm²), treated with fungicides before or after detachment from the plant, were inoculated with sporangia in water drops and, after incubation in beakers and Petri plates, the disease severity and/or production of sporangia was determined 4–7 days after treatment with the fungicides. Of 15 systemic fungicides applied to detached leaves, eight N-phenylamides at 0.066?1.0 μg ml^?1 controlled blue mould; metalaxyl was the most effective fungicide. Isolates of P. tabacina, collected in the field from tobacco plants grown in soil treated with metalaxyl, were not resistant to the fungicide applied to detached leaves prior to inoculation. The fungicide, applied to leaves before detachment, was used to measure the efficacy of five systemic N-phenylamide fungicides sprayed on the basal and unsprayed distal portions of the leaves. Blue mould was controlled on the basal portion of the leaf by all the fungicides at 0.66?1.0 μg ml^?1, but it required the application of 3–30 times more chemical on the basal portion to achieve comparable blue mould control on the distal part of the leaf.     

Resistance to acylalanines in Phytophthora infestans in The Netherlands1

In The Netherlands in 1980 a severe late-blight epidemic involving metalaxyl-resistant strains of Phytophthora infestans did considerable damage to the potato crop. As a consequence metalaxyl or metalaxyl-containing products were withdrawn from the Dutch fungicide market for the control of potato late blight. In 1981 the majority of the P. infestans isolates obtained from various parts of the country were sensitive to metalaxyl. In three areas where metalaxyl mixtures were used on a relatively large scale metalaxyl-resistant strains dominated the population. Incidental use of metalaxyl mixtures in 1982 and 1983 showed adequate late-blight control and, when in 1984 an early and in some areas severe epidemic developed, a metalaxyl/mancozeb mixture was reintroduced for curative application in combination with conventional fungicides. Although disease control was adequate, resistant strains were present in a small number of fields. Whether resistant strains will increase in frequency and threaten the usefulness of mixtures of acylalanines will heavily depend on how well potato farmers adopt strategies involving a limited use of mixtures of acylalanines in a spray schedule with conventional late-blight fungicides.     

Fenpropimorph: a promising fungicide for postharvest diseases in citrus fruits

Sour rot, green mold and blue mold are postharvest diseases of citrus fruit. Benzimidazole and imidazole fungicides control molds, and guazatine controls sour rot, but strains ofPenicillium spp. resistant to these chemicals have been reported. Aqueous formulations of fenpropimorph, a morpholine fungicide, are very active in controlling fungi attacking postharvest citrus fruits. The fungicidal effect of the chemical in the coating wax was investigated in combined treatments with guazatine in dip or spray applications on various citrus fruit varieties. Fenpropimorph alone was as good as or a better curative and protective treatment than the current commercial treatments applied in packinghouses in Israel for decay control.     

小麦白粉病菌对喹氧灵和苯菌酮的敏感基线及药剂的生物活性

采用离体叶段法,分别测定了从河北、河南、湖北、陕西和四川5省分离的53个小麦白粉病菌单孢菌株对苯菌酮和喹氧灵的敏感性,并分析了白粉病菌对三唑酮和苯菌酮以及喹氧灵之间的 交互抗性。结果表明:小麦白粉病菌群体对苯菌酮和喹氧灵的平均EC50值分别为(0.001 9±0.000 6) 和(0.013 1±0.002 0) mg/L,苯菌酮比喹氧灵具有更高的抑菌活性;小麦白粉病菌对三唑酮和苯菌酮与喹氧灵之间均不存在交互抗性(R2值分别为0.102 6和0.491 9);室内盆栽试验结果显示:接种前1 d和接种后1d施药,苯菌酮和喹氧灵对小麦白粉病的保护与治疗作用防效分别为92.21%、84.25%和82.43%、70.25%,表明这2种药剂不仅具有优异的保护作用,同时还具有较好的治疗作用。     

New Trends in the Chemical Control of Wheat Diseases1

Following a list of the economically most important fungal wheat diseases, recent trends in chemical seed treatment are discussed. Different fungicide mixtures are now available for the replacement of mercurial dressings, but are generally more expensive. The control of fungal diseases by spraying has become more and more common over the past ten years in certain countries. Advantage has been taken of the curative action of the modern systemic chemicals. The major diseases are powdery mildew, rusts, eyespot, glume-and leaf-blotch. The general application of a fungicide programme is restricted by regional wheat prices, and should also be limited to reduce environmental contamination. Knowledge about economic thresholds and correct timing of control are indispensable, and in special cases the development of warning systems is advisable. The role of Cycocel (chlormequat) is also discussed. A danger of fungicide resistance in populations of plant pathogenic fungi has arisen with the introduction of the systemic fungicides (one-site-inhibitors). As yet, however, no economically important case of fungicide resistance within cereal pathogens is known. Factors favouring the stepwise selection of resistant strains under field conditions are discussed in detail, and experimental data are presented on this subject. Other positive or negative side-effects of the modern fungicides are described.     

Integrated control of potato late blight: predicting the combined efficacy of host resistance and fungicides

Integrating cultivars that are partially resistant with reduced fungicide doses offers growers an opportunity to decrease fungicide input but still maintain disease control. To use integrated control strategies in practice requires a method to determine the combined effectiveness of particular cultivar and fungicide dose combinations. Simple models, such as additive dose models (ADM) and multiplicative survival models (MSM), have been used previously to determine the joint action of two or more pesticides. This study tests whether a model based on multiplicative survival principles can predict the joint action of fungicide doses combined with cultivars of differing partial host resistance. Data from eight field experiments on potato late blight (Phytophthora infestans) were used to test the model; the severity of foliar blight was assessed and scores used to calculate the area under the disease progress curve (AUDPC). A subset of data, derived from the most susceptible cultivar, King Edward, was used to produce dose–response curves from which parameter values were estimated, quantifying fungicide efficacy. These values, along with the untreated values for the more resistant cultivars, Cara and Sarpo Mira, were used to predict the combined efficacy of the remaining cultivar by fungicide dose combinations. Predicted efficacy was compared against observations from an independent subset of treatments from the field experiments. The analysis demonstrated that multiplicative survival principles can be applied to describe the joint efficacy of host resistance and fungicide dose combinations.     

Microscopy reveals disease control through novel effects on fungal development: a case study with an early-generation benzophenone fungicide

The benzophenones are a new class of agricultural fungicides that demonstrate protectant, curative and eradicative/antisporulant activity against powdery mildews. The chemistry is represented in the marketplace by the fungicide metrafenone, recently introduced by BASF and discussed in the following paper. The benzophenones show no evidence of acting by previously identified biochemical mechanisms, nor do they show cross-resistance with existing fungicides. The value of microscopy in elucidating fungicide mode of action is demonstrated through identification of the effects of an early benzophenone, eBZO, on mildew development. eBZO caused profound alterations in the morphology of powdery mildews of both monocotyledons and dicotyledons, affecting multiple stages of fungal development, including spore germination, appressorial formation, penetration, surface hyphal morphology and sporogenesis. Identification of analogous effects of eBZO on sporulation in the model organism Aspergillus nidulans (Eidam) Winter provides a unique opportunity to elucidate important morphogenetic regulatory sites in the economically important obligate pathogens, the powdery mildews. Benzophenones provide a further example of the benefits of whole-organism testing in the search for novel fungicide modes of action.