Seed treatment for the control of Sphaerotheca fuliginea in muskmelon seedlings

The effects of powdery mildew (caused by Sphaerotheca fuliginea )on muskmelon seedlings and the efficacy of seed treatment with systemic fungicides were examined under controlled environmental conditions. The fresh weight of seedlings infected with powdery mildew was substantially less than that of uninoculated seedlings 5 weeks after inoculation, and the inoculated seedlings shrivelled 1 week later. The fungicides fenarimol and triadimenol applied to the seeds did not affect germination and suppressed powdery mildew effectively when applied at a rate equivalent to 8 g fungicide product per kg seed. Under conditions moderately conducive to the pathogen, fenarimol markedly reduced disease severity and its effect when applied as a seed treatment was as effective as foliar treatment. When conditions were highly conducive to the pathogen, seed treatment with fenarimol was not effective. Development of powdery mildew and efficacy of the seed treatments were related to soil type: disease developed earlier and more intensely on seedlings grown in sandy soil than those in organic medium, and seed treatment had a more pronounced effect on seedlings grown in sandy soil. The results indicate that fungicidal treatment of muskmelon seeds may offer an adequate means of reducing powdery mildew infections on seedlings.     

Evaluation of the systemic activity of simeconazole in comparison with that of other DMI fungicides

The systemic activity of simeconazole (RS-2-(4-fluorophenyl)-1-(1H-1,2,4-triazol-1-yl)-3-trimethylsilylpropan-2-ol) in plants was compared with those of eight other sterol demethylation inhibitor (DMI) fungicides. Simeconazole prevented the infection of Blumeria graminis (DC) Speer f sp hordei Marchal on barley leaves within a radius of several centimeters from the edge of local treatment on the leaves when the compound was separated from the leaves by glass coverslips. This reveals that simeconazole has prominent vapour-phase activity. Simeconazole showed excellent curative activity against barley powdery mildew when treated 1-3 days after inoculation. Furthermore, this indicates that simeconazole has notable translaminar activity because, when the compound was applied onto either the adaxial or abaxial leaf surface, it showed excellent efficacy against powdery mildew on the opposite side of the leaf surface of barley and cucumber. Simeconazole also showed excellent efficacy against barley powdery mildew by soil drench 24h after inoculation. This suggests that simeconazole was absorbed very quickly into the barley plant after treatment. The permeability of the compound through cuticular membranes prepared from tomato fruits was about 20% at 22 h after the treatment and was much superior to that of the other DMI fungicides tested.     

Crop damage caused by powdery mildew on hop and its relationship to late season management

Powdery mildew of hop (Podosphaera macularis) may cause economic loss due to reductions in cone yield and quality. Quantitative estimates of crop damage from powdery mildew remain poorly characterized, especially the effect of late season disease management on crop yield and quality. Field studies in Washington State evaluated cone yield, bittering acid content and quality factors when fungicide applications were ceased at different stages of cone development. The incidence of cones with powdery mildew was linearly correlated with yield of cones, bittering acids and accelerated cone maturation. In cultivar Galena, the cumulative effect of every 1% increase in cones powdery mildew incidence was to reduce alpha‐acid yield by 0·33%, which was due to direct effects on cone yield but also indirect effects mediated by dry matter. In the more susceptible cultivar Zeus, alpha‐acid yield was increased 20% by controlling powdery mildew through the transition of bloom to early cone development compared to ceasing fungicide applications at bloom: additional applications provided only modest improvements in alpha‐acid yield. In both cultivars, the impact of powdery mildew on aroma characteristics and bittering acid content were less substantial than cone yield. The damage caused by powdery mildew to cone colour and alpha‐acid yield, as well as the effectiveness of fungicide applications made to manage the disease, appears inseparably linked to dry matter content of cones at harvest. Realising achievable yield potential in these cultivars requires control of the disease through early stages of cone development and harvest before maturity exceeds c. 25% dry matter.     

Defining the resistance risk of the new powdery mildew fungicide quinoxyfen

The new powdery mildew fungicide quinoxyfen belongs to the novel quinoline class of chemistry. Although its biochemical mode of action is unknown, quinoxyfen does not act in the same way as other cereal fungicides. It is a systemic protectant which inhibits the early stages of mildew infection on a wide range of crops, and provides season-long protection from a single early-season spray applied around GS 31. The base-line sensitivity profile of quinoxyfen was defined for barley powdery mildew (Erysiphe graminis f.sp. hordei) from over 340 field isolates collected from different parts of the UK from 1991 onwards. Sensitivities ranged from <0·0001→0·16 mg litre^-1 with a mean of 0·003 mg litre^-1. Current work is extending the base-line sensitivity studies to wheat powdery mildew (E. graminis f.sp. tritici), and includes isolates from European trials, but so far this new data set has shown no differences from barley powdery mildew. Quinoxyfen-resistant mutants were generated in the laboratory, and some similar resistant strains were obtained from treated field crops. These laboratory and field strains were always defective, in some way, for sporulation and, curiously, all required the presence of quinoxyfen for survival in culture. Attempts to generate resistant mutants that sporulated normally were unsuccessful. These studies suggested that the resistance risk for quinoxyfen is low. The recommended anti-resistance strategy accompanying introduction of quinoxyfen avoids seed treatments and late-season applications. Instead, a single early (GS 31) treatment using either pre-formulated mixtures or alternating with a fungicide with different mode of action is recommended. This strategy will be supported by continued monitoring of wheat and barley powdery mildew. ©1997 SCI     

Sensitivity of Podosphaera aphanis isolates to DMI fungicides: distribution and reduced cross‐sensitivity

BACKGROUND: Management of strawberry powdery mildew, Podopshaera aphanis (Wallr.), requires numerous fungicide treatments. Limiting epidemics is heavily dependent on sterol demethylation inhibitors (DMIs) such as myclobutanil or penconazole. Recently, a noticeable reduction in the efficacy of these triazole fungicides was reported by strawberry growers in France. The goal of this study was to investigate the state of DMI sensitivity of French P. aphanis and provide tools for improved pest management. RESULTS: Using leaf disc sporulation assays, sensitivity to myclobutanil and penconazole of 23 isolates of P. aphanis was monitored. Myclobutanil EC₅₀ ranged from less than 0.1 to 14.67 mg L^?1 and for penconazole from 0.04 to 4.2 mg L^?1. A cross‐analysis and a Venn diagram showed that there was reduced sensitivity and a positive correlation between the less sensitive myclobutanil and penconazole isolates; 73.9% of isolates were less sensitive to a DMI and 47.8% exhibited less sensitivity to both fungicides. CONCLUSION: The results show that sensitivity to myclobutanil and, to a lesser extent, penconazole has become less efficient in strawberry powdery mildew in France. Therefore, urgent action is required in order to document its appearance and optimise methods of control. Copyright © 2009 Society of Chemical Industry     

Comparison of three biological control agents against cucumber powdery mildew (Sphaerotheca fuliginea) in semi-commercial-scale glasshouse trials

The effect of three reported biological control agents, Ampelomyces quisqualis, Verticillium lecanii and Sporothrix flocculosa, was tested against cucumber powdery mildew (Sphaerotheca fuliginea). Two glasshouse experiments, one in the summer and one in winter/spring were conducted on a semi-commercial scale. In both experiments, a susceptible and a partially resistant cultivar were used. In the second experiment, the additional effect of integration of biological control and silicon amendments to the nutrient solution was also assessed. In both experiments, A. quisqualis did not control the disease. V. lecanii had a small effect on powdery mildew in the first experiment but not in the second. S. flocculosa gave the best control of powdery mildew in both experiments. In the first experiment, weekly application of S. flocculosa reduced disease in the partially resistant cultivar to the same level as a treatment in which the fungicides bupirimate and imazalil were each applied once. Addition of silicon in the nutrient solution in a concentration of 0.75 mM reduced disease by 10–16%, averaged over all treatments. There was no interaction between silicon and the biocontrol agents. Yield was recorded in the second experiment and was significantly increased by the fungicide treatment compared to the control in the partially resistant cultivar. Yield in the treatment with S. flocculosa was not significantly different from the fungicide treatment in this cultivar. Silicon had no effect on yield in either cultivar.     

Comparative efficacy of strobilurin fungicides against downy mildew disease of pearl millet

Three commercial formulations of strobilurins, viz., azoxystrobin, kresoxim-methyl, and trifloxystrobin were evaluated for their efficacy against pearl millet downy mildew disease caused by Sclerospora graminicola. In vitro studies revealed inhibition of S. graminicola sporulation, zoospore release, and zoospore motility at 0.1-2 μg ml⁻¹ of all the three fungicides. The fungicides were evaluated for phytotoxic effects on seed quality parameters and for their effectiveness against downy mildew disease by treating pearl millet by: (1) seed dressing, (2) seed dressing followed by foliar spray, and (3) also by foliar spray alone. The highest non-phytotoxic concentrations of 5, 10, and 10 μg ml⁻¹ for azoxystrobin, trifloxystrobin, and kresoxim-methyl, respectively, were selected for further studies. Under greenhouse conditions, these fungicides showed varying degrees of protection against downy mildew disease. Among the three fungicides, azoxystrobin proved to be the best by offering disease protection of 66%. Further, seed treatment along with foliar application of these fungicides to diseased plants showed enhanced protection against the disease to 93, 82, and 62% in treatments of azoxystrobin, kresoxim-methyl and trifloxystrobin respectively. Foliar spray alone provided significant increase in disease protection levels of 91, 79, and 59% in treatments of azoxystrobin, kresoxim-methyl, and trifloxystrobin, respectively. Disease curative activity of azoxystrobin was higher compared to trifloxystrobin and kresoxim-methyl. Tested fungicides showed weaker translaminar activity, as the disease inhibition was marginal when applied on adaxial leaf surface. Partial systemic activity of azoxystrobin was evident by root uptake, while trifloxystrobin and kresoxim-methyl showed lack of systemic action in pearl millet. A trend in protection against downy mildew disease similar to greenhouse results was evident in the field trials. Grain yield was significantly increased in all strobilurin fungicide treatments over control and maximum increase in yield of 1673 kg ha⁻¹ was observed in combination treatments of seed treatment and foliar spray with azoxystrobin.     

防治葡萄白粉病新型杀菌剂的筛选及增效剂的增效作用

为了筛选防治葡萄白粉病的绿色高效新型药剂和适宜的增效剂,以达到减量增效防病的目的,本研究选用10种杀菌剂对葡萄白粉病进行田间药效试验,同时评价5种增效剂对杀菌剂的减量增效作用。结果表明,20%氟唑菌酰羟胺·苯醚甲环唑悬浮剂和29%吡萘·嘧菌酯悬浮剂效果最好,对葡萄白粉病的防效分别为75.75%、63. 80%。在推荐剂量下Silwet 636、Silwet 806、Y-20079、杰效利等4种增效剂对29%吡萘·嘧菌酯悬浮剂具有明显的增效作用,当减少30%药剂使用量或减少30%药液量时添加这4种增效剂的处理防效均优于单一药剂处理,其中Silwet 636表现最佳。推荐施用20%氟唑菌酰羟胺·苯醚甲环唑悬浮剂1 500倍液和29%吡萘·嘧菌酯悬浮剂2 000倍液田间防治葡萄白粉病。在减30%药剂量或药液量条件下,在29%吡萘·嘧菌酯悬浮剂中添加Silwet 636、Silwet 806、Y-20079、杰效利等增效剂也可达到同等或更优防效。     

生物源杀菌剂与化学杀菌剂协调防控黄瓜病害

本文研究枯草芽孢杆菌Bacillus subtilis BAB-1水剂、解淀粉芽孢杆菌B.amylololiquefaciens SAB-1水剂、大花旋覆花内酯乳油与化学杀菌剂交替或混合使用对温室黄瓜病害发展的影响.寿光试验包括以下处理:交替或混合喷施50%啶酰菌胺WG、68.75%氟吡菌胺·霜霉威SC的桶混液、60%唑醚·代森联WG、40%嘧霉胺SC、50%烯酰吗啉WP、10%苯醚甲环唑WG、69%烯酰·锰锌WP、68.75%噁唑·锰锌WG、52.5%噁唑·霜脲氰WG等不同作用机理和防治谱的化学杀菌剂;混施生防菌剂BAB-1水剂、SAB-1水剂及68.75%氟吡菌胺·霜霉威SC、50%烯酰吗啉WP、25%双炔酰菌胺SC、25%吡唑醚菌酯EC等对霜霉病特效化学杀菌剂;将不同化学杀菌剂桶混液与BAB-1水剂、SAB-1水剂和化学杀菌剂桶混液交替喷施.其对黄瓜霜霉病的防效分别为94.5%、92.3%和93.6%,对黄瓜白粉病分别为90.7%、89.9%和90.4%,对灰霉病的防效分别为69.3%、85.6%和85.7%,每种病害的病害发展曲线下面积(AUDPC)相当.在定州试验中,化学杀菌剂与SAB-1混施对白粉病的防效(84%)明显高于其与BAB-1混施的防效(72.8%),对灰霉病的防效(61.3%)明显低于后者的防效(95.1%),与SAB-1、BAB-1混施后对白粉病、灰霉病及霜霉病防效分别为90.2%、89.3%和92.6%.在保定郊区试验中,将大花旋覆花内酯乳油与化学杀菌剂及BAB-1水剂、SAB-1水剂交替喷施显著降低霜霉病、白粉病及灰霉病的严重度及AUDPC,对其防效分别为83.5%、87.4%和88.5%,AUDPC分别为219、352和249,延缓了3种黄瓜病害的发展.     

Variation in the response of cashew genotypes to the targeted application of fungicide to flower panicles for control of powdery mildew disease

Application of the fungicide triadimenol (Bayfidan) directly to inflorescences of cashew was investigated as a means of controlling powdery mildew disease caused by Oidium anacardii. Disease development and nut production were studied in 12 cashew genotypes that differed in their susceptibility to mildew. Panicle colonization by O. anacardii reached 100% coverage in all genotypes without fungicide treatment, but rates of infection differed significantly. Triadimenol sprays reduced mildew to less than 9%, even in panicles of highly susceptible genotypes. In the absence of disease, particularly good yield responses with more than nine times more nuts set than untreated controls were achieved by AM6 and AC1, which were categorized as highly susceptible and intermediate, respectively, in reaction to powdery mildew. By contrast, the partially resistant genotypes AZA2 and AC6 both produced yield response ratios of less than 3·0. The targeted treatment of flower panicles to control mildew is recommended, rather than the current practice of wastefully treating whole trees on which all mature leaves are naturally immune to infection.     

Suppression of cucumber powdery mildew (Sphaerotheca fuliginea) by foliar sprays of pbospbate and potassium salts

Powdery mildew, caused by Sphaerotheca fuliginea , was significantly controlled by a single spray of aqueous solutions (25 mm) containing various phosphates and potassium salts. Phosphates were suppressive when applied alone; however, treatments in combination with Tween-20 were more effective in causing the disappearance of powdery mildew pustules from diseased foliage. Efficiency of control, as expressed by the disappearance of 99% of pustules, was recorded 1 or 2 days after application of single sprays of phosphate and potassium salt solutions. Treatment was effective for up to 12 or 15 days, respectively, following application to small or large greenhouse-grown plants with established mildew infection. Treatments also markedly reduced (> 99%) the production of eonidia from colonies. A further application of these salts to the same plants resulted in the elimination of about 50% of mildew colonies present prior to the application. Further spray application inhibited disease development compared with water-sprayed plants, but did not reduce the number of existing lesions. Phosphate was more effective than the systemic fungicide pyrifenox and reduced established powdery mildew infection up to 11 days after application, but the converse was true when assessments were made after 15 days. These properties of phosphates and potassium salts make them appropriate for use as foliar fertilizers with a potential beneficial influence on disease control.     

The effect of fungicide dose on the composition of laboratory populations of barley powdery mildew

The effect of the use of different doses of the fungicide fenpropimorph on populations of barley powdery mildew Blumeria ( Erysiphe ) graminis f. sp. hordei was investigated in a laboratory selection experiment. A sample from the Danish aerial population of powdery mildew was split into populations, and these were kept separately for 31 generations on susceptible barley seedlings treated with fungicide at two concentrations, as well as on a control. Samples from these populations were tested for their resistance to fenpropimorph and their virulence spectra. There was a large amount of environmental variation in the ED₅₀ values used to measure fungicide resistance. In both treated populations, the average level of fungicide resistance increased, this increase being faster and greater in the population treated with the high dose. The diversity of pathotypes of the treated populations decreased, with the decline being more rapid in the population treated with the high dose, where one pathotype dominated the population after 31 generations. This pathotype was apparently not the fittest in the population treated with the low dose. This implies that knowledge of ED₅₀ is not sufficient to predict pathotype evolution under different fungicide treatments. The dominant pathotype in the high-dose treatment may not have been clonal, as there was evidence of two levels of fungicide resistance. The large environmental variation observed in estimated ED₅₀ values for resistance towards fenpropimorph may help to explain why this resistance has evolved at a slower rate than resistance towards other fungicides.     

Biological evaluation of neopeptins isolated from a Streptomyces strain

BACKGROUND: Microbial secondary metabolites are a rich source of antifungal agents and have merit as alternatives to synthetic fungicides. To develop disease control agents against powdery mildew, the lipopeptide antibiotic neopeptins were identified from the culture broth of a Streptomyces sp., and in vivo control efficacy of the compounds was evaluated on cucumber plants under glasshouse conditions. RESULTS: The Streptomyces sp. KNF2047 antagonistic against powdery mildew development in cucumber plants was isolated from a soil sample. Antifungal compounds were purified from the culture broth and identified as neopeptin A and B. In vitro microtitre assays revealed the inhibitory activities of the compounds in the range 128-512 microg mL(-1) against the mycelial growth of Alternaria mali, Botrytis cinerea, Cladosporium cucumerinum, Colletotrichum lagenarium, Didimella bryoniae and Magnaporthe grisea. Although neither compound showed remarkable in vitro antifungal activity against other plant pathogenic fungi, a mixture of neopeptins (484 mg of neopeptin A and 290 mg of neopeptin B per gram of partially purified powder) showed potent protective and curative activity against cucumber powdery mildew in vivo. The disease control activity of the neopeptins at a concentration of 2.4 mg L(-1) was 92.1%, which was similar to that of the commercial fungicide fenarimol (89.3% at 63 mg L(-1)) and that of the commercial biocontrol agent Actinovate (67.4% at 2 x 10(7) cfu L(-1)). CONCLUSION: Neopeptin mixtures isolated from Streptomyces sp. KNF2047 showed potent disease control activity against powdery mildew development on cucumber plants. .     

Cytological studies on the mode of action of systemic fungicides on the host pathogen complex barley-powdery mildew (Erysiphe graminis f. sp. hordei marchal)

The effects of systemic fungicides on the host-pathogen interface between barley and powdery mildew were studied using cytological methods and specific staining procedures. Propiconazole, etaconazole, bitertanol, triforine, imazalil, nuarimol, tridemorph and fenpropimorph, which are all inhibitors of sterol biosynthesis, stopped growth of the fungus 2 days after application and led to deposits of plant origin around haustoria; these contained polysaccharides, especially callose. This encapsulation resembled the reaction often observed in resistant plants. In contrast, pyrazophos and ethirimol, applied at reduced concentrations, inhibited the fungus at the haustorial stage but did not induce encapsulation. These results suggest that encapsulation is not simply a reaction to the previously damaged fungus, but may be an indirect effect of sterol biosynthesis-inhibiting fungicides on the host metabolism which is elicited by the fungus. The results are discussed in the context of previous observations on the modes of action of these fungicides.     

不同机制杀菌剂对小麦白粉病的敏感性及与三唑酮的交互抗性

为明确三唑酮和氟环唑、吡唑醚菌酯、啶酰菌胺、嘧菌环胺、乙嘧酚5种不同作用机制的杀菌剂对小麦白粉病的敏感性及交互抗性,采用田间小区试验和室内喷雾离体叶段法测定了不同杀菌剂对小麦白粉病的防治效果。结果表明,5种不同作用机制杀菌剂对小麦白粉病的防治效果可达90%以上,而三唑酮最高的防治效果仅为72.17%;小麦白粉病菌群体对氟环唑、吡唑醚菌酯、啶酰菌胺、嘧菌环胺、乙嘧酚的敏感性EC50分别在0.087~1.901、0.058~1.402、0.186~3.014、0.222~6.005、0.006~1.742μg/mL之间,5种不同作用机制杀菌剂的敏感性均呈连续单峰曲线,可作为小麦白粉病菌对5种不同作用机制杀菌剂的敏感基线。研究表明,三唑酮与氟环唑、吡唑醚菌酯、啶酰菌胺、嘧菌环胺、乙嘧酚之间不存在交互抗性。     

Distributions of Sensitivities to Three Sterol Demethylation Inhibitor Fungicides Among Populations of Uncinula necator Sensitive and Resistant to Triadimefon

ABSTRACT Single-conidial isolates of Uncinula necator from (i) a population representing two vineyards with no previous exposure to sterol demethylation inhibitor (DMI) fungicides ("unexposed," n = 77) and (ii) a population representing two vineyards in which powdery mildew was poorly controlled by triadimefon after prolonged DMI use ("selected," n = 82) were assayed to determine distributions of sensitivities to the DMI fungicides triadimenol (the active form of triadimefon), myclobutanil, and fenarimol. Median 50% effective dose (ED(50)) values (micrograms per milliliter) in the selected versus unexposed populations were 0.06 versus 1.9 for triadimenol, 0.03 versus 0.23 for myclobutanil, and 0.03 versus 0.07 for fenarimol, respectively. Isolates were grouped into sensitivity classes according to their ED(50) values, and those from the selected population were categorized as resistant if the frequency of their sensitivity class had increased significantly relative to levels found in the unexposed population (ED(50) values exceeding 0.56, 0.18, and 0.18 mug/ml for triadimenol, myclobutanil, and fenarimol, respectively). Of the 76 isolates defined as resistant to triadimenol, 64% were classified as cross-resistant to myclobutanil, 18% were classified as cross-resistant to fenarimol, and 17% were classified as resistant to all three fungicides; 25% of the isolates classified as resistant to myclobutanil also were classified as resistant to fenarimol. Similar cross-resistance relationships were revealed when all isolates were examined by regressing log ED(50) values for each fungicide against those for the remaining two fungicides to determine the correlation coefficients (e.g., r = 0.85 for triadimenol versus myclobutanil and 0.56 for triadimenol versus fenarimol). The restricted levels of cross-resistance indicated by these data, particularly between fenarimol and the other two fungicides, is in sharp contrast to the high levels of cross-resistance among DMIs reported for some other pathogens and has significant implications with respect to programs for managing grapevine powdery mildew and DMI resistance.     

Assessment of fungicide resistance and pathogen diversity in Erysiphe necator using quantitative real-time PCR assays

BACKGROUND: Management of grapevine powdery mildew Erysiphe necator Schw. requires fungicide treatments such as sterol demethylation inhibitors (DMIs) or mitochondrial inhibitors (QoIs). Recently, reduction in the efficacy of DMIs or QoIs was reported in Europe and the United States. The aim of the present study was to develop real‐time qPCR tools to detect and quantify several CYP51 gene variants of E. necator: (i) A versus B groups (G37A) and (ii) sensitive versus resistant to sterol demethylase inhibitor fungicides (Y136F). RESULTS: The efficacy of the qPCR tools developed was better than the CAPS method, with a limit of 2 pg for E necator DNA, 0.06 ng for genetic group A and 1.4 ng for the DMI‐resistant allele. The detection limits of qPCR protocols (LOD) ranged from 0.72 to 0.85%, and the quantification limits (LOQ) ranged from 2.4 to 2.85% for the two alleles G47A and Y136F respectively. The application of qPCR to field isolates from French vineyards showed the presence of DMI‐resistant and/or QoI‐resistant alleles in French pathogen populations, linked to genetic group B. CONCLUSION: The real‐time PCR assay developed in this study provides a potentially useful tool for efficient quantification of different alleles of interest for fungicide monitoring and for population structure of E. necator. Copyright © 2010 Society of Chemical Industry     

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.     

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.     

Development of a grower‐conducted inoculum detection assay for management of grape powdery mildew

Management of grape powdery mildew (Erysiphe necator) and other polycyclic diseases often relies on calendar‐based pesticide application schedules that assume the presence of inoculum. An inexpensive, loop‐mediated isothermal amplification (LAMP) assay was designed to quickly detect airborne inoculum of E. necator to determine when to initiate a fungicide application programme. Field efficacy was tested in 2010 and 2011 in several commercial and research vineyards in the Willamette Valley of Oregon from pre‐bud break to véraison. In each vineyard, three impaction spore traps were placed adjacent to the trunk. One trap was maintained and used by the grower to conduct the LAMP assay (G‐LAMP) on‐site and the other two traps were used for laboratory‐conducted LAMP (L‐LAMP) and quantitative PCR assay (qPCR). Using the qPCR as a gold standard, L‐LAMP was comparable with qPCR in both years, and G‐LAMP was comparable to qPCR in 2011. Latent class analysis indicated that qPCR had a true positive proportion of 98% in 2010 and 89% in 2011 and true negative proportion of 96% in 2010 and 64% in 2011. An average of 3·3 fewer fungicide applications were used when they were initiated based on spore detection relative to the grower standard practice. There were no significant differences in berry or leaf incidence between plots with fungicides initiated at detection or grower standard practice plots, suggesting that growers using LAMP to initiate fungicide applications can use fewer fungicide applications to manage powdery mildew compared to standard practices.