Antifungal activity of metalaxyl and furalaxyl

The systemic acylalanines metalaxyl and furalaxyl proved in vitro highly selective to fungi of the order of the Peronosporales, the former being somewhat more active than the latter. Various other fungal, and bacterial, species did not show sensitivity to the toxicants. Metalaxyl was strikingly more active on Pythium splendens and Phytophthora cinnamomi at low than at high temperature. With Phytophthora species metalaxyl displayed improved activity in combination with sodium dodecylsulphate and Triton X-100. Neither the composition of the medium nor its pH influenced activity. None of many compounds tested could antagonize their effect. The fungitoxicity caused by metalaxyl in the gas phase was strikingly better than that of furalaxyl against P. splendens. The toxicants had little effect on germination of the hyphal swellings of P. splendens, but had significant influence on the subsequent hyphal development. This included reduced growth, abnormal variation in the fungal thickness, and inhibition of the formation of hyphal swellings. Metalaxyl and furalaxyl were fungistatic at minimal inhibitory concentration (MIC) values during the first 24 hr. Thereafter, the toxicants became fungicidal. Metalaxyl and furalaxyl did not inhibit respiration of P. splendens at MIC values or somewhat higher concentrations. Neither did metalaxyl inhibit the [¹⁴C]carbon dioxide evolution from externally supplied radiolabeled glucose.     

Control of crown rot (Phytophthora cactorum) of apple trees with the systemic fungicides metalaxyl and fosetyl-aluminium

Four fungicides were evaluated as combined soil drench and trunk treatments for the control of crown rot, caused by Phytophthora cactorum, in naturally infected apple trees. In a 3-year preliminary study, metalaxyl at 1 and fosetyl-aluminium at 8 g a. i. per tree, applied twice a year, prevented death of infected trees showing only initial, but not more severe, symptoms of crown rot. This indicates that these fungicides have the ability to arrest further symptom development in naturally infected trees if they are treated as soon as symptoms appear. Healthy trees remained free of infection if they were treated with these fungicides, suggesting a preventative action. Repeated bi-annual application of metalaxyl or fosetyl-aluminium should be sufficient to prevent the loss of trees to crown rot.     

After-effects of systemic fungicides in the control of soil-borne pathogens,and the interaction between systemic fungicides and growth regulators

After benomyl treatment of mustard seedlings, grown in Rhizoctonia-infested soil, root remainders left in the soil significantly suppressed Rhizoctonia infection in two successive, later ‘crops’ of mustard seedlings. This effect was even larger with the combination tomato — Verticillium albo-atrum.Antagonistic interactions between growth-regulating substances (chlormequat, dimas; chlorflurenol and ethephon) and benomyl were shown upon treatment of Phialophora cinerescens-infected carnations and of Verticillium albo-atrum-infected snapdragons. Application of growth regulators before fungicide treatment reduced the effect of the fungicide on Phialophora and Verticillium wilt. When applied after fungicide treatment, these growth substances did not interfere with benomyl activity.Also, observations on stem growth pointed to an interaction between growth regulators and benomyl. Growth substances, in themselves slightly inhibitory to growth, diminished the growth-promoting effect of benomyl.     

两种候选甲氧基丙烯酸酯类杀菌剂对黄瓜霜霉病的作用方式

20%唑胺菌酯EC、20%SYP-3998 SC是甲氧基丙烯酸酯类候选杀菌剂,为探索两药剂对黄瓜霜霉病的作用方式,采用盆栽植株喷雾-叶碟法、叶碟喷雾法、盆栽植株喷雾-叶碟法分别测定两药剂对黄瓜霜霉病的保护、治疗及持效期,并采用离体叶片法、叶碟法测定二者对黄瓜霜霉病的铲除作用.结果表明:20%唑胺菌酯EC和20%SYP-3998 SC具有良好的保护、治疗及铲除作用.两药剂的铲除作用表现在能抑制黄瓜霜霉病菌病斑扩展、孢子囊产生及孢子囊再侵染,与孢子囊混合接种能显著降低孢子囊的致病性.此外,20%唑胺茵酯EC和20%SYP-3998 SC具有7～10天的持效期;20%唑胺茵酯EC预防、治疗、铲除效果及持效性均优于20%SYP-3998 SC及对照药剂25%嘧菌酯SC.     

Similarities between the systemic fungicides triforine and triarimol

The fungicides triforine and triarimol, though structurally unrelated have a similar antifungal spectrum. Neither fungicide inhibited germination of conidia of Cladosporium cucumerinum, but both inhibited subsequent mycelial growth. Triforine, like triarimol, proved to be an effective inhibitor of ergosterol biosynthesis. Two mutants of C. cucumerinum selected for resistance to triarimol also exhibited resistance to triforine and to the triarimol analogues ancymidol and bis(4-chlorophenyl)-3-pyrimidinemethanol. Resistance of these mutants, however, did not extend to the sterol inhibitors triparanol and trans-clomiphene or to sodium o-phenylphenate and 2,6-dichloro-4-nitroaniline, two compounds usually tolerated by fungi exhibiting general hydrocarbon resistance. Toxicity of either triforine or triarimol to C. cucumerinum was annuled by β-carotene, vitamin A, progesterone, testosterone and farnesol. The various similarities between triforine and triarimol suggest a common mode of action for the two compounds.     

Bioassay and transcuticular movement of systemic fungicides

A sensitive bioassay method was developed using bidirectional diffusion of fungicides in agar bands instead of diffusion through 360°. This method permitted the measurement of fungicide movement through isolated cuticular disks into agar bands underneath. Oil dispersible formulations of oxycarboxin and pyracarbolid penetrated through cuticles of coffee much more efficiently than wettable powder formulations.     

Mode of action of oxathiin systemic fungicides : III. Effect on mitochondrial activities

Carboxin (5,6-dihydro-2-methyl-1,4-oxathiin-3-carboxanilide) was tested for its effect on the activities of mitochondria from several fungi, pinto beans and rat liver. Succinate oxidation by mitochondria from the sensitive fungus Ustilago maydis was inhibited by low concentrations of carboxin, the K_i being 0.32 μM. The inhibition was of a noncompetitive nature. Succinate oxidation was also inhibited in the mitochondria from other sources but not to the extent as in those from U. maydis. Carboxin had little effect on the oxidation of reduced nicotinamide adenine dinucleotide. The dioxide of carboxin, oxycarboxin, was not as effective in inhibiting succinate oxidation as was carboxin, but was more effective than the monoxide. Carboxin did not appear to uncouple oxidative phosphorylation in the presence of succinate in tightly coupled rat liver mitochondria but did decrease the respiratory control ratio. Carboxin was ineffective in releasing oligomycin inhibition in coupled rat liver mitochondria while dinitrophenol and salicylanilide were effective in this respect. It is believed that carboxin inhibits mitochondrial respiration at or close to the site of succinate oxidation and does not greatly affect the remaining portion of the electron transport system or the coupled phosphorylation reactions.     

Uptake of systemic fungicides by maize roots

The absorption of nine benzimidazole derivatives and four thiophanates by excised maize roots was shown to be due to passive mechanisms because a. the temperature coefficient was low, b. anaerobic conditions or metabolic inhibitors had little or no effect, c. the rate of uptake was a linear function of external concentration, d. compounds of similar structure did not compete for absorption.For benzimidazole derivatives, we observed a very rapid initial uptake which reached a maximum after one or two hours; this saturation did not occur with thiophanates.The effect of pH on the root absorption of benzimidazole derivative indicates that molecular (or unionized) forms of these amphoteric compounds were taken up preferentially; the behaviour of thiophanates was different.As observed with other pesticides, root absorption was greater for lipophilic than for lipophobic substances and in our experiments the rate of uptake of fungicides was well correlated to their partition coefficient in an octanol/ water system at pH 6.5.Generally, the various fungicides were taken up to the same extent all along the length of the roots.     

Detachment of sprayed colloidal copper oxychloride–metalaxyl fungicides by a shallow water flow

BACKGROUND: Flow shear stress induced by rainfall promotes the loss of the pesticides sprayed on crops. Some of the factors influencing the losses of colloidal‐size particulate fungicides are quantified by using a rotating shear system model. With this device it was possible to analyse the flow shear influencing washoff of a commercial fungicide formulation based on a copper oxychloride–metalaxyl mixture that was sprayed on a polypropylene surface. A factor plan with four variables, i.e. water speed and volume (both variables determining flow boundary stress in the shear device), formulation dosage and drying temperature, was set up to monitor colloid detachment. RESULTS: This experimental design, together with sorption experiments of metalaxyl on copper oxychloride, and the study of the dynamics of metalaxyl and copper oxychloride washoff, made it possible to prove that metalaxyl washoff from a polypropylene surface is controlled by transport in solution, whereas that of copper oxychloride occurs by particle detachment and transport of particles. Average losses for metalaxyl and copper oxychloride were, respectively, 29 and 50% of the quantity applied at the usual recommended dosage for crops. CONCLUSION: The key factors affecting losses were flow shear and the applied dosage. Empirical models using these factors provided good estimates of the percentage of fungicide loss. From the factor analysis, the main mechanism for metalaxyl loss induced by a shallow water flow is solubilisation, whereas copper loss is controlled by erosion of copper oxychloride particles. Copyright © 2009 Society of Chemical Industry     

Vapour phase action of some foliar fungicides

Benomyl, maneb, fentin acetate, thiabendazole, a dichloro derivative of thiabendazole, and thiophanate all liberated vapours inhibitory to the germination of Cercospora beticola spores. In tightly closed containesr benomyl and maneb were the most toxic materials. On sprayed leaves the vapour action diminished with time; 11 days after treatment only benomyl still exhibited extreme fungitoxic action.     

Evaluation of systemic fungicides for use in the glasshouse industry

The primary evaluation of ten fungicides for the control of cucumber powdery mildew (Sphaerotheca fuliginea), tomato leaf mould (Cladosporium fulvum) and tomato grey mould (Botrytis cinerea) indicated that nine of them were systemically active against one or more of the pathogens when applied as soil drenches. Benomyl, thiophanate, thiophanate-methyl, thiabendazole and Cela W52A showed activity against all three diseases, but dimethirimol, triarimol and dodemorph were more specific and mainly active against cucumber powdery mildew. An in vitro bioassay generally indicated that fungitoxicity was not translocated from sprayed to unsprayed leaves, and though toxicity to B. cinerea, following soil drenches of benomyl, thiophanate and thiophanate-methyl, was detected by bioassay in leaf sap and calyces it was not detected in fruit. Furthermore, extended evaluation of benomyl for the control of grey mould on cropping tomotoes showed that in the presence of abundant B. cinerea inoculum, benomyl soil drench treatment effectively controlled flower and leaf infection but not fruit ghost-spotting.     

Recent progress in the field of N-acylalanines as systemic fungicides

The influence of structural variations in compounds of the N-acylalanine type, on their fungicidal activity towards Peronosporales, was examined. Within a series of methyl N-(acyl)-N-(2,6-xylyl)alaninates ( I ), a quantitative structure-activity relationship was given for the curative action against Plasmopara viticola, through a Hansch-type equation. A deviation from this equation is discussed with reference to benalaxyl ( I ; acyl=phenylacetyl). Syntheses and qualitative indications of activity are reported for structural changes in the xylyl and in the alanine moieties. Progress in the latter approach is briefly outlined.     

Analytical methods for the detection and determination of residues of systemic fungicides

A review of the analytical methods for the detection and determination of residues of systemic fungicides in foodstuffs is presented.     

Experiments with some of the newer systemic fungicides on apple and marrow

In field trials against apple scab (caused by Venturia inaequalis) and powdery mildew (caused by Podosphaera leucotricha), improved control of one or other disease has been given by the newer systemic fungicides benomyl, triarimol and the thiophanates. However, in tests on apple seedlings in the greenhouse, biological evidence of translocation from individual deposits was generally limited to movement within the treated leaf. In greenhouse tests with cucumbers and marrows, using Oidium sp., there was again little evidence for movement of toxicant from a treated leaf, although effective disease control was readily obtained by root application of several compounds at low dosage. These results suggest that the systemic properties of the compounds evident when used as soil or seed treatments are of little account when they are applied as foliar sprays.     

Comparison of cuprous oxide and metalaxyl with mixtures of these fungicides for thecontrol of Phytophthora pod rot of cocoa

Experiments were conducted using small-scale, detached pod evaluation methods to compare the likely effectiveness in controlling black pod of cuprous oxide-metalaxyl mixtures with these fungicides alone at approximately equivalent cost doses. All fungicide treatments were about equally effective and persistent except when rain fell soon afterspraying. Treatments containing cuprous oxide then gave very poor control of artificialinoculations with Phytophthora palmivora zoospores . Further laboratory' scale tests confirmed that cuprous oxide was readily leached by washing before the deposit completely dried whereas metalaxyl was very rapidly adsorbed on to ihe pods. A black pod control strategy is proposed using metalaxyi during critical wet periods and cuprous oxide for the rest of the year to reduce the possibility of metalaxyl resistance becoming apractical problem.