Tests of fungicides against Alternaria brassicicola and studies on some factors enhancing attack by the fungus

When various fungicides were sprayed on detached cabbage cotyledons in the laboratory and on young plants in the glasshouse, propineb and mancozeb at 0·2 % a.i. consistently gave good protection against subsequent infection by spores of Alternaria brassicicola. Copper oxychloride, zineb, thiram and maneb showed promise in the laboratory, but were less successful in the glasshouse. Two fentin compounds were active at low concentrations against the fungus but were phytotoxic. Increased pathogenicity of A. brassicicola in the presence of cabbage pollen and of downy mildew infection in the laboratory is reported.     

The chemical control of chrysanthemum petal blight caused by Itersonilia perplexans Derx

Laboratory bioassays of fungicides against Itersonilia perplexans showed that disease developed more readily on outer mature chrysanthemum petals than on immature inner florets and that inoculations on floret tips were more successful than on bases. In glasshouse trials, seven of the fungicides tested significantly decreased disease development without inducing phytotoxicity: of these, maneb and mancozeb, but not zineb, left unsightly deposits. Tank-mixed zineb was more fungitoxic, especially in continuing high humidities, but was also more phytotoxic than wettable powder and dust formulations, but this phytotoxicity could be avoided by spraying the crop at the opening bud stage and by increasing the interval between applications from 5 to 7 days.     

Control of Botrytis cinerea on glasshouse tomato by high volume sprays

The new fungicides iprodione, vinclozolin and prochloraz, and also a mixture containing carbendazim and maneb, were compared with the established protectant fungicides dichlofluanid and chlorothalonil for effectiveness against grey mould ( Botrytis cinerea ) in an unheated tomato crop. Iprodione and vinclozolin gave the best control of lesions on leaves and stems but dichlofluanid was the most effective in controlling ghost-spotting of fruit. The carbendazim/maneb mixture was effective against a carbendazim-sensitive isolate but not against an insensitive isolate of B. cinerea . When applied 1 or 2 days after inoculation, all five protectant fungicides controlled the insensitive isolate better than the sensitive isolate.     

Organotin-induced hyperglycemia in the crab, Oziotelphusa senex senex Fabricius

Injection of three different organotin compounds such as tripalmitin, fentin and fenbutatin produced a significant increase in the hemolymph sugar level of intact crabs at Oziotelphusa senex senex apparently by stimulating release of the hyperglycemic hormone (HGH).     

Effect of wax and lanolin emulsions on the efficiency of potato-blight fungicides in laboratory tests

Four potato-blight fungicides (copper oxychloride, tetrachloroisophthalo-nitrile, zineb and fentin acetate) were formulated either by adding emulsions of paraffin wax or lanolin to solid fungicide dispersed in water, or by dissolving the fungicide in wax or lanolin and then emulsifying the solution; all emulsions were non-creaming and extremely stable. These formulations were compared in the laboratory with commercial wettable powders of the same fungicides for their ability to protect detached potato leaflets against infection by Phytophthora infestans (Mont.) de Bary; in these and in other laboratory tests, the quality of rain-fastness, or tenacity, was involved directly or indirectly. Most of the wax or lanolin formulations gave better protection than the wettable powders. It is suggested that the wax and lanolin acted as viscous stickers, suitably increasing the rain-fastness of deposits on leaflets; and that when the fungicide was dissolved in the wax or lanolin before emulsification, the particle size of the dispersed fungicide was extremely small, a quality that increases biological action.     

Investigations into the cytokinin-like properties of benzimidazole -derived fungicides

Of seven systemic benzimidazole fungicides tested, four showed cytokinin activity in a modified Amaranthus betacyanin bioassay. In the presence of the gibberellins A₄ and A₇, in the dark at 25°C, the four active compounds stimulated the germination of seeds of two celery cultivars dependent on cytokinin for germination under these conditions. One cytokinin-active fungicide was methyl benzimidazol-2-yl carbamate (MBC) and the other three break down into this compound in solution. The three inactive fungicides do not. However, the hormonal properties of the cytokinin-active fungicides may not be due to the MBC moiety alone because sometimes they were more cytokinin-active than pure MBC.     

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.     

The effects of organic pesticides on inner membrane permeability in <Emphasis Type="Italic">Escherichia coli</Emphasis> ML35

We have tested whether some pesticides might cause inner membrane leakage in ML35 Escherichia coli cells, which express β-galactosidase (lacZ; EC 3.2.1.23) constitutively but lack the permease (lacY) required for substrate entry. The activity of β-galactosidase (indicative of substrate leakage through the inner membrane) was increased by various concentrations of pesticides, including the organometallic fungicides maneb and mancozeb, the insecticide Thiodan, and the herbicide Ally, as well as by antibiotics such as ampicillin, gramicidin D, and the calcium ionophore A23187. The enzyme activity was increased by up to ∼30% when the E. coli ML35 strain was exposed to various concentrations (between 50 and 250 ppm) of both fungicides. Thiodan had only a slight effect on β-galactosidase activity (increase of 12.8%), whereas, among the antibiotics, the calcium ionophore at 20 μg/ml caused a significant increase in enzyme activity by up to 61.8%. This effect is similar to that of sodium dodecyl sulfate, used as positive control (∼70% increase). Accumulation of maneb and mancozeb by bacterial cells was also studied taking advantage of their metal content and using atomic absorption spectrophotometry. In parallel with the increase in enzyme activity, both fungicides accumulated in the cells as a function of their concentration. Time course experiments (3, 6, and 9 h) of fungicide accumulation and of bacterial growth at various pesticide concentrations were also carried out. Maneb seems to inhibit the bacterial growth better than mancozeb. In addition, maneb uptake increases with time up to 9 h at all tested concentrations, whereas the accumulation of mancozeb is similar at all the exposure times tested. This indicates a different uptake and/or metabolizing strategy by E. coli cells for the two 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.     

Mycorrhizal growth in pure cultures in the presence of pesticides

The effects of pesticides on 64 ectomycorrhizal fungi of boreal forest trees were studied in vitro. The pesticides (fungicides: benomyl, chlorothalonil, copper oxychloride, maneb and propiconazole; herbicides: chlorthiamid, glyphosate, hexazinone, linuron and terbuthylazine; insecticide: cypermethrin) were selected as those commonly used in Nordic forest nurseries and afforestation sites. In general, the fungicides proved to be more toxic to ectomycorrhizal fungi than the herbicides and cypermethrin. The fungicides, chlorothalonil and propiconazole, had the clearest inhibitory effect on growth of mycorrhizal fungi. Conversely, maneb, glyphosate and terbuthylazine stimulated the growth of some mycorrhizal fungi. Leccinum versipelle and L. scabrum, Paxillus involutus and Cenococcum geophilum were the most sensitive ectomycorrhizal fungi to the various pesticides.     

Chemical control of Alternaria brown spot on Minneola tangelo in South Africa

The effectiveness of several groups of fungicides was compared with that of copper and mancozeb for their ability to control Alternaria brown spot on Minneola tangelo. Variables used for comparing fungicides in order of importance were: performance index, the number of exportable fruits per tree, the number of fruits per tree free of Alternaria lesions and total number of fruits per tree. Percentage exportable fruits was not a reliable variable for comparing treatment efficiency. During the 1992/1993 evaluations iprodione, difenoconazole, and procymidone showed promising control of the disease. Other than for difenoconazole, members of the triazole group were not effective, especially at dosages below 10 g a.i. 100 litre ^] water. Moderate control of Alternaria brown spot was obtained using copper and mancozeb. During the 1993/1994 season spray programmes with copper oxychloride, mancozeb, maneb plus zinc oxide, procymidone, iprodione, and tebuconazole were compared in field trials, for the control of Alternaria brown spot on Minneola tangelo. Mancozeb applied at 2-weekly intervals was the most effective spray programme, followed in order of efficiency by programmes using procymidone, maneb plus zinc oxide, and mancozeb applied at 4- and at 3-weekly intervals. Iprodione and tebuconazole were not particularly effective in this evaluation, although they performed significantly better than the control treatment. Trees treated with copper oxychloride produced poorly, in spite of a high percentage exportable fruits.     

Spraying bananas in Fiji to control black leaf streak disease

Three sprays, maneb in water applied by hydraulic knapsack sprayer and maneb in an oil/water emulsion or an oil/water emulsion alone applied by mistblower were compared for the control of black leaf streak disease of banana caused by Mycosphaerella sp.
Although there were no differences in yield in the 'plant' crop, maneb, especially as a water-based spray, resulted in much better disease control and leaf survival. Oil seemed to have an adverse effect on fruit quality but not on plant growth.
Since it is unlikely that oil alone will adequately control the disease in ratoon crops fungicides may be necessary.     

Laboratory Examination of Organic Fungicides Against Zoopathogenic Fungi in Soil

Seven commercial and five experimental organic fungicides were tested against Histoplasma capsulatum, Cryptococcus neoformans, Allescheria boydii, and Sporotrichum schenckii in a series of laboratory studies. Preliminary agar dilution plate tests indicated that Lanstan, DAC 649, DAC 469, DAC 2787, He 3944, maneb, and nabam, in order of decreasing activity, inhibited all test fungi. Terraclor, Dexon, and He 13274 were active only in high concentration. The best fungicidal properties were exhibited by Lanstan, Vapam, and DAC 649; maneb, nabam, DAC 469, and DAC 2787 were fungicidal but to a lesser degree than the former compounds. In subsequent tests against H. capsulatum and C. neoformans in artificially infested soil or by use of the buried plug technique, Lanstan, Vapam, and DAC 649 showed good activity and merit further study.     

Evaluation of genotoxicity of captan,maneb and zineb in the wing spot test of Drosophila melanogaster: role of nitrosation

The wing spot test in Drosophila melanogaster is a suitable system for the analysis of genotoxic activity of compounds that need metabolic transformation to render them active. We have analysed the genotoxicity of three fungicides for which it was reported that the metabolic processes taking place in vivo may determine their activity. The compounds analysed are captan, maneb, zineb and ethylenethiourea (ETU) (a metabolic derivative of ethylenebisdithiocarbamates like maneb and zineb). We have also evaluated the ability of ETU to form genotoxic derivatives in vivo analysing this compound in combined treatments with sodium nitrite. Both standard and high bioactivation NORR strains have been used. Captan, usually considered a mutagen in vitro but a non-mutagen in vivo, gave negative results in the wing spot test with both crosses. Positive results were obtained for maneb in the standard cross and for ETU in both the standard and the high bioactivation cross. The genotoxicities of maneb and ETU were higher when treatments were made on media in which nitrosation is favoured. A low absorption of the fungicide and an inefficient availability of the compound in the target may explain negative results obtained with zineb in both crosses. The results obtained in this study with the wing spot test demonstrate once again the suitability of this in vivo assay, in which absorption, distribution and metabolism processes take place, for the evaluation of genotoxicity of compounds to which humans are exposed.     

Effects of fungicide timing on control of Rhynchosporium secalis in barley plants

Sprays of captafol, carbendazim, carbendazim + tridemorph + maneb, diclobutrazol, triadimefon or triadimefon + carbendazim all completely protected barley plants in a glasshouse against R. secalis for at least 30 days. However, their effectiveness in preventing disease development when applied after inoculation differed: triadimefon, traidimefon + carbendazim, or diclobutrazol were the most effective, completely preventing symptom development when applied up to 5 days after inoculation to plants grown above 16 °C, and up to 8 days below 8 °C. All the fungicides decreased the number of viable conidia produced by leaf blotch lesions, and when applied to infected plants at G. S. 30, greatly decreased the upward spread of the disease under simulated rain conditions; the most effective fungicides in these respects were triadimefon and triadimefon + carbendazim. The above fungicides and fungicide mixtures, together with the recently introduced materials fenpropimorph and propiconazole were applied to diseased winter barley crops in winter or in spring. All treatments decreased leaf blotch development and increased yields. In most cases, a winter application was more effective than spring applications, particularly if applied in mid-November. The most effective fungicides were triadimefon and propiconazole. The field trials data fitted well with the predictions of performance indicated by the glasshouse investigations.     

The effect of fungicides on field populations of Aphis fabae and on the infection of the aphids by Entomophthoraceae

Numbers of Aphis fabae on spring-sown field beans were little affected by weekly applications of the systemic fungicides benomyl or tridemorph or the non-systemic captafol, manocozeb or maneb. Benomyl diminished the mortality of aphids caused by Erynia neoaphidis but not that caused by other species of entomophthoraceous fungi. The other fungicides failed to affect consistently the proportion of aphids infected by any fungus.     

Tests of aryltin compounds as potato blight fungicides

Triphenyl(phenylthio)tin and triphenyl(p-chlorophenylthio)tin were as effective as fentin acetate in controlling potato blight (Phytophthora infestans) in laboratory tests on detached leaflets. Diphenyltin dichloride and bis(triphenyltin)sulphide were moderately effective. Dibenzyltin and some diphenyltin compounds were ineffective. A small change in the bioassay conditions, bringing them slightly closer to field conditions, increased the relative effectiveness of bis(triphenyltin)-sulphide, making it about one-quarter as effective as fentin acetate; however, the change did not increase the relative effectiveness of triphenyl(phenylthio)tin or dibutyltin diacetate.     

Reducing whiteflies on cucumber using intercropping with less preferred vegetables

The effectiveness of four less preferred vegetables – celery, asparagus lettuce, Malabar spinach, and edible amaranth – were investigated for suppression of two biotypes of sweet potato whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) on cucumber, Cucumis sativus L. (Cucurbitaceae). Intercropping celery and Malabar spinach with cucumber significantly reduced whitefly numbers on cucumber. Y‐tube olfactometer behavioral assays revealed that whiteflies were strongly repelled from the aqueous extracts of the less preferred vegetables. The level of whitefly repellency varied with combinations of intercropped vegetables, and also differed between the two whitefly biotypes. For whitefly biotype B, the greatest repellency was observed with asparagus lettuce extract, whereas celery and Malabar spinach extracts were more repellent to whitefly biotype Q. Two major volatile constituent compounds were identified, D‐limonene from celery and geranyl nitrile from Malabar spinach. Sprayable 1% formulations of these compounds significantly reduced whitefly colonization on cucumber under field conditions.     

Glasshouse evaluation of systemic compounds, derivatives of dithiocarbamic acid and other fungicides for the control of clubroot

Seventy-one fungicides were mixed with an artificially infested soil/peat mixture in which cabbage seedlings were subsequently grown in pots in a glasshouse. The incidence and severity of clubroot and any toxic effects on the plants were recorded. Carbendazim, chloraniformethan, maneb, ferbam, zinc N-methyl dithiocarbamate, zinc diethanolamine dithiocarbamate and ziram were selected as suitable for further evaluation as they gave disease control as good as the standard calomel treatment and were of comparably low phototoxicity.     

Compatability of Metarhizium anisopliae var. anisopliae with chemical pesticides

The effects of various insecticides on the mycelial growth, sporulation and conidial germination of Metarhizium anisopliae var. anisopliae isolate E₉ were studied in the laboratory. Chlorpyrifos was the most toxic organophosphate to mycelial growth and sporulation at all concentrations. Temephos, malathion and leptophos were highly toxic to sporulation while malathion was the most inhibitory to germination. The carbamates, carbofuran, methomyl and oxamyl were moderately toxic to mycelial growth and sporulation while oxamyl had an adverse effect on germination. The pyrethroids (pyrethrin, permethrin and resmethrin) and the insect growth regulators (diflubenzuron and methoprene) were not inhibitory to the various developmental stages of isolate E₉. The chlorinated hydrocarbons (chlordane, lindane and toxaphene) were more deleterious than all other insecticide groups tested. Among the fungicides, benomyl and maneb produced the greatest inhibition.