Laboratory and field tests of zineb and other fungicides against downy mildew of lettuce (Bremia lactucae Regel)

In laboratory tests on young lettuce plants, the protection provided by sprays of zineb wettable powder against artificial inoculations with Bremia lactucae was less than that obtained with tank-mix zineb, and with several other dithiocarbamates and related fungicides. Experiments on autumn lettuce in the field also showed that tank-mix zineb was more effective than the wettable powder. On winter lettuce in frames, however, zineb wettable powder gave control similar to or better than that given by any of the other materials tested. Infection in most of these outdoor experiments was not heavy. None of the fungicides gave very high control or markedly increased the number of hearted or marketable plants. When zineb wettable powder was sprayed on autumn lettuce at the rate of 2 lb./acre it gave similar disease reductions whether applied in low, medium or high volumes of water.     

Local redistribution of fungicides on leaves by water

Local redistribution of various fungicides applied as large or small droplets to detached broad-bean leaflets was examined by laboratory bio-assay with Botrytis fabae and by leaf-printing techniques. The results showed that fungicidal particulate and soluble material will spread in water from the initial deposits and that the protected areas on leaves inoculated after washing were often much greater than on unwashed leaves. The extent of redistribution was related to the inherent toxicity, physical form, duration of weathering and tenacity of the fungicides. The effects of formulating copper oxychloride and zineb fungicides with surface-active agents and adhesives seemed due to differences in the tenacity of the deposits. Results indicated that similar types of redistribution would occur in the field, but the possible importance of the electrokinetic theory of redistribution was not proven.     

Laboratory tests of fungicides against Peronospora parasitica (Pers. ex Fr.) Fr

Methods were investigated of culturing Peronospora parasitica on detached cotyledons in plastic box moist chambers in constant-temperature cabinets. Light was essential and a temperature of 15 °C was most suitable for infection and survival of cotyledons. Using such cotyledons the protectant and eradicant actions of various fungicides against P. parasitica were compared with those of zineb. Captafol, Daconil 2787, dichlofluanid and propineb were markedly superior to zineb as protectants, being highly effective at 0·025 % a.i. None of these compounds (at 0·2 % a.i.) checked fungal development when applied 5 h after inoculation, during which time the fungus had penetrated the cotyledons, and it was concluded that the fungicides had thus no internal effect. Internal fungistasis was shown, however, by a maneb-nickel sulphate fungicide and also by nickel sulphate. The latter (at 0·4% NiSO₄.6H₂O) gave some disease control when applied up to 72 h after inoculation and appeared to be translocated within the tissue of the cotyledon.     

Influence of fungicides and insecticides on the entomogenous fungus Metarhizium anisopliae a pathogen of the vine weevil,Otiorhynchus sulcatus

In the laboratory, the fungicides chlorothalonil and zineb prevented germination of Metarhizium anisopliae conidia when incorporated into Sabouraud dextrose agar (SDA) at the commercial concentration (based on the manufacturers’ recommended rates for horticultural crops). Twelve other fungicides and six insecticides had no effect on spore germination when applied at the same rate. Mycelial growth of M. anisopliae on SDA plates containing the recommended rate of all the pesticides (except propamocarb) was reduced compared with SDA alone. Two fungicides, benomyl and carbendazim, totally inhibited growth at 0.1 times the recommended rate. Growth was also completely prevented by the fungicides etridiazole, triforine and zineb, and the insecticides dichlorvos and hostathion, at 10 times the recommended rate. In a glasshouse experiment, a prophylactic drench of M. anisopliae conidia reduced vine weevil (Otiorhynchus sulcatus) populations on Impatiens plants by 88%. This level of control was not significantly reduced by subsequent application (7 days after egg infestation) of any of the pesticides at the recommended concentration. Larval control in pots treated with M. anisopliae plus any one of the 12 fungicides and four insecticides examined, ranged from 82% to 98%. The insecticide diazinon applied alone reduced larval numbers by 100%. Two other insecticides, dichlorvos and cypermethrin, and the fungicide pyrazaphos, also reduced weevil populations by over 50%. These experiments demonstrate the limitations of laboratory based in vitro screening programmes for assessing the chemical compatibility of M. anisopliae.     

The effect of six systemic fungicides on halo spot disease of barley caused by Selenophoma donacis

Six systemic fungicides were applied at growth stage 10 in a spring-barley field trial, artificially inoculated with Selenophoma donacis at each of three growth stages. Barley cultivars used were Mazurka and Zephyr. The level of disease was significantly reduced by the application of chemicals, benomyl and thiophanate methyl giving the best control. Yield results did not reflect the control of disease although benomyl and thiophanate methyl applications gave slight increases in 1000 grain weight and mean yield per head. Three of the fungicides caused some phytotoxicity in cv. Zephyr and prevented grain formation.     

Biotoxic effects of Sumisclex and Carbomar fungicides on four Aspergillus species isolated from the rhizosphere of some Taif plants

Abstract

The antifungal activities of two systemic fungicides (Sumisclex and Carbomar) on four rhizospheric Aspergillus species (A. candidus, A. sydawi, A. niger1 and A. niger2) were studied. Also the phytotoxicity against some saudian seeds was analysed. Results indicated that Sumisclex fungicide was more effective on the growth of A. candidus and A. sydawi under laboratory conditions (the IC₅₀ of 3 and 4 ppm were recorded, respectively) than Carbomar where an IC₅₀ of 11 ppm for A. candidus and 35 ppm for A. sydawi were observed. The growth of the two strains of A. niger was completely inhibited by Carbomar even at the lowest 10 ppm concentration. On the other hand results revealed that phytotoxicity was apparently linked with the type of the fungicide and its concentration. However, the root system was more sensitive to the tested fungicides especially at higher concentrations.     

In vitro efficacy of some fungicides on mycelial growth of Alternaria alternata and Mucor pyriformis

Various chemical fungicides, systemic and non-systemic, were tested against fruit rot pathogens viz. Alternaria alternata and Mucor pyriformis for the evaluation of inhibition of mycelial growth. In A. alternata, among the systemic fungicides used, hexaconozole showed highest inhibition of mycelial growth followed by carbendazim and least effective was myclobutanil. While in M. pyriformis, hexaconozole showed highest inhibition and least effective was bitertanol. Among the non-systemic fungicides tested in both A. alternata and M. pyriformis, mancozeb showed highest inhibition of mycelial growth followed by capton and the least inhibition was shown by zineb.     

Tomato leaf mould: its assessment and effects on yield

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

Apparent induction of mutants and enhancement of conidial formation by fungicides in Alternaria mali

Of approximately 120.000 homokaryotic conidia ofAlternaria mali exposed to 6 fungicides, 22 variants were induced. Six were induced by zineb, 5 by maneb, 4 by nabam, 3 by ferbam, 2 by thiram, and 2 by captan. Colonies of the variants could be distinguished by growth rate, colony characteristics, and conidial production on 5 different media: Sabouraud's, cornmeal, potato dextrose, Czapek's and male extract agars. The homokaryotic organisms did not adapt to any of the fungicides after 10 generations. When exposed to fungicide decomposition products conidial germination was greatly reduced; conidial production, however, was greatly enhanced.     

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.     

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.     

Comparison of fungicides for the control of Rhizoctonia solani causing datnping-off of mung bean (Phaseohis aureus)

Of 41 fungicides tested in the laboratory, copper carbonate, copper sulphate, mercuric chloride, Agrosan GN, quintozene, kasugamycin, carboxin, pyracar-bolid, carbendazim, chloroneb, benomyl, Ohric, RH 893 (2-n-octyl-4-isothiazole-3-one) and Terrazole were most inhibitory to the mycelial growth of Rhizoctonia solani on Czapek's agar plates and had EC₅₀ values of less than 1 μg a.i./ml, while copper oxychloride, Udonkor, zineb, ziram, F 319 (3-hydroxy-5-methyl isoxazole) and anilazine were much less toxic, ziram being least inhibitory with an EC₅₀ of 214 μg a.i./ml. Of 17 fungicides tested in the greenhouse as seed treatments, thiabendazole, carbendazim, benomyl, thiophanate-methyl, dichlozoline and Ohric gave 80–90% control of damping-off of mung bean seedlings. A single soil drench with thiophanate-methyl and two drenches with benomyl gave about 90% disease control, More seedlings with R. solani infection survived when thiophanate-methyl was used as a post-inoculation soil drench than when benomyl or chloroneb were used.     

Effects in vitro of nine fungicides on growth of entomopathogenic fungi

The effects of nine fungicides were evaluated in vitro on the entomopathogenic fungi Beauveria bassiana, Conidiobolus coronatus, C. thromboides, Metarhizium anisopliae, Paecilomyces farinosus, P. fumosoroseus, Scopulariopsis brevicaulis and Verticillium lecanii. The susceptibility of the fungi to the fungicides varied. The dithiocarbamate derivations zineb + copper oxychloride, and mancozeb completely inhibited germination of C. coronatus, C. thromboides, B. bassiana, P. farinosus, M. anisopliae and V. lecanii. The fungicides triadimefon, copper oxychloride, metalaxyl, sulfur, sulfur + nitrothal‐isopropyl and hymexazol exhibited various effects on the fungi. Usually, fungistasis was more pronounced at 15°C than at 25°C and the inhibitory effects were in direct proportion to the dosage of active ingredient (recommended field rate, 10‐fold higher and 10‐fold lower). In a few combinations, fungi partially overcame or even recovered from the initial inhibition of growth which might have resulted from delayed germination. In other cases, inhibition of growth occurred only after a delay and its intensity increased with time. Stimulation of fungal growth when it occurred was rarely permanent. Generally, adverse effects were much greater against the entomophthoraleans C. coronatus and C. thromboides than against the Hyphomycetes. Extrapolation of the results to practice and to the field situation is difficult. Nevertheless, the data presented give an idea of possible side‐effects in nature.     

Effects of delaying fungicide treatment on the incidence of gangrene in stored potato tubers

Potato titbers infested with Phoma exigua var. foveata were uniformly wounded and sprayed or dipped in fungicide suspensions either immediately or after periods of up to 21 days' storage at 5, 10, 15 or 20 °C. Tubers were then stored at 5 °C and gangrene assessed after 12 wk. Incidence of gangrene on untreated tubers was progressively decreased by increasing the length of storage at 15 or 20° (curing) but was not affected by 3 days' storage at any temperature. Fungicide treatment immediately after wounding gave best control of the disease; treatment after 3 days' delay was less effective and after 14 or 21 days was usually ineffective. Gangrene was decreased by fungicides more on tubers stored for 3 or 7 days at 5 °C than at higher temperatures. Control of gangrene by curing or fungicides diminished when the amount of inoculum on tubers was increased. Increasing the amount of fungicide applied improved control and fungicides were more effective in decreasing gangrene on cut and crush wounds than on cut wounds. At the arbitrary concentrations used in these experiments imazalil gave better disease control than thiabendazole, prochloraz, carbendazim plus quinolin 8-ol or triadimefon.     

Control of tomato grey mould on unheated crops using non- systemic fungicide sprays

High volume sprays of dichlofluanid (0.1 % a.i.) reduced total fruit numbers but gave better control of Botrytis cinerea infections of tomato stems, leaves and fruit than sprays at 0.05 or 0.025% a.i. Surface residues from the sprays at 0–1, 0.05 or 0.025% a.i. were respectively 5.4, 1.6, 0.7 μg/g fresh weight of ripe fruit at harvest. Tank-mixed zineb (0.12% a.i.) and captan (0.2% a.i.) were less effective and increasing the spray intervals from 1 wk to 2 and 3 wk reduced the fungitoxicity of captan and zineb more than that of dichlofluanid. Harvest residues on ripe fruit were 7.1, 2.8 or 2.4 μg/g when dichlofluanid (0.1 % a.i.) sprays were applied at 1, 2 and 3 wk intervals respectively. Good control of B. cinerea was achieved if the whole plant was sprayed initially with dichlofluanid as soon as the second truss was flowering and subsequent sprays were restricted to the upper section of stem including the four or five youngest trusses of buds, flowers and fruit. When used as a post-infection spray there was a period of c. 8 wk before dichlofluanid markedly reduced the incidence of grey mould. Tank-mixed zineb (0.12% a.i.) controlled Botrytis fruit spotting but not leaf and stem infections. Botrytis stem lesions extended more rapidly on zineb-sprayed plants than on unsprayed plants or on plants treated with captan or dichlofluanid.     

The Control of Fusarium solani f. sp. phaseoli by Fungicide Mixtures

Six fungicides were used either alone or in binary combination to control Fusarium solani f. sp. phaseoli. Of the three methods of application used, seed treatments and soil drenches were the best, although phytotoxicity was evident in some instances. Application as a seed soak for 1 h proved to be the worst method with most treatments showing signs of phytotoxicity. The results are discussed with reference to the use of fungicide mixtures to control foot rot of beans.     

Integrated use of biocontrol agents with fungicides to control wilt incidence in pigeon-pea

When Trichoderma harzianum and Aspergillus niger, as biocontrol agents, were included with two fungicides, Foltaf 80W (Captafol 80%) and Blue Copper-50, for the treatment of pigeon-pea wilt, the disease was more effectively controlled than when the fungicides were used alone. Accordingly, decreased amounts of the fungicides could be used to control the disease without adversely affecting the growth of pigeon-pea.     

Glasshouse experiments on apple scab

Experiments with fungicide mixtures used protectively and curatively against apple scab showed no advantage from adding phenylmercury chloride (PMC) to certain protective fungicides. Sulphur fungicides greatly impaired the curative activity of PMC, especially in mixtures applied 24 hr. after infection, but captan showed little and dodine acetate no such effect. PMC, however, contributed appreciably to the curative effectiveness of mixtures with captan or dodine acetate. Commercially prepared mixtures of dispersible sulphur with phenylmercury dimethyldithiocarbamate and of zineb with mancozeb gave promising results, and an experimental mixture of dodine/glyodin acetates at low rates was effective protectively and especially curatively. Dodine acetate, dichlofluanid, lime-sulphur, and isobutyl-o-coumarate showed little translocated activity against scab when applied after infection, and PMC, which earlier showed strong translocated activity when applied in summer before infection, was much less effective when applied in spring 24 hr. after infection. Uncontrolled powdery mildew early in the scab-incubation period greatly reduced the establishment of scab infection on the test plants (clonal root-stocks); methods of mildew control in such experiments are suggested.     

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

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

A comparison ofin vitro andin vivo effect of clay minerals,humic acid and micronutrients on the activity of fungicides againstRhizoctonia solani

Activity of nine fungicides against mycelial growth ofRhizoctonia solani in potato dextrose broth and in pot tests as seed treatment against cowpea seedling rot in infested soil was differentially in fluenced by clay minerals, humic acid and micronutrients. Humic acid, extracted from farmyard manure, considerably lowered the activity, bothin vitro andin vivo, of all fungicides except chloroneb. Montmorillonite caused substantial decrease in disease control by fungicides but enhanced the toxicity of 2-methoxyethyl mercury chloride (MEMC), and quintozene in culture. Kaolinite inactivated carbendazim, benomyl and thiophanatemethyl in nutrient broth but had little effect on disease control by these fugicides. The six micronutrients altered the activity of fungicides to varying levels often without definite correlation betweenin vitro andin vivo results. The results ofin vitro growth inhibition tests are largely inapplicable to dieseas control tests in infested soil mainly due to the differences in the ambient conditions of the two systems.