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`TRANSACTIONS OF THE
`
`BRITISH MYCOLOGICAL SOCIETY
`Volume 85 Part 2 September
`1985
`
`CONTENTS
`
`ECOLOGY
`hyphomycetes .
`and aquatic
`of aeroaquatic
`on survival
`FIELD, J. I. & WEBSTER, J. Effects of sulphide
`on mycehal
`Boooy, L., GIBBON, 0. M. & GRUNDY, M. A. Ecology of Daldinia
`effect of ab1011c variables
`concmtrica:
`201-211
`interactions
`and interspecific
`extension
`
`TAXONOMY
`as an aid for
`chromatography
`Kmo, C. B. M., CADDY, B., ROBERTSON, J., TEBBl!TT, I. R. & WAnING, R. Thin-layer
`213-221
`species
`of Cortinari
`identification
`of Dennocybe
`us
`223-238
`of aecia of the rust fungi
`SATO, T. & SATO, S. Morphology
`239-255
`A. & SUTTON, B. C. Microfun gi on Xanrhorr hoe a
`SIVANESAN,
`37<>-374
`A. & GoMEZ, L. D. The teleomorph
`of Sphace/oma
`SrvANESAN,
`erythrinae
`374-377
`in Taiwan
`gen. et sp.nov.
`on Leucaena
`)ANG, J. C. & CHEN, T. Pseudalagarobasidium
`ltguminicola
`37S-38o
`sp.nov.
`species
`of Pestalotiopsis:
`MORDUE, J.E. M. An unusual
`P. sreyaerrii
`38o-384
`in smuts on Dipsacaceae
`ornamentation
`MORDUE, J.E. M. Ustilospore
`
`ULTRASTRUCTURE
`ar tripartite
`mem­
`extracellul
`H. & ROHR, M. Wood decay by basidiomycetes:
`R., MESSNER, K., STACHBLBBRGBR,
`Fo1SNBR,
`257-266
`structures
`branous
`
`MYCORRHIZAL FUNGI
`za l fun gi in soil
`mycorrhi
`of vesicular--arbuscular
`of spore germination
`I. C. Inhibition
`ToMMBRUP,
`mycorrhizas
`KoSKE, R. E., FRIESE, C. F., OLllXlA, P. D. & HAUKE, R. L. Vesicular--11rbuscular
`in Equisetum
`
`PHYSIOLOGY
`from yeast grown in con-
`of intermediates
`leakage
`influencing
`FRANCO, C. M., SMITH, J.E. & BERRY, D.R. Factors
`culture
`tinuous
`of conidiation
`in Alrernaria
`inhibition
`C. Blue-light
`D. J. & CHRISTIAS,
`V AKALOUNAKIS,
`cichorii
`protoplasts
`of A,pergillu,
`in mycelial
`synthesis
`lsMC, S. & PEIIERDY, J. F. Protein
`nidulans
`in the Saprolegniaccae
`activity
`A. & Due, N. J. Cellulase
`THOMPSTONE,
`fungi by oils and fatty acids
`of growth ofkeratinophilic
`GARG, A. P., SMITH, S. N. & PuGH, G. J. F. Inhibition
`
`279-283
`285-289
`35S-361
`361-366
`367-37o
`
`PLANT PATHOLOGY
`cucumber
`protected
`and systemically
`from unprotected
`of cell wall material
`MtLLs, P.R. & Wooo, R. K. S. Degradation
`291-298
`by extracellular
`enzymes of Colletotrichum
`plants
`/ag enarium
`299-3o6
`modes of action
`with different
`of fungicides
`interactions
`H. & RIMBACH, E. Synergistic
`Gm, U., BINDER,
`307-3!2
`coni�ia .
`A. Role of wind and rain in dispersal
`of Borryrisfabae
`N. F. & BAINBRIDGE,
`F1TT, B. D. L., CREIGHTON,
`m
`of peach twigs and flowers and its possible
`E. Mycoflora
`R. & M.-SAGASTA,
`P., CARRILLO,
`MELGAREJO,
`significance
`313-317
`control
`biological
`of Moni/inia
`lax a
`319-327
`of wheat in South Africa
`{stunting)
`disease
`with crater
`solani associated
`DEACON, J. W. & SCOTT, D. B. Rhizocronia
`329-334
`with root rots of annual Medicago spp. in Australia
`T. W. Fungi associated
`BRETAG,
`D. W. Characterization
`N. F., L1, K. Y. & HOLLOMON,
`BATEMAN, G. L., SMITH, C., CREIGHTON,
`popu-
`of wheat eyespot
`335-338
`resistance
`of fungicide
`lations before development
`33S-34t
`insensitivity
`in Pyrenophora
`J.E., GRBAVAC, N. & SHERIDAN, M. H. Triademol
`SHERIDAN,
`teres
`341-343
`burn ing
`and stubble
`herbicide
`T. W. Control of ergot by a selective
`BRETAG,
`344-345
`of winged bean flowers in Sri Lanka
`blight
`N. P. & PRICE, T. V. Choanephora
`GUNASEKARA, S. A., LIYANAGE,
`
`GENETICS
`in hop wilt isolates
`of
`of pathogenicity
`of the generics
`investigation
`CLARKSON, J. M. & HEALE, J. B. A preliminary
`alboarrum
`Verticillium
`MOORE, R. T. Mating type factors
`in Pleurotus
`cystidiosus
`
`INVERTEBRATE PATHOLOGY
`aphids with capilhconidia
`GLARE, T. R., CHILVERS, G. A. & Mn.NER, R. J. A simple method for inoculating
`
`353-354
`
`© The British
`1985
`Society
`Mycological
`C AM BRIDGE UNIVERSITY PRESS
`CB2 1RP
`Cambridge
`Street,
`Trumpington
`The Pitt Building,
`USA
`New York, NY 10022,
`32 East 57th Street,
`Melbourne 3166, Australia
`10 Stamford Road, Oakleigh,
`
`Cambridge
`Press,
`by the University
`in Great Britain
`Printed
`
`

`

`
`
`in Great Britain Trans. Br. mycol. Soc. 85 (2), 299-306 (1985) Printed
`
`
`
`[ 299 ]
`
`SYNERGISTIC INTERACTIONS OF FUNGICIDES WITH
`DIFFERENT MODES OF ACTION
`
`MATERIAL AND METHODS
`
`BY U. GISI, H. BINDER AND E. RIMBACH
`Agrobiological Research Station, Sandoz Ltd, CH-4108 Witterswil, Switzerland
`Seventeen fungicides were tested, singly and in mixtures, on Phytophthora cactorum and P.
`
`
`
`
`
`
`
`
`cinnamomi in vitro, and on the disease development by Phytophthora inf es tans on tomato or
`
`potato leaves and Plasmopara viticola on grape vine leaves under greenhouse and field
`
`
`
`
`
`
`
`conditions. Results indicated synergistic interactions of different intensities up to a ratio of
`
`
`
`
`
`
`7. Ratios were calculated by comparing theoretical with observed EC90 values of the mixture.
`
`
`
`
`
`
`Among mixtures containing phenylamide fungicides like oxadixyl, metalaxyl or cyprofuram,
`
`
`
`
`
`
`mixtures of oxadixyl with mancozeb and/or cymoxanil showed the highest synergism. When
`
`
`
`tested on Phytophthora or Plasmopara diseases under greenhouse conditions, the highest
`
`
`
`
`
`synergism was observed in combinations of oxadixyl with mancozeb, cymoxanil, or phosetyl-Al
`
`against both diseases; with fentin acetate, fol pet or thiram against Phytophthora; and with
`
`
`
`
`
`
`
`
`captan or maneb against Plasmopara. None of the tested oxadixyl mixtures showed antago­
`
`
`nistic interactions.
`
`
`Fungicide mixtures are used to broaden the
`
`
`
`spectrum of activity of the product, or to minimize
`Fungicides
`
`
`
`
`the selection pressure for resistant strains. Examples
`All compounds were used as aqueous suspensions
`
`
`
`for the enlargement of spectrum are triadimefon/
`
`
`of one or more commercial formulations. They
`
`
`carbendazim for controlling powdery mildews,
`
`rusts and eyespot in cereals, and metalaxyl/
`
`
`were incorporated into the solidifying agar for in
`
`
`mancozeb for activity against Phytophthora and
`
`
`
`vitro experiments, and sprayed directly on plants,
`
`
`either until near run-off in greenhouse experiments,
`
`in potatoes. There are theoretical
`Alternaria
`
`or at about 800 1 ha-1 in field experiments. All
`
`
`
`models (Kable & Jeffery, 1980; Skylakakis, 1981;
`
`concentrations are given as amount of active
`
`
`examples I Levy, Levi & Cohen, 1983) and practical
`
`
`
`ingredient per volume. Fungicides used were three
`
`
`(Delp, 1980) suggesting that there is a significant
`
`
`
`phenylamide fungicides (acylalanine type) formu­
`
`
`
`delay of resistance build-up when mixtures of
`
`
`lated as 25 WP: oxadixyl (Sandoz), metalaxyl
`
`
`
`fungicides with different modes of action are used,
`
`
`
`(Ciba-Geigy), and cyprofuram (Schering); five
`
`
`e.g. benlate/captan against apple scab; dicarboxi­
`
`
`mides/folpet against Bo try tis in grapes; and
`
`
`
`dithiocarbamate fungicides: mancozeb (WP 80 ),
`
`maneb (WP 80), propineb (WP 70), zineb (WP 70),
`
`
`
`mixtures of phenylamide fungicides with suitable
`
`and thiram (WP 80); three phthalimide fungicides:
`
`partners against potato late blight.
`
`folpet (WP 50), captan (WP 83), and captafol (WP
`
`
`An additional reason for combining fungicides
`
`
`80); copper salts (as hydroxide, oxychloride or
`
`with different modes of action but a similar
`
`
`oxide, WP 50); fen tin acetate (WP 2 5); dichlofluanid
`
`
`spectrum of activity, often overlooked, is that they
`
`
`(WP 50); chlorothalonil (WP 75); cymoxanil (WP
`
`
`may be synergistic. This phenomenon is well-known
`
`in weed (Colby, 1967; Nash, 1981) and insect
`
`50); and phosetyl-Al (WP 80).
`
`
`
`control (Koziol & Witkowski, 1982), but little
`
`
`
`knowledge is available for fungicides. The few
`In vitro experiments
`
`studies with fungicides were done in vitro only
`Phytophthora cactorum (Leb. & Cohn) Schroet.
`
`
`(Corbaz, 1963; De Waard & Van Nistelrooy, 1982)
`
`(strain F 29, an apple isolate), and Phytophthora
`
`
`and tended to show antagonism rather than
`
`cinnamomi Rands (strain F 222, mating type A2, an
`
`
`synergism (Buchenauer, 1980).
`
`
`
`avocado isolate) from the Sandoz collection were
`
`
`
`
`In this paper, possible synergistic interactions of
`
`
`used. They were cultivated on malt agar (Difeo) in
`
`
`fungicides with different modes of action were
`
`
`9 cm diam Petri dishes. Radial growth measurements
`
`
`
`studies on mycelium growth in vitro, and on disease
`
`were made after 6 d incubation at 24 °C in the dark.
`
`
`development under greenhouse and field conditions
`
`using different Phytophthora and Plasmopara
`
`Inoculum was a 5 mm diam disk from the edge of
`
`a 7-day-old culture.
`species.
`
`

`

`Synergism in fungicide mixtures
`or seven times (grapes) at intervals of 14-16 d. Five
`Greenhouse experiments
`concentrations for each component, with four
`replicates, were tested. Disease was assessed I
`Plant production. Tomato plants, cv. Rheinlands
`visually as described above.
`Ruhm, were produced from seeds grown at about
`25° for 3-4 wk; potted plants with four leaves were
`used for the experiments. Grape plants, cv.
`Riesling-Sylvaner, were produced from 1-year-old
`cuttings (with one bud per cutting) incubated at 25°
`for about 6 wk in per lite; after transplanting, the
`young potted plants were grown for another 2 wk
`until the five leaf stage was reached.
`Inoculum production. Potato tubers, cv. Bintje,
`were cut into 0·5 cm slices, washed with water,
`dried with a paper rowel and put into 18 cm diam.
`Petri dishes. After one hour the slices were sprayed
`with a suspension of sporangia of Phytophthora
`infestans (Mont.) de Bary, strain F 58 (about
`0·5 x 106 ml-1) using a glass atomizer, and
`incubated at 15° in the dark. After 7 d the slices
`were completely covered with sporangia, and a
`suspension was made by rinsing the slices with
`water, using a pipette and collecting the drops of
`suspension in glass dishes. For the production of
`sporangium suspension of Plasmopara viticola
`(Berk. & Curt.) Berlese & de Toni, (strain F 56),
`about 10-15 diseased leaves were collected in a 2 1
`Erlenmeyer flask containing 250 ml of water and
`then vigorously shaken by hand. A small portion of
`carborundum was added and, after filtration
`through a tea sieve, the suspension was ready for
`immediate use. Sporangium concentrations of
`1-5 x 105 m1-1 were used.
`Infection, incubation and evaluation. About 2 h
`after application, when the spray deposit had dried,
`the plants (three replicates per fungicide concentra­
`tion) were inoculated by intensively treating the
`plants (especially the lower leaf surfaces) using a
`Jato colour pistol (type 232 FR) with two bar
`working pressure. The plants were then incubated
`in the dark at 100% r.h. and 16° for two days. Plants
`were then exposed to a 16/8 h light/dark cycle.
`Phytophthora-infected plants were kept at 16° for
`the rest of the incubation period (another 3-4 d);
`Plasmopara-infected plants were moved to 23°.
`Disease was assessed as % leaf area damaged, and
`converted to % disease control (% DC), according
`to Abbott:
`% DC = 100 x [(untreated-treated)/untreated].
`
`Assessment of synergism
`Fungicides in mixture can interact in different
`ways:
`Additive interactions. Simultaneous action of I
`components in which the total observed response I
`(E0b) of an organism to a mixture is equal to the
`sum of the responses (Eth) to the individual
`components.
`Synergistic interactions. Simultaneous action of
`b is greater than Eth·
`components in which E0
`Antagonistic interactions. Simultaneous action of
`components in which E0b is less than Eth·
`The result of the interactions of fungicides can
`be calculated only when the mixture as well as all
`single components are tested in the same experi­
`ment. The sum of the responses (Eth) to the
`individual components is called theoretical response
`to the mixture; it can be calculated according to
`Colby (1967) or Wadley (1945, 1967). The Colby
`method does not allow proper quantification of the I
`level of interaction, and gives only an indication of
`synergism or antagonism. It is most accurate when
`the responses to the individual components are near 1
`the 50 % level.
`To study the
`level of interaction between
`components in a mixture, linear regression analysis
`is probably the best method.
`In
`the same )
`experiment, four to five concentrations of each
`)
`component and of the combination are tested, to
`give dose-response curves, which can be made
`linear using the logit-log or probit-log systems
`(Finney, 1971). Equipotent doses (EC90, the
`effective concentration resulting in 90 % response)
`of mixtures with different ratios of the single I
`components can be represented graphically with
`' isoboles' (lines of equal effects), which can be used )
`to identify synergistic, additive, or antagonistic
`interactions (Tammes, 1964). The theoretical
`is calculated
`response EC9o(th)
`to a mixture
`according to Wadley (1945, 1967) and compared
`with the observed response EC9ocob> as follows:
`For a two component mixture
`a + b
`ECso(th) =
`
`300
`
`Field experiments
`Small plot trials were carried out in a potato field,
`cv. Bintje, naturally infected with Phytophthora
`infestans, and in a grape nursery, cv. Riesling­
`Sylvaner, naturally
`infected with Plasmopara
`viticola. Both fields were sprinkled artificially to
`encourage disease development. Plots were treated
`preventively with fungicides four times (potatoes)
`
`a
`-- +--­
`
`b
`EC( A)90 EC(B)90
`and for a three component mixture
`a + b + c
`EC90(th) =
`b
`EC(A) 90 EC(B)90 EC{C)90
`
`C
`a
`-- + -- -+ -­
`
`

`

`3 0 1
`
`R
`
`=
`
`U. Gisi, H. Binder and E. Rimbach
`The EC90 of the mixtures refer to the combined
`where A , B , and Care the components and a , b , and
`concentrations of the two components in the ratio
`care the ratios of these components in the mixture.
`applied. When oxadixyl was mixed with mancozeb
`The level of interaction (ratio R) is calculated as :
`(ratio 1 : 5) or with mancozeb and cymoxanil (ratio
`ECDO(th) •
`1 : 7 : OA), the amount of oxadixyl was considerably
`EC90(ob)
`less than when used alone, e.g. for P. cactorum from
`1 6 mg 1-1 to 3 and 5 mg 1-1 and for P. cinnamomi
`Statistical analysis to indicate the significance of the
`from 12 mg 1-1 to 3 and 4 mg 1-1• Thus, the EC90
`Jevel of interaction was made with EC90 values
`was reduced by a factor of 3-5; according to
`rather than with interaction ratios R. The observed
`Wadley's criteria there are clear
`interactions
`EC.o value of a single component represents a figure
`between oxadixyl/mancozeb and oxadixyl/manco­
`derived from several dose-response curves from
`zeb/cymoxanil, with synergism ratios of 1 "4-2·7. It
`different experiments. The standard deviations of
`is important to realize that the lower synergism
`the observed EC90 values (as a simplification
`ratios of the three component mixture do not
`mentioned only in Table 2) were used to estimate
`represent antagonistic interactions compared to the
`the limits of the interaction ratio R of a given
`two component mixture (see Wadley formula). On
`mixture. With this procedure and based on the
`the other hand, the amount of metalaxyl in mixture
`experience of hundreds of single test results, it
`with mancozeb remained unchanged or even
`could be shown that, in these test systems,
`increased compared to the EC90 of metalaxyl alone;
`interaction ratios not significantly different from
`there are no synergistic interactions in this mixture.
`1·0 (between 0·5 and 1 ·5) are examples of additive
`responses, ratios � 1 · 5 (synergism ratio SR)
`indicate synergism, and ratios � 0·5 indicate
`antagonism. Thus, the interaction ratio, given by a
`single figure without significance data, represents a
`reliable index for the effectiveness of a fungicide
`mixture.
`
`R E S U L T S
`
`In vitro experiments
`The two Phytophthora species differed in their
`sensitivity to the fungicides, which varied in their
`effectiveness (Table 1 ) . Cymoxanil and mancozeb
`were significantly less active against P. cactorum
`and P. cinnamomi than both oxadixy I and metalaxy I.
`
`Greenhouse experiments
`Mancozeb and cymoxanil were significantly less
`active against both diseases than metalaxyl, oxadixyl,
`and cyprofuram (Table 2). Plasmopara is slightly
`more sensitive to the fungicides tested than
`Phytophthora. All mixtures showed synergism, with
`ratios of 2·8-4·3 for Phytophthora and 2-5·5 for
`Plasmopara. All two-component mixtures contain­
`ing mancozeb were more synergistic against
`Plasmopara, whereas all mixtures containing
`cymoxanil were more synergistic against Phyto­
`phthora. When analogue mixtures are compared, the
`oxadixyl (A) mixtures showed significantly higher
`
`Table 1. Fungicidal activity (EC90) and level of interaction of fungicides tested against Phytophthora spp.
`on malt agar
`P. cactorum
`P. cinnamomi
`Ee90 (mg 1-1)
`Ee,0 (mg 1-1)
`th
`ob
`th
`ob
`16
`12
`3
`2
`440
`313
`94
`73
`20
`15
`(3 + 12)
`(3 + 17)t
`14
`60
`(7+ 53)
`(2+ 12)
`40
`36
`(5 + 33 + 2)
`(4+ 30+ 2)
`SR = Synergism ratio.
`
`( * Ratios correspond
`
`
`
`
`
`t:7:0·4) respectively.
`(mg 1-1) at Ee90•
`t concns of mixture
`components
`
`Fungicides
`and ratios
`
`Oxadixyl (A)
`
`Metalaxyl (B)
`
`eymoxanil (D)
`
`Mancozeb (E)
`A:E =1: 5*
`B:E = 1: 8*
`
`54
`21
`61
`
`SR
`
`2·7 40
`0'4 14
`1·5 50
`
`SR
`
`2·6
`
`to standard formulations of Sandofan M� (1: 5), Ridomil Fitorex® (1: 8), and Sandofan YM®
`
`

`

`302
`
`Synergism in fungicide mixtures
`) and synergism ratio of fungicides tested on tomato (Phytophthora infestans)
`Table 2. Fungicidal activity (EC90
`and grape vine (Plasmopara viticola) under greenhouse conditions
`Tomato/ Phycophchora Grape vine/ Plasmopara
`Fungicides EC00 (mg 1-1)
`EC90 (mg 1-1)
`th
`ob*
`ob
`th
`and ratios
`(A)
`Oxadixyl
`
`Metalaxyl (B)
`
`Cyprofuram (C)
`
`Cymoxanil (D)
`
`Mancozeb (E)
`
`SR
`
`SR
`
`A :E =1 : 7
`B : E= 1: 7
`C :E =1 : 7
`
`1 2 ± 5
`1 9 ± 6
`4 ± 2
`12± 4
`38± 7
`37± 4
`54± 13
`103 ± 22
`109 ± 21
`70± 15
`68 19± 5 3·6 44 8 ± 2 5 · 5
`54 1 8 ± 4 3·0 23 6 ± 2 3 · 8
`88 25± 6 3 · 5 63 1 2 ± 4 5 · 2
`7 ± 2 3 · 5 1 5 7 ± 2 2 · 1
`25
`A : D = 1 : 0·4
`A : E : D = 1 : 7: 0'4 70 1 6 ± 4 4·3 44 1 1 ± 3 4·0
`20± 5 2·8 24 1 2 ± 4 2·0
`B : E : D = 1 : 7: 0·4 5 5
`C : E : D = 1 : 7 : 0·4 89 25± 6 3·6 62 27± 8 2·3
`
`
`• Values are means with standard deviations from at least three experiments.
`
`synergism than the metalaxyl (B) and cyprofuram
`(C) mixtures, especially against Plasmopara and
`when three-component mixtures were used.
`When the absolute EC90 values of analog
`mixtures are compared, the oxadixyl and metalaxyl
`mixtures were similar, whereas the cyprofuram
`mixtures are less active against both Phytophthora
`and Plasmopara. The slight differences observed
`between oxadixyl and metalaxyl, when used alone,
`are fully compensated in the mixtures because of
`the stronger synergism in the oxadixyl mixtures.
`The cyprofuram mixtures, however, did not fully
`compensate for the weaker activity of the active
`ingredient alone.
`
`Field experiments
`Oxadixyl and metalaxyl, each applied alone, gave
`much better control of disease (EC90 much lower)
`than cymoxanil, mancozeb, and phosetyl-Al, when
`applied at equal intervals of 14-16 d in the field
`(Table 3). This interval, of course, is not the
`recommended one for the latter three fungicides,
`but is necessary for direct comparison with the
`mixtures. For control of Phytophthora, the EC90 of
`oxadixyl alone (25 g hl-1) could be lowered to 9 or
`even 4 g hl- 1 in the mixtures. Similar results were
`obtained against Plasmopara; the EC90 of oxadixyl
`could be lowered from 42 g hl-1 when used alone,
`to 18-29 g hl-1 in the mixtures. The decrease in
`amount of oxadixyl required is based on the
`significant synergism between the single com­
`ponents up to ratios of2·4. In the greenhouse trials,
`the slight differences observed between oxadixyl
`
`and metalaxyl, when used alone, are compensated
`in the mixtures. Again, the mixture containing
`metalaxyl showed only weak synergism, as did the
`oxadixyl/phosetyl-Al mixture (A: F = 1 : 5). On the
`other hand, the often observed, but not properly
`documented, synergism between mancozeb and
`cymoxanil, especially when mixed in the ratio 8: o·8
`(corresponding nearly to the ratio of Remiltine
`Sandoz, which is 7:0·6) was demonstrated to be
`very pronounced (SR = 7·8).
`
`Selection of best oxadixyl mixtures and ratios
`In a series of special greenhouse experiments a great
`variety of components, combined in different ratios
`with oxadixyl, were tested for their synergistic
`interactions (Table 4). None of the tested mixtures
`showed antagonistic interactions. Against both
`diseases the greatest synergism was observed in
`mixtures of oxadixyl with mancozeb, cymoxanil, or
`phosetyl-Al. Fentin acetate, folpet and thirarn
`showed strong synergism with oxadixyl especially
`against Phytophthora, whereas captan and maneb
`showed strong synergism especially against Plasmo·
`para. For both pathogens propineb, zineb, and
`dichlofluanid showed medium synergistic effects,
`whereas chlorothalonil, captafol and copper·
`components showed weak synergism. Generally,
`the three component mixtures showed synergistic
`effects at least as high as the two-component
`mixtures. In some mixtures it was possible to find
`the optimum ratio; for example it was 1 : 7 for
`oxadixyl/mancozeb, and between 1 : 0'4 and 1 : 1 for
`oxadixyl/ cymoxanil.
`
`

`

`U. Gisi, H. Binder and E. Rimbach
`1lble 3. Fungicidal activity (EC90) and synergism ratio of fungicides tested on potato (Phytophthora
`inf es tans)
`and grape vine (Plasmopara viticola
`) under field conditions
`
`Grape vine/ Plasmopara
`EC90 (g hl-1)
`SR
`th
`ob*
`
`Potato/
`Phytophthora
`EC90 (g hl-1 )
`ob*
`th
`
`SR
`
`Fungicides
`and ratios
`
`Oxadixyl (A)
`
`
`Metalaxyl (B)
`
`Cymoxanil (D)
`
`Mancozeb (E)
`
`Phosetyl-Al (F)
`
`25
`
`350
`
`42
`2 1
`495
`4540
`
`A :E =1 : 7
`
`A :F =1 : 5
`
`E : D = 8 :0·8
`
`E : F = 5 : 7
`
`133 54
`(9+ 45)
`
`
`
`1 · 8
`
`57
`
`34
`(4+ 28 + 2)
`
`655
`2·4 3 1 6 1 75
`(22+ 1 53)
`163 1 3 1 1 · 2
`(16 + 115)
`1 ·4
`40
`(29 + 1 1)
`321 154 2 · 1
`( 1 8 +1 29 + 7)
`191 169 1 ' 1
`(28+ 141)
`394 263 1 · 5
`(20 + 1 0 1 + 142)
`3149 927 3·4
`(877+ 50)
`26o5 334 7·8
`(304+ 30)
`1 308 392 3'3
`( 1 63 + 229)
`* Values are means of four replicates.
`
`Table 4. Synergism ratio of different fungicides with oxadixyl tested under greenhouse conditions
`
`Ratio of
`fungicides
`in mixture Synergism ratiot
`
`with P. infestans P. viticola
`oxadixyl* tomato grape vine
`4·5
`
`Mancozeb
`
`Maneb
`Propineb
`Thiram
`
`3
`7
`2 1
`7
`7
`1
`
`2·9
`3·6
`3 · 1
`2·3
`2·4
`1 ·4
`3·8
`2·0
`2·2
`3 · 1
`4·1
`1 ·5
`
`5'5
`3·6
`3·2
`1 ·4
`o·6
`0·7
`1 · 7
`2·0
`1 ·2
`1
`·5
`3·2
`o·8
`0·5
`0·6-2·9 0·6-2·3
`0 · 7
`2 · 1
`1 ·4
`7·0
`2 · 1
`3·5
`3 · 6
`3 · 2
`2 · 1
`2·8
`3
`4·0
`+ cymoxanil 7 +0·4 3·2
`Mancozeb
`7 + 1 2·0
`+ cymoxanil 4·5+ 0·4 3·0
`Folpet
`+ cymoxanil 1 · 6 +0·4 1 · 1
`Captafol
`Phosetyl-Al
`3 · 1
`5
`3·0
`
`Mancozeb + phosetyl-Al
`7+5
`Dichlofluanid 4
`2·5
`1 · 3
`Chlorothalonil 3
`
`Zineb
`Folpet
`
`5
`5
`2
`3
`4·5
`Captan
`1
`Captafol
`1 ·6
`Cu-components 4
`Fentin acetate
`o·6
`1 ·2
`0·4
`
`Cymoxanil
`
`5·0
`2·6
`1 ·4
`2 · 1
`3·5
`2·0
`1 · 1
`
`* Oxadixyl = 1 .
`
`
`
`t Values are means of at least two experiments.
`
`

`

`D I S C U S S I O N
`
`Most of the fungicide mixtures (about 120) tested
`in these experiments showed clearly syngeristic
`interactions between their components. About
`40 % of the tested mixtures showed slight synergism
`
`(SR < 2), about 20 % medium (SR 2-3), and about
`30 % strong (SR 3-5) synergism. A few mixtures
`Koziol & Witkowski (1982). Nevertheless, it is
`
`resulted in greater synergistic effects, up to SR 7.
`The synergism of all tested fungicide mixtures is
`not as high as that reported for insecticides by
`
`Synergism in fungicide mixtures
`dependent synergism in mixtures of oxadixyl and
`folpet tested on Botrytis cinerea Pers. : Fr. on beans
`and with mancozeb tested on Alternaria solanj
`Sorauer on tomato has also been observed·
`synergism ratios up to 2·8 and 2·0, respectively'.
`were found (Gisi, Binder & Rimbach, unpubl.).
`Since oxadixyl is not active against these diseases
`when tested alone, synergism in oxadixyl mixtures
`is not just a phenomenon affecting oomycetes.
`We have no explanations for the different levels
`of synergism in different mixtures, e.g. the strong
`effects between oxadixyl and mancozeb as compared
`to the rather weak interactions between oxadixyl
`and copper components. f'ifferential permeability
`in the fungus, combined with more or less specific
`fungitoxicity of the partner compound, might
`result in different intensities of interaction. The
`observed synergism is not restricted to phenylamide
`fungicide mixtures ; we also found clear synergism
`between mancozeb and cymoxanil as well as
`mancozeb and phosetyl-Al when tested on Plasma­
`para on grape vine.
`The consistency of the results found both in vitro
`and in vivo raises the question of the basic
`mechanism(s) of the synergism. As stated by De
`
`remarkable to have found synergism ratios that
`allow a two to five fold saving in the quantity of a
`single fungicide when applied in mixture with a
`suitable partner. To our knowledge, these are the
`first published results (besides our own earlier data,
`Gisi et al., 1983) quantifying the level of synergism
`of fungicide mixtures.
`The lack of data in the literature may be
`attributed to limitations of methods which have
`been used. Most authors working on fungicide
`interactions have used the 'cross-paper strip '
`technique (fungicide treated paper on agar) first
`described by Bonifas (1952) and adapted for
`
`fungicides by Corbaz (1963) and De Waard & Van
`
`Nistelrooy (1982). Unfortunately no quantification
`of the interactions is possible with this in vitro test,
`although the visual result reflects exactly the
`calculated isobole diagram. No predictions about
`synergism on plant diseases can be made with this
`method.
`Others (Leroux & Gredt, 1978 ; Rahimian &
`Banihashemi, 1982) have added test compounds
`singly and combined
`into nutrient agar and
`measured the effect of the fungicides on mycelial
`growth of Botrytis or Pythium. Using this method,
`we have clearly shown synergistic effects (SR
`1 ·5-2·7) in mixtures of oxadixyl, mancozeb and/or
`cymoxanil against P. cactorum and P. cinnamomi.
`Similar levels of synergism were recently found
`when different strains of P. nicotianae B. de Haan
`var. parasitica (Dastur) Waterh. and P. capsici
`Leonian were tested with oxadixyl (or other
`phenylamide fungicides) and cymoxanil mixtures
`(A. Garibaldi, Univ. Torino, Italy, pers. comm.).
`Synergism between phenylamide fungicides and
`mancozeb or cymoxanil against Phytophthora may,
`therefore, be a general phenomenon. This sugges­
`tion is further supported by the greenhouse and
`field observations with late blight on potato and
`tomato (P. infestans) presented in this paper and by
`Gisi et al. (1983). Even stronger synergism with
`the same mixtures was found against Plasmopara
`viticola. Synergism was generally less under field
`conditions than
`in the greenhouse. A ratio-
`
`Waard & Van Nistelrooy (1982), the first com­
`
`than fungicidal (Coffey & Young, 1984). If the
`
`ponent may accumulate in fungal cell membranes
`and hence stimulate the passive uptake of the other
`component; or it may inhibit the energy-dependent
`efflux of the second component that consequently
`accumulates in the mycelium and enhances fungi­
`toxicity. The latter possibility may apply especially
`for mixtures with fungicides provoking non-specific
`inhibition of fungal respiration, e.g. many dithio·
`carbamates and phthalimides. These two explana­
`tions for synergistic interactions could also apply to
`mixtures containing phenylamide fungicides. The
`phenylamides are believed to be fungistatic rather
`fungistatic mode of action reflects the specific, but
`never complete, inhibition of RNA polymerases
`(Davidse, Hofman & Velthuis, 1