the effect of simulated rain on folpet and mancozeb residues on grapes and on vine leaves

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THE EFFECT OF SIMULATED RAIN ON FOLPET ANDMANCOZEB RESIDUES ON GRAPES AND ON VINELEAVESPaolo Cabras a , Alberto Angioni a , Vincenzo L. Garau a , Marinella Melis a , Filippo M.Pirisi a , Franco Cabitza b & Mario Pala ba Dipartimento di Tossicologia, Universitàa di Cagliari, Cagliari, Italyb Centro Regionale Agrario Sperimentale, Cagliari, ItalyPublished online: 06 Feb 2007.

To cite this article: Paolo Cabras , Alberto Angioni , Vincenzo L. Garau , Marinella Melis , Filippo M. Pirisi , Franco Cabitza& Mario Pala (2001): THE EFFECT OF SIMULATED RAIN ON FOLPET AND MANCOZEB RESIDUES ON GRAPES AND ON VINELEAVES, Journal of Environmental Science and Health, Part B: Pesticides, Food Contaminants, and Agricultural Wastes,36:5, 609-618

To link to this article: http://dx.doi.org/10.1081/PFC-100106189

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J. ENVIRON. SCI. HEALTH, B36(5), 609–618 (2001)

THE EFFECT OF SIMULATED RAINON FOLPET AND MANCOZEB RESIDUES

ON GRAPES AND ON VINE LEAVES

Paolo Cabras,1,* Alberto Angioni,1 Vincenzo L. Garau,1

Marinella Melis,1 Filippo M. Pirisi,1 Franco Cabitza,2

and Mario Pala2

1Dipartimento di Tossicologia, Universita di Cagliari, Cagliari, Italy2 Centro Regionale Agrario Sperimentale, Cagliari, Italy

ABSTRACT

Artificial rainfalls were used to determine the effect of the amount of the rain-fall and the time interval between pesticide application and rainfall event, onfolpet and mancozeb residues on grapes and vine leaves. Forty-five mm ofrain were administered to the vineyard in different amounts (45; 30�15;15�15�15 mm). Folpet showed good rainfastness on the grapes and on theleaves. A modest decrease was observed only in the experiments that had re-ceived 45 mm of rain at one go. Mancozeb showed a lower rainfastness, sincea portion of the deposit was easily washed off also by a modest rainfall. Thepercentage of this portion was higher in the grapes (38%) than in the leaves(20%). The data obtained in these experiments show that, in the case of folpet,it is not necessary to repeat the treatment when it rains the day after, while it isrecommendable to repeat it in the case of mancozeb.

Key Words: Folpet; Mancozeb; Washoff; Rain; Residues

Copyright � 2001 by Marcel Dekker, Inc. www.dekker.com

*Corresponding author. E-mail: pcabras�unica.it

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INTRODUCTION

Pesticides have two modes of action: the systemic and the contact action.Systemic pesticides penetrate the plant, while nonsystemic pesticides lie on itssurface and, depending on their chemical-physical characteristics, may diffuse intothe epicuticular waxes (1). The behaviour of rainfall shortly after treatment is dif-ferent in these two categories of pesticides, having no effect on the systemic pes-ticide, while in the nonsystemic, the portion of pesticide that is not diffused intothe epicuticular wax may be washed off. Since a loss in active ingredient (a.i.)could cause a loss in efficacy (2– 4) it is important to know the behaviour of thepesticides in response to washoff, especially when it rains shortly after the treat-ment. Among the many factors that could affect washoff are: rain intensity, rainamount, interval of time between treatments and rainfall, commercial formula-tion of pesticides, solubility in water of pesticides, and type of crop. Some papers(5–9) have shown that the effect of the amount of rainfall on pesticide washoff isgreater than that of its intensity. Pesticide rainfastness to washoff is higher whenthe formulate contains surfactants (10 –12).The time between treatments and rain-fall deeply affects the washoff effect, but this depends on the pesticide and/or theformulation (9, 13–17). Downy mildew (Plasmopora viticola) is the most impor-tant cryptogamic disease of vine; it strikes grapes and leaves. Folpet (N-(trichloro-methylthio)phthalimide) and mancozeb (manganese ethylenebis (dithiocarbamate)(polymeric) complex with zinc salt) are two non systemic fungicides with pro-tective action extensively used to control this parasite for their low resistance-generating risk. Experience has taught that are necessary 4 –5 treatments withintervals of 7–8 and 8–10 days for mancozeb and folpet, respectively, when envi-ronmental conditions are favourable to the growth of the disease. Solubility inwater is 0.8 mg/l for Folpet and 6.2 mg/l for mancozeb (18); therefore a plentifulrainfall could washoff pesticides and reduce their efficacy. No studies have beenfound in literature on the dynamics of pesticide washoff by rainfall in vine and, toour knowledge, the whashoff of folpet and mancozeb had not been studied in othercrops as well. In this study some experiments have been carried out to determineby simulated rains the effect of the amount of rain on fruits and vine leaves andthat of the time lapse between treatment and rainfall on the residues of folpet andmancozeb.

MATERIALS AND METHODS

Experimental Preparation

Field Trials

The trials were carried out on a grape vineyard (cv. Chardonnay), located atUssana, near Cagliari, Italy. The plant distance was of 2.5 � 1.5m. A random blockscheme with four replicates for each experiment was used. Every plot consisted of30 plants. Treatments were carried out on June 18, 28, and July 9 and 19, 1999.

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Folpan 80 WDG (80% folpet) and M 70 (70% Mancozeb) were applied at the dosesrecommended by the manufacturers (125 g/hl e 200 g/hl respectively; 10 hl/ha)with a portable motor sprayer (AM150, Oleo-Mac, Reggio Emilia, Italy).

Artificial Rain

An overhead irrigation pipeline was placed above the rows, with sprinklersmounted on alternate sides at 3.0 m intervals, without overlapping any of the areascovered by the sprinklers. The vineyard was divided into three blocks, A, B and C,and 45 mm of rain were administered to each block. On the day after the lasttreatment, 15, 30, and 45 mm of artificial rain were given respectively to blocks A,B, and C. Two days later, a further 15 mm were given to blocks A and B, and afteranother two days yet another 15 mm only to block A. The intensity of the appliedrain was constant at 60 mmh�1.

Sampling

The samples (2 kg of grapes, and 20 mature leaves) were collected before andafter each artificial rainfall, and ten days after the last pesticide application. Mete-orological data were constantly recorded with an AD-2 automatic weather station(SILIMET, Modena), located near the vineyard. During the trials the maximumand minimum temperatures were 32.2 and 16.7�C. No precipitation was registeredduring the experiments.

Pesticides Analysis

Folpet and its metabolite phthalimide were analysed as reported in Cabraset al., (19), while mancozeb was detected following the spectrophotometric meth-ods described by Keppel (20).

Chemicals

The pesticides were all analytical standards. Folpet, mancozeb and vinclo-zolin were purchased from Ehrenstorfer (Augsburg, Germany), and phthalimidefrom Lancaster Synthesis (Muhleim am Main, Germany). Acetone, benzene andpetroleum ether were pure solvents for analysis (Carlo Erba, Milan, Italy), Sodiumchloride, stannous chloride, cupric acetate, and diethanolamine were analyticalgrade reagents (Carlo Erba).

Standard stock solutions (ca. 400 mg/kg) of folpet and phthalimide wereprepared in acetone. For GC analysis vinclozolin (99%) was used as an internalstandard (i.s.) at 0.6 mg/Kg. Working standard solutions were obtained by dilutionwith the extract containing the i.s. of untreated grapes and leaves.

FOLPET AND MANCOZEB RESIDUES 611

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Folpet Analysis

Gas chromatographic (GC) determination. An HRGC Mega 2 (Fison, Mi-lano, Italia), equipped with an ECD 800 detector, a split-splitless injector, an AS800 autosampler, and a HP 3396 A (Hewlett Packard, Avondale, PA, USA) inte-grator, was used. The capillary column was WCOT silica fused column, CP Sil8CB low bleed/MS (30 m � 0.25 mm i.d., 0.10 mm, Chrompack, Middelburg, TheNetherlands). The injector and detector were operated at 250� e 300�C respectively.The sample (2ml) was injected in the split mode (1 :10), and the oven temperaturewas programmed as follows: 110�C for 1 min, raised to 150�C (5�C � min), raisedto 220�C (25�C � min), and held for 3 min. Helium was the carrier gas (100 kPa)and nitrogen was the make-up gas at 150 KPa . Calibration graphs were con-structed with the internal standard method, by plotting height against concentra-tions. A good linearity was achieved in the range 0 –5 mg/Kg, with correlationcoefficients of 0.9992 and 0.9995.

Extraction Procedure

Grapes. A 10 g aliquot of homogenised samples was weighed in a screw-capped 40 ml tube. Ten ml of extracting solvent (acetone/petroleum ether; 50/50)were added, and the resulting mixture was agitated in a rotary shaker for 30 min.The phases were allowed to separate, and the organic layer was injected for GCanalysis.

Leaves. A 2 g aliquot of chopped samples (chopping knife) was weighed ina screw-capped 40 ml tube. Twenty ml of extracting solvent (acetone/petroleumether; 50/50) were added, and the resulting mixture was agitated in a rotary shakerfor 30 min. The phases were allowed to separate, and 1ml of the organic layer wasdiluted with 4 ml of the extracting solvent and the resulting mixture was injectedfor GC analysis. Cleanup of grapes and leaves was not necessary because therewere no interference peaks (Fig.1).

Recovery Assay

Samples of untreated leaves were fortified with 50 and 300 mg/kg of folpetand subjected to the extracting procedure. The recoveries obtained from four rep-licates ranged between 90 and 101% with a maximum coefficient of variation(CV) of 11%.

Mancozeb Analysis

The dithiocarbamate in the samples (10 g of grapes and 2 g of leaves) washydrolysed in CS2 in acid ambient and in the presence of stannic chlorine. Quan-

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titative determination of the coloured complex between CS2 and Cullen reagent(cupric acetate and diethanolamine) was made by spectrophotometry at a wave-length of 435 nm. The data are reported as mg/kg of mancozeb (CS2 � 1.78). Therecoveries obtained from four replicates at 10 mg/kg for grapes and at 300 mg/kgfor leaves ranged between 82 and 111% with a maximum coefficient of variation(CV) of 13%.

Statistical Analysis

Analysis of variance (ANOVA) was carried out with the STATISTICA pro-gram, using Turkey’s test at P � 0.05.

Figure 1. Chromatograms of folpet (2) and its metabolite phthalimide (1) on grapes and leavesunder the operating conditions described under Experimental preparation: c � control ( untreatedsample); s � samples of grapes and leaves after 10 days treatment at 45 mm rainfall.

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RESULTS AND DISCUSSION

Three rain levels were used: plentiful (15 mm), high plentiful (30 mm) andvery high plentiful (45 mm) (referred to Italian environmental conditions). In thefirst experiment with plentiful rain (15 mm), following the first rain there weresimulated two other rains with 15 mm spaced two days apart. In the second ex-periment with high plentiful rain (30 mm), a second rain with 15 mm followed twodays later. These experiments were carried out to evaluate the effect on pesticideresidues of the time lapsed between treatment and rainfall. In the third experiment,to simulate extreme conditions, 45 mm of rain were administered all at once. Veryhigh rain intensity (60 mm/h) were used, besides, to set conditions of maximumpotential washing.

Folpet.- a) Grapes. The average folpet residue in grapes after the first artifi-cial rain (Table 1) was unchanged in the plots that received 15 and 30 mm of rain,while it decreased by about 22% in those receiving 45mm of rain. The metabolite,phthalimide, that was present with about 2% of the active ingredient (a.i.), showeda similar behaviour to folpet. No washoff effect was observed in the other plotsafter the second rain. The same behaviour was observed after the third rain. Afterten days the residues found in grapes in all three experiments were not statisticallydifferent. A previous paper (21) showed that folpet had a limited diffusion into theepicuticular wax and that it was almost all on the surface of the fruit. Since therewas only a little washoff after 45 mm administered at one go, the formulation mayhave increased the rainfastness of the a.i. in the fruit, preventing washoff.

b) Leaves. The effect of the rain on the leaf residues was similar to that foundon the grapes (Table 2). A loss of about 24% was found only in the plots that hadreceived 45 mm at one go. Considering that the standard deviation due to samplingand analysis was about 10%, the loss due to washoff may be considered small. Therate of decrease of folpet, calculated according to a pseudo-first-order kinetic, wasslower in the leaves than in the grapes, with a half time of 13.6 days versus8.6 days. These data show that is not necessary to repeat treatments with folpetwhen it rains after its administration because this active ingredient is not washed-off either with high plentiful and with intense rain.

Mancozeb. a) Grapes. After the first rain, all plots showed a similar decreasein residues (about 38%), which was unrelated to the amount of rain in the differentexperiments. After the second and third rain, no decrease in residues was observedin any of the experiments. These data show that about of the residues was lightly1

bound to the fruit surface and easily washed off by rain, while the remaining were2

sufficiently bound and therefore could not be washed off. Unlike folpet, the resi-dues of mancozeb in the grapes did not degrade after the pesticide application.

b) Leaves. After the first rain the residues decreased by about 20% in allexperiments, independently of the amount of rainfall (Table 2). Taking into ac-count the variability of the data from sampling and analysis, the residue decreasein leaves was modest, and was about half the decrease observed in the grapes.The second and the third rain did not cause any decrease in the pesticide resi-

614 CABRAS ET AL.

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dues. The comments on the rainfastness of mancozeb in the grapes are also validfor the leaves. While in the fruit mancozeb decreased only by effect of washoff, inthe leaves it was also affected by degradation (about 50% in a week). The rapiddegradation of mancozeb in leaves gives an elucidation of necessity, proved byexperience, of treatments with shorter intervals (7–8 days) as compared with fol-pet (8–10 days). The levels of mancozeb left on grapes after the first rainfall couldnot be sufficient to protect grapes from downy mildew attacks and therefore shouldbe recommendable to repeat the treatment after rains near to treatment.

CONCLUSIONS

Since the deposit of folpet on the grapes and on the leaves showed goodrainfastness, a modest decrease was observed only in the experiments that hadreceived 45 mm of rain at one go. This shows that since that folpet does not pene-trate into the epicuticular strata, and is sufficiently bound to the surface, probablydue to the action of the surfactant, it is not affected by rainfall, which usually fallsduring the viticultural season in Italy. Mancozeb showed a different behaviour,since a portion of the deposit showed mild rainfastness and was easily washed offalso by a modest rainfall. The percentage of this portion was higher in the grapesthan in the leaves. This behaviour could be due to the fact that the composition ofepicuticular wax of the fruit is different from that of the leaves1. The data obtainedin these experiments show that, in the case of folpet it not necessary to repeat thetreatment when it rains the day after, while it is recommendable to repeat it in thecase of mancozeb.

REFERENCES

1. Kirkwood, R.C. Uptake and movement of herbicide from plant surfaces and the ef-fects of formulation and environment upon them. In Pesticide on plant surface Ed.H.J. Cottrell J. Wiley & Sons, 1987, 1–25.

2. Reddy, K.N., Locke, M.A., Bryson, C.T. Foliar washoff and runoff of lactofen, nor-flurazon, and fluometron under simulated rainfall. J. Agric. Food Chem. 1994, 42,2338–2343.

3. Reddy, K.N., Locke, M.A., Howard, K.D. Bentazon spray retention, activity and fo-liar washoff in weed species. Weed Technol. 1995, 9, 773–778.

4. Reddy, K.N., Locke, M.A. Imazaquin spray retention, foliar washoff and runoff lossesunder simulated rainfall. Pestic. Sci. 1996, 48, 179–187.

5. Willis, G.H., Mc Dowell, L.L., Meyer, L.D., Southwick, L.M. Toxaphene washofffrom cotton plants by simulated rainfall. Trans. Am. Soc. Agric. Eng. 1982, 25, 642–646.

6. Willis, G.H., Mc Dowell, L.L., Smith, S., Southwick, L.M. Permethrin washoff fromcotton plants by simulated rainfall. J. Environ Qual. 1986, 15, 116 –120.

7. Willis, G.H., Smith, S., Mc Dowell, L.L., Southwick, L.M. Carbaryl washoff fromsoybean plants. Arch. Environ Contam. Toxicol. 1996, 31, 239–243.

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8. Mc Dowell, L.L., Willis G.H., Southwick, L.M., Smith, S. Methyl parathion and EPNwashoff from cotton plants by simulated rainfall. Environ. Sci. Technol. 1984, 18,423– 427.

9. Pick, F.E., Van Dyk, L.P., De Beer, P.R. The effect of simulated rain on deposits ofsome cotton pesticides. Pestic. Sci. 1984, 15, 616 –623.

10. Phillips, F.T., Gillham, E.M. Persistence to rainwashing of DDT wettable powders.Pestic. Sci. 1971, 2, 97–100.

11. Coble, H., Brumbaugh, E.H. Effect of nonionic surfactants on the rainfastness ofgliphosate. Pestic. Sci. 1993, 38, 247–250.

12. Sandbrink, J.J., Dayawon, M.M. and Kassebaumm J.W. Non-silicone-based surfac-tants as gliphosate rainfastness adjuvants. Pestic. Sci. 1993, 38, 272–273.

13. Smith, C.N., Payne, W.R., Mulkey, L.A., Benner, J.E., Parrish, R.S., Smith, M.C. Thepersistence and disappearance by washoff and dryfall of methoxychlor fro soybeanfoliage. J. Environm. Sci. Health B 1981, 16, 777–794.

14. Mayo, Z.B. Influence of rainfall and sprinkler irrigation on the residual activity oninsecticides applied to corn for control of adult western corn rootworm (Coleoptera:Chrysomelidae). J. Econ. Entomol. 1984, 77, 190 –193.

15. Mc Dowell, L.L., Willis, G.H., Smith, S., Southwick, L.M. Insecticide washoff fromcotton plants as a function of time between insecticide application and rainfall. Trans.Am. Soc. Agric. Eng. 1985, 28, 1896 –1900.

16. Mc Dowell, L.L., Willis, G.H., Southwick, L.M., Smith, S. Fenvalerate wash-off fromcotton plants by rainfall. Pestic. Sci. 1987, 21, 83–92.

17. Willis, G.H., Mc Dowell, L.L., Smith, S., Southwick, L.M. Foliar washoff of oil-applied malathion and permethrin as a function of time after application. J. Agric.Food Chem. 1992, 40, 1086 –1089.

18. The Pesticide Manual,. Ed. Tomlin, 11th Edition, B.C.P. C., Farnham, UK, 1997,614, 761.

19. Cabras, P., Angioni, A., Garau, V.L., Melis, M., Pirisi, F.M., Farris, G., Sotgiu, C.,Minelli, E.V. Persistence and metabolism of folpet in grapes and wine. J. Agric. FoodChem.1997, 45, 476 – 479.

20. Keppel, G.E. Collaborative study of the determination of dithiocarbamate residues bya modified carbon disulfide evaluation method. J.A.O.A.C. 1971, 54, 528–532.

21. Cabras, P., Angioni, A., Caboni, G., Garau, V. L., Melis, M., Pirisi, F. M, Cabitza, F.Distribution of folpet on the grape surface after treatment. J. Agric. Food Chem. 2000,48, 915–916.

Received January 29, 2001

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the effect of simulated rain on folpet and mancozeb residues on grapes and on vine leaves

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