Efficiency and safety assurance of six fungicides applied on post

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Food Safety and Toxicology

Efficiency and safety assurance of six fungicides applied on post-harvest cabbages stored at natural environment Guopeng Miao, Juan Han, Tao Ye, Zhina Chen, and Kegui Zhang J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.8b03910 • Publication Date (Web): 01 Oct 2018 Downloaded from http://pubs.acs.org on October 6, 2018

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Journal of Agricultural and Food Chemistry

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Efficiency and safety assurance of six fungicides applied on post-harvest cabbages

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stored at natural environment

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Guopeng Miao, Juan Han∗, Tao Ye, Zhina Chen, Kegui Zhang

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Department of Bioengineering, Huainan Normal University, Huainan, Anhui Province

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232038, China

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ABSTRACT: Post-harvest disease is a major factor in the limited shelf life of many

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fruits and vegetables, and it is often managed by using fungicidal spraying or soaking.

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In this study, we first tested the efficiency of six common fungicides on post-harvest

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head cabbage (Brassica oleracea var. capitata) against Botrytis cinerea. Afterward,

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the elimination abilities of these six fungicides on different layers of cabbage heads

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were examined, and the effects of the household processes on residue removal were

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evaluated. Results showed that very low contents of residue reached the inner layers,

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and that peeling the three outmost leaves of cabbage could eliminate most of the

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investigated fungicides. All six fungicides disappeared during washing, stir-frying, or

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boiling, among which cyprodinil was the easiest to be eliminated. Furthermore, the

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combined processes reduced the residues below the limits of quantification for all the

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six investigated fungicides, even after 2 days of spraying.

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KEYWORDS: household processing; cabbage; fungicides; post-harvest; layers

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∗

Corresponding author. Tel.: +86 05546641722; fax: +86 05546863183. E-mail addresses: [email protected] (Juan Han).

ACS Paragon Plus Environment


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INTRODUCTION

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Cabbage is an economically important crop and a major table vegetable in most

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countries of the temperate zone1. In China, cabbage is a leading commercial crop that

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is grown in open fields and in protected environments, such as greenhouses and

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plastic sheds, for more than one season in a year2. Post-harvest disease is a major

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factor in the limited shelf life of fruits and vegetables, including cabbages. The

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principal causal organisms are fungi that may contaminate produce with mycotoxins,

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in addition to causing rot. Fungal post-harvest diseases, especially by Peronospora

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parasitica, Sclerotinia sclerotiorum, and Botrytis cinerea, are managed by various

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controlled environments, chemical measures, and biocontrol agents. Preservation of

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cabbages by using artificial conditions, such as low temperature (0 °C to 1 °C), high

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humidity (as near saturation as possible without accumulation of free water), and

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composition-optimized atmosphere, has been adopted by certain commercial

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cabbage-storing operations in developing countries long ago3; however, the cost

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remains too high for developing countries like China, and the method of choice in

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many cases is fungicidal sprays or dips4.

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Worldwide, the most commonly applied fungicides on cabbage include

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azoxystrobin5,

tebuconazole6, carbendazim7, chlorothalonil8, cyprodinil3, and

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fluazinam9. Azoxystrobin (CAS No.131860-33-8) is a broad-spectrum, preventative

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fungicide with systemic properties. It inhibits spore germination and mycelial

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growth10 and shows good efficacy against mold disease in cabbage6. Tebuconazole

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(CAS No.107534-96-3) is a broad-spectrum triazole fungicide for controlling many


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plant diseases by inhibiting the biosynthesis of ergosterol to prevent fungal mycelium

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development11. It is a systemic fungicide with preventive, curative, and eradicative

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actions and is used to control grey mold in cabbage. Carbendazim, a systemic

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broad-spectrum benzimidazole fungicide, is widely used to control powdery mildew,

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anthracnose, and phytophthora blight in melons7. Chlorothalonil (CAS No. 1897-45-6)

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is an organic compound mainly used as a broad-spectrum, nonsystemic fungicide,

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with other uses, such as wood protectant, pesticide, and acaricide, and for controlling

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mold, mildew, bacteria, and algae8. Cyprodinil (CAS No. 121552-61-2) is a systemic

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fungicide that inhibits methionine biosynthesis12. Fluazinam (CAS No. 79622-59-6) is

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a protective fungicide with little curative or systemic activity and can effectively

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control clubroot disease in Chinese cabbage13. However, pesticides may cause adverse

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human health or environmental effects depending on exposure levels14. For safety and

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efficiency, the dosage and application duration of pesticides should be carefully

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managed. The maximum residue limits (MRLs) of azoxystrobin, tebuconazole,

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carbendazim, chlorothalonil, cyprodinil, and fluazinam in head cabbages are

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prescribed as 5, 0.7, 0.1, 0.6, 0.7, and 0.01 mg/kg, respectively, by the European

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Union. Among these six fungicides, only tebuconazole is prescribed in the Chinese

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food safety standards (GB 2763-2016), with an MRL of 1 mg/kg.

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Besides good pesticide management, household processing, such as peeling,

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washing, and cooking, which lead to significant reduction of pesticide residues15, 16,

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could provide further safety assurance. Peeling could remove pesticides that have

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penetrated the cuticles of the fruits or vegetables, such as apples, peaches, and



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tomatoes17. A previous study has observed a significant reduction of residue in the

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core and middle side leaves of cabbage18. However, whether this convenient and

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effective home process could be effective on pesticide removal for multi-layered

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vegetables, such as cabbages and onions, remains unclear. Washing, stir-frying and

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boiling are common cooking methods for cabbage worldwide; however, the effects of

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these cooking methods on the removal of pesticide residues on cabbages remain

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largely unexplored.

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In this study, we first tested the efficiency of the six fungicides on post-harvest

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head cabbage (Brassica oleracea var. capitata) against a common pathogen, Botrytis

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cinerea. Afterward, the elimination of six fungicides on different layers of

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post-harvest head cabbage was examined, and the effects of washing, boiling, and

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stir-frying on residue removal were evaluated. The results of this study can guide

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cabbage storage strategies, home cooking methods, and industrial deep processing,

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especially for developing countries.

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MATERIALS AND METHODS

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Chemicals and reagents

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Certified pesticide standards were purchased from National Standards of

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Material Resources Network (Beijing, China). The physicochemical properties of the

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pesticides are listed in Table 1. Formulations of pesticides were purchased from

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FengNong trade co., LTD (Shouguang, China).

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Dichloromethane, acetonitrile, anhydrous magnesium sulphate (MgSO4), and

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sodium chloride were AR grade and purchased from China National Pharmaceutical


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Group (Beijing, China). The adsorbent of primary secondary amine (PSA, 40 µm

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diameter) was obtained from Anpel (Shanghai, China). Ultra-pure water was obtained

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from a Milli-Q system (Bedford, MA, USA).

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Preparation and application of pesticides

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The included pesticides were Dacotech (75% chlorothalonil WP), Amistar (25%

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azoxystrobin SC), Derosal (50% carbendazim WP), Shirlan (50% fluazinam SC),

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Unix (50% cyprodinil WDG), and Horizon (43% tebuconazole SC). All products

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were applied at the dosage recommended by regulation guidelines (150 g of Dacotech,

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30 mL of Amistar, 100 g of Derosal, 30 mL of Shirlan, 80 g of Unix, and 15 mL of

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Horizon per 30 L).

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Cabbages that were grown for about 4 months were collected from an organic

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farm in Huainan City (China) on the end of November. After being separately placed

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on a steel rack in a dark room, whole fresh white cabbages heads (without loosely

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connected leaves) were sprayed with 10 mL working solution of each pesticide twice.

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The storage duration was from the beginning of December to the end of March in the

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next year. On the end of January (two months after collection), another round of

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spraying was conducted with the same dose. During storage, natural temperature and

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atmosphere were retained.

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Fungal infection and disease assessment

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Inoculum of B. cinerea was produced on potato dextrose agar (PDA) in 20-cm

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petri dishes. Four mycelial disks (8 mm diameter) from the edge of an actively

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growing colony was transferred to fresh PDA and incubated under fluorescent light



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for 7 days to produce spores. PDA plates were flooded with sterile distilled water and

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rubbed with a sterile camel-hair brush. The spore concentration was adjusted to 104

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cfu/mL and sprayed on the cabbage heads (10 mL per head) that had been stored for 2

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d with or without fungicide treatment.

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After 4 months of storage, the infected layers on the surfaces of the cabbage

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heads were evenly spread and photographed. The area percentage covered by fungal

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growth was calculated using ImageJ (NIH, USA) by manually integration.

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Dissipation of fungicides

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Five cabbage heads for each pesticide or control (water) were sampled after 2, 7,

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14, 28, and 56 days of spraying. The outermost three leaves and remaining inner

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leaves were separated and observed for pesticide content. Each of these different parts

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was chopped into about 2×2 cm pieces and mixed well to eliminate their position

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differences before extraction and quantification of fungicides. Exponential function of

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the data was stimulated and the half-life of dissipation was estimated using

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“Exponential Decay 1” in Nonlinear Curve Fit of Origin 8.0 (OriginLab,

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Massachusetts, USA).

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Household processing

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Washing

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Two days after the first round of fungicide spraying, cabbage heads were rinsed

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for 30 s with 500 mL running water (25 °C), warm water (60 °C), or dishwashing

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detergent (Liby enterprise group co., LTD, China, 10-fold diluted with water), and

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each washing was repeated thrice. Afterward, the outermost leaf from each cabbage


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head was sampled and analyzed.

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Stir-frying and boiling

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To analyze stir-frying and boiling effects on removal of fungicides, freshly

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collected cabbage heads were cut into about 2×2 cm pieces and soaked in fungicide

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working solutions for 5 min and dried in room temperature for 2 days. Samples (30±1

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g) were put in an electric frying pan with 5 mL of preheated corn oil at 220 °C to

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250 °C. The samples were stirred evenly and vigorously for 2, 4, and 6 min. Moreover,

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samples mixed with the equal volume of oil but without stir-frying treatment were

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used as the control. For boiling experiments, fungicide-soaked cabbage pieces (30±1

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g) were put in a pot with 500 mL boiling water and boiled for 2, 4, and 6 min.

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Fungicides extraction and quantification

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Extractions

of

chlorothalonil,

carbendazim,

tebuconazole,

azoxystrobin,

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fluazinam, and cyprodinil in cabbage samples were carried out according to the

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original buffered QuEChERS method19. All the samples were homogenized before

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weighing in order to avoid errors caused by different original locations of leaves.

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Moreover, because we used little oil in stir-frying, the cabbage pieces were

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homogenized with oil before further extraction. Soup materials were extracted using

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ethyl acetate (for tebuconazole and fluazinam) or dichloromethane (for other

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fungicides). The anhydrous extract was evaporated on a rotary evaporator, and then a

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solvent exchange was performed with methanol. The extract was concentrated to a

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final volume of 1 mL and filtered before further analysis through UPLC-MS/MS.

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Chromatographic separation was achieved using a Waters Acquity Ultra



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Performance Liquid Chromatography (UPLC) equipped with a Waters Acquity UPLC

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HSS T3 column (1.8µm, 2.1 x 100 mm) at constant column temperature of 50 °C.

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UPLC-MS/MS mobile phase A was 0.1% formic acid in water by volume and mobile

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phase B was 0.1% formic acid in methanol by volume. The gradient program was as

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follows: 90% A was hold for 0.5 min; a linear gradient was established from 90% to 2%

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A over 7 min, followed by a holding period of 3 min. The concentration was returned

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to 90% A over 0.5 min, with a holding period of 2 min (13 min total run time). A flow

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rate of 0.3 mL/min and an injection volume of 1 µL were used. MassLynx was used

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for instrument control and QuanLynx was used for data analysis.

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For the MS/MS analysis, a triple quadrupole mass spectrometer (Waters Xevo

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TQ Detector) equipped with an ESI source in positive ionization mode was employed

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for analysis . The source temperature was set to 150 °C and desolvation temperature

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was set to 450 °C, with the gas flow (N2) rate of 850 L/h. Cone and collision gas

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flows were set at 25 L/h and 0.25 mL/min, respectively. Based on the selection of the

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precursor ions in full scan mode, two product ions with the highest sensitivity and

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optimal selectivity were selected for the qualification of each compound in the

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multiple reaction monitoring (MRM) parameters. The ion with the higher response

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was used for quantification. MS/MS parameters included retention time, MRM

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transitions, and collision energies, and were optimized individually for the six target

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compounds, as summarized in Table 1. Typical chromatograms are presented in

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Figure S1.

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For recovery assays, untreated cabbage samples were fortified with known


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amounts of pesticides (1.00, 0.50, and 0.25 mg/kg) and processed according to the

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above procedure. Every recovery was done in four replicates.

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Statistical Analysis

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All the data presented were the mean values of three replicates and statistically

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analyzed via one-way ANOVA and Duncan’s Multiple Range Test (DMRT) using the

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Statistical Package for the Social Sciences (SPSS, IBM, USA). All experiments were

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repeated twice.

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RESULTS

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Method validation

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The recoveries of analytical methods were 72.3%−109.0% for the residue

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determination of six fungicides on cabbage. The limits of quantification (LOQ) were

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considered to be the concentration that was produced from the signal to-noise (S/N)

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ratio of 10, and LOQ was estimated from the chromatogram corresponding to the

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lowest point used in the matrix-matched calibration. In this work, the LOQ was

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estimated to be 5–10 µg/kg (Table 2).

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Effects of fungicides spraying on the infection of B. cinerea

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After 4 months of storage, the percentages of infection by B. cinerea were

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recorded (Figure 1). All six fungicides showed protective effects against the pathogen.

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Lowest infections were observed on cabbages treated with cyprodinil, carbendazim,

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and fluazinam, with protection efficiencies of 85.96±7.70%, 83.32±8.35%, and

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80.45±6.92%, respectively. Though statistically significant, the protection efficiency

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of azoxystrobin was only 35.23±4.21%.



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Dissipation of fungicides

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To investigate the dissipation of fungicides in cabbage, fungicide residues on

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each of the outermost three leaves and inner leaves were measured along the storage

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duration (Figure 2). Results showed that most of the fungicides remained on the

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outermost three layers and low fungicide residues were observed in the inner layers.

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After 2 days of spraying, the residues of four fungicides, namely, chlorothalonil,

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tebuconazole, azoxystrobin, and cyprodinil, in the inner layers were already lower

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than their MRLs. However, the residues of carbendazim and fluazinam took longer to

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decrease under their MRLs at 17.77 and 17.17 days, respectively, according to the

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dissipation curve function.

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The residues in all the different layers decreased with time. Different fungicides

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showed slightly different distribution patterns and dissipation rates. As shown in

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Table 3, significantly higher residue levels were detected on the outer layers of

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cabbages sprayed with chlorothalonil and less in the inner layers. While, more

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residues were found in the third leaf and inner layers for azoxystrobin compared with

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chlorothalonil. Other fungicides showed similar distribution patterns with values

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between chlorothalonil and azoxystrobin. On the first leaf, cyprodinil, azoxystrobin,

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and fluazinam showed faster rates of dissipation with half-life values of 4.94, 6.10,

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and 7.25 days, respectively (Table 4). The dissipation rate in the inside leaves was

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significantly lower than that of outer layers. The largest difference was observed on

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cyprodinil, in that the half-life on the third leaf was 3.09-fold longer than the first leaf,

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whereas this fold was 1.71, 2.14, 2.46, 1.95, and 2.11 for chlorothalonil, tebuconazole,


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azoxystrobin, carbendazim, and fluazinam, respectively.

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The effects of washing on fungicide removal

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Washing is the most common form of processing and is a preliminary step in

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both household and commercial preparations. To assess the effects of washing on

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fungicide residue, cabbage heads that were sprayed with fungicides for 2 days were

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rinsed with water, hot water, and detergent (Figure 3). Washing with detergent

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showed significantly better performance for chlorothalonil, cyprodinil, and fluazinam

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than other washing methods and the control, and resulted in 74.75%, 74.90%, and

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83.88% reductions. Moreover, significant reduction of residues was observed on

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carbendazim with efficiencies of 79.91% and 83.99% for hot water and detergent,

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respectively. For tebuconazole and azoxystrobin, a little more than a half of the

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residues were washed away by hot water or detergent. Detergent showed high

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efficiency, but did not reduce the residue of fungicides below their MRLs, except for

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azoxystrobin, of which the MRL is so high that even the contents of control were

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already lower than MRL.

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The effects of stir-frying on fungicide removal

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A gradual reduction of residues was noted along the time of stir-frying for all the

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tested fungicides (Figure 4). Fungicides with high logKow values, such as cyprodinil,

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tebuconazole, chlorothalonil, and fluazinam, showed higher reductions under

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stir-frying compared with fungicides with low logKow values, including azoxystrobin

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and carbendazim (59.44% and 55.29%, respectively). The highest reduction of 98.55%

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was observed in cyprodinil after 6 min of stir-frying, followed by tebuconazole



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(84.13%), chlorothalonil (74.34%), and fluazinam (72.71%).

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The effects of boiling on fungicide removal

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Figure 5 show the residue magnitudes of fungicides before and after boiling.

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High reduction of residues was observed for fluazinam and cyprodinil with reduction

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percentages of 83.31% and 81.00%, respectively, followed by those of tebuconazole

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(77.34%) and carbendazim (74.13%). Chlorothalonil and azoxystrobin were more

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resistant than other fungicides, with reduction percentages of 50.41% and 44.42%,

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respectively. Residues that transferred from plant tissue into soup were higher for

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azoxystrobin and carbendazim than those of other fungicides (Figure 5), which may

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be associated with their low values of logKow and high solubility in water.

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DISCUSSION

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Post-harvest disease is a major factor in the limited shelf life of many fruits and

252

vegetables, and it is managed in many cases by fungicidal spraying or soaking. In this

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study, the residual behaviors of six fungicides applied on post-harvested cabbage were

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described and the effects of household processing on residue removal were

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investigated. To reduce the total cost of storage, natural storage environment was used

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in this study. The temperature of Huainan City in each month is almost the same with

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that of Mainland China (data from China Meteorological Bureau); thus, this natural

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storage condition should also be applied most in China.

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Experimental results showed that very low contents of residues were detected in

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the inner layers. Apparently, diffusion between leaf gaps could result in this

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accumulation gradient between leaves at different depths. However, this simple


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diffusion could not explain the different distribution patterns showed by different

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fungicides. Moreover, this phenomenon may be associated with the capability of

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translocation20. For example, chlorothalonil is a non-systemic fungicide; thus, its

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residues accumulated more on the surface and were barely translocated into inner

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layers. However, this interpretation does not work in every case. Having a systemic

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property, tebuconazole did not translocate into the cabbage. Foliar penetration ratio

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may be another explanation for this phenomenon, which may be further influenced by

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different formulations or physicochemical properties of the fungicides21. Furthermore,

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with tebuconazole as an example, high water solubility may prevent the passing

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through of the residues to the plasma of cabbage cells.

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The dissipation rate of pesticides is related with many factors22. In this study,

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these factors mainly include volatilization and chemical and microbial decomposition.

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In general, the half-life values of investigated fungicides were longer compared with

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other researches that were used on leaves of various species22. The average

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temperatures in December, January, February, and March in Huainan City are 5.0 °C,

277

2.6 °C, 4.5 °C, and 9.1 °C, respectively, and this cold storage condition could reduce

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biological and chemical reaction activities and thus reduce dissipation rates.

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Cyprodinil showed the fastest degradation rate among other fungicides, with a

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half-life of 4.94 days, which was not only due to its easy evaporation but also its

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enzymatic degradation23.

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Residues in the inner leaves took significantly longer to degrade, and this

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elongation effects seems to be more significant on fungicides with short half-life



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values on the surface, such as cyprodinil, azoxystrobin, and fluazinam, possibly

285

because of the prevention of evaporation and protection from microbial degradation

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provided by cabbage leaves.

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Fungicide dissipation experiments proved that peeling the outmost three layers

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could significantly reduce residue and improve food safety. Among the six

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investigated fungicides, even after short periods of spraying (2 days), peeling could

290

lower the residues of four fungicides (chlorothalonil, tebuconazole, azoxystrobin, and

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cyprodinil) under their MRLs. Like peeling, washing is another convenient household

292

and industrial process. Generally, fungicides with higher water solubility are more

293

easily removed by washing with water and hot water24, 25. In our study, carbendazim,

294

which has a low logKow of 1.52 and high water solubility at 29 mg/L, exhibited

295

highest reduction of 68.65%. However, high water solubility does not have an

296

influence on the effectiveness of washing in all cases. For tebuconazole, though it has

297

high water solubility (36 mg/L), it also has high lipophilicity with logKow of 3.7.

298

These properties may help tebuconazole dissolve in the cuticle and penetrate into the

299

first leaf of the cabbage (retained there and less translocated to inner leaves as

300

discussed above), thereby making washing with water or detergent have relatively

301

little effect. For fungicides with high value of logKow and low water solubility, such

302

as fluazinam, washing with detergent performed significantly better than water.

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All six fungicides were removed during stir-frying or boiling. After 6 min of

304

stir-frying, fungicide residues were reduced by between 56.6% for chlorothalonil and

305

98.5% for cyprodinil (Figure 4). This phenomenon was similar with results in


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previous works, and we speculated that the residues with high logKow were more

307

easily transferred from cabbage surface into the oil, where the temperature was

308

higher25,

309

volatilization, hydrolysis, or other chemical degradation and thus reduce residue

310

levels27-29, which was proven effective in our study. The residues of fungicides with

311

low melting temperature and/or high values of logKow, such as fluazinam and

312

cyprodinil, were reduced more than the other fungicides. Residues that were

313

transferred to the soup showed slower dissipation rates for chlorothalonil and

314

azoxystrobin, relative to other fungicides, of which the mechanism was unclear for us.

315

Among the six fungicides, cyprodinil, carbendazim, and fluazinam showed

316

higher protection efficiencies. Among these three fungicides, cyprodinil was the

317

easiest to be eliminated. However, combined processes (peeling, washing, and then

318

stir-frying or boiling) could reduce the residues below the LOQs for all the six

319

investigated fungicides, even after 2 days of spraying (data not shown).

26

. Moreover, boiling involving washing and heating can increase

320

In conclusion, certain fungicides can protect post-harvest head cabbages against

321

fungal pathogen efficiently, and will be eliminated to safety levels with proper

322

household processes.

323

ACKNOWLEDGEMENTS

324

This study was supported by Educational Commission of Anhui Province of

325

China (KJ2016A668), the National Natural Science Foundation of Anhui Province

326

(1708085QC52).

327

SUPPORTING INFORMATION



328

Typical UPLC-MS/MS chromatograms in MRM acquisition mode are presented

329

in Figure S1. This material is available free of charge via the Internet at

330

http://pubs.acs.org.

331

CONFLICT OF INTERESTS The authors declare that there is no conflict of interests.

332 333

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Page 21 of 32


423

Figure captions

424

Figure 1. Efficiency of six fungicides applied on post-harvest cabbages against B.

425

cinerea. The area percentage covered by fungal growth on the surface of cabbage was

426

measured after 4 months of storage.

427

Figure 2. Dissipation of fungicides in different layers of cabbages during the 4

428

months of storage.

429

Figure 3. Residues of six fungicides after washing.

430

Figure 4. Residues of six fungicides after stir-frying.

431

Figure 5. Residues of six fungicides in cabbages and soup after boiling.

432



Page 22 of 32

433

Tables

434

Table 1. UPLC-MS/MS parameters and physicochemical properties of six fungicides

435

used in this study UPLC-MSMS parameters

Physicochemical properties

Retention

Precursor

Product

Collision

Log

Water

Melting

time

ion

Ion

energy

Kow*

solubility

point

(mg/L) #

(°C)

Fungicide

(eV) Chlorothalonil

1.78

244.9

181.9

30

3.05

0.81

252

Azoxystrobin

6.01

404.1

372.1

14

2.50

6

116

Carbendazim

5.43

192.0

132.0

30

1.52

29

302

Fluazinam

8.32

462.5

397.9

17

4.1

0.135

116

Cyprodinil

6.86

225.8

107.9

25

3.59

13

75.9

Tebuconazole

9.87

308.1

70.1

22

3.7

36

105

436 437 438

*

: Octanol/Water partition coefficient, used as a measure of molecular

lipophilicity; #

: 20°C in water with a neutral pH of 7.0.

439


Page 23 of 32


440

Table 2. Recoveries and LOQs of six fungicides used in this study. Fungicide

Fortified level (mg/kg) Average recovery±RSD LOQ (%)

Chlorothalonil 0.25

Azoxystrobin

Carbendazim

Fluazinam

Cyprodinil

Tebuconazole

(µg/kg)

88.5±5.3

0.5

90.1±3.4

1.0

92.6±4.7

0.25

85.5±6.3

0.5

92.3±5.8

1.0

90.8±2.7

0.25

78.8±5.1

0.5

86.4±4.7

1.0

88.4±6.3

0.25

95.3±5.4

0.5

99.7±7.5

1.0

101.2±5.5

0.25

84.5±2.5

0.5

90.0±3.4

1.0

91.8±3.0

0.25

96.6±6.7

0.5

100.2±3.8

1.0

98.7±4.4

441


10

5

10

5

5

5


442

Page 24 of 32

Table 3. Distribution of fungicide residues in different layers after 2 d of spraying. Distribution of fungicide residues in different layers (%) Fungicides First leaf

Second leaf

Third leaf

Inner leaves

Chlorothalonil

63.78±3.21 a

27.35±4.78 a

8.38±3.27 b

0.50±0.64 c

Tebuconazole

59.16±6.55 ab

25.54±3.54 a

13.42±5.62 a

1.92±0.88 b

Azoxystrobin

47.81±6.73 c

31.65±5.37 a

15.03±4.91 a

5.51±1.45 a

Cyprodinil

54.21±5.16 bc

30.62±3.11 a

12.06±2.28 a

3.10±1.72 ab

Carbendazim

50.97±4.20 c

31.26±4.38 a

13.84±1.95 a

3.93±2.05 ab

Fluazinam

55.77±2.99 bc

28.10±3.33 a

12.41±1.45 a

3.72±0.89 ab

443


Page 25 of 32


444

Table 4. Half-life of fungicide residues in different layers of head cabbages. Half-life of fungicide residues in different layers (days) Fungicides

445

First leaf

Second leaf

Third leaf

Inner leaves

Chlorothalonil

8.02

11.29

13.69

NA*

Tebuconazole

11.87

12.63

25.42

NA

Azoxystrobin

6.10

9.78

14.98

NA

Cyprodinil

4.94

7.04

15.25

NA

Carbendazim

10.48

14.97

20.43

25.10

Fluazinam

7.25

11.32

15.33

16.97

*

: NA indicates no half-life data is available due to an incomplete curve.



446


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Figure 1 999x698mm (96 x 96 DPI)



Figure 2 173x187mm (300 x 300 DPI)


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264x148mm (96 x 96 DPI)


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Efficiency and safety assurance of six fungicides applied on post

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