DSpace at VNU: Pesticide residues in soils, sediments, and vegetables in the Red River Delta, northern Vietnam

Crop Protection 20 (2001) 897–905 Pesticide use in rice and rice–fish farms in the Mekong Delta, Vietnam H(akan Berg* Department for Research Cooperation (SAREC), Swedish International Development Cooperation Agency (Sida), SE-105 25 Stockholm, Sweden Received 30 June 2000; received in revised form January 2001; accepted 26 February 2001 Abstract Pest management practices among rice and rice–fish farmers and their perception of problems related to pests and pesticides were surveyed in the Mekong Delta A total number of 64 different pesticides were identified during the survey Approximately 50% were insecticides, 25% were fungicides and 25% were herbicides The main insecticides used were pyrethroids (42%) carbamates (23%) and cartap (19%) Non-IPM farmers used twice as many pesticides as IPM farmers Their application frequency and the amount of active ingredient used were 2–3 times higher per crop, as compared to IPM farmers During the last three years IPM farmers estimated that they had decreased the amount of pesticides used by approximately 65%, while non-IPM farmers said that they had increased the amount of pesticide used by 40% Also, farmers growing fish in their rice fields used less pesticide than farmers growing only rice, as pesticides adversely affect cultures of fish Taking a long-term perspective integrated rice–fish farming with IPM practices provides a sustainable alternative to intensive rice mono-cropping, both from an economic as well as an ecological point of view # 2001 Elsevier Science Ltd All rights reserved Keywords: IPM; Rice–fish farming; Integrated agriculture; Pesticides; Mekong Delta; Aquaculture Introduction Production of rice has been intensified in Vietnam, to meet the increasing food demand Rice is planted on million ha, which is more than 60% of the total farmed area 27.6 million tonnes were produced in 1997, having increased by about 5% per year since 1990 (Anonymous, 1997) The intensified farming systems and expanded area of rice has transformed Vietnam from an importer of rice in 1989 to one of the top rice exporters in 1997 (Anonymous, 1996, 1997) With these changes, the amount of pesticides used increased from 20 000 tonnes in, for example, 1990 to 30 000 tonnes in 1994 (Quyen et al., 1995; Noda et al., 1998; Dung et al., 1999) The increased reliance on pesticides in rice production has, in some areas, proved to be unsustainable and cost ineffective due to pesticide-induced outbreaks of insect pests, development of pesticide resistant pests, rising cost of pesticide use, and the negative effects of pesticide use on human health and the environment (Heong et al., 1995; Pingali and Roger, 1995; Settle et al., 1996; Pingali *Tel.:+ 46-8-698-5298; fax: +46-8-698-5656 E-mail address: hakan.berg@sida.se (H Berg) and Gerpacio, 1997) Prolonged misuse of pesticides and fertilizers over the years has also halted the development of inland fisheries and aquaculture (Moulton, 1973; Cagauan and Arce, 1992; Halwarth, 1995; Abdullah et al., 1997) In an attempt to reduce pesticide use, important changes have taken place in strategic approaches to plant protection Integrated Pest Management (IPM) methods have brought ecological principles and social scientific perspectives into traditional crop management These ecology-based pest control methods have resulted in markedly improved rice farming systems, which are not only higher yielding but also more sustainable (Stone, 1992; Settle et al., 1996; Noda et al., 1998; Huan et al., 1999) In addition to this, increased adoption of rice–fish farming, with fish as a natural control agent of pest organisms, provides a promising alternative for further developing ecological sound management strategies of the rice field environment (Cagauan, 1995a; Dela Cruz, 1994; Halwarth, 1995, 1998) This paper reports a survey of pest management practices among rice farmers in the Mekong Delta, and their perception of problems related to pests and pesticides The influence from the IPM programs is evaluated by comparing pesticide use patterns of 0261-2194/01/$ - see front matter # 2001 Elsevier Science Ltd All rights reserved PII: S - ( ) 0 - 898 H Berg / Crop Protection 20 (2001) 897–905 farmers with findings from earlier studies and by comparing the attitude and pest management strategies adopted among non-IPM and IPM farmers in the area The study also addresses the extent to which integrated rice–fish farming could encourage farmers to start with integrated pest management practices and vice versa A healthy environment is a prerequisite for successful fish farming, which should provide rice–fish farmers with strong incentives to adopt integrated pest management strategies Methods Use of pesticides among rice and rice–fish farmers in the Mekong Delta, was analysed by interviews with 120 farmers from three different districts in the Can Tho and Tien Giang provinces during the spring of 1999 (Fig and Table 1) All three districts are situated in major rice producing areas of the Mekong Delta Fig Can Tho and Tien Giang are major rice producing provinces in the Mekong Delta Farmers were interviewed in the districts of Cai Be, Go Cong Tay and O man Table Some charactaristics of Go Cong Tay, Cai Be and O man in 1998a Tien Giang Area of district (ha) Population size Number of farmers Number of rice farmers Area of ricefields (ha) Number of rice-fish farmers Area of rice-fish farms (ha) Crops per year Yield of rice (ton) Can Tho Go Cong Tay Cai Be O mon 25 745 158 183 33 043 30 596 13 746 50 15 143 076 40 107 287 243 48 000 31 538 19 980 1500 1200 318 400 54 856 281 535 56 807 42 600 38 111 4500 4500 2–3 450 000 a Pers com of Subplant Protection Department in Tien Giang (My Tho) 2.1 Study area The Vietnamese Mekong Delta covers an area of 39 000 km2, and is the most important agricultural region in Vietnam (Fig 1) Covering only 12% of Vietnam’s total land area, it supplies half of the national rice output (Noda et al., 1998) Approximately 400 000 of the Mekong Delta is suitable for freshwater aquaculture, but less than 10% of the area is used for this purpose (Halwarth, 1995; Duong et al., 1998) (cf Table 1) The climate is characterised as tropical semiequatorial with a mean temperature of 278C The mean annual rainfall is 1600 mm and approximately 90% of the rain comes during the rainy season in May to October (Xuan and Matsui, 1998) The districts of Go Cong Tay (N 108400 , E 1068700 ), and Cai Be (N 108300 , E 1068) represent two different rice producing areas in the Tien Giang province (Fig 1) The area around Cai Be has a very good irrigation system consisting of a network of many canals and natural rivers (Ha, 1997) The first rice crop is from November to February, the second crop from February to May and the third crop is from May to August (Ha, 1997) Go Cong Tay lies in an area that is relatively higher and has a much poorer irrigation system as compared to the first area The first rice crop is from November to February, the second crop from May to August and the third crop is from August to November (Ha, 1997) The O mon district (N 108100 , E 1058600 ), which lies in the Can Tho province, is also representative for the irrigated rice areas of the Mekong Delta, in aspects of both physical environment and productivity (Lai, 1998) (Fig 1) Rice is cultivated in the dry and wet seasons in double rice system and in the dry, spring–summer and wet seasons in the triple rice system The rice yield is 4–5 tonnes per hectare and crop for all three districts (Table 1) 2.2 Field sampling In each district approximately 40 rice farmers were interviewed These farmers were categorised into four groups: Rice (R) and rice–fish farmers (RF) without IPM-methods and rice (RIPM) and rice–fish farmers (RFIPM) with IPM methods IPM farmers were identified with the help of local Plant Protection staff, as farmers who had attended Farmers Field Schools and that applied some form of IPM methods Each group consisted of approximately ten farmers As less than 10% of all farmers grow rice and fish in their field or apply IPM methods these farmers were, thus, overrepresented in the study (Duong et al., 1998; Heong et al., 1998; Huan et al., 1999) (cf Table 1) In all districts interviews were conducted with farmers who had two or three crops per year, as these are the systems with the heaviest use of pesticides 899 H Berg / Crop Protection 20 (2001) 897–905 A questionnaire in English was pre-tested by interviewing three farmers (not included in the study) After this some changes were made in the questionnaire, and tested again on an additional seven farmers Some minor changes were made before translating the questionnaire into Vietnamese The interviews were conducted in co-operation with local extension officers from each district, trained in agriculture and aquaculture Before the interviews were conducted the extension officers were informed on how to use the questionnaire and smaller changes were made to fit the local conditions in each district When finished, the questionnaires were checked and translated into English by co-ordinators at regional research institutes Additional information was also collected at extension offices and plant protection stations in the districts The data were analysed by dividing the farmers into the four different categories (R, RF, RFIPM, RIPM) in each district If the answers between districts were similar, they were aggregated into the same category Differences between categories were investigated using analysis of variance (ANOVA) onefactor analysis Result During the survey a total of 64 different pesticides were identified Approximately 50% were insecticides, 25% were fungicides and 25% were herbicides Small amounts of different rodenticides were also found (Table 2) The most common pesticide was validamycin, followed closely by two other fungicides, propiconazole and hexaconazol (Table 2) The most common insecticides were fenobucarb, cartap and lambdacyhalothrin (Table 2) Among the herbicides fenoxaprop-P-ethyl, 2,4D, pretilachlor and fenclorim were the most popular (Table 2) Rice farmers use the greater range of pesticides, while rice–fish farmers with IPM use the least number of pesticides (Table 3) In general, non-IPM farmers use almost twice as many different pesticides as compared to farmers applying IPM methods Especially, the number of insecticides used by non-IPM farmers was much higher compared to IPM farmers (Table 3) A majority of the farmers (>80%) thought that pesticides are a problem for their health (Table 4, Points and 5) The most common answer, is that they feel tired after spraying Other symptoms of health effects are ‘‘hot’’ skin, dizzyness or headaches (Table 4, Point 6) Almost all farmers (85–100%) regarded insecticides as the most problematic pesticide (Table 4, Point 7) In Cai Be, lambdacyhalothrin, fenobucarb and delthamethrin were mentioned and in O man farmers were concerned about endosulfan and carbofuran Despite Table The 20 most common pesticides used by rice and rice–fish farmers in Tien Giang and Can Tho provinces in 1999a Pesticide formulation Active ingredient Fungicides (16) Validacin Tilt Anvil Fuji-one Rovral Bonanza Validamycin A Propiconazol Hexaconazol Isoprothiolane Iprodione Cyprocozol 9.6 8.4 8.0 4.4 3.8 1.9 Herbicides (15) 2, D Sofit Tiller’s 4.1 3.9 3.6 Whip’s Sirius Cantanil 2, D Pretilachlor, Fenclorim Fenoxaprop-P-Ethyl, 2,4 D, MCPA Fenoxaprop-P-Ethyl Pyrazosulfuron Ethyl Butachlor, Propanil Bassa Padan Karate Decis Applaud Fastac Regent Trebon Fenobucarb Cartap hydrochloride Lambdacyhalothrin Delthametrin Buprofezin, Isoprocarb Alpha-cypermethrin Fipronil Etofenprox Insecticides (33) % use by farmers Others Total (64) a 2.6 2.2 1.9 6.0 4.4 3.8 3.6 3.4 2.4 2.2 2.0 18 100 Figures in brackets give the total number of pesticides found Table Average number of different pesticides, used per farmer from Cai Be, Go Cong Tay and O man in the Mekong Delta in 1999 Fungicides Herbicides Insecticides Total R RF RFIPM RIPM 2.8 1.5 2.9 7.2 1.7 0.9 2.5 5.1 1.8 0.7 0.7 3.2 1.9 0.9 0.8 3.7 this, less than half of the farmers seem to take any action to protect themselves from the pesticides (Point in Table 4), and it is possible that the hot climate decreases the farmers willingness to wear any protective clothing Protection using, a mask or cloth over the face, are most common among rice–fish IPM farmers (Point 8* in Table 4) The attitude to environmental effects from pesticides, is less uniform among farmers Generally, non-IPM rice farmers seem to be quite unaware or unconcerned about the environmental drawbacks of pesticides The main methods (>90%) used by these farmers to control pests involve application of pesticides (Point of Table 4) The majority (80–100%) of the farmers have learned how to use pesticides from other farmers or pesticide retailers (Point of Table 4) Some of these have a very 900 H Berg / Crop Protection 20 (2001) 897–905 Table Answers (% of famers) related to pests, pest control methods and their effects among rice and rice-fish farmers in the Mekong Delta 1999 R RF RF IPM R IPM Which methods you use to control pests? Pesticide 94 93 IPM Resistant rice varieties No answers 31 29 Where did you learn how to use From plant protection staff From other farmers TGa From pesticide shop/retailer No answers the pesticide? 18 55 36 35 49 16 33 49 100 93 59 46 41 36 0 29 28 28 29 How often you see plant protection staff (times/yr)? average stdv 1.1 2.1 3.8 Any problems related to pesticides that is important? Cost of pesticide 53 34 19 Health effects 33 45 48 Environment 14 21 33 effects No answers 36 29 42 Have the pesticides been a problem for your health? Yes 87 82 84 No 13 18 10 Do not know 0 No answers 31 28 31 Kind of health problem from pesticide spraying? Get tired 52 65 52 TG Feel hot and 14 10 19 itchy Ca Feel dizzy 20 15 19 C Get headache 14 10 10 No answers 21 20 21 Which pesticides are a problem for your health? Fungicides Herbicides Insecticides 97 92 No answers 29 26 12 88 16 Do you use any protection when spraying? Yes 33 37 No 67 63 No answers 30 27 8* % of yes Carrying a mask 10 20 Can pesticides have a negative effect on the yield Yes 12 42 No 84 50 Do not know No answers 25 24 9* If yes, Pesticides are 100 50 why? toxic to fish Natural feed for 19 6.4 21 42 37 52 89 11 28 84 11 19 11 84 19 59 41 29 47 41 59 29 25 40 60 30 48 32 64 22 50 42 30 Table (Continued) R the fish decrease Fish growth decrease No answers RF RF IPM R IPM 31 10 20 16 21 10 10 Do you know any natural enemies to pests in your field? Yes 26 100 No 93 70 Do not know No answers 30 23 29 96 26 11 Which natural enemies you know? Spider 50 Beetle 50 Dragon fly No answers 67 33 38 36 26 47 12 What effect can pesticides have Kill natural enemies to pests No effect No idea No answers 74 27 41 35 24 37 on natural enemies to pests? 22 74 79 97 31 23 31 13 Can pesticides increase pests problems in your field? If yes, Increased no of 15 19 37 how? resistent insect Decreased no of 54 natural enemies No 85 78 No answers 27 27 35 14 How you decide to spray? According to field survey TG Scheduled sprays C According to other farmers Other No answers 21 29 41 56 39 25 31 70 74 71 44 25 12 28 36 27 33 14 34 13 14 87 86 0 31 29 15 How you select pesticide for pest control? Pesticide that 91 78 can kill all pest Pesticide that kill 11 only target pest According to 11 other farmers No answers 31 27 16 Do you make changes in the ricefield before applying pesticides? Yes 45 63 55 33 No 55 37 45 67 16*.% of yes Decrease water 78 75 92 71 level in ricefield No answers 20 19 22 21 ? 17 Have you changed your use of pesticides during Yes increased 93 65 use Yes decreased 12 use No 23 No answers 29 26 the last yr? 87 100 10 31 29 H Berg / Crop Protection 20 (2001) 897–905 Table (Continued) R RF RF IPM R IPM 18 Which pesticides have increased/decreased most? Increase Insecticide 50 70 Fungicide 28 17 Herbicide 18 Decrease Insecticide 13 Fungicide 0 Herbicide 0 No answers 40 23 19 Why did you change your use of pesticides? Increase Problem with 78 100 resistant pests Increased 22 number of pest Decrease Use IPM 0 No answers 20 Which are the most problematic pests? Diseases 25 Insects 75 Rats Weeds No answers 36 21 69 10 29 0 65 16 16 31 0 70 21 33 0 0 100 100 40 50 30 55 31 10 29 24 44 56 41 21 Do you apply IPM? (if yes give example) No insecticides } } the first 40.days Adjust pesticide } } use to pest infestation Limit pesticide } } use No answers } } 20 15 25 27 22 Would you like to start with IPM? Yes 32 No 68 No answers 28 63 37 24 } } } } } } 38 44 18 57 31 12 49 31 20 16 51 59 23 Reason for applying/start with IPM? Lower cost 43 Protect health 43 Protect the 14 environment No answers 14 a TG refers to answers from farmers in TienGiang and C to farmers in Can Tho poor knowledge of the use and properties of pesticides, and widespread gaps in the knowledge of farmers and unfavourable attitudes of farmers toward natural methods of pest management have probably continued to encourage pesticide use and misuse Most of the non-IPM rice farmers (84%) thought that pesticides have no negative effect on the yield from their fields (Point of Table 4) Only a few knew about natural enemies to pests (Point 10 of Table 4)and consequently most were not aware that pesticides can 901 decrease the number of natural enemies (Point 12 of Table 4) and thus increase the number of pests in their field (Point 13 of Table 4) In 1994 farmers in Long An were asked if they thought that killing of natural enemies can cause more pest problems (Heong et al., 1998) Only 27% of the farmers agreed to this statement After an information campaign about negative effects of insecticides, approximately 80% of the farmers agreed to this statement, implying that farmers had developed stronger beliefs that a selective spraying of insecticides is possible and can save money, protect the health and the environment (Heong et al., 1998) The ongoing IPM programme further shows that improved ecological knowledge is an important tool for changing farmers’ perception of pests and their management, resulting in increased understanding of natural control mechanisms in the rice field ecosystem and, thus, reduced use of pesticides (Points 10, 11 and 19 of Table 4) IPM farmers receive comparatively large support from the plant protection services on how to use pesticides (Point of Table 4) and meet local extension officers much more frequently than non-IPM farmers (Point of Table 4) This not only helps them to restrict their use of pesticides but probably also increases their knowledge about negative side effects from pesticides The majority of the IPM farmers (>70%), for example, thought that pesticides can have a negative effect on natural enemies of pests (Point 12 of Table 4) and increase the number of pests in their fields (Point 13 of Table 4) Many IPM farmers are also aware that pesticides may lead to pests that are resistant to pesticides (Point 13 of Table 4) As a consequence, the majority of the IPM farmers (>70%) base their decision to spray on field observations and adjust their pesticide applications according to the pest infestation level in the rice field (Points 14 and 21 of Table 4) They also try to use pesticides that only kill the target organisms (Point 15 of Table 4)and avoid using insecticides during the first 40 days (Point 21 of Table 4), as earlier sprays can increase pest problems in the field (Heong et al., 1998) (Table 4, Fig 2) In contrast, 80–90% of the non-IPM farmers use brand spectrum pesticides (Point 15 of Table 4) The majority of these farmers also applied pesticides according to scheduled sprays, implying that they sprayed whether or not pests were present As a consequence, non-IPM farmers apply pesticides more frequently than IPM farmers Non-IPM rice farmers, for example, apply insecticides 3.2 times per crop on an average and up to times in extreme cases including applications during the first 40 days (Fig 2), while IPM farmers only apply insecticides 0.6 times per crop (Fig 3, Table 5) Also, the amount of active ingredient (a.i), applied per crop, is higher for non-IPM farmers compared to IPM farmers (Table 6) This is not only because the number of applications is higher (Table 5), 902 H Berg / Crop Protection 20 (2001) 897–905 Table Average dose (kg a.i./ha) of pesticides on the first rice crop among farmers from Cai Be, Go Cong Tay and O man in the Mekong Delta in 1999 R Fungicides Herbicides Insecticides Total Fig Number of days between sowing and the first application of insecticides among IPM and non-IPM farmers from Cai Be, Go Cong Tay and O man in the Mekong Delta in 1999 average stdv average stdv average stdv average stdv a 0.55 0.55 0.31a 0.27 0.93a 1.16 1.80a 1.22 RF RFIPM RIPM 0.29 0.45 0.20a 0.26 0.54b 0.53 1.04 0.73 0.27 0.45 0.17 0.30 0.13c 0.33 0.57 0.58 0.26 0.40 0.14 0.22 0.20b,c 0.50 0.60 0.66 Superscript letters in columns R, RF, RFIPM and RIPM denote significant difference among farmers Means that not share the same letter are significantly different (P50:05) Table Average number of pesticide applications on the first rice crop among farmers from Tien Giang in 1994 (Ha, 1997) and 1999 1994 Fungicides Herbicides Insecticides Total 1999 R RIPM R RIPM 1.6 0.9 3.2 5.7 1.2 0.8 1.5 3.5 3.7 0.8 3.7 8.2 3.0 0.6 0.4 4.0 Fig Number of insecticide applications on the first rice crop among IPM and non-IPM farmers from Cai Be, Go Cong Tay and O man in the Mekong Delta in 1999 Table Average number of pesticide applications (no/ricefield) on the first rice crop among farmers from Cai Be, Go Cong Tay and O man in the Mekong Delta in 1999 R Fungicides Herbicides Insecticides Total average stdv average stdv average stdv average stdv a 3.2 1.4 0.9 0.6 3.1a 1.5 7.2a 2.3 RF RFIPM RIPM 2.1 1.7 0.8 0.7 3.2a 2.0 6.1a 2.7 1.8 1.1 0.7 0.8 0.6 0.8 3.1 1.4 2.5 1.8 0.6 0.5 0.6 0.9 3.7 1.7 Superscript letters in columns R, RF, RFIPM and RIPM denote significant difference among farmers Means that not share the same letter are significantly different (P50:05) but also because non-IPM farmers use a higher dose per application compared to IPM farmers Discussion The results from this study clearly show that IPM farmers use much less pesticides than non-IPM farmers Also, farmers growing fish in their rice field tend to use less pesticides than farmers growing only rice, as pesticides have a negative effect on aquaculture activities Based on these results it is argued that rice farming, integrated with fish and IPM practices in the long-term provide an economic as well as ecologically sustainable alternative to intensive rice mono-cropping Compared to 1994, the number of applications of insecticides per rice crop in the Tien Giang province has increased slightly among non-IPM farmers, but decreased threefold among IPM farmers (Table 7) The number of fungicide applications has more than doubled, while the number of herbicide applications remains almost the same for both IPM and non-IPM farmers (Table 7) In total, the number of applications of pesticides has increased, especially among non-IPM farmers, as compared to 1994 During the last three years most (90%) non-IPM farmers said that they had increased their use of pesticides, mainly insecticides, by approximately 40% (Table (Points 17 and 18) and Table 8) This should be compared to IPM farmers, where the majority (90– 100%) said that they had decreased their use of pesticides, mainly insecticides, by 65% (Table (Points 17 and 18) and Table 8) The most common reason for the increased use of pesticides among non-IPM farmers was that they experienced an increased number of H Berg / Crop Protection 20 (2001) 897–905 Table Experience (number of years since starting with IPM methods) and its effect on pesticide use and income among farmers in Cai Be, Go Cong Tay and O man in the Mekong Delta in 1999 Cai be Years of experience in IPM stdv Changed use of pesticides during the last yr (cf Table 4, Pt 17) Average decrease for IPM farmers (%) stdv Average increase for non-IPM farmers (%) stdv Changed income since IPM Percentage (number) farmers with increase Avarage increase in income (%) stdv 4.6a 1.4 Go Cong Tay O mon 4.0a,b 1.5 3.4b 1.4 85.0a 63.8b 40.2c 7.7 52.5a 20.6 41.9b 20.9 29.3c 12.7 15.9 13.2 100 (20) 100 (20) 86 (19) 18.8a 12.6b 6.5c 2.6 3.5 4.0 Superscript letters in the last columns denote significant difference among farmers Means that not share the same letter are significantly different (P50:05) Table Main insecticides (in % applications) used by rice and rice–fish farmers in the Mekong Delta 1992, 1997 (Huan et al., 1999) and 1999a Insecticides 1992 1997 1999 Organochlorines Organophosphates Pyrethroids Carbamates Cartap Phenylpyrazole Others 43.9 14.7 32.1 6.5 n.a 1.8 0.4 29.8 42 9.1 8.9 n.a 9.8 1.6 2.8 41.6 23.0 19.2 4.1 7.7 a n.a.}not analysed pesticide resistant insects in their fields (Point 19 of Table 4), which is a well known consequence of the overuse of pesticides (Pingali and Gerpacio, 1997; Settle et al., 1996) As a result of the increased resistance, farmers must find new pesticides This, in turn, could explain the comparatively large number of different pesticides used by non-IPM farmers (Table 3) Due to a lack of knowledge about these new chemicals and with greater market liberalisation, there has been a tendency towards the application of cheaper and sometimes more hazardous pesticides with less conformity to the guidelines issued by the plant protection department (Quyen et al., 1995) Compared to insecticide use patterns in the Mekong Delta in the 1992 and 1997 seasons (Huan et al., 1999) the use of organophosphates has decreased while there has been an increase in the use of pyrethroids, carbamates and other active ingredients such as cartap 903 and phenylpyrazole (Table 9) These changes have probably had an adverse impact on both human health and the environment Cagauan (1995b), for example, ranked synthetic pyrethoids as more toxic to fish than organophosphates, while carbamates were ranked as less toxic to fish Thus, although the overall impact from the changed insecticide use patterns is difficult to assess, these will most likely have a large impact on the shaping of future farming systems (e.g rice–fish farming) in the Mekong Delta Due to their intense use of pesticides many non-IPM farmers have become concerned about the high cost of pesticides (Point of Table 4) and production costs is a strong incentive for the farmer to start with IPM (Point 23 of Table 4) Similar to the results of Heong et al (1998), the most important reason for farmers to apply IPM, and thus reduce their pesticide use, is savings in costs followed by reduction in health risks and less pollution to the environment (Point 23 of Table 4) Thus, from the farmers point of view decreased use of pesticides makes not only ecological sense but, probably more important, also economic sense On an average, IPM farmers estimated that after applying IPM, their income had increased by 13% The largest increase was found in Cai Be (19%), which coincided with the largest decrease in pesticide use (Table 8) Similarly, the smallest increase was found in O mon (6.5%), where pesticide use had decreased the least (Table 8) Thus, in the case of implementation of IPM, economic incentives ‘‘pave the way’’ for ecologically sound strategies In the perspective of increased economic benefits based on improved ecological management, rice–fish farming provides an interesting option for further encouraging the adoption of integrated pest management in the Mekong Delta There are many arguments for fish farmers to reduce their use of pesticide Decreased pesticide use enhances fish farming practices and the fish, in turn, can act as a natural control agent of pest organisms (Cagauan, 1995a; Dela Cruz, 1994; Halwarth, 1995) In rice monoculture, the chance of pests reaching a population level which economically justifies control action is usually low (Halwarth, 1998) For a farmer who stocks fish in his field, there is also a trade-off between prevention of losses due to pests and the loss of fish that may incur due to pesticides Consequently, the loss of fish has to be considered as an additional cost of pest control (Waibel, 1992) Thus, the potential income from fish shifts the economic threshold for applying pesticides to a level which is even less likely to be reached by pests (Halwarth, 1998) If costs associated to health and environmental effects also are accounted for by the farmer, his willingness to use pesticides will decrease even further (Waibel, 1992) Rice–fish farmers therefore tend to use less pesticides than 904 H Berg / Crop Protection 20 (2001) 897–905 rice farmers (cf Tables 5–7) and may increase their income not only from decreased cost of pesticides, but also from increased yield of fish With savings on pesticides and earnings from fish sales, it is no surprise that twice as many rice–fish farmers wanted to take up IPM methods compared to rice farmers (Point 22 of Table 4) Rice–fish farmers were more aware of the benefits from a healthy rice field ecosystem than farmers growing only rice In all questions related to the environment, for example, farmers culturing fish show a higher environmental awareness than rice farmers (Table 4, Points 4, 9, 9*, 10 and 12) This is probably because farmers culturing fish must pay attention not only to the rice plant, but also to the whole rice field ecosystem to succeed with their farming practices This increases their ecological understanding of the rice field ecosystem and thus also their insight into potential negative side effects of pesticides on non-target organisms For example, compared to rice farmers there were more rice–fish farmers, who thought that pesticide could have a negative effect on the yield from their field (Point of Table 4) Not only did the farmers think that the fish growth and survival could be negatively affected, but also that the natural food for the fish would decrease (Point 9* of Table 4) Understanding that the fish is a part of and, thus, depends on the whole rice field ecosystem is a good incentive for the farmer to apply ecologically sound pest control methods This in turn generates further insight into the complex interactions in the rice field ecosystem, on which integrated pest management strategies could be built Many rice–fish farmers have actually adopted integrated pest management strategies without being part of any integrated pest management program For example, non-IPM rice–fish farmers make the first application of insecticides 40 days after transplanting the rice plant, which is almost ten days later compared to non-IPM rice farmers (cf Fig 2) They also often decrease the water in their field before applying pesticides (Point 16 of Table 4) and keep it low for a longer period compared to rice farmers Also, from an IPM point of view, fish culture and rice farming can be complementary activities because it has been shown that fish in some cases reduce pest populations (Halwarth, 1995, 1998) Evidence from the FAO IPM Intercountry Program shows that, through IPM and rice–fish farming practices, the number of pesticide applications in rice can be reduced from 4.5 to 0.5 (Waibel, 1992) In this study rice–fish farmers with IPM methods used the lowest number of different pesticides (Table 3), used the lowest dose (Table 6) and applied pesticides less frequently compared to the other farmers (Table 5) As mentioned earlier, this not only reduces costs but also eliminates an important constraint in the adoption of fish farming An unpolluted environment is a prerequisite for successful fish farming and the high use of pesticides associated with the adoption of high yielding rice varieties has been considered as a constraint in the adoption integrated agriculture and aquaculture in South-East Asia (Rudolfo and Arsenia, 1988; Cagauan and Arce, 1992; Halwarth, 1995; Abdullah et al., 1997) Therefore training in IPM for many farmers participating in the regional programme in Bangladesh, Indonesia, or Vietnam has been an entry point to rice–fish farming (Halwarth, 1998) Fish farming activities would in turn probably motivate the farmer to continue with IPM In conclusion, increased pressure to maintain high levels of rice output for consumption and export has resulted in increased use of pesticides on rice fields in the Mekong Delta The continued high use of pesticides is a problem for farmers health and the environment It is also a constraint in the development of inland fisheries and aquaculture In order to minimise further damage, alternative or redesigned methods of pest control must be further implemented in the Mekong Delta The IPM program is an alternative pest and weed control mechanism that is eco-friendly and facilitates natural production yields It enhances ecological awareness among rice farmers and has probably broad and longlasting benefits compared to traditional plant protection strategies, especially if integrated with aquaculture The use of fish in integrated pest management of rice fields provides a promising alternative for further developing ecologically sound management strategies of the rice field environment Acknowledgements This study was done with financial support from the Swedish international development cooperation agency (SIDA) Practical support was given by a number of institutions in Southern Vietnam Special thanks are due to Mr Ngoc Ngo Van, Dr Nguyen Van Tu and Dr Bui Catch Tuyen at the University of Agriculture and Forestry, Dr Nguyen Thanh Phoung at the Can Tho University and Dr Hao, Dr Zsigmond Jeney and Mr Nguyen Minh Thanh at the Research Institute for Aquaculture No The author is also grateful to a number of people working at the extension offices in Tien Giang and Can Tho, and to all the farmers who patiently took part in the study Valuable comments were provided by two anonymous referees References Abdullah, A.R., Bajet, C.M., Matin, M.A., Nhan, D.D., Sulaiman, A.H., 1997 Ecotoxicology of pesticides in the tropical paddy field ecosystem Environ Toxicol Chem 16, 59–70 H Berg / Crop Protection 20 (2001) 897–905 Anonymous, 1996 Statistical Data of Agriculture, Forestry and Fishery, 1985–1995 Statistical Publishing House, Hanoi Anonymous, 1997 Statistical Yearbook, 1997 Statistical Publishing House, Hanoi Cagauan, A.G., 1995a Overview of the potential roles of pisciculture on pest and desease control and nutrient management in ricefields In: Symoens, J.J., Micha, J.C (Eds.), The Management of Integrated 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