Pest Management in Vegetable Production: The Case of...

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Pest Management in Vegetable Production: The Case of the Rainfed Lowlands in Ilocos Norte

Leticia A. Lutap* and Marissa I. Atis

Abstract

This survey was conducted in ten rainfed-lowland vegetable-growing towns in Ilocos Norte within a rice-vegetable cropping system. It documented the farmers’ pest management practices, determined their knowledge and attitudes toward pests and their management; and assessed pesticide residues of vegetables commonly planted in the lowland areas.

Farmers varied in their pest management practices and other cultural practices like sowing, planting, and harvesting. Most of them were dependent on inorganic fertilizers and synthetic chemical pesticide spray. Their practices influenced the growth and development of their plants.

Moreover, farmers were knowledgeable on the insects and weeds attacking their plants, but not on diseases. The major insect pests were aphids (Aphis craccivora, Koch.), fruitworms (H. armigera Hubner), thrips (Thrips palmi Karny), fruitborers (L. orbonalis Guenee), fruitflies (Bactrocera sp.), and diamondback moth (P. xylostella L.). Meanwhile the major diseases were damping off, bacterial wilt, mosaic, purple blotch, and tangle top caused by pathogenic organisms like fungus, bacteria, and viruses. On the other hand, the weed species associated with their crops were bermuda grass (C. dactylon), pig weed (T. portulacastrum), jungle rice (E. colona), Chinese lantern (C. halicacabum), and purple nutsedge (C. rotundus). To control these pests, farmers relied on chemical pesticide spray. Pepper, eggplant, bittergourd, pole sitao, tomato and cabbage were mostly sprayed with pesticides. Related to this, pesticide residues were detected in some vegetables sampled directly from farmers’ field and in the local market through the pesticide residue kit for carbamates and organophosphate residues. All the vegetables sampled in the local market exhibited positive results for carbamates, except for cabbage and sweet pepper, which had residues of organophosphate.

On the whole, the present cultural practices of the farmers could lead to pest outbreak or resurgence such as unsynchronous planting, excessive nitrogen fertilizer use, but they reduced the amount of phosphorous and potassium, and caused poor seed reliance. Additionally, the practices of Ilocos rainfed-lowland farmers would aggravate insect pest and disease problems in producing vegetables. Other constraints that were identified other than pests were lack of capital, lack of quality seed material, natural calamities like drought and typhoon/flood, and labor.

Keywords: pest management, rainfed lowlands, vegetable production, pesticides

MMSU Science and Technology Journal ISSN: 2012 0060

Vol. 3. No. 1 January-June 2013

*Corresponding Author: Current Address: R&D Directorate, CRL

Compound. Mariano Marcos State University, City of Batac, Ilocos

Norte; email: [email protected]

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Introduction

Pests always cause problems in growing vegetables. In the Ilocos, vegetables

are among the major crops planted after rice because typical monsoon climate with

alternating dry and rainy season favors their growth and development. The different

kinds of vegetables that are usually planted are tomato, eggplant, pepper, pole sitao,

cowpea, and bittergourd. Other than being sources of cash, these vegetables are also

adequate sources of vitamins and minerals. However, like any other crops, these

vegetables are prone to pests, which cause substantial loss in yield as a result of direct

and indirect damage. Relatively poor knowledge and improper implementation of pest

control management practices further aggravate the problems of vegetable growers.

The intensive use of insecticides leads to insect resistance. However, farmers

have indiscriminately used insecticides like doubling the recommended dosage.

Likewise, they usually spray chemical pesticides without considering the chemical

residues on the products and their effect on the consumers. Pesticide residues may

remain in the vegetable for some time; as such, it is unhealthy to sell them.

Residues in food are the main sources of contaminants. This is often the result

of repeated application and other abusive use of pesticides. According to Rola et al

(1972), chronic health problems affecting farmers have become evident due to

intensive chemical use and exposure. Nevertheless, pesticide risk to health as

perceived by farmers and laborers is one area that has so far received minimal

attention.

Surveys are integral part of research activities to determine the importance of

pests in farmers’ field. However, there is no information on actual pests and infestation

on crop-to-crop or year-to-year basis. Pest distribution and management practices

in a certain area can be documented by interviewing farmers. As such, this study was

conducted to document farmers’ pest management practices, as well as determine their

knowledge and attitudes toward pests and pesticides; and assess pesticide residues of

vegetables commonly planted in the rainfed lowland areas of Ilocos Norte.

Methodology

A survey was conducted in ten rainfed-lowland towns that grow vegetables in

Ilocos Norte, preferably within a rice-vegetable cropping system. A list of possible

farmer-respondents was taken from the Municipal Agriculture offices. After determining

the number of respondents of the study, the Agricultural Technicians assigned assisted

in looking for the respondents. From a total of 1,411 farmers listed, 319 farmer-

respondents were identified based on the formula:

LA Lutap and MI Atis

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N

n = -------

1+ Ne 2

where n = sample

N = population

E = number of percentage error of Margin 1-5%

The farmer-respondents were distributed based on their place of origin as

follows: Batac - 84, Badoc - 26, Pinili - 25, Currimao - 2, Paoay - 30, San Nicolas - 39,

Laoag City - 9, Bacarra - 20, Sarrat - 36 and Dingras - 48. The pest management

practices, knowledge on and attitudes of the farmers toward pests and their

management practices were noted for these may influence decisions regarding

pesticide use and their risks vis-a-vis the farmers’ own view of pesticide health effects.

The survey was undertaken via an interview schedule. Meanwhile, descriptive statistics

such as frequencies and means were used to analyze the gathered data.

On the whole, the respondents’ age ranged from 20 to 77 years old. The group

with the highest frequency included the elementary graduates (43%). Most of them

were married and their farming experience ranged from 1 to 63 years. Additionally, their

household size ranged from 2 to 11.

Pesticide Residue Analysis

Collection of samples. The farmers identified as highly dependent on pesticides

in ten vegetable-growing municipalities in Ilocos Norte provided plant samples for the

pesticide residue analysis. The first testing involved samples taken directly from the

farmers’ fields. Vegetables freshly harvested and ready for marketing were collected

and analyzed. Meanwhile, the second testing involved collecting samples from selected

market outlets during open market day.

Preparation and extraction of plant samples. The procedure followed the rapid

detection technique developed by the Crop Protection Center Cluster base at the

University of the Philippines Los Baños. That technique is specifically used for

carbamate and organophosphate residue analysis in plants and fruits. For extraction

purposes, a volume of each type of different vegetables amounting to 0.5 to 1.0kg was

prepared as sample source:

The procedural steps in testing carbamates residues are as follows:

Cut the plants/fruits into small pieces;

Place about 5g in a vial;

Add 5ml acetone and shake;

Pour the acetone extract in another vial;

Pest management in vegetable production

90

Concentrate 1 ml of extract to about 0.1 ml over an alcohol lamp or stream of

air (electric fan);

Treat the paper strips by adding a drop of solution 1 and let it dry;

Spot the sample into the paper strips; and

Heat the sample for 30 seconds then spray it with solution 2.

On the other hand, the steps in testing organophosphate pesticide residues include

the following:

Cut the plants/fruits into small pieces;

Place about 5g in a vial;

Add 5ml of acetone and shake;

Pour the acetone extract in another vial;

Concentrate 1ml of extract to about 0.1ml over an alcohol lamp or stream of air

(electric fan);

Treat the paper strips by adding a drop of solution 1 and let it dry;

Place 5 drops of the concentrated solution on treated paper strips using the

capillary tubing;

Make the drop as small as possible;

Place filter paper between glass slides, heat for 1 minute;

Cool for 3 minutes and add a drop of solution 2; and

Match the resulting color with the color chart.

Analysis of results. The presence or absence of carbamates in the vegetable

samples was noted; likewise, the level of organophosphates was calculated. For

carbamates, development of pink, blue, orange, and violet spots indicated residues of

BPMC, carbaryl, methomyl, and carbofuran, respectively.

On the other hand, the amount of organophosphates was calculated based on

the concentration of the color chart that matched the color of the reactant solution.

Solution was prepared by dissolving one capsule in 4ml methanol. Positive results

give pink (BPMC), blue (carbaryl), orange (methomyl), and violet (carbofuran) spots.

Interpretation of results. Blue color indicates the presence of organophosphate

pesticide residues. Each resulting color corresponds to the amount of pesticide

present in the sample. The concentration was calculated as follows:

Concentration = Amount from visual comparison (ug) x final volume (ml)

(ug/g) weight of sample extracted (g)


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Color Chart:

0.05 0.10 0.15 0.25 0.50 0.75

Results and Discussion

Survey of Pest Management Practices

Various management practices were employed by the farmers in the rainfed

lowland farms of Ilocos Norte. These practices affected their pest management

strategies in producing their vegetable crops. One of the principles for effective pest

management is growing a healthy crop that can resist pests and compensate for

damage caused by diseases and insect pests. According to Dively (2005), integrating

pest management with other activities is a component of the total crop production

system involving the interaction of physical, biological, and management functions, to

determine crop yield. Thus, pest populations are managed starting from the time of

planning of what to plant in a particular area up to harvesting.

Vegetables planted by rainfed-lowland farmers in the Ilocos include tomato,

eggplant, pepper, garlic, cowpea, pole sitao, and bittergourd. Only a few planted ridged

gourd, winged beans, bottlegourd, squash, and cabbage. However, a larger area was

planted with garlic, tomato cabbage and ridged gourd as compared to the other

vegetables. The average yields obtained per hectare from the different vegetable crops

are: 33 tons of tomato; 13 tons of eggplant; 12 tons of cabbage;10 tons of sweet

pepper; 3.8 tons of bontoc pepper; 3 tons of sitao; 3 tons each of bittergourd, garlic,

sitao, and squash; 2 tons of ridged gourd; one ton each of bottlegourd and winged

beans.

Cultural Practices

Sources of planting materials. In order to grow a healthy crop, planting materials

should be resistant to prevalent pests in the area, well adapted to local conditions; and

free from seedborne diseases and mixtures with other varieties. Most of the planting

materials were produced by farmers except for cabbage (Figure 1). This was a

limitation because having excellent quality and seedborne-disease-free materials could

hardly be guaranteed. Seeds must be properly selected and these should only be used


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for two to three times to produce quality vegetable crops. Other seed sources included

agencies like the Department of Agriculture, state colleges and universities, agricultural

supply centers, local markets, neighbors, and friends.

Land preparation. Farmer-respondents preferred to plow and harrow their

vegetable farms using a tractor during the dry and wet seasons; however, they opted to

use animals in furrowing their field during the dry season but not during the wet season.

Using either of the options during land preparation did not influence pest occurrence

but rather changed the soil properties. Meanwhile, number of passes of plowing and

harrowing minimized the growth of weeds, destroyed pupae present in the soil, and

ensured even water distribution throughout the area.

Time of sowing, planting and harvesting. Farmers started sowing their vegetable

crops from January to December. Specifically, they sowed pepper twice a year: the

first one was from January to February; the second was from July to November. In

contrast, they sowed eggplant almost all-year round. Meanwhile, they sowed tomato

from June to December. The other vegetables were sown only in a month but majority

of them were sown from September to November. Time of sowing and planting was

done simultaneously to avoid continuous build up of pest population that could damage

the plants. Since eggplant was sown and planted in different periods, the life cycle of

major insect pests attacking the crops was continuous. Harvesting vegetables crops

varied from one crop to another, but generally, it started in September until October and

extended up to January.

Spacing/planting distance. The farmers followed various hill and row spacings of

their vegetable plants. Spacing ranged from 10-200cm per hill x 10-200cm per row.

However, they commonly used 20-50cm x 40-100cm spacing for tomato, eggplant, and

pepper. For the viny plants, like bittergourd, bottlegourd, pole sitao, winged beans,

Fig. 1. Sources of materials sown by vegetable farmers in Ilocos rainfed lowland areas.


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ridged gourd and squash, the farmers used spacing that ranged from 20-100cm x 50-

100cm. Meanwhile, spacing for their garlic was at 20cm x 25cm. Although the farmer-

respondents properly spaced their vegetable crops at the outset, there were instances

when their plants became closely spaced as they grew taller. As shown in findings of

research studies done through closer spacing produces unhealthy plants, which

increases their susceptibility to insect pests and diseases.

Fertilizer application. Farmers relied on inorganic fertilizers with varying

amounts and modes of application to maximize the yield of their vegetable crops. They

either used the whole amount of fertilizer or split it. Majority of the farmers practiced two

to three splits of the recommended amount of fertilizer. However, farmers, who planted

tomato, pole sitao, and cowpea, applied two to three splits of fertilizer; while they

applied the whole amount to their winged beans. The fertilizers that the farmers used

were urea, complete, ammonium phosphate (16-20-0 and 18-46-0), ammonium sulfate,

and muriate of potash. The rates of fertilizer applied varied from one crop to another. In

contrast, few farmers used organic and foliar fertilizers.

Specifically, farmers applied 205-191-59kg N, P2O5 and K2O for tomato, 206-

174-149kg for eggplant, 178-187-49kg, 108-51-51kg for garlic, 122-94-66kg for

bittergourd, 95-50-50kg for bottlegourd, 135-30-30kg for squash, and 182-98-90kg for

cabbage. Based on the recommended rates for these crops, the amount of N fertilizers

applied by farmers was significantly high. Likewise, the amount of P2O5 applied for

tomato, eggplant, and pepper was high, but not for the other crops. On the other hand,

the farmers applied very low amounts of K2O, except for eggplant.

Irrigation practices. Water is essential in insuring better growth and

development of vegetables. That is so, because it carries and distributes the nutrients

throughout the plant. If the plant experiences water stress, it may also become weak;

hence, it is susceptible to pest attack. However, when the plant receives excessive

amounts, soil-borne diseases are activated, which favors the growth and development

of diseases.

Further, the frequency of irrigation as practiced by the farmers varied across

their crops. While sweet pepper, eggplant, and squash were irrigated once a week,

tomato and garlic were irrigated twice a week. In addition, cabbage farmers usually

irrigated their plants every after fertilizer application, while they only irrigated their

bittergourd when needed. Other crops like ridged gourd and winged beans were

weather-dependent. Only few farmers variably irrigated their crops like every month,

every two weeks, every three weeks, and twice a week.

Pest Management Practices

Insects. Majority of the farmers observed that H. armigera, L. orbonalis attacked

their tomato and eggplant, from the vegetative to the fruiting stage. Likewise, they said


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that Bactrocera sp. infected their bittergourd and squash from the vegetative until the

fruiting stage. For pepper, farmers observed the presence of Thrips palmi from the

vegetative up to the fruiting stage. They also observed the same pest in garlic during

bulb formation. Moreover, the respondents mentioned that A. craccivora commonly

occurred in all the crops, but more prevalent in pole sitao and cowpea. Likewise, they

reported that Aulacophora sp. attacked their bottlegourd, ridged gourd and squash,

while P. xylostella L. and Helulah undalis infected their cabbage.

Diseases. Bacterial wilt, damping off, and mosaic diseases caused by fungus,

bacteria and viruses, were the most common diseases infecting the vegetables grown

in the Ilocos rainfed lowlands. These were mostly observed from the vegetative to the

flowering stage. Other diseases such as soft rot and canker were prevalent during the

fruiting stage. In garlic, purple blotch was very high during the latter part of its

vegetative stage attacking only the old leaves; while tangle top started to occur during

bulb formation.

Weeds. The most common weeds that the farmer-respondents observed were

C. dactylon, T. portulacastrom, E. colona and C. halicacabum. These weeds occurred

throughout the vegetative to the fruiting period. Similarly, C. rotundus, Amaranthus sp.,

E. indica and I. triloba were observed mostly during the vegetative to the flowering

period. According to the respondents, all of the weeds mentioned were dominant during

the vegetative stage.

Management control. To control pests in vegetables, most of the farmers relied

on pesticide sprays (Figures 2-2b). The chemical pesticides used were methomyl,

lambacyhalothrin, carbaryl and chlorpyrifos + BPMC, and metamidophos. Moreover,

farmers who planted tomato, eggplant, sweet pepper, and cabbage used more kinds of

pesticides than those planting other crops. Farmers applied pesticides more frequently

in pepper, eggplant, bittergourd, cowpea, pole sitao, tomato, and cabbage. Meanwhile,

they sprayed the same less frequently in garlic, ridged gourd, bottlegourd, and winged

beans.

Other pest control measures of the farmer-respondents were handpicking of

larvae present in tomatoes and garlic. In addition, they practiced spraying plus

overhead irrigation to control garlic mites and thrips.

Likewise, Trichogramma chilonis was done by an eggplant farmer to control fruit

borer. The use of botanicals like hot pepper and Lantana camara to control fruitfly in

bittergourd was also observed. Meanwhile, to prevent the spread of the disease in the

whole crop area, crops that showed symptoms of wilting particularly in tomato,

eggplant, and pepper were uprooted.

Aside from the biological method of pest control, farmer-respondents also used

pesticides. The frequency of spraying pesticides was once a week (Figures 3-3b).

Almost all (90%) of the cabbage had that spraying frequency. They were followed by


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Fig. 2. Management control measures practiced by Ilocos vegetable farmers to control

insects attacking their crops.

Fig. 2a. Management control measures practiced by Ilocos vegetable farmers for the

control diseases attacking their crops.


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Once a wk 2x a wk Every 2 wks Once a mo.

Fig. 2b. Management control measures practiced by Ilocos vegetable farmers for con-

trolling weeds associated with their crops.

Fig. 3. Frequency of spraying chemicals to control insects pests as practiced by Ilocos

vegetable farmers.


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Once Twice

Frequency of spraying Herbicides per cropping season

Once a wk Every 2 wks

Fig. 3a. Frequency of spraying chemicals to control diseases as practiced by Ilocos

vegetable farmers.

Fig. 3b. Frequency of spraying chemicals to control weeds in as practiced by Ilocos

vegetable farmers.


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farmers planting squash (82%), pepper and garlic (76%), and tomato (68%).

Further, twice a week spraying was practiced by at least one (18%) of the

farmers who produced bottlegourd, eggplant, tomato, pepper, pole sitao, and squash,

as well as at least one out of 20 (5%) of those planting bittergourd, cabbage, ridged-

gourd, and garlic.

Majority of the farmers sprayed pesticides once a week, twice a week and every

two weeks. Only few farmers did the same once a month. Spraying every two weeks

was practiced by farmers growing ridged gourd (43%), bittergourd (31%), and other

crops (5-19%), except those who produced cabbage, squash, and bottlegourd. Less

than 5% of the farmers sprayed their ridged-gourd monthly.

To control diseases, farmers sprayed their crops either once a week or every

two weeks. Majority (54%) of the garlic farmers practiced such. They were followed by

farmers who produced bottlegourd (36%), tomato (34%), as well as squash,

bottlegourd, pepper, and eggplant (13-24%).

To control weeds, majority of the farmers seldom used herbicides to control

weeds because they commonly did manual weeding. For farmers who sprayed

herbicides, they did such only once, specifically on garlic, pepper, eggplant, and

tomato. Only few of the farmer-respondents sprayed herbicides twice per cropping

season.

The farmer-respondents’ practices of applying pesticides, which were done

once and twice a week, could lead to pest resurgence or outbreak. Pest resurgence

occurs when pesticides destroy the natural enemies of a target pest. Because the

natural enemies depend on pests for food, it takes much longer for the pests to build

up. Likewise, secondary outbreak can occur when a pesticide destroys the natural

enemies that are not necessarily the immediate target of the application.

Cultural practices such as planting unsynchronously, using N fertilizers heavily,

but phosphorous and potassium sparingly, and using poor quality seeds further

aggravates problems on insect pests and diseases.

Pest Management Practices, Knowledge and Attitudes

of Farmers Regarding Pest Management

Majority (61%) of the farmer-respondents were knowledgeable on pests

attacking their vegetable crops and were able to identify the weeds growing in their

vegetable farms. On the other hand, only few of them had correctly identified the

diseases (Table 1).

Similarly, majority (71%) of the farmer-respondents were aware and adopted

some of the cultural practices related to pest management except that of using


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CROPS PEST

KNOWLEDGE LEVEL

Sufficient Insufficient None

F % F % F %

Tomato Insect Disease

Weed

109

39

107

58.9

23.5

55.1

63

47

5

34.1

28.3

2.6

13

80

82

7.0

48.2

42.3 Pepper Insect

Disease

Weed

87

18

127

61.7

18.0

71.4

36

3

47

25.5

3.0

26.4

18

79

4

12.7

79.0

2.3 Eggplant Insect

Disease

Weed

166

13

66

67.0

23.6

44.8

76

23

11

30.7

41.8

7.5

5

19

70

34.0

34.5

4.7 Garlic Insect

Disease

Weed

46

50

50

53.5

54.3

50.5

13

2

4

15.1

2.2

4.0

27

40

45

31.4

43.5

45.4 Bittergourd Insect

Disease

Weed

74

5

38

69.2

6.5

39.6

20

0

5

18.7

0.0

5.2

13

72

53

2.2

93.5

58.2 Pole sitao Insect

Disease

Weed

36

3

49

56.3

5.8

57.7

16

0

4

25.0

0.0

4.7

12

49

32

18.8

94.2

37.7 Ridged gourd Insect

Disease

Weed

23

5

13

62.5

16.7

34.2

12

0

0

30.0

0.0

0.0

3

25

25

7.5

83.3

63.8 Squash We Insect

Disease

Weed

7

2

14

30.4

11.8

60.9

15

2

0

65.2

11.7

0.0

1

4

9

4.3

76.5

39.1

Bottlegourd Ins Insect Disease

Weed

5

2

16

25.0

11.8

69.6

11

1

0

55.0

5.8

0.0

4

14

7

20.0

82.3

30.4 Winged Beans Insect

Disease

Weed

4

0

10

40.0

0.0

52.6

3

0

0

30.0

0.0

0.0

3

10

9

30.0

100.0

47.4

Onion Insect Disease

Weed

6

5

46

18.8

16.7

82.1

10

17

0

31.3

56.7

0.0

16

8

10

50.0

26.7

17.9

Table 1. Knowledge of vegetable farmer-respondents on pest management.


100

botanicals and traps as control measures against insect pest populations (Table 2).

They were also aware that applying pesticides is done when necessary; however, they

were not practicing it.

Most (82.5%) of the farmer-respondents mentioned that pests observed during

the early stages of plant growth and development caused severe damage to their

crops. Similarly, most (89.0%) of the farmers believed that applying pesticides would

increase yield, but doing that frequently would eradicate the natural enemies of their

crops (Table 3).

Pesticide Residue Analysis

Knowledge on the pesticidal residues of vegetables among farmers is essential

because of their hazardous effect not only on humans but on the environment as well.

PRACTICE AWARENESS (%) ADOPTION (%)

Aware Not Aware Adopted Not Adopted

Plowing 84.60 15.36 80.53 19.44

Using resistant varieties 88.09 11.91 88.40 11.06

Cleaning bunds 83.02 16.93 91.85 8.15

Synchronized planting 72.10 27.90 64.89 35.10

Timing of fertilizer application

89.34 10.66 90.00 10.03

Applying water 88.09 11.91 87.46 12.54

Applying pesticide 78.75 21.25 47.70 52.30

Using traps 42.00 58.00 18.50 81.50

Observing pests 87.46 12.54 83.10 16.03

Observing natural enemies

77.74 22.26 23.67 26.33

Using botanicals 47.34 52.66 30.41 69.60

Digging and hilling up 91.22 8.78 93.42 6.60

Ensuring sanitation

Mulching

Collecting infected fruits

0.63

0.31

0.63

-

-

-

0.63

0.31

0.63

-

-

Table 2. Awareness and adoption of Ilocos vegetable farmers in pest management

practices.


101

The pesticide residue kit from the Crop Protection Cluster Center successfully

provided results of the residue analysis. All of the samples of sweet pepper and pole

sitao had residues of carbamates (Table 4). The same residues with lesser proportion

was also tested in bittergourd (long), tomato, pole sitao, eggplant, and finger pepper. In

the case of other vegetables like bottlegourd and okra, no residue of carbamate and

organophosphate was detected.

Meanwhile, cabbage produced by all farmer-respondents had

organophosphates. Only few farmers (7-25%), who produced eggplant, tomato,

bittergourd, and finger pepper had organophosphate residues. These vegetables,

however, were positive of carbamate residues (43 to 75%). On the other hand,

vegetable samples collected from market outlets were all positive of carbamates (Table

5); only sweet pepper and cabbage from the same outlets were positive to

organophosphates. Specifically, sweet pepper, bittergourd, pole sitao, cabbage, and

finger pepper sampled in farmers’ fields had the highest percentage of carbamates

residues (67-100%).

The presence of residues was detected within 14 days after spraying, because

it was impossible to do so beyond that period. Most of the pesticides used by the

farmers had carbamates and organophosphates (Table 6). These groups are classified

as contact, stomach, and systemic, as well as moderately (yellow) and highly toxic

(red). Small proportion of farmers used pyrethoids (green), which are relatively non-

ATTITUDINAL STATEMENT AGREE (%) DISAGREE (%) NOT SURE

1. Applying pesticides increases yield 89.0 6.8 4

2. Not all insects present in the field are harmful

91.0 8.0 0.9

3. Frequent spraying of pesticides kills natural enemies

96.4 3.2 0.4

4. Insects attracting crops in the early growth stages cause severe damage

82.5 10.6 6.9

5. Disease occurrence in the early growth stages of the crops cause severe damage

86.8 10.9 2.2

6. Weeds present in the field during early growth stages cause severe damage

80.0 13.4 6.2

7. Spraying pesticides early is effective

74.4 18.3 7.3

Table 3. Attitudes of the Ilocos vegetable farmers toward pest management.


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CROP

FARMER (%)

Carbamate (%) Organophosphate (%)

(+) (-) (+) (-)

Bittergourd 75 25 25 75

Bottlegourd 0 100 0 100

Cabbage 0 0 100 0

Cowpea 71 29 0 100

Eggplant 67 33 7 93

Finger pepper 43 57 14 86

Okra 0 100 0 100

Pole sitao 100 0 0 100

Sweet pepper 100 0 0 100

Tomato 73 27 9 91

Table 4. Pesticide residues detected on vegetables grown by farmers in the rainfed-

lowland areas of Ilocos Norte.

Table 5. Distribution vendors selling vegetables with pesticide residues in selected

market outlets in Ilocos Norte.

CROP

VENDOR (%) Carbamates (%) Organophosphates (%) (+) (-) (+) (-)

Bittergourd (long) 100 0 0 0

Bitergourd (native) 33 67 0 0

Cabbage 67 33 67 33

Eggplant 33 67 0 0

Eggplant round 67 33 0 0

Finger pepper 75 25 0 0

Okra 25 75 0 0 Pole sitao 80 20 0 0

Sweet pepper 100 0 25 75

Tomato 67 33 0 0


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toxic and are recommended for vegetable crops.

Organophosphates are the most toxic group of pesticides that farmers use in

rice and vegetable production. They are nerve-poisons, which inhibit the action of

certain enzymes in the nervous system (cholinesterase). Most of them have short

residual activity, but are problematic when longer protection is desired. Meanwhile,

carbamates are closely related to biological action. These are persistent with high oral,

dermal, and inhalation toxicity.

Nevertheless, carbamates present less serious problem than those of

organophosphates, but repeated exposure to carbamates may lower the symptoms of

poisoning. If these do not evaporate from the soil surface, they leach into the ground

water. On the other hand, pyrethroids have a synthetic structure resembling the natural

pyrethrins. They have lower mammalian toxicity than other insecticide groups. They are

biodegraded by soil microorganisms; hence, they do not contaminate underground

water via run-off or leaching (Oudejans, 1982).

The permissible daily intake and the maximum residue level depend upon the

kind of pesticides used and the vegetable crops. Table 7 shows that the computed

values of those vegetables with positive residues were still within the allowable daily

intake for organophosphates as compared with ADI (mg/kg body wt). However,

consumers should be aware of the hazard of repeated intake of vegetables with

pesticide residues.

CROP FARMER (%)

Carbamate Organophosphate Pyrethroid

Eggplant 95 46 33

Tomato 55 18 36

Bittergourd 88 14 28

Sweet pepper 100 71 28

Finger pepper 57 57 28

Cowpea 100 14 42

Pole sitao 100 20 20

Bottlegourd 100 50 50

Okra 100 50 0

Cabbage 100 100 0

Table 6. Distribution of farmers who used pesticides for their vegetables grown in the rainfed-

lowland areas of Ilocos Norte.


104

PE

ST

ICID

E

Ma

lath

ion

M

eth

om

yl

Ca

rbary

l C

hlo

rpyri

fos

Me

tam

ido

ph

os

Pro

fen

os

Dim

eth

oate

AD

I (m

g/k

g b

ody w

t)

0.3

0.0

03

0.0

03

0.0

1

0.0

04

0.0

1

0.0

02

CR

OP

S

Ma

xim

um

Re

sid

ue L

eve

l (m

g/k

g b

od

y w

t)

Eg

gp

lant

0.5

0

.2

5.0

0

.2

- -

-

Tom

ato

3

.0

1.0

5

.0

0.5

-

2.0

1

.0

Po

le s

ita

o

8.0

2

.0

5.0

0

.2

- 0

.1

-

Bitte

rgo

urd

-

- -

- -

- -

Sw

eet

pep

pe

r 0

.5

1.0

5

.0

0.5

-

0.5

-

Fin

ge

r p

ep

pe

r -

1.0

5

.0

- 1

.0

- -

Ca

bb

ag

e

8.0

5

.0

5.0

0

.05

0.5

1

.0

2.0

Okra

-

- 1

0.0

-

- -

-

Leafy

ve

ge

tab

le

- -

10.0

-

- -

-

Ta

ble

7.

Allo

wa

ble

da

ily in

take (

AD

I) a

nd

ma

xim

um

re

sid

ue

lim

it (

MR

L)

of

ve

ge

tab

les.

(Cro

p P

rote

ctio

n C

luste

r, U

PL

B).


105

There is lesser damage from carbamates than organophosphates; but then,

repeated exposure to carbamates still causes poisoning. Meanwhile, chemical pesticide

residues leach into the ground water, which may cause water poisoning, and may later

affect irrigation water. When there is continuous spraying of chemical pesticides to

vegetables being grown in the province, absorption of chemicals by these vegetables

will become routinary or continuous.

To convert µg to mg g kg 1µg = 10 -6 mg 1g = 10 -3 kg

2 µg= 0.000002 mg

g 0.001 kg

Concentration = 0.002 mg/kg

Actual Daily Intake

Assuming an average person (50kg) consumes 250g of eggplant per day,

containing 0.002 mg/kg concentration of organophosphate residues, the actual daily

intake of pesticides is as follows:

ADI computed = 0.250 kg X 0.002 mg X 10 (safe factor)

50 kg

ADI computed = 0.0001 mg

CROP COLOR CHART

EQUIVALENT (µg) CONCENTRATION

(mg/kg)

ACTUAL DAILY INTAKE

(mg/kg body wt) Eggplant 0.05 0.002 0.0001

Tomato 0.5 0.002 0.0001

Bittergourd 0.15 0.01 0.0005

Finger pepper 0.05 0.002 0.0001

Sweet pepper 0.15 0.01 0.0005

Cabbage 0.05 0.002 0.0001

Table 8. Concentration (mg) of the pesticide residues found in farmers’ vegetables with positive amounts of organophosphates.


106

Conclusions and Recommendations

Farmers in the rainfed-lowlands of Ilocos Norte planted various kinds of

vegetables but they differed in their pest management and other cultural practices like

sowing, spacing, planting, and harvesting, as well as irrigation and fertilizer application.

Most of them relied on inorganic fertilizers and pesticide spray.

Insect pests that attacked vegetables were chewing, piercing, and sucking types

like fruit worm, fruit borer, fruitfly, thrips, aphids and diamondback moth. Meanwhile, the

most common vegetable diseases were damping-off, bacterial wilt, and mosaic. Weeds

that were prevalent in the area were broadleaves and grasses.

Moreover, majority of the farmers used chemical spray in controlling the pests

attacking their vegetables. Just a few of them seldom used handpicking, spraying plus

overhead irrigation, uprooting, as well as biological and botanical control measures. In

controlling weeds, majority of the farmers seldom used chemical herbicides, instead,

they did that by manual weeding.

Further, farmers were moderately knowledgeable on insects and weeds

attacking their plants, but not that much on diseases.

In addition, majority of the farmers used carbamates and organophosphates.

As such, pesticide residues were positive in some vegetables sampled in

farmers’ fields within 14 days after spraying. Likewise, vegetables sampled in market

outlets had carbamates residues; but then, only cabbage and sweet pepper

hadorganophosphates.

Rapid technique contributes significantly to the simplicity of the pesticide

residue analysis for only samples with positive results would be subjected to Gas

Chromatography for further identification.

Based on the results, the farmer’s safe entry period in the field can easily be determined and pre-harvest can be extended.

Since the government has an IPM program, continuing efforts of concerned agencies like DA, DTI and SCUs should be done to disseminate appropriate, safe, and sustainable pest management practices to vegetable farmers and consumers.

Acknowledgement

The authors would like to thank the agriculture technicians in the different vegetable-growing towns of Ilocos Norte who provided the list of respondents for the conduct of the survey part of this study. They also wish to acknowledge the National Crop Protection Center staff at UPLB for sharing the kit used in vegetable residue analysis and for their technical assistance.


107

Literature Cited

Bonina, J.R. and Cantliffe, D.J. (1994). Seed production and seed sources of organic Vegetables.

Dively, G. (2005). A philosophy of pest control founded on the principles of ecology. University of Maryland.

IPM on Vegetable Lecture Series. August 20-22, 2002. ATI, Batac, Ilocos Norte.

Ocampo, P.D. and Lumaban, M. D. Classification of pesticides. Hoechst Far East Marketing Corp. and Ciba Philippines.

Oudejans, J.H. (1982). Toxicity of pesticides. Agro-pesticides: Their management and application. United Nations.

Pingali, P.L. and Roger, P.A. (1995). Impact of pesticides on farmer health and the rice environment. Natural Resource Management and Policy. Ariel Dinar and David Zilberman, Series Editors. IRRI. pp. 59-93.

Rola, A.C. and Pingali, P. L. (1993). Rice productivity, pesticides and farmer’s health. IRRI, Manila, Philippines.

Tejada, A.W. (1984). Rapid test kit for pesticide residue detection. National Crop Protection Center. UPLB, Laguna.


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