CHAPTER 2

Pest management practices of lowland rice farmers in CambodiaG.C. Jahn, P. Sophea, K. Bunnarith, and P. Chanthy

AbstractWe interviewed 1,265 lowland rice farmers in Cambodia on their pest management practices from June 1995 to April 1996. Forty-three percent of the farmers were not aware of natural enemies of rice pests; 59% thought that pesticides increased rice yields. Only 19% believed the insecticide applications could produce pest outbreaks by killing natural enemies. More farmers applied pesticides in the dry season than in the wet season, and more men than women used pesticides. Pesticide users and nonusers did not differ significantly in average age, education, or farming experience. Nationally, 22% of wet-season farmers and 57% of dry-season farmers used pesticides. The rice yields of pesticide users and nonusers did not differ significantly, except in the wet season among farmers who did not use fertilizers. Insecticides and rodenticides were the most commonly used pesticides. None of the farmers used fungicides. An estimated 224,000 liters of pesticides were used annually on rice. In both the wet and dry seasons, nearly half of those applying pesticides used a knapsack sprayer. The average reported dry-season rice yield of 2.5 t /ha was significantly higher than the average reported wet-season yield of 1.4 t /ha.Introduction

Pest management in Cambodia

Several surveys have been conducted in Cambodia in recent years to address aspects of determining farmers’ knowledge, attitudes, and practices concerning rice pests. The first of these, made by the International Rice Research Institute in 1989 (Rapusas et al 1989), revealed that 28% of the 42 wet-season (WS) rice farmers interviewed in Takeo Province used insecticides. This survey, however, was conducted in areas where the government distributed insecticides to farmers, so the sample may have been biased in favor of insecticide use. Prom (1993) found that 40% of 60 dry-season (DS) rice farmers surveyed in Kandal Province used insecticides and that 70% believed insecticides increase yields. Joshi et al (1994) reported that of the nearly 100 WS and DS farmers in four provinces interviewed, more than 40% of those in the three provinces near the Vietnam border used insecticides, but none of those living in the province not bordering Vietnam used insecticides. Rickman et al (1995) interviewed 197 rice farmers (with no regard to season or ecosystem) in five provinces and found that 10% applied liquid pesticides.

Yech (1994) revealed that methyl parathion was the most popular insecticide among vegetable and rice farmers in Cambodia. He also found that of the pesticides being sold in 24 markets in 10 provinces, most belonged to the World Health Organization’s (WHO) hazard class I [WHO category I pesticides are “extremely and highly hazardous to human health.”]. According to Yech (l994), more than 50 pesticides- 73% of which were insecticides—were available in Cambodia representing 30 different active ingredients. Most pesticides are labeled in Thai or Vietnamese. The only ones with Khmer labels are the Japanese-produced insecticides fenvalerate, fenitrothion, diazinon, and cartap (Pisani 1996). Most of the pesticides in Cambodia were found to have far less active ingredients than indicated on the label (Nesbitt et al 1996).

Integrated pest management (IPM) survey

About 70% of Cambodians are rice farmers (CIAP 1995a). Lowland rice (irrigated and rainfed) is grown on most of the cultivated rice land in Cambodia; the most important crop protection issues focus on that crop. Through the Cambodia-IRRI-Australia Project (CIAP) IPM Program, we conducted a national survey to determine key rice pests, defined as ones that regularly exceed economic threshold levels (Bottrell l979).

The goal of the study was to document which lowland rice pests that farmers consider important and then focus research on determining the effects of those pests on yields. No laws or regulations deal with pesticides in Cambodia and anyone can purchase pesticides—unrestricted—from Thailand and Vietnam (Pisani 1996). Pesticide use is also unregulated. For example, some merchants spray pesticides on fish sold in open air markets to repel flies (Chaumeau 1996).

This survey was conducted to determine:• pest management practices of lowland rice farmers.• attitudes of lowland rice farmers toward pests and pesticides,• what farmers would like to know about pest management, and• farmers’ knowledge of the rice ecosystem.

These findings will be used to:• address the pest problems farmers consider as the most pressing, • evaluate farmer practices scientifically so that recommendations can be made to

farmers and organizations that assist farmers,

• identify dangerous or ineffective pest management practices,

• conduct research to improve on dangerous or ineffective practices,

• assist the Cambodian Government in developing training courses for rice farmers, and• understand misconceptions.

Survey site

Geographic location

Thailand, Lao PDR, and Vietnam border Cambodia. Four mountain ranges—the Cardomen and Elephant mountains to the west and southwest, the Dangrek Mountains to the north, and the central highlands of Vietnam to the east—are near Cambodia’s borders. These mountains surround a vast central plain containing the Tonlé Sap Lake and river complex (Nesbitt 1996). The rice-growing areas of Cambodia consist of the soils developed (from underlying parent material) on the old alluvial or colloidal plains and on the active floodplains (White et al 1996).

Current state of Cambodian development

Cambodia is one of the poorest and least developed countries in Asia. There is one telephone for every 1,200 people and more than 9,500 people per doctor. In comparison, Lao PDR has 300 people per telephone and 4,400 people per doctor. Only 38% of Cambodia’s population is literate, whereas literacy rates exceed 80% in Lao PDR, Thailand, and Vietnam. Of the four countries, Cambodians consume the least calories per day. Cambodia has the highest infant mortality rate in Southeast Asia, with 11% of Khmer babies dying before turning one year old. Nevertheless, Cambodia’s population is growing by 2.5% per year (Asiaweek 1996).

Rice production in Cambodia

From 1960 to 1969, the area planted to rice in Cambodia averaged 2.4 million ha per year (Khush et al 1986). Cambodian rice production peaked in 1969-70 at 4 million t (Helmers 1996, MAFF 1996). From 1970 to 1975, rice production declined drastically as the country plunged into civil war. The area cultivated to rice decreased by 77% between 1970 and 1974, and production dropped 84% (Hildebrand and Porter 1976). In 1975 the Khmer Rouge took over Cambodia. For the next four years, its members attempted to create a classless, agrarian, pure Khmer society. To boost rice production, the Khmer Rouge forced almost the entire population to grow crops or build irrigation canals. But the Khmer Rouge’s efforts to increase rice production were generally unsuccessful (Watts et al 1989). Vietnam succeeded in removing the Khmer Rouge from power in 1979 and pushed its forces to the Thai border. The regime continues to control territory in western Cambodia. In 1979, only 770,000 ha of rice were sown and a mere 588,000 ha were harvested, producing about 565,000 t of grain (FA0 1980, MAFF 1996). As a result, 35% of Cambodia’s 1980 food needs were supplied from international sources (Mason and Brown 1983).

The area under rice has grown steadily since 1979: 1.4 million ha in 1987, 1.7 million ha in 1992, and 2 million ha in 1995 (CIAP 1991, 1995b, MAFF 1996). About 1.6% of the potential lowland rice area cannot be used because of land mines (Nesbitt, unpublished data). Cambodian rice production reached 3.3 million t in 1995—about the same production level as achieved in 1967 on 2.5 million ha (CIAP 1991, 1995b, MAFF 1996). The major difference is that in 1967 the population was 6.6 million, whereas in 1995 it was 10 million (Asiaweek 1996, Tichit 1981).

Rice ecosystems in Cambodia

Wet-season rice. Most (93%) Cambodian rice land is classified as lowland, and the rest (7%) as upland and deep water. Most of Cambodia's lowland rice is grown during the wet season. Rainfed lowland rice (RLR) accounts for 88% of Cambodia's cultivated rice land, while the remaining 5% is irrigated. Most of this land is planted to late-maturing varieties, some to medium-maturing varieties, and limited amounts to early maturing varieties (Lando and Mak 1994a). Late-maturing varieties are usually planted in low fields where the water levels frequently exceed 50 cm. Medium-maturing varieties are usually planted in middle fields, where the highest standing water levels seldom exceed 40 cm, and in high fields, where the water levels seldom exceed 20 cm. Early maturing varieties are commonly planted in high fields (Lando and Mak 1994b). Roughly 90% of WS rice seed is sown in May through July, and 60% is harvested in December (FAO 1996).

Dry-season rice. Since 1982, DS rice has accounted for no more than 5-8% of the total rice area cultivated nationally (Lando and Mak 1991). It is not known what portion of DS land is used for two or more crops per season. The ability to grow DS rice depends on the presence of water, generally from wetlands and rivers. More than 30% of Cambodia is considered wetland (Selvanathan 1993), suggesting considerable potential to expand DS rice cultivation. DS rice seed is sown from late October to mid-November and harvested in March. Nearly all DS land is planted to early maturing varieties (Javier 1996). The modern, photoperiod-insensitive varieties can be grown virtually any time of the year, as long as the drainage and irrigation system is adequate. For example, in parts of Suay Rieng Province near Vietnam, farmers plant an early maturing irrigated crop from May to July. At least 15 orders of arthropods inhabit Cambodian lowland rice. Most of these are not herbivores or plant feeders (Arida and Banion 1995, Jahn et al 1996).

Rice research in Cambodia

Agricultural research ceased in 1970 because of the government's preoccupation with the civil war. During the Khmer Rouge regime, nearly all scientists were killed or fled the country, educational institutions were closed, and research libraries and government publications were burned. With the exception of some papers published in French journals before 1953, nearly all Cambodian agricultural research documentation was destroyed (CIAP Khmer staff members, pers. comm.). Rice research began again in 1986 when IRRI and the Cambodian Ministry of Agriculture, Forestry, and Fisheries (MAFF) signed a Memorandum of Understanding. Since 1987, the Australian Agency for International Development (AusAID) has financed this collaborative rice research effort, known as CIAP (CIAP 1994).

Methods

We collected data on farmers’ pest management knowledge, attitudes, and practices through structured personal interviews using a questionnaire. The survey instrument was based on one used in Vietnam to test the effects of a no-early-spray campaign (Heong et al 1994, Rapusas et al 1994). We did five pretests using 25 different farmers each time.

Pretesting revealed one serious obstacle. Farmers were originally asked to name the most common pests, but little agreement existed on local names of arthropods even within the same village. To overcome this problem, we created a poster of randomly mixed photographs and drawings of common rice insect pests and natural enemies, weeds, and diseases. Instead of providing names, farmers were asked to point to the pests that caused problems in their fields. They were then asked if there were other pests not shown on the poster. The questionnaire was originally written in English and then translated into Khmer. Fourteen Cambodians, trained in survey techniques and in using the questionnaire, served as the interviewers.

From June 1995 to April 1996, we interviewed 1,265 farmers from 154 villages in 10 provinces—Battambang, Kampong Cham, Kampong Chhnang, Kampong Speu, Kandal, Prey Veng, Pursat, Siem Reap, Svay Rieng, and Takeo (Fig. 1). These provinces, out of the country’s 21, represent 76% of the total lowland rice area. Survey sites were chosen on the basis of accessibility, security, and lowland rice production. In each village, a group of two to five interviewers conducted the survey. No lists of the residents of the villages existed, so the interviewers simply chose farmers for the survey. They were, however, instructed to include both men and women of different economic status and of a variety of ages. A given farm was only represented once in the survey.

While not truly a random sample, the survey results do not appear to represent any bias in farmer selection on the part of the interviewers. Given that parametric tests are robust, we assumed a normal distribution and a random sample for the purpose of data analysis.

The survey data were coded and entered into the Microsoft Excel® spreadsheet (Version 5.0) on a computer. Data were analyzed with the Microsoft Excel® and Statistica® software programs (Microsoft Corporation 1993). Averages were compared by t-tests, and frequency associations were measured by chi-square tests.

Fig. 1. Map of Cambodia. Each dot represents one of the 168 villages included in the IPM survey.

Survey results and discussion

Farmer profiles

Fifty-seven percent of the respondents were men and 43% women. These percentages should not be taken to indicate the sex ratio of rice farmers because we made no attempt to record the number of men and women in each household. Their ages ranged from 17 to 76 years and averaged 43 years. Respondents had 0- 13 years of education, with the average being 3.7 years. Most had spent the greater part of their lives as rice farmers, with their farming experience ranging from 1 to 60 years and averaging 23 years. Since the 1993 elections, land tenure remains an unresolved issue in Cambodia; nonetheless, 99% of WS farmers and 100% of DS farmers claimed that they owned their largest fields.

Wet season. Families growing WS rice had 1-14 fields; the average was three. Field size ranged from 0.05 to 7.0 ha, with an average of 0.6 ha. About 77% of WS fields are never flooded by river water, 22% are flooded once a year, and 1 % twice a year. Most farmers said they grow traditional varieties. Only 1% of WS farmers reported growing IRRI-derived varieties, representing an estimated 0.9% of the national area planted to rice.

Dry season. Families planting DS rice had one to seven fields, with an average of two. The DS fields ranged from 0.05 to 3.5 ha, with an average of 0.5 ha. Ninety-two percent of these DS fields are flooded with river water once a year; the rest are not. Most DS farmers (82%) grow IRRI-derived varieties, representing 92% of the national DS rice area. This high percentage of IRRI-derived varieties used in the Cambodian DS is consistent with the findings of Joshi et al (1994).

Farmer knowledge of pests and natural enemies

Nationwide, farmers named more than 50 different pests they consider important in rice. Except for umbrella sedge Cyperus difformis in the DS, no particular pest was cited by more than half the respondents. The ones most commonly reported were umbrella sedge, rats, yellow leaf, stem borers, and jungle rice Echinochloa colona. Yellow leaves can be caused by any number of diseases or nutrient deficiencies. Tungro disease can cause yellow leaves, although its vector, the green leafhopper Nephotettix virescens, was rarely reported as a pest. More than 20% of WS farmers considered crabs to be a major pest, but less than 10% of DS farmers did. Joshi et al (1994) also found farmers to frequently mention stem borers, rats, and crabs as major pests.

More than 30% of DS growers considered caseworms to be a serious pest, whereas only 17% of WS growers did (Table 1). Of the farmers reporting caseworm problems, one-third of WS farmers and more than 70% of DS farmers attempt to manage them. Ironically, caseworms should be easier to manage in the dry season when farmers have more control over the water in their fields. Draining rice fields provides good control of caseworms in Cambodia, with damage occurring only in those parts of the field with stagnant water (Kun 1994). DS farmers, however, mainly use pesticides on caseworms. Only one DS farmer reported controlling them by draining water from the field.

Farmers are generally aware of pest damage to their rice but do not necessarily understand the cause. For example, more farmers reported stem borer damage than reported stem borers (Table 1). About 43% of farmers were unaware that natural enemies exist, and some reported natural enemies as their major pests. The most extreme case of this was in Kandal, where 43% of DS farmers reported ladybird beetles as pests. Besides eating insects, ladybird beetles do in fact eat rice pollen, but there is no evidence that this affects yield. Except for ladybird beetles, less than 8% of farmers reported any given species of natural enemy as a major pest in any province in any season (Table 2).

Only 1 % of farmers mistakenly thought that some pests, such as crabs and mole crickets, do not damage rice. On the other hand, 87% of farmers knew that some animals in the field do not damage rice; frogs were cited the most often. Of these farmers, 66% knew that frogs and other predators eat insects, and more than half of the 66% thought that pesticides could kill natural enemies.

Attitudes toward pesticide use

Farmers were asked to express their agreement or disagreement with several attitude statements. The majority (59%) agreed with the statement "Applying pesticides to rice increases yields,” whereas 36% disagreed, 4% said they did not know, and the rest said it depends on the situation. This is consistent with Prom (1993), who also found that most Cambodian rice farmers thought that pesticides increase rice yields.

Among the farmers aware of natural enemies, 33% agreed that killing natural enemies with pesticides can cause pest outbreaks, 45% disagreed, and 22% said they did not know. Overall, only 19% of the farmers interviewed thought that pesticide applications could produce pest outbreaks by killing natural enemies.

Pest management practices

Pesticide use. The percentage of farmers using pesticides varied greatly from one province to another: 8-50% of WS farmers, and 40-100% of DS farmers. Nationally, 27% of farmers used pesticides in the WS, and 59% in the DS. Among those applying pesticides in the WS, 20% used insecticides, 8% used rodenticides, and 1% used herbicides. Among those applying pesticides in the dry season, 41% used insecticides, 25% used rodenticides, and 1% used herbicides (Table 3). Like Yech (1994), we found that methyl parathion is the most commonly used insecticide. Interestingly, methyl parathion is one of the few pesticides sold in Cambodian markets that contains as much active ingredient as claimed on the label (Nesbitt et al 1996). Our findings agreed with those of Yech (1994) that zinc phosphide is the only rodenticide used in Cambodia.

Herbicide users did not know what kind of herbicide they used, although 2,4-D, paraquat, and alachlor are the ones available in Cambodian markets. Herbicide use was highest in Battambang, which is consistent with findings of Rickman et al (1995). Rapusas et al (1989) found no herbicide use in Takeo (Table 3).

None of the farmers interviewed used fungicides, though some erroneously applied insecticides for fungal diseases such as brown spot.

Pesticides were the most common method of controlling major DS pests except for weeds. Among the farmers using insecticides, more than 93% looked for insect damage to decide when to apply insecticides. The other farmers sprayed on a schedule or simply copied their neighbors’ spraying schedules. Of those who looked for pests or damage, 73% applied insecticides whenever they saw pest damage, and 26% sprayed when they observed a certain number of insects (regardless of type). The remaining 1% of farmers sprayed any insect, only sprayed certain kinds of insects, or sprayed when pests exceeded predators.

The 10 provinces in this survey have 1.3 million ha of WS lowland rice and 159,000 ha of DS lowland rice (Javier 1996). Assuming that 20% of WS farmers and 41% of DS farmers used insecticides and that the same percentage of rice received insecticides, then about 260,000 ha of WS rice and 65,000 ha of DS rice received insecticide applications. Farmers were not usually certain how many times they applied insecticides in a season, but knew at which stages of the rice crop they applied them. By counting the number of stages in which they applied pesticides, we were able to determine the minimum number of insecticide applications in a season for each farmer. In the DS, farmers applied an average of 0.7 liters /ha of insecticide an average of 2.7 times. We therefore estimated that DS farmers (in these 10 provinces) applied at least 123,000 liters of insecticide. WS farmers applied an average of 0.5 liters /ha of insecticide at least 1.3 times, for a total of 169,000 liters. Thus, we estimate that at least 29 in the 10 provinces surveyed.

It appears that knapsack sprayers are becoming more popular in Cambodia. In 1989, not a single WS lowland rice farmer of the 42 interviewed in Takeo used a farmers in the province (107 respondents) and 19% of the DS lowland farmers (52 respondents) used knapsack sprayers. Nationally, 10% of the 1,103 lowland WS farmers interviewed and 27% of the 281 lowland DS farmers used knapsack sprayers. This means that 48% of the WS and DS lowland farmers applying pesticides used knapsack sprayers. Rickman et al (1995) found that 2% of 197 farmers across ecosystems used knapsack sprayers. In this survey, 3% of pesticide users reported pouring insecticides into bowls and flicking the chemicals over their fields with brushes or leaves. About 9% used a homemade plunger-type sprayer that squirts large volumes of insecticide over a few spots in the field. These plunger-sprayers consist of one metal or bamboo tube inside of another. They are usually used for applying insecticides to seedbeds. The rest of the farmers mix pesticides with bait and place it in the field for rat control. Only 6% of DS farmers and 1% of WS farmers who use pesticides reported that they regularly mix different pesticides together. A few farmers mixed pesticides in the same container they used to fetch drinking water or to feed domestic animals.

Cultural and physical control. Farmers reported using mainly hand weeding to control weeds. Diseased or pest-damaged rice plants are commonly pulled from fields. According to Rickman et al (1995), farmers spend an average of 15.6 days /ha hand-pulling weeds from fields each season.

Botanical pest control. Several farmers mentioned that they chop up a cactus-like plant and place it in the water to kill or repel crabs. A few farmers reported that when they see yellow rice plants in the field, they stick Chromolaena odorata branches into the ground upright to make a fence around the yellow rice, which then turns green within a week. C. adorata, called kanthraing khait in Khmer, is usually not cultivated.

Joshi et al (1994) reported that some farmers chop up the leaves of C. orlorata, eucalyptus, or papaya and broadcast them in the rice field to drive away crabs or insects. Eucalyptus oils are known to repel ants (Jahn 1991), but the insect repellent properties of papaya and C. odorata are unknown. Surprisingly, no one has reported Cambodian rice farmers using the neem tree (Azadirachta indica) for pest control, although some farmers use neem leaves to help preserve stored grain. The neem tree is common in the country and neem parts are used in the traditional Khmer diet and medicine. Neem leaves and extracts are well documented to have adverse effects on many insects (Lim and Bottrell 1994).

Unusual pest management practices. Several farmers reported that they treat pest problems by applying handfuls of fertilizer, ashes, or salt to the damaged area. Many use smoke to drive away rice bugs and other insects. Some farmers unwind old videotape and encircle their fields with it to keep the birds away. As the tape flutters in the wind and reflects sunlight, it scares the birds. Some farmers mix fish oil with crushed rice bugs to attract other rice bugs to traps (Rapusas et al 1989).

Many farmers (60%) reported receiving their pest management advice from their neighbors, whereas only 22% obtain advice from extension workers (Fig. 2). One farmer said he did not seek advice—instead, he performs his own experiments to see what works best.

Farmers were asked what subjects they would like to know more about. About 35% had questions about pests, 30% wanted to know about fertilizers, 20% had no questions, 18% had questions about pesticides, and the remainder were interested in farm management. When asked how they would like to get this information, 45% said in school or a training program, 23% reported radio, 23% mentioned pamphlets or magazines, 7% indicated TV, and 1 % specified extension. Some respondents mentioned more than one preferred means of receiving information. About 6% expressed no interest in receiving additional information. The relatively strong desire to learn in school or attend a training program suggests that such programs could have a significant impact in Cambodia.

Relationships and patterns in pest management Yield and pest control. Farmers were asked how much rice they harvested from their largest field in the previous season. National average DS yields of 2.5 t /ha were significantly higher than average WS yields of 1.3 t /ha (P<0.05). Farmers controlling pests, regardless of method, had higher average yields in both seasons than farmers who did not practice pest control. Farmers using fertilizer also had significantly higher yields than those not using fertilizer in both seasons (Table 4).

Because pest control is associated with fertilizer use in both seasons (Table 5), we compared the yields of those controlling and not controlling pests among fertilizer users and nonusers in both seasons. This analysis revealed that pest control, which includes all methods of pest management (hand weeding. setting traps, and applying pesticides), produces significantly higher yields (Table 6). Among the 214 DS farmers using fertilizer, only eight did not practice any form of pest control so the yield comparison cannot be made for this group.

To determine whether pesticides themselves have a measurable effect on average yield, we compared the yields of pesticide users and nonusers. Pesticide users did not have significantly higher yields in either season. In fact, in the wet season, farmers using pesticides had significantly lower yields (Table 7). This may indicate that WS farmers do more harm than good with their pesticide applications (by destroying natural enemies), or it may mean that pesticides are being applied in the WS after the pests have already reduced yields.

Sociodemographic factors and pesticide use. Male farmers were more likely than female farmers to use pesticides: 24% of the men and 18% of the women reported using pesticides on their WS rice crop, whereas 73% of the men and 48% of the women did so in the DS. When women used pesticides, they generally had a man, usually a relative, apply the chemicals. In every province in both seasons, more than 80% of the persons actually applying the pesticides were men. Prom (1993) found that in most households the husband and wife decide jointly whether pesticides should be used, but that the husband usually applies them. Our survey detected no significant differences in the national average age, education, or experience of pesticide users and nonusers.

Conclusions

Farmer knowledge

Lowland rice farmers generally have a poor understanding of the broad-spectrum nature of pesticides, as indicated by only 19% of the respondents believing that pesticides can cause pest outbreaks. An awareness of natural enemies is common, but their importance in the rice ecosystem is usually not grasped.

Farmer practices

Most WS growers do not use pesticides, whereas most DS growers do. The overwhelming majority of pesticide users decide when to spray based on seeing pests or damage. Spraying on a schedule is rare. Nearly half the farmers who use pesticides in each season apply them with knapsack sprayers. Analyses of yield data indicate that fertilizers and pest management increase rice yields significantly in both seasons, but pesticides by themselves do not seem to improve yields. These results do not necessarily mean that pesticides cannot contribute to increased yields, but instead suggest that most farmers surveyed do not use pesticides effectively.

Socio-demographic factors

In both seasons, more men than women use pesticides. Most pesticides are applied by men, even on farms owned by women. Pesticide users and nonusers did not differ significantly in national average age, education, or years of farming experience.

Implications for research

Rice pest constraints. Farmers named more than 50 pests that cause problems in their rice fields. With the exception of umbrella sedge, no single insect pest or disease was cited as a problem by more than half the farmers in either season. To determine which pests named by farmers actually affect yields negatively, we are conducting a rice pest constraint study. We are collecting and identifying pests from five DS and 15 WS rice fields four times per season for four years. By relating the information on pest abundance in each field to the yields in each field, we will detect which pests suppress yields. Tungro-like symptoms were reported in both the WS and DS, which led to a search for tungro in Cambodia. IRRI virologist Ossmat Azzam, through immunological tests, has positively determined the presence of tungro virus, although at low levels.

Effects of pest management practices on yields. We will conduct the same analysis on the rice pest constraint yield data that we conducted on the survey yield data to see whether the relationship between fertilizers, pesticides, and yield is the same. In addition, we will conduct replicated field trials comparing the yields of untreated plots, plots treated with pesticides by farmers following their usual practices, and plots treated with pesticides based on the economic thresholds described by Reissig et al (1986).

Botanical control. More than 20% of WS farmers consider crabs a pest problem. Some farmers reported that placing pieces of a cactus in the water prevents crab damage. We are conducting experiments to see whether this technique has merit.

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Notes

Authors’ addresses: G.C. Jahn, International Rice Research Institute, Cambodia-IRRI-Australia Project, P.O. Box 1, Phnom Penh, Cambodia; P. Sophea, K. Bunnarith, and P. Chanthy, Department of Agronomy, Ministry of Agriculture, Forestry, and Fisheries (MAFF), 14 Monireth Street, Phnom Penh, Cambodia.

Acknowledgments: We thank the Ministry of Agriculture, Forestry, and Fisheries, and the provincial agricultural offices for helping to coordinate visits to remote villages, particularly in areas where there were security risks. Ms. Chhem Chantha, Mr. Hor Sophal, Mr. Khiev Chan Theavy, Mr. Khuon Samoeun, Mr. Men Chhon, Mr. Nhem Sokha, Mr. San Vuthy, Ms. Seung Keo Viseth, Mr. Som Sarun, Mr. Soun Kimsan, and Ms. Suy Sakunthea of the Department of Agronomy and the provincial agricultural offices helped conduct interviews and we are grateful for this assistance. We also thank the staff of PRASAC 3 in Svay Rieng for conducting interviews. We appreciate the helpful editorial comments of Dr. K.L. Heong, Ms. Carolyn Dedolph, and Dr. M.M. Escalada. Special thanks go to Dr. Harry Nesbitt for access to unpublished data on land mines; and to Mr. Joseph Rickman, Mr. Kent Helmers, Dr. Peter White, Dr. Edwin Javier, and Dr. G.S. Sidhu for useful suggestions on the survey format and data analysis.

This study was a collaborative effort among the Cambodian Department of Agronomy, IRRI, and the Australian Agency for International Development (AusAID); the Government of Australia, through AusAID, funded the research.

Citation: Jahn GC, P Sophea, K Bunnarith, P Chanthy. 1997. Pest management practices of lowland rice farmers in Cambodia. p. 35-51. In: Heong KL, Escalada MM (editors). 1997. Pest management of rice farmers in Asia. Manila, Philippines: International Rice Research Institute. 245 p.