Characteristics of water balance in a rainfed paddy field in Northeast Thailand

Rice productivity in rainfed paddy fields varies with seasonal changes of water availability in which the conditions of flooding are affected by the water balance. Hydrometeorological measurements were performed in a rainfed paddy field in Northeast Thailand from July 2004 to December 2006 to analyze the water balance. As a result of our measurements, climatologically conditions were classified as semi-humid with an annual precipitation of 1,100 mm/year and annual potential evaporation of 1,660 mm/year in both the year. The surface layer of the paddy soil was clayey and the hydraulic conductivity was very low, so groundwater levels remained below the soil surface even under flooded conditions during the rainy season. Seasonal changes in the amount of soil water were very small, comprising only less than 16% of the total precipitation during the rainy season. Consequently, an effective precipitation of less than 180 mm was enough to establish standing water in the rainfed paddy field. Shinkichi Goto, Tsuneo Kuwagata and Pisarn Konghakote contributed equally to the paper.     

Genetic analyses of heading date of Japonica rice cultivars from Northeast China

Northeast regions of China (38–55°N latitude) play an important role in Japonica rice planting. Heading dates of 10 Japonica rice cultivars native to the Northeast of China were investigated and their sensitivities to photoperiod and temperature were analyzed. The results showed that these Japonica rice cultivars were insensitive to photoperiod but strongly sensitive to temperature, i.e. a high temperature can markedly shorten the heading date. Genetic analyses were conducted on these 10 cultivars using a set of heading date tester lines. All these Japonica cultivars carried a dominant early heading gene Ef-1, and most of these cultivars carried the photoperiod insensitivity allele e₁, and two types of alleles were presented at the Se-1 locus, including recessive photoperiod insensitivity gene Se-1^e and dominant strong photoperiod-sensitivity (PS) gene Se-1ⁿ. The PS of these cultivars carrying E₁ or Se-1ⁿ can be repressed or weakened by Ef-1 and the recessive allele hd2 they carried. These results provided a reasonable explanation to the adaptability of Japonica rice to the high latitude environment of the Northeast China, and could be useful for breeding new cultivars well adapted to the high latitude regions and expanding the rice cultivation range.     

Research on genetics of rice heading date

Heading date is one of the most important traits for rice adaptation to cultivation area and crop seasons, and it is mainly determined by photoperiod, basic vegetative growth, and temperature of cultivars. The diversity of combinations of photo-sensitive varieties and the basic vegetative, makes the heading date varied. On one hand, this supplies abundant resources for different ecotypes breeding; on the other hand, it complicates the inheritance of heading date. In recent years, transgression of late maturity has often been encountered, especially between indica and japonica subspecies, this had inhabited the use of hybrid vigor. Therefore, understanding the inheritance basis of heading date is very important for breeding practices.     

Nutrient management for rainfed lowland rice in northeast Thailand

Average grain yields of rainfed lowland rice in northeast Thailand are the lowest in the region, and they barely changed in the past decade. Improved fertilizer management is one of the few options to enhance cropping system productivity but related results from previous studies were often disappointing and sometimes contradictory, possibly due to the large variability of soil and water resources. Therefore, the objectives of this study were to develop a site-specific nutrient management approach, and to propose a related decision tool for farmers. For this purpose, we conducted on-farm experiments in Kumpa-Oong Village, Roi Et Province, during the 2003–2005 cropping seasons. Tested fertilizer treatments were designed based on topographic field position. A comparison of soil characteristics between lower and upper fields revealed significantly higher soil fertility for lower fields (higher pH, TOC, TSN, CEC, clay, and silt content; lower sand content). Across seasons and treatments, grain yields were higher in the valley bottom (VB; 2.82 t ha⁻¹) than on upper and middle terraces (UMT; 1.68 t ha⁻¹). In all seasons, significant fertilizer treatment effects were detected only in UMT fields. But the comparison of treatment effects in individual fields and in both toposequence positions showed that the limited average fertilizer response was mainly caused by low or even negative responses in fields with a higher control yield, i.e., with higher indigenous nutrient supply. A missing or even negative fertilizer response occurred at lower control yields in UMT fields, most probably because attainable yields in these fields were lower as a result of limited water resources. Thus, site-specific fertilizer recommendations need to take toposequence and the field-specific indigenous nutrient supply into account. Based on these results, we proposed a decision tool that helps farmers to choose the most adequate fertilizer treatment for their fields, based on their knowledge of specific field characteristics. On-farm testing of the proposed decision tool is the next step to show whether this approach is acceptable to farmers and can contribute to higher resource-use efficiency and system productivity.     

Simulation model of rainfed rice production on sloping land in northeast Thailand

In northeast Thailand, the rapid expansion of rainfed paddy fields has decreased the stability of rice production. This paper describes a model that computes rice production on the basis of the hydrologic conditions of rainfed paddy fields on hill slopes. The model well expressed the hydrologic processes, rice yield, and production at the study site. We simulated rice production as uphill paddy plots are abandoned, increasing catchment area, under various rainfall conditions. The simulation showed that rice yield and stability increase as uphill plots are abandoned, although the total rice production decreases. Thus, the effect of catchment size on rice production in each plot was quantified. The model proved to be useful for analyzing rainfed rice production under various land and water conditions.     

A water balance model for characterization of length of growing period and water stress development for rainfed lowland rice

There is large year-to-year variation in rice production across the Mekong region (Laos, Cambodia and Thailand) due to uncertainty in the timing of the onset of the wet season and drought stress that may develop at any time during the growth of rainfed lowland rice. Unique to the nature of lowland water balance is a large component of deep percolation water loss, which depends on soil texture. The objectives of this study were to develop a soil water balance model for calculating the amount of water held in field storage (i.e. in soil and, if there is standing water, above the soil surface) and to apply it to determine the length of growing period (LGP) and water stress development in relation to soil type and rainfall pattern for the rice ecosystem. The water balance is computed separately for above-ground plus topsoil layer and subsoil layer. Components of the water balance are the existing amount of stored water, rainfall, evapotranspiration, deep percolation, and runoff. The deep percolation rate was determined from clay content in each soil layer. The model runs with daily or weekly weather data to estimate the soil water level for the growing period in the wet season. The model was validated with data collected from top, middle and bottom of rainfed lowland fields in Savannakhet province, Laos. The best correlation between the observed and simulated water level was obtained (r² = 0.41) for middle fields. The simulation results showed that LGP varied greatly from year to year, particularly in locations with sandy soils, due mostly to variation in monthly rainfall occurring at the early part of the growing season (April), but also to some extent by variation at the end of growing season (October). Soil texture on the other hand is shown to have a large influence on the end of the rice growing period and hence LGP, and also water stress development during growth. Sandy soils with clay content less than 7% that are prevalent in the province are shown to cause frequent water stress and early finish in rainfed lowland rice. The model accordingly provides reasonable outputs that can provide a geographical dimension of soil hydrological patterns for various rice growing environments, and also identify the spatial pattern of drought stress that is likely to occur. Model outputs can be used to provide guidelines for practical advice to the rice farmers and researchers for determination of appropriate crop management strategies (e.g. time of planting, varieties), and policy makers for investment decisions on inputs (e.g. fertilizer price) aimed at increasing rice productivity in this Mekong region.     

Effects of planting date and variety on flooded rice production in the deepwater area of Thailand

Crop management plays an important role in the transition from a deepwater rice to a flooded rice production system but information about optimum management strategies are currently lacking. The goal of this study was to determine the effect of planting date and variety on flooded rice production in the deepwater area of Thailand. Two experiments were conducted at the Bang Taen His Majesty Private Development Project in 2009 and 2010 to represent conditions prior to flooding (early rainy season) and after flooding (dry season). The early rainy season crop covered the period from May to October 2009, while the dry season crop covered the period from November 2009 to April 2010. The experimental design was a split plot with four main plots and three sub plots replicated four times. The treatments for the main plot were various planting dates, while the treatments for the sub plots were rice varieties. The dates of the critical developmental phases of rice were recorded and biomass was sampled during the growing period. The collected data were statistically analyzed using ANOVA and treatment means were compared to identify the appropriate plating date and the best variety for the area. The highest average yield was obtained for variety PSL2 across transplanting dates from June 19 to July 23, with an average yield of 3898 kg ha⁻¹. The dry season crop showed that both biomass and yield were affected by the interaction between planting date and variety. The highest yield was obtained for variety PTT1 transplanted on November 9. The research showed that the variety PSL2 is the most suitable variety for early rainy season production with a transplanting date ranging from June 19 to July 23, while the variety PTT1 planted on November 9 was the best management practice for the dry season crop. However, a high yielding flooded rice variety that has a short growth duration is still needed for this area.     

Genotypic differences in grain yield of transplanted and direct-seeded rainfed lowland rice (Oryza sativa L.) in northeastern Thailand

We evaluated the genotypic differences in grain yield of 14 rice (Oryza sativa L.) genotypes with different phenology under four growing conditions: transplanting (TP) or direct-seeding (DS) in a toposequentially lower (with favorable water conditions) or upper (drought at around flowering stage) field at Ubon Ratchathani, northeastern Thailand. Thirteen of the genotypes – five early-maturing, four intermediate, and four late – had been bred for rainfed lowlands in northern and northeastern Thailand. IR24, a semi-dwarf, high-yielding, and early-maturing genotype bred for irrigated lowlands, was included for comparison. Genotypic differences in grain yield were significant in a combined analysis of all 4 growing conditions, and both high sink size (spikelet number per area) and high ripened grain percentage were associated with high yield. IR24 did not out-yield the rainfed-lowland genotypes, and its yield was particularly low in DS, owing to poor shoot dry matter production and low spikelet number per panicle. In the lower field, the interaction between cultivation method and genotype was also significant. In the lower field, late maturity was more strongly related to high shoot dry weight at maturity in TP than in DS; some of the early- to intermediate-maturing genotypes in DS produced shoot dry weights at maturity that were comparable to those of the late-maturing genotypes. High shoot dry matter production and large spikelet number per panicle were associated with high grain yield in DS genotypes in the lower field, whereas in TP genotypes with large numbers of panicles were required for high grain yield. Although the field location–genotype interaction and the field location–cultivation method–genotype interaction were not significant, regression analysis showed that late-maturing genotypes yielded less than earlier maturing genotypes, owing to the smaller ripened grain percentage resulting from late-season drought, in the upper field but not in the lower field. The presence of a trade-off between number of ripened grains and grain size in the lower field indicated the possibility of increasing the yield in rainfed-lowland genotypes by increasing assimilation capacity during grain filling. Phenology is important in the development of higher-yielding genotypes for different cultivation methods and different toposequential positions.     

Modeling the dependence of the crop calendar for rain-fed rice on precipitation in Northeast Thailand

Rain-fed lowlands are major agricultural ecosystems used for rice production in Northeast Thailand. Developing a tool to assess the effects of variable water conditions on the regional scale yield is also important to predict the effects of climate change on food supply. To estimate regional yields, we need a simple but accurate measure of the crop calendar (i.e., the distribution of planting dates), which has a strong influence on grain yield. In this article, we modeled the dependence of the crop calendar on rainfall patterns based on a survey of the region’s farmers as a part of an effort to provide a stronger basis for regional yield estimates. Our survey, conducted in 11 provinces for 2 years, confirmed the existence of large windows for sowing and transplanting versus narrow windows for heading and harvesting for rain-fed lowland rice culture in all the provinces. Variable water, soil, and toposequential conditions in the paddy fields were responsible for the large sowing and transplanting windows, whereas the use of photoperiod-sensitive varieties explained the narrow windows for heading and harvesting. The crop calendar was well expressed as a function of cumulative precipitation from June onward. When the crop calendar model was combined with a simple phenology-based model that uses growing degree-days adjusted by a day-length factor, we could estimate the rice crop calendar under rain-fed lowland conditions with acceptable accuracy. The model described in this article will be combined with a crop growth model to improve regional yield estimates for rain-fed lowland rice.     

Spatial variability in the growth of direct-seeded rainfed lowland rice (Oryza sativa L.) in northeast Thailand

Large within-field variation in rice growth often causes production loss in broadcast-seeded (BC) rainfed lowland rice. The spatial variability of direct-seeded rainfed lowland rice was evaluated in 2004, 2005, and 2007 in on-station experiments at Ubon Ratchathani, northeast Thailand, in relation to soil water content and weed infestation, by adopting semivariogram and block kriging, including comparisons among BC with harrowing (BCH; no weeding), BC with no harrowing (BCNH; no weeding), and row-seeded (RS; interrow weeding once) fields. BCH and BCNH were also compared in 11 farmers’ fields in 2006 and 2007, to assess the effect of harrowing on rice growth and weed infestation. During most of the rice growing periods, flooded and non-flooded portions existed simultaneously in the fields, with different proportions among years and among seeding methods in the on-station experiment. BCH and BCNH rice had large within-field variation in seedling density, heading date, shoot dry matter, grain yield, harvest index, panicle density, and filled spikelet per panicle, as well as in weed infestation, measured by a quick visual estimation. Many of the measured variables (except mean soil water content in RS in 2007, seedling density in BCH in 2005 and 2007, shoot dry matter in BCH and BCNH in 2007, and panicle density in BCH in 2007) were spatially dependent (i.e., data from nearby locations were most similar) by geostatistical analysis. Analysis of correlations using the 420 data sets of BCH plots in 2005 and BCH, BCNH, and RS plots in 2007 revealed a positive correlation between soil water content and grain yield and negative correlations between weed infestation and soil water content and grain yield. Compared with BCH, in 2007 BCNH had much lower grain yield because of lower soil water content after establishment and more weed infestation. BCH had higher grain yield than BCNH in weedy fields in the farmers’ fields experiment. RS with interrow weeding resulted in a smaller coefficient of variation, smaller sill value, and higher grain yield than BCH, due to less weed infestation and a higher proportion of flooded water. These results indicated that reducing the spatial variability in rice growth requires careful field preparation, such as harrowing to level the soil surface and to reduce the uneven distribution of standing water and the variability in soil water content, combined with effective crop and weed management (i.e., harrowing and row-seeding). This is the first study that examined spatial variability in the growth of direct-seeded rice as a function of soil water content and weed infestation in a rainfed lowland environment.     

Genotype-by-environment interactions for grain yield associated with water availability at flowering in rainfed lowland rice

While a large genotype-by-environment (G × E) interaction component of variance for grain yield (GY) has been widely reported for rainfed lowland rice, the reasons for such large interactions are not well known. A random reference population of 34 genotypes taken from the Cambodian rice improvement program was used to examine the magnitude and nature of G × E interactions for GY in Cambodia. These genotypes were evaluated in a multi-environment trial (MET) conducted across 3 years (2000–2002) and eight locations in the rainfed lowlands. The G × E interaction was partitioned into components attributed to genotype-by-location (G × L), genotype-by-year (G × Y) and genotype-by-location-by-year (G × L × Y) interactions. The G × L × Y interaction was the largest component of variance for GY. The G × L interaction was also significant and comparable in size to the genotypic component (G). The significant G component was partly explained by a group of four genotypes that were broadly adapted to different environmental conditions represented by three environmental groups. The three environmental groups were identified from a pattern analysis, and the grouping was partly related to the time of sowing, and hence water availability at flowering. A major factor contributing to the large G × L × Y interactions for GY was late maturing genotypes being affected greatly when soil water availability at flowering was reduced greatly, compared to earlier maturing genotype groups. While the differential genotypic responses to the water availability environment explained part of a large G × E interaction for GY, other non-water related environmental conditions also appeared to have contributed to the interaction. Three target environments were identified for focusing efforts of the breeding programs in Cambodia, and four putative genotypes were selected for their high yield and wide adaptation in the rainfed lowlands.     

A model driven by crop water use and nitrogen supply for simulating changes in the regional yield of rain-fed lowland rice in Northeast Thailand

Climate change will have significant impacts on the rain-fed rice production ecosystem, and particularly on the ecosystem’s hydrology and water resources. Under rain-fed lowland conditions, substantial variations among fields in grain yield are commonly observed, but a method that can account for field-scale yield variability to produce regional-scale yield estimates is lacking, thereby limiting our ability to predict future rice production under changing climate and variable water resources. In this study, we developed a model for estimating regional yields of rain-fed lowland rice in Northeast Thailand, by combining a simple crop model with a crop calendar model. The crop model incorporates the effects of two important resources (water and nitrogen) on crop growth. The biomass accumulation is driven by water use, whereas the nitrogen supply determines canopy development and thereby constrains crop water use. Accounting for the wide range of planting dates and the strong photoperiod-sensitive characteristics of rice varieties through the calendar model is an essential component in determining regional yield estimates. The present model does not account for the effects of mid-season drought or flooding, but was nonetheless able to explain the spatial and temporal yield variations at the province level for the past 25 years. Thus, it can be used as a prototype for simulating regional yields of rain-fed lowland rice.     

Effects of topography on the construction and efficiency of earthen weirs for rice irrigation in Northeast Thailand

Farmers in some parts of the Indochina Peninsula have been using earthen weirs to supply water to their rice fields, and the use of such weirs is especially prevalent in Northeast Thailand. Although now a typical rain-fed rice cultivation area, a significant percentage of rice fields in Northeast Thailand used earthen weirs before the extensive expansion of rain-fed rice fields that occurred in the early 20th century. In this study, we clarified some of the historical changes associated with the construction and use of earthen weirs and their effects on rice production. In particular, we investigated some of the topographic effects, such as terrain, catchment size, and slope grade, on water delivery. In addition, water delivery methods, construction periods, and the discontinued use of earthen weirs were examined with respect to regional influences and topography. Earthen weirs were found to be most suitable in areas that exhibited complementarity between the riverbed slope and the water catchment. The type of earthen weir was dependent on the magnitude of the riverbed slope. Earthen weirs have been constructed continuously on steeper upstream slopes of rivers for more than a century, while weir construction on lower riverbeds with larger catchments appears to be more recent.

Chlorophyll fluorescencein vivo as an indicator of water stress in potato leaves

Potato plants, cv. Desirée, were exposed to a -0.3 MPa polyethylene glycol-induced water stress for 24 h in a hydroponic system. Leaves with a Leaf Plastochron Index of 3 to 3.99, 4 to 4.99 and 6 to 6.99 were measured for total, osmotic and pressure potential, leaf conductance andin vivo chlorophyll fluorescence transients F_o, F_p and F_T. Leaf conductance and F_o significantly declined with leaf age in unstressed leaves. Water potential components and leaf conductance were significantly lower after 4 h of water stress whereas all three chlorophyll fluorescence transients measured after 24 h were significantly higher. The increase in fluorescence transients suggested that PSII electron acceptors were reduced faster than PSI and the Calvin cycle could oxidize them.In vivo chlorophyll fluorescence provides a greater understanding of the physiological effects of water stress but it requires additional experimentation to make it useful in screening for water stress tolerance.     

Study on structure and function of an earthen bund irrigation system in Northeast Thailand

In Northeast Thailand, which overlaps with an erosional plain that is not suitable for irrigation because of poor water resources and terrains that prevent efficient water distribution, farmers have long supplied water to surrounding paddy fields by blocking rivers completely with earthen bunds. Although such a traditional irrigation system fits well with the characteristics of Northeast Thailand, those who are concerned with modern irrigation development projects in Northeast Thailand seem to have been paying little attention to it. The present study was performed to facilitate development of more appropriate irrigation systems in Northeast Thailand by providing information regarding traditional irrigation methods. We investigated the traditional irrigation methods with earthen bunds at three study sites, and our results indicated that styles of irrigation vary with riverbed slope. The traditional irrigation system that is used in most of Northeast Thailand is different from ordinal weir irrigation, in that paddy fields are not irrigated by gravity flow but by backwater of earthen bunds. Our results suggest that the development of more successful irrigation systems would be possible through improvement of the design ideas of traditional irrigation methods.

Genetic analysis of rainfed lowland rice drought tolerance under naturally-occurring stress in eastern India: Heritability and QTL effects

Drought tolerance is an important rainfed rice breeding objective, but because the heritability (H) of yield under drought stress is thought to be low, secondary physiological traits are considered better targets for selection than yield under stress per se. This assumption has rarely been tested, and there are no reports on H for yield under drought stress from experiments repeated over seasons in rainfed lowland rice. To assess the potential for improving yield under drought stress via direct selection, and to identify associated quantitative trait loci (QTL), doubled haploid lines with a narrow range of flowering dates, derived from the population CT9993-5-10-1-M/IR62266-42-6-2, were screened under full irrigation and severe drought stress induced by draining the paddy before flowering in 2000–2002 at Raipur, India. Drought stress reduced mean yield by 80%. H was similar in stress and non-stress trials, as was the relative magnitude of the genotype and genotype × year variances. The genetic correlation between yield in stress and non-stress conditions was 0.8, indicating that about 64% of the genetic variation for yield under stress was accounted for by differences in yield potential also expressed in irrigated environments. These results indicate that direct selection for yield under drought stress can produce yield gains under stress without reducing yield potential. There was no secondary trait for which selection resulted in greater predicted response in yield under stress than direct selection for stress yield per se. A QTL was detected on chromosome 1 near sd1 that explained 32% of the genetic variation for yield under stress, but only 4% under non-stress. Its effect was consistent across years. This QTL accounted for much of the variation in drought yield not accounted for by variation in yield potential.     

Yield constraints of rainfed lowland rice in Central Java, Indonesia

The low and unstable yields of rainfed lowland rice in Central Java can be attributed to drought, nutrient stress, pest infestation or a combination of these factors. Field experiments were conducted in six crop seasons from 1997 to 2000 at Jakenan Experiment Station to quantify the yield loss due to these factors. Experimental treatments—two water supply levels (well-watered, rainfed) in the main plots and five fertilizer levels (0-22-90, 120-0-90, 120-22-0, 120-22-90, 144-27-108 kg NPK ha⁻¹) in the subplots—were laid out in a split-plot design with four replications. Crop, soil, and water parameters were recorded and pest infestations were assessed.

In all seasons, rice yield was significantly influenced by fertilizer treatments. Average yield reduction due to N omission was 42%, to K omission 33–36%, and to P omission 3–4%. Water by nutrient interactions did not affect rice yield and biomass production. In two of the three dry seasons, an average of 20% of the panicles were damaged by pests and estimated yield loss from pests was 56–59% in well-watered and well-fertilized treatments. In one out of six seasons, yields under rainfed conditions were 20–23% lower than under well-watered conditions. Drought, N and K deficiencies, and pest infestation are the major determinants for high yields in rainfed environments in Jakenan. Supplying adequate nutrient and good pest control are at least as important as drought management for increasing crop productivity of rainfed rice-growing areas in Central Java. The relative importance of drought, nutrient and pest management may vary in other rainfed areas. Yield constraints analysis should be systematically carried out to identify appropriate management strategies.     

Yield of rice under water and soil salinity risks in farmers’ fields in northeast Thailand

This study focused on the variability of rice yield under water and soil salinity risks in farmers’ fields in northeast Thailand. A rice plot was monitored in 24, 16 and 11 farmers’ fields during the rice seasons 2005, 2006 and 2007, respectively. The results emphasized that few plots were continuously submerged during the 2005 season, when rainfall was low. Drought significantly affected the rice yield, yield components and the internal efficiency (IE) of the absorbed nutrients, while slight soil salinity had the only significant effect of increasing the IE of potassium (IEK). In the very rainy 2006 and 2007 seasons, most fields were continuously submerged, and in contrast to 2005, the slight soil salinity that was recorded had significant effects not only on IEK, but also on rice yield, spikelet sterility and 1000-grain weight. The yield decrease due to drought was about 87% and that due to salinity was 20%. When neither salinity nor water were limiting, the soil nutrient supply was high enough to achieve about 80% of the maximum yield reported in the literature for the rice cultivar in this area. As both drought and salinity risks are hardly avoided by the current farmers’ management they should be taken into account in the way technical recommendations to farmers are formulated.     

Dynamic change in rice leaf area index and spectral response under flooding stress

Paddy and Water Environment - Analysis of the canopy structure change and spectral response mechanism of rice under flooding stress is an important prerequisite for large-scale monitoring of rice...     

Evaluation of neonicotinoids as pyrethroid alternatives for rice water weevil management in water-seeded rice

The rice water weevil (RWW), Lissorhoptrus oryzophilus (Kuschel) (Coleoptera: Curculionidae), is the most destructive insect pest of rice in the United States. Water-seeded rice, which is flooded at an earlier stage of crop development than drill-seeded rice, is at heightened risk of loss from root-feeding RWW larvae. Pyrethroids, the most widely used group of foliar insecticides for RWW control, have inherent limitations such as limited residual activity, narrow window of activity and extreme toxicity to non-target aquatic organisms. An array of field, lab and greenhouse experiments was conducted to compare the activity of two neonicotinoids with that of λ-cyhalothrin, a widely used pyrethroid, against the RWW. Small-plot efficacy trials were conducted during 2009, 2010 and 2011. Foliar clothianidin (Belay 2.13 SC) and a granular formulation (3%) of dinotefuran applied to plots were as effective as, and showed greater residual activity than, foliar applications of λ-cyhalothrin. Topical bioassays on adult weevils revealed that clothianidin possessed lower contact toxicity than λ-cyhalothrin. Residual assays using weevils placed on foliage of sprayed plots revealed that the toxic and sublethal behavioral effects of clothianidian on adult weevils were more persistent for clothianidin than for λ-cyhalothrin. Granular dinotefuran applied to greenhouse-grown plants previously infested with weevil larvae showed excellent larvicidal activity. Overall, these studies showed that neonicotinoids have potential as pyrethroid replacements against the RWW in water-seeded rice culture.