Soybean Ecosystem Research Articles

Impact of a new herbicide molecule on weed communities and soybean ecosystem services

Impact of a new herbicide molecule on weed communities and soybean ecosystem services

Determination of Residues and Degradation Kinetics of Oryzalin in Different Soils of Soybean Ecosystem

ABSTRACT Dinitroanilines group are persistent pesticides and important pollutants of soil and water. Their dissipation is needed to accurately predict the environmental risk entailing its use in different ecosystems. Degradation kinetics is not reported under subtropical conditions thus, kinetics of oryzalin under soybean field conditions at two application rate in texturally different Pantnagar soils were investigated for two cropping years. Oryzalin was extracted with acetone: methanol from soils followed by florisil SPE cleanup and residues were identified by HPLC-UV. Oryzalin persisted for more than 120 days in soils and slowly dissipated with biphasic first order kinetics. Dissipation was faster in sandy loam compared to silty clay loam soil. At 1.5 & 3.0 kg ha−1 initial half-life in silty clay loam and sandy loam soils were 5.892 & 5.675 and 6.015 & 5.770 days, while, in later phase it were 49.500 & 52.105 and 37.459 & 40.290 days, respectively. Recovery in soil, plant straw, seed husk, soybean oil, deoiled cake, and water samples varied from 77.50–88.85%, 79.50–89.25%, 78.05–88.20%, 75.45–83.92%, 77.40–84.75% and 81.75–93.75%, respectively. Minimum detection limit was 0.001 μg mL−1 and quantitation limit for soil, straw, oil, cake, husk and water were 0.007, 0.01, 0.04, 0.05, 0.03 µg g−1 and 0.005 µg mL−1, respectively. At harvest the oryzalin residues were below detection & MRL in all samples. Study revealed that under subtropical conditions oryzalin is safe for weed control in soybean fields and at harvest soybean crop could be used safely for human/animal consumption and would not create any residual/environmental problem.

Management practices regulate the response of canopy and ecosystem water use efficiency in cropland ecosystems

ContextWith rising global temperature and frequent drought events, water resource supply is facing to great challenge. Understanding the effects of different management practices on cropland water use efficiency (WUE) is crucial to promote effective allocation of water resources and food security. ObjectiveThe objective of this study was to reveal the contrasting effects of different farm management practices including continuous and rotational, tillage and no-till, irrigated and rainfed on cropland water use efficiency from canopy (WUET) to ecosystem (WUEET) scales, respectively. MethodsOn the basis of 26 site-years eddy covariance-based carbon and water flux observations, this study used the underlying WUE (uWUE) model to partition evapotranspiration (ET) across maize and soybean ecosystems. Three control groups were used to compare the effects of different management practices on the coupling relationships between terrestrial carbon and water cycles, respectively. ResultsCompared with the rotational maize-soybean site, both WUET and WUEET at the continuous maize site were larger, which was mainly ascribed to stronger gross primary productivity (GPP) for the C4 crop. But over the maize-planting years, both WUET and WUEET at the rotational site were higher than the continuous site owing to the nitrogen fixation by rhizobia for preceding year, especially for WUET. Under conventional tillage and no-till management, multi-year mean WUEET and WUET were contrasting. WUEET under no-till was apparently larger than WUEET under till, because of similar GPP but relatively lower ET. Meanwhile, more water was consumed by crop transpiration (T) under no-till, which led to lower WUET in comparison with WUET under till. In comparison with the rainfed farming, GPP, ET and T all increased apparently after irrigation. However, both WUET and WUEET at the irrigated site were not improved owing to more water lost with relatively fewer GPP increase. ConclusionsThe study suggested that the crop rotation system can improve both WUEET and WUET apparently. Meanwhile, fewer water resource was consumed by cropland under no-till management. Finally, irrigation farming improved the cropland GPP but reduced WUEET and WUET. ImplicationsOur results provide valuable management implications for understanding the mechanisms that can enhance water use efficiency and result in significant water savings and high yield.

The Use of Herbicides to Control Weeds in Soybean Crops (Glycine max L. Merrill)

An experiment was conducted at ‘The Research Farm, College of Agriculture, Tikamgarh, during the kharif season, 2016-17. The field was mainly infested with monocot weeds like Brachiaria ramosa, Commelina benghalensis, Cyperus rotundus and Echinochloa crusgalli. Dicot weeds Digera arvensis, Phyllanthus niruri and Mollugo pentaphylla were less dominant in the soybean ecosystem. The treatments comprised of pre-emergence herbicides; clomazone @ 1 kg/ha, pendimethalin @ 1 kg/ha and alachlor @ 1 kg/ha and post-emergence herbicides; imazethapyr @ 75 g/ha, imazethapyr + imazamox @ 70 g/ha, quizalofop-p-ethyl @ 50 g/ha+ chlorimuron-ethyl @ 9 g/ha,quizalofop-p-ethyl @ 50 g/ha, chlorimuron-ethyl @ 9 g/ha, two hand weeding at 20 and 40 DAS and weedy check., dry matter and weed index. It was also found superior in respect of various growth and yield attributes. The highest seed yield (825 kg/ha) and straw yield (1152 kg/ha) of soybean and maximum gross return (₹ 37,611 ha-1) and net return (₹ 23,951 ha-1) were also recorded in imazethapyr + imazamox 70 kg/ha as postemergence with highest B:C ratio of 2.75. It was also found responsible for the highest N, P and K uptake by soybean crops and the lowest uptake of these plant nutrients by weed plants.

Bionomics of Soybean Pod Borer, Cydia ptychora (Meyrick) (Lepidoptera: Tortricidae) under in vitro Condition

Background: The post-flowering pest pod borer, Cydia ptychora causing huge yield losses in soybean. It is said to be active in soybean ecosystem from September to December with 10.50-91.29 per cent incidence. The maximum incidence (95.55%) was observed to be in July sown crop. Methods: Culture of the insect was initiated by collecting larvae and pupae from infected soybean crop and was shifted to rearing cages. Ten pairs of newly emerged adult moths were released in plastic container containing soybean pods for oviposition. On hatching, larvae were reared on soybean pods till pupation. Moist sand was provided for pupation. Further, the life cycle was tracked thoroughly to understand bionomics. Result: Freshly laid eggs were pearly white, translucent, spherical having mean length of 0.49±0.016 mm and 0.31±0.009 mm width. Larval development completed within 20.86±4.59 days passing through five instars. The pupal period lasted for 9.13±2.45 days. Longevity of male and female was 1.90±0.80 and 4.93±1.60 days respectively. The total life cycle of the pod borer from egg to adult was 34.53±4.90 days.

Survey on the seasonal incidence of insect pests of soybean in Bemetara district of Chhattisgarh state

Survey work for visualization of real pest problem of four blocks i.e. Bemetara, Berla, Saja and Nawagarh of Bemetara district (C.G.) was conducted during Kharif, 2017-18 and 2018-19. Ten villages in each block were visited during crop growth period. Girdle beetle, S. litura, C. acuta, B. tabaci and E. kerri were observed as major insect pests in soybean ecosystem under the blocks of Bemetara district. The maximum block seasonal mean activity of girdle beetle was recorded in Berla block with 5.3 damaged plants/mrl in which the Damai village of Berla block having maximum intensity of girdle beetle with 9.5 damaged plants/mrl. Bemetara block was earmarked for maximum block seasonal mean population of leaf defoliators i.e. S. litura and C. acuta with 3.2 larvae/mrl and 3.7 larvae/mrl, respectively. However, Mohbatta village of Bemetara block received maximum population of S. litura (7.6 larvae/mrl) and C.acuta (6.2 larvae/mrl). In Nawagarh block, highest block seasonal mean intensity of B. tabaci was recorded with 19.0 whiteflies/five plants. Another sucking pest E. kerri showed maximum block seasonal mean population in Bemetara block (6.9 jassids/five plants). Among the different blocks, Bemetara and Berla blocks were found favourable for maximum activities of predatory insects.

Simultaneous Analysis and Dietary Exposure Risk Assessment of Fomesafen, Clomazone, Clethodim and Its Two Metabolites in Soybean Ecosystem

A commercial formulation, 37% dispersible oil suspension (DOS) (fomesafen, clomazone, and clethodim), is being registered in China to control annual or perennial weeds in soybean fields. In this paper, a liquid chromatography tandem mass spectrometry method with QuEChERS (quick, easy, cheap, effective, rugged, and safe) sample preparation was developed for the simultaneous determination of fomesafen, clomazone, clethodim, and its two metabolites (CSO and CSO2) in soybean, green soybean, and soybean straw samples. The mean recoveries of our developed method for the five analytes in three matrices were ranged from 71% to 116% with relative standard deviations (RSDs) less than 12.6%. The limits of quantification (LOQs) were 0.01 mg/kg in soybean, 0.01 mg/kg in green soybean, and 0.02 mg/kg in soybean straw while the limits of detection (LODs) ranged from 0.018 to 0.125 μg/kg for these five analytes. The highest final residual amount of CSO2 in green soybean samples (0.015 mg/kg) appeared in Anhui, and the highest in soybean straw samples was 0.029 mg/kg in Guangxi, whilst the terminal residues of fomesafen, clomazone, clethodim and CSO were lower than LOQs (0.01 mg/kg) in all samples. Furthermore, these terminal residues were all lower than the maximum residue limits (MRLs) set by China (0.1 mg/kg for fomesafen and clethodim, 0.05 mg/kg for clomazone) at harvest. Additional chronic dietary risk was evaluated using a risk quotients (RQs) method based on Chinese dietary habits. The chronic dietary exposure risk quotients were 4.3 for fomesafen, 0.12 for clomazone, and 19.3 for clethodim, respectively, which were significantly lower than 100. These results demonstrated that the dietary exposure risk of fomesafen, clomazone, and clethodim used in soybean according to good agricultural practices (GAP) was acceptable and would not pose an unacceptable health risk to Chinese consumers. These results not only offer insight with respect to the analytes, but also contribute to environmental protection and food safety.

Study on the effect of different levels of organic and inorganic fertilizers on microbial enzymes and soil mesofauna in soybean ecosystem

Soybean (Glycine max (L) Merril). is also called Golden bean belongs to family Fabaceae is native to China having high nutritive value and oil content. Due to usage of inorganic fertilizers the fertility of soil and yield soybean has declined. Organic manures known to increase the soil fertility, structure and also influence the microbial enzymes activity and soil mesofauna. In this context the present investigation was undertaken to study, the different doses of farm yard manure and chemical fertilizers on the soil mesofauna and microbial enzymes at GKVK, Bangalore during the year 2013-2014. The investigation revealed that higher abundance of soil mesofauna (18.53) was recorded in 20 tons of FYMha-1 compared to the treatments with recommended package of practices (12.35) and inorganic fertilizer (10.30) alone. Soil mesofauna exhibited a significant positive relation with the microbial enzymes like dehydrogenase, acid and alkaline phosphtases and urease. The results of the multiple linear regression analysis showed that the influence of exchangeable calcium, available potassium and available phosphorous, exchangeable magnesium, dehydrogenase, alkaline phosphatase and urease on the abundance of soil mesofauna was up to 79 per cent. Higher rhizobium nodule number (64.93/plant) and yield (16.01 q/ha) of soybean found to increase with increase in farmyard manure application.

Growing season variability in carbon dioxide exchange of irrigated and rainfed soybean in the southern United States

Measurement of carbon dynamics of soybean (Glycine max L.) ecosystems outside Corn Belt of the United States (U.S.) is lacking. This study examines the seasonal variability of net ecosystem CO2 exchange (NEE) and its components (gross primary production, GPP and ecosystem respiration, ER), and relevant controlling environmental factors between rainfed (El Reno, Oklahoma) and irrigated (Stoneville, Mississippi) soybean fields in the southern U.S. during the 2016 growing season. Grain yield was about 1.6tha−1 for rainfed soybean and 4.9tha−1 for irrigated soybean. The magnitudes of diurnal NEE (~2-weeks average) reached seasonal peak values of −23.18 and −34.78μmolm−2s−1 in rainfed and irrigated soybean, respectively, approximately two months after planting (i.e., during peak growth). Similar thresholds of air temperature (Ta, slightly over 30°C) and vapor pressure deficit (VPD, ~2.5kPa) for NEE were observed at both sites. Daily (7-day average) NEE, GPP, and ER reached seasonal peak values of −4.55, 13.54, and 9.95gCm−2d−1 in rainfed soybean and −7.48, 18.13, and 14.93gCm−2d−1 in irrigated soybean, respectively. The growing season (DOY 132–243) NEE, GPP, and ER totals were −54, 783, and 729gCm−2, respectively, in rainfed soybean. Similarly, cumulative NEE, GPP, and ER totals for DOY 163–256 (flux measurement was initiated on DOY 163, missing first 45days after planting) were −291, 1239, and 948gCm−2, respectively, in irrigated soybean. Rainfed soybean was a net carbon sink for only two months, while irrigated soybean appeared to be a net carbon sink for about three months. However, grain yield and the magnitudes and seasonal sums of CO2 fluxes for irrigated soybean in this study were comparable to those for soybean in the U.S. Corn Belt, but they were lower for rainfed soybean.

Safety of selected insecticides against lady bird beetle in soybean

Field trial was conducted during Kharif 2014 to determine the effects of different treatments against lady bird beetle Coccinella septumpunctata in soybean ecosystem in the College of Agriculture Nagpur. Least average number of grubs recorded in treatment of Fenvalerate 20 EC @ 0.50 ml found to be superior as compared to other treatments. The next effective treatments were emamectin benzoate 5 S G @ 0.3 g per lit. and also in Spinosad 45 SC @ 0.25 ml per lit., Indoxacarb 15.8 EC @ 0.60 ml per lit., which were at par with T 6 and T 3 . However, the treatment Neem oil 2 per cent recorded grubs per 5 plants. Whereas, NSE @ 5 per cent and Beauveria bassiana 1x10 8 CFU @ 4 g per lit. were found to be least effective in reducing grubs population.

Mitigation of soil N2O emission by inoculation with a mixed culture of indigenous Bradyrhizobium diazoefficiens.

Agricultural soil is the largest source of nitrous oxide (N2O), a greenhouse gas. Soybean is an important leguminous crop worldwide. Soybean hosts symbiotic nitrogen-fixing soil bacteria (rhizobia) in root nodules. In soybean ecosystems, N2O emissions often increase during decomposition of the root nodules. Our previous study showed that N2O reductase can be used to mitigate N2O emission from soybean fields during nodule decomposition by inoculation with nosZ++ strains [mutants with increased N2O reductase (N2OR) activity] of Bradyrhizobium diazoefficiens. Here, we show that N2O emission can be reduced at the field scale by inoculation with a mixed culture of indigenous nosZ+ strains of B. diazoefficiens USDA110 group isolated from Japanese agricultural fields. Our results also suggested that nodule nitrogen is the main source of N2O production during nodule decomposition. Isolating nosZ+ strains from local soybean fields would be more applicable and feasible for many soybean-producing countries than generating mutants.

The influence of drought and heat stress on long-term carbon fluxes of bioenergy crops grown in the Midwestern USA.

Perennial grasses are promising feedstocks for bioenergy production in the Midwestern USA. Few experiments have addressed how drought influences their carbon fluxes and storage. This study provides a direct comparison of ecosystem-scale measurements of carbon fluxes associated with miscanthus (Miscanthus × giganteus), switchgrass (Panicum virgatum), restored native prairie and maize (Zea mays)/soybean (Glycine max) ecosystems. The main objective of this study was to assess the influence of a naturally occurring drought during 2012 on key components of the carbon cycle and plant development relative to non-extreme years. The perennials reached full maturity 3-5 years after establishment. Miscanthus had the highest gross primary production (GPP) and lowest net ecosystem exchange (NEE) in 2012 followed by similar values for switchgrass and prairie, and the row crops had the lowest GPP and highest NEE. A post-drought effect was observed for miscanthus. Over the duration of the experiment, perennial ecosystems were carbon sinks, as indicated by negative net ecosystem carbon balance (NECB), while maize/soybean was a net carbon source. Our observations suggest that perennial ecosystems, and in particular miscanthus, can provide a high yield and a large potential for CO2 fixation even during drought, although drought may negatively influence carbon uptake in the following year, questioning the long-term consequence of its maintained productivity.

Evaluation of different insecticides against green semilooper, Thysanoplusia orichalcea (Fab.) in soybean ecosystem

A field study was conducted during Kharif season 2014-15 to determine the efficacy of different insecticides against semilooper Thysanoplusia orichalcea (Fab.) in soybean ecosystem in the insectory premises of Agricultural Entomology Section, College of Agriculture Nagpur. Least cumulative average number larvae (0.05/mrl) was recorded in treatment of Fenvalerate 20 EC @ 0.50 ml/l (T 7 ) found to be superior compared to other treatments. The next effective treatments were emamectin benzoate 5 SG @ 0.3 g/ l (T 6 : 0.06/mrl) and also in Spinosad 45 SC @ 0.25 ml/l (T 3 :0.07/mrl), Indoxacarb 15.8 EC @ 0.60 ml/l (T 5 :0.08/mrl) found to be at par with T 6 and T 3 . However, the treatment Neem Oil 2 per cent (T 2 ) recorded 0.78 larvae/mrl. Whereas, NSE @ 5 per cent (T 1 :0.95/mrl) and Beauveria bassiana 1x10 8 CFU @ 4 g/l (T 4 :0.99/mrl) were found to be least effective in reducing larval population/mrl. Maximum mean larval population (1.48/mrl) was recorded in control (Water spray; T 8 ). Fenvalerate 20 EC @ 0.50 ml/l, Indoxacarb 15.8 EC @ 0.60 ml/l, Spinosad 45 SC @ 0.25 ml/l were found to be most effective treatments which recorded highest yield of 21.05 q/ha, 20.10 q/ha and 19.02 q/ha, respectively. From the seed production point of view Fenvalerate 20 EC @ 0.50 ml/l, Indoxacarb 15.8 EC @ 0.60 ml/l, Spinosad 45 SC @ 0.25 ml/l were most effective in recording highest yield.

Seasonality of the common cutworm Spodoptera litura in a soybean ecosystem

Seasonal occurrence of the common cutworm Spodoptera litura (Fab.) (Lepidoptera: Noctuidae) moths captured in synthetic sex pheromone traps and associated field population of eggs and larvae in soybean were examined in India from 2009 to 2011. Male moths of S. litura first appeared in late July or early August and continued through October. Peak male trap catches occurred during the second fortnight of September, which was within soybean reproductive stages. Similarly, the first appearance of S. litura egg masses and larval populations were observed after the first appearance of male moths in early to mid-August, and were present in the growing season up to late September to mid-October. The peak appearance of egg masses and larval populations always corresponded with the peak activity of male moths recorded during mid-September in all years. Correlation studies showed that weekly mean trap catches were linearly and positively correlated with egg masses and larval populations during the entire growing season of soybean. Seasonal means of male moth catches in pheromone traps during the 2010 and 2011 seasons were significantly lower than the catches during the 2009 season. However, seasonal means of the egg masses and larval populations were not significantly different between years. Pheromone traps may be useful indicators of the onset of numbers of S. litura eggs and larvae in soybean fields.

Mitigation of nitrous oxide emissions from soils by Bradyrhizobium japonicum inoculation

Soybean hosts the symbiotic nitrogen-fixing soil bacterium Bradyrhizobium japonicum, that can produce the greenhouse gas nitrous oxide. This study shows that nitrous oxide emissions from soybean ecosystems can be biologically mitigated at a field scale by inoculation with strains of B. japonicum that have increased nitrous oxide reductase activity.

Radiation balance in a soybean ecosystem in the Amazon

The continuous advance of the agricultural border in the Amazon has been worrying the scientific community due to the possible environmental impacts caused by this change in land use. The present work evaluated the behavior of the radiation balance components over the soybean crop (Glycine Max (L.) Merryl) in an Amazon area of continuous advance of the agricultural border. The radiation components were continuously monitored during the soybean cycle in 2006 and 2007 in an area of 200 ha. The soybean cultivation in the Amazon presented an abrupt change in the radiation balance components, with the consequent reduction in the energy available to the environment due to the increase in the surface reflection. There was a significant contribution of the diffuse radiation component in the soybean interception during cloudy conditions, even under incomplete canopy covering. Moreover, after the canopy closure, a similar interaction between soybean and solar radiation occurs, regardless of the cloud condition.

A modeling investigation of canopy‐air oxygen isotopic exchange of water vapor and carbon dioxide in a soybean field

The oxygen isotopes of CO2 and H2O (18O‐CO2 and 18O‐H2O) provide unique information regarding the contribution of terrestrial vegetation to the global CO2 and H2O cycles. In this paper, a simple isotopic land surface model was used to investigate processes controlling the isotopic exchange of 18O‐H2O and 18O‐CO2 between a soybean ecosystem and the atmosphere. We included in a standard land surface model a nonsteady state theory of leaf water isotopic composition, a canopy kinetic fractionation factor, and a big‐leaf parameterization of the 18O‐CO2 isoforcing on the atmosphere. Our model simulations showed that the Péclet effect was less important than the nonsteady state effect on the temporal dynamics of the water isotopic exchange. The model reproduced the highly significant and negative correlation between relative humidity and the ecosystem‐scale 18O‐CO2 isoforcing measured with eddy covariance. But the model‐predicted isoforcing was biased high in comparison to the observations. Model sensitivity analysis suggested that the CO2 hydration efficiency must have been much lower in the leaves of soybean in field conditions than previously reported. Understanding environmental controls on the hydration efficiency and the scaling from the leaf to the canopy represents an area in need of more research.

How do elevated CO2 and O3 affect the interception and utilization of radiation by a soybean canopy?

AbstractNet productivity of vegetation is determined by the product of the efficiencies with which it intercepts light (ɛi) and converts that intercepted energy into biomass (ɛc). Elevated carbon dioxide (CO2) increases photosynthesis and leaf area index (LAI) of soybeans and thus may increase ɛi and ɛc; elevated O3 may have the opposite effect. Knowing if elevated CO2 and O3 differentially affect physiological more than structural components of the ecosystem may reveal how these elements of global change will ultimately alter productivity. The effects of elevated CO2 and O3 on an intact soybean ecosystem were examined with Soybean Free Air Concentration Enrichment (SoyFACE) technology where large field plots (20‐m diameter) were exposed to elevated CO2 (∼550 μmol mol−1) and elevated O3 (1.2 × ambient) in a factorial design. Aboveground biomass, LAI and light interception were measured during the growing seasons of 2002, 2003 and 2004 to calculate ɛi and ɛc. A 15% increase in yield (averaged over 3 years) under elevated CO2 was caused primarily by a 12% stimulation in ɛc , as ɛi increased by only 3%. Though accelerated canopy senescence under elevated O3 caused a 3% decrease in ɛi, the primary effect of O3 on biomass was through an 11% reduction in ɛc. When CO2 and O3 were elevated in combination, CO2 partially reduced the negative effects of elevated O3. Knowing that changes in productivity in elevated CO2 and O3 were influenced strongly by the efficiency of conversion of light energy into energy in plant biomass will aid in optimizing soybean yields in the future. Future modeling efforts that rely on ɛc for calculating regional and global plant productivity will need to accommodate the effects of global change on this important ecosystem attribute.

Persistência do herbicida sulfentrazone em solo cultivado com soja e seu efeito em culturas sucedâneas

Esta pesquisa foi realizada em Engenheiro Coelho-SP, Brasil e teve como objetivo estudar a persistência do herbicida sulfentrazone em solos cultivados com soja, bem como os efeitos da toxicidade do resíduo nas culturas sucedâneas de milheto, girassol, aveia, trigo e feijão. O solo do ensaio teve as seguintes características: 46% de argila, 12% de silte, 42% de areia, 4% de matéria orgânica e pH de 5,8. A metodologia usada na determinação da persistência foi a de bioensaios, utilizando-se a beterraba como planta-teste crescendo dentro de um fitotron com as condições climáticas constantes, utilizando o solo amostrado 24 vezes na área experimental até 539 dias após os tratamentos (DAT). A persistência foi determinada em 376 dias após a aplicação de 0,6 kg a.i.ha-1 de sulfentrazone; já na dose maior, 1,20 kg a.i.ha-1, não foi possível determinar o final da persistência, pois mesmo na última época amostrada (539 DAT) a beterraba mostrou-se sensível ao herbicida. Pela análise das diversas características de desenvolvimento nas culturas que sucederam a soja, foi demonstrado que o resíduo do sulfentrazone afetou significativamente o crescimento e o rendimento das culturas de milheto e aveia; o girassol e o feijão não foram afetados; e, no trigo, somente a dose mais elevada foi capaz de sensibilizar negativamente a cultura.

Interactive Effects of Steinernema carpocapsae and Spodoptera exigua Nuclear Polyhedrosis Virus on Spodoptera exigua Larvae

Laboratory experiments were conducted to assess the interactive effect of the entomopathogenic nematode Steinernema carpocapsae and Spodoptera exigua multinucleocapsid nuclear polyhedrosis virus (SeMNPV) when applied in combination against the beet armyworm, Spodoptera exigua, larvae on soybean. The LC 25 and LC 50 for S. carpocapsae and SeMNPV were determined and tested as single and combination treatments. The LC 25 and LC 50 for S. carpocapsae were 117 and 263 nematodes/ml, respectively, and for SeM-NPV were 7.6 × 10 3 and 1.9 × 10 4 polyhedral inclusion bodies/ml, respectively. S. carpocapsae and SeMNPV produced additive effects on beet armyworm mortality in all combination treatments. Combinations of S. carpocapsoe + SeMNPV at LC 25 + LC 25 and LC 50 + LC 50 resulted in a significantly higher larval mortality than treatments with either pathogen alone at the corresponding concentrations. Combinations of the pathogens at LC 25 + LC 25 and LC 50 + LC 25 produced a significantly higher larval mortality than treatments with LC 25 of either pathogen alone. However, these mortalities were not significantly different from those in LC 50 treatments of either pathogen alone. The reproductive ability of S. carpocapsae in the infected hosts was not affected by SeMNPV in the combination treatments. These results suggest that treatments with S. carpocapsae + SeMNPV at appropriate combinations of concentration levels may result in greater control of beet armyworm than applications of either pathogen alone, particularly in a soybean ecosystem.