Soil Insecticides Research Articles

Persistence and retention of active ingredients in four granular cholinesterase‐inhibiting insecticides in agricultural soils of the lower Fraser River valley, British Columbia, Canada, with implications for wildlife poisoning

AbstractThe persistence and retention of active ingredients in granules of Thimet 15G (phorate 15% by weight), Dyfonate 10G (fonofos 10% by weight), Counter 15G (terbufos 15% by weight), and Furadan 10G (carbofuran 10% by weight) were determined in silt loam and organic muck agricultural soils typical of the lower Fraser River valley (BC, Canada). In June 1995, treatment bags made of polyester cloth (7.5 × 7.5 cm) containing granules of a single insecticide, either alone or with soil, were placed during spring planting in the bottom of the furrow and retrieved periodically until April 1996. The parent component of each insecticide declined monotonically except for carbofuran (logistic decline). In the silt loam (organic muck) soil, the average June‐to‐October first‐order rate constants and half‐lives were 0.009 (0.010)/d and 80 (71) d for fonofos, 0.012 (0.009)/d and 58 (82) d for phorate, and 0.032 (0.015)/d and 21 (47) d for terbufos; the half‐life of carbofuran was 129 (97) d. By December, the average amounts of fonofos and phorate in silt loam (organic muck) were 26% (range: 17–40%; 14% [range: 3.4–21%]) and 21% (range: 15–30%; 10% [range: 5.0–24%]) of the initial amounts of active ingredients measured at time zero, respectively. By April, the percentages dropped to 16% (range: 7.8–24%; 2.3% [range: 0–7.7%]) and 7.3% (range: 1.9–25%; 0.6% [range: 0–1.9%]). During this period, about 95% of the active ingredients were granule bound, the rest remaining in the bag. Only low levels of terbufos and carbofuran persisted in both soils from December to April of the following year. Results indicate an enhanced probability for poisoning of waterfowl and raptors because of the high levels of active ingredients retained on granules of all four insecticides in both soils in the fall. The risk of acute poisoning by phorate and fonofos continued though the winter.

Persistence and retention of active ingredients in four granular cholinesterase-inhibiting insecticides in agricultural soils of the lower Fraser River valley, British Columbia, Canada, with implications for wildlife poisoning.

The persistence and retention of active ingredients in granules of Thimet 15G (phorate 15% by weight), Dyfonate 10G (fonofos 10% by weight), Counter 15G (terbufos 15% by weight), and Furadan 10G (carbofuran 10% by weight) were determined in silt loam and organic muck agricultural soils typical of the lower Fraser River valley (BC, Canada). In June 1995, treatment bags made of polyester cloth (7.5 x 7.5 cm) containing granules of a single insecticide, either alone or with soil, were placed during spring planting in the bottom of the furrow and retrieved periodically until April 1996. The parent component of each insecticide declined monotonically except for carbofuran (logistic decline). In the silt loam (organic muck) soil, the average June-to-October first-order rate constants and half-lives were 0.009 (0.010)/d and 80 (71) d for fonofos, 0.012 (0.009)/d and 58 (82) d for phorate, and 0.032 (0.015)/d and 21 (47) d for terbufos; the half-life of carbofuran was 129 (97) d. By December, the average amounts of fonofos and phorate in silt loam (organic muck) were 26% (range: 17-40%; 14% [range: 3.4-21%]) and 21% (range: 15-30%; 10% [range: 5.0-24%]) of the initial amounts of active ingredients measured at time zero, respectively. By April, the percentages dropped to 16% (range: 7.8-24%; 2.3% [range: 0-7.7%]) and 7.3% (range: 1.9-25%; 0.6% [range: 0-1.9%]). During this period, about 95% of the active ingredients were granule bound, the rest remaining in the bag. Only low levels of terbufos and carbofuran persisted in both soils from December to April of the following year. Results indicate an enhanced probability for poisoning of waterfowl and raptors because of the high levels of active ingredients retained on granules of all four insecticides in both soils in the fall. The risk of acute poisoning by phorate and fonofos continued though the winter.

Biology and management of the Japanese beetle.

The Japanese beetle, Popillia japonica Newman, an introduced scarab, has become the most widespread and destructive insect pest of turf, landscapes, and nursery crops in the eastern United States. It also damages many fruit, garden, and field crops. This review emphasizes recent research on the beetle's biology and management. Adults feed on leaves, flowers, or fruits of more than 300 plant species. Adaptations mediating their host finding, dietary range, mating, and oviposition are discussed. We also address abiotic and biotic factors affecting population dynamics of the root-feeding larvae. Japanese beetle grubs are widely controlled with preventive soil insecticides, but options for remedial control of adults and larvae presently are limited. Advances in understanding host plant resistance, entomopathogens, and other biorational approaches may provide more options for integrated management. Despite ongoing regulatory efforts, the Japanese beetle remains a threat as an invasive species.

INFLUENCE OF TERBUFOS AND NICOSULFURON ON IRON CHLOROSIS AND GROWTH OF CORN

The larval stage of the spotted cucumber beetle (Diabrotica vigifera zeae), the Mexican corn rootworm, is a highly devastating pest of cornfields in Texas and the Southwest. A systemic organophosphate insecticide, standard release terbufos (ST), applied in row with the corn seed at planting, has been termed effective in reducing crop damage from the Mexican corn rootworm. However, recent field observations have indicated possible association of micronutrient deficiency symptoms with use of terbufos and over-the-top sulfonyl urea herbicides (nicosulfuron, primisulfuron) on crops such as corn. This experiment was conducted to determine if this systemic soil insecticide would affect plant metabolic activities as measured by nutrient deficiency chlorosis and plant growth. The study also involved testing a controlled release terbufos (CR) version of the same insecticide. Each soil insecticide was compared with and without foliar treatments with one of the sulfonyl urea herbicides (nicosulfuron) used in controlling grass-type weeds in corn. The greenhouse study was conducted on a Monteola sandy clay loam (Typic Pellusterts), which is a typical soil used in corn production in southern Texas. Standard release (ST) and CR forms of terbufos were compared at the label recommended rate (1.1 kg a.i./ha) and also at 2 kg a.i./ha. All materials were banded in the seed row at planting. Treatments were arranged in a randomized block design with three replications. Early visual chlorosis ratings (7 days) and chlorophyll readings at 28 days indicated increased interveinal chlorosis with soil insecticide applications. Plants overcame these early effects with time and showed higher chlorophyll than untreated plants at 42 days. Depressed early plant growth and reduced tissue levels of certain micronutrients indicated these systemic insecticides both with and without over-the-top herbicide could be injurious during early stages of plant growth. However, the affected plants were able to overcome most of the effects later in the growing season. Tissue iron (Fe) concentrations were slightly reduced by terbufos alone and reduced further when nicosulfuron was applied. Zinc was reduced substantially by terbufos but appeared to not change when the over-the-top herbicide was included.

Effect of Systemic Soil Insecticides and a Plant Product on Microbial Load of Soil in Root (wilt) Affected Coconut Monocropping Ecosystem

The changes undergoing in the microorganism population due to the application of phorate 10G, carbofuran 3G (@ 10 g a.i./ palm) and neem oil cake (@ 1.5 kg / palm) in the basin region of coconut growing in root (wilt) affected area was studied. Generally, a high microbial population was observed in the control plot. Carbofuran proved to be more toxic as compared to phorate as it suppressed the bacterial, actinomycetal, and free-living N2 -fixer’s number significantly. Against Nitrosomonas and Nitrobacter (nitrifiers), the influence was inconsistent. Neem oil cake enhanced bacterial and free-living N2-fixer count; against actinomycetes and fungi there was an initial stimulatory, and then antagonistic impact, whereas, it proved detrimental to the nitrifiers. From the six soil samplings done, spread over a period of six months, the microbial load was recorded to be high whenever there was moderate rainfall and medium temperature. Application of neem oil cake produced positive effect on the beneficial microorganisms as compared to the systemic insecticides.

Multiresidue analysis of insecticides in soil by gas chromatography with electron–capture detection and confirmation by gas chromatography–mass spectrometry

A rapid multiresidue method has been developed for the analysis of nine insecticides (organochlorines, pyrethroids and organophosphorus) in soil. The method is based on the sonication extraction of residues from a certain amount of soil placed in a small column, using ethyl acetate. The effect of the residence time of insecticides in soil, the material of the columns used (glass or plastic columns) and the soil moisture content on the recovery of these compounds was also studied. Residues were determined by gas chromatography with electron-capture detection. The average recovery through the method obtained for these compounds varied from 90 to 108% with a relative standard deviation between 1 and 11%. The results of this study pointed out that the recoveries of insecticide residues obtained with plastic or glass columns at different soil moisture content were similar and that the residence of these compounds in soil during several days did not affect their recovery from soil. Confirmation of residue identity was performed by gas chromatography coupled with mass spectrometry.

Tillage and Chlorpyrifos Treatment Effects on Peanut Arthropods—An Incidence of Severe Burrower Bug Injury

Abstract A 2-yr study was conducted on the effects of tillage and soil insecticide (chlorpyrifos) treatment on peanut arthropod pests. A 3 by 2 split-plot experiment with five replications was subjected to factorial ANOVA. Main plot treatments consisted of three tillage systems: conventional moldboard plow, strip tillage into a killed wheat cover crop, and strip tillage into corn stubble residue. Subplot insecticide treatments were granular chlorpyrifos applied at early pegging (growth stage R2) and untreated. Populations of corn earworn, Helicoverpa zea (Boddie), and velevetbean caterpillar, Anticarsia gemmatalis Hübner, were lower in strip tillage systems. Chlorpyrifos applications caused corn earworm outbreaks in all tillage systems, but these applications were more disruptive in strip tillage. Chlorpyrifos treatment also increased populations of fall armyworm, Spodoptera frugiperda (J.E. Smith), but had no measurable effect on velvetbean caterpillar populations. Pod damage from lesser cornstalk borer, Elasmopalpus lignosellus (Zeller), and wire-worms, Conoderus spp., was lower in strip tillage systems, and chlorpyrifos suppressed pod damage in all systems. Threecornered alfalfa hopper, Spissistilus festinus (Say), damage to peanut was greater in the wheat residue strip tillage system. Chlorpyrifos treatment reduced threecornered alfalfa hopper damage in all systems. Spider mite injury was not affected by tillage, but chlorpyrifos treatments resulted in mite outbreaks in all tillage systems. Burrower bug, Pangaeus bilineatus Say, injury to peanut kernels was greater in the strip tillage systems in 1999; and burrower bug injury was suppressed in the strip tillage systems by chlorpyrifos treatment. There was a significant interaction effect for burrower bug injury between tillage and insecticide treatment. Incidence of tomato spotted wilt virus also was reduced by strip tillage. Use of an effective fungicide program and a 3-yr crop rotation out of peanut production probably obscured any potential tillage effects on fungal diseases (southern stem rot, Rhizoctonia limb rot, and leaf spot). However, chlorpyrifos treatment increased Rhizoctonia limb rot incidence. Weed populations were generally greater in strip tillage systems, but postemergence herbicides effectively eliminated any potential confounding effect on yield and grade. Yield was not affected by tillage in either year, and chlorpyrifos had no effect on yield in 1998. In 1999, however, chlorpyrifos increased yield in both strip tillage systems. Neither tillage nor insecticide treatment affected grade (percentage total mature kernels) in 1998, but in 1999 grade was highest in conventional tillage and grade was improved by chlorpyrifos treatment in strip tillage systems. Crop value losses of $249 and $388/ha were attributed to burrower bug injury in untreated corn and wheat residue strip tillage systems, respectively. This injury may have been an anomaly of drought conditions but, given the potential economic impact, burrower bug merits further study in conservation tillage peanut production.

A Comparative Study of Onion Maggot “Delia Antiqua” Monitoring Techniques

Onion maggots have reduced green onion and leek production in southern New Jersey for at least the last 80 years. Growers routinely apply soil insecticides at planting and spray for larvae and adult flies during the season. Two monitoring methods are available for determining adult fly activity. New York researchers have demonstrated that cone traps can be used. Two traps are placed near onion fields and checked for adult flies twice per week to determine peak fly emergence. Ontario researchers use yellow sticky cards for monitoring onion maggot flies in the onion fields. Three 10 × 15-cm cards are placed on each side of the field and are checked twice per week. An experiment was conducted in New Jersey to determine which system is more reliable and easier for consultants and growers to use. Two cone traps were placed at the edge of one onion field and yellow cards were placed in another field on four farms. The traps were checked twice per week from 29 Mar. to 22 Oct. Both monitoring methods tracked the adult flights, but the average number of flies captured was higher on the sticky cards. Ease of use is important if either system will be used as a monitoring tool. Sticky cards are more difficult to maintain since they must be replaced at least every 2 weeks. Since fields are irrigated or cultivated every week in southern New Jersey, the cards become covered with soil, reducing effectiveness. Also, it is more difficult to determine male and female flies on sticky cards.

Sweetpotato Insect Management in North Carolina

The 199 sweetpotato growing season was one of extremes: early high temperatures, cool temperatures at planting, drought early and extended, and then hurricane floods. Insect species and population levels were highly variable. Thrips early and armyworms late. Insect control tactics and management strategies were used and include the following. Insect presentations and handouts were made at field days, annual meeting and at several county meetings. A sweetpotato insect field guide was prepared to assist fieldmen with insect scouting. Insect scouting schools were held in several counties to show insects, their damage, and traps to use in detecting their presence and numbers over time. Control studies with insecticide formulations and rates along with timing studies were conducted and prepared for the annual report. Spintor and Admire received registations for worms late and for early season insect control. Aphid vector studies centered on aphid suction traps, yellow sticky traps, and aphid identifications. Foliar and soil insecticides were discussed as to their use and impact. Insecticides of the future were presented and discussed. Cooperative studies and long term plans were discussed.

Incidência de danos de Diabrotica speciosa em cultivares e linhagens de batata

A cultura da batata é atacada por diversas pragas subterrâneas, sendo que a principal é a vaquinha, Diabrotica speciosa (Col. Chrysomelidae). O objetivo deste trabalho foi o de estudar a incidência de larvas de D. speciosa em tubérculos de cultivares e linhagens de batata para consumo de mesa e de indústria. Foram conduzidos dois experimentos: um com a exclusão total de qualquer outra praga que não a vaquinha e outro em condições naturais de lavoura. No primeiro, as cultivares de batata foram plantadas em solo intensamente hortado e sob gaiolas teladas (confinamento). O segundo, foi desenvolvido em condições normais de plantio de batata. Os experimentos foram desenvolvidos na EMBRAPA-CPACT, em Pelotas, RS, durante a safra de primavera. Foram estudadas cultivares de mesa Baronesa, Cristal, Macaca, Monte Bonito, Trapeira e as linhagens C-1485687, C-12263580, CR-1290582 e de indústria, Atlantic, Asterix, Baraka, Bintje, Catucha, Cicklamen, Panda e a linhagem C-15822590. No experimento de confinamento, não houve diferença significativa entre as cultivares para indústria. Nas cultivares Panda, Asterix e Atlantic, a média geral de furos por tubérculo foi muito maior do que nas demais cinco cultivares, sugerindo que essas três cultivares teriam maior suscetibilidade à incidência e dano de larvas de vaquinha. Nesse mesmo tipo de experimento, entre as cultivares de mesa, ocorreu diferença significativa na cultivar Baronesa e na linhagem C-12261580, sendo as duas com maiores médias de furos por tubérculo, indicando a possibilidade de serem mais suscetíveis à incidência e dano de larvas de vaquinha. As demais cultivares e linhagens constituíram um grupo em que não foi possível detectar diferenças entre si. A cultivar Baronesa foi a que teve maior número médio de furos por tubérculo. As cultivares para indústria podem ser separadas em dois grupos extremos quanto à incidência de larvas e danos causados pela vaquinha em condições naturais. As cultivares que tiveram menor incidência, independentemente do tamanho do tubérculo, foram Catucha, Baraka e Atlantic. As que tiveram maior incidência foram Asterix e Bintje. Nas cultivares de mesa, a linhagem C-1485687 e a cultivar Cristal foram as que tiveram maior quantidade de tubérculos enquadrados na categoria sem furo, diferindo das demais. A linhagem C-1485687 foi a menos atacada pelas larvas de vaquinha, sugerindo a menor suscetibilidade à incidência dessa praga. Conclui-se que existem diferenças quanto à incidência de larvas de vaquinha entre as cultivares e linhagens de batata, tanto para indústria como para mesa.

Larval susceptibility of an insecticide-resistant western corn rootworm (Coleoptera: Chrysomelidae) population to soil insecticides: laboratory bioassays, assays of detoxification enzymes, and field performance.

Soil insecticides were evaluated in laboratory and field studies against larvae of an insecticide resistant population (Phelps County, NE) of western corn rootworm, Diabrotica virgifera virgifera LeConte. Insecticide toxicity was evaluated by topical application of technical insecticides to 3rd instars from Saunders County, NE (susceptible) and Phelps County populations. Resistance ratios (LD50 Phelps County/LD50 Saunders County) for the insecticides methyl parathion, tefluthrin, carbofuran, terbufos, and chlorpyrifos were 28.0, 9.3, 8.7, 2.6 and 1.3, respectively. Biochemical investigation of suspected enzymatic resistance mechanisms in 3rd instars identified significant elevation of esterase activity (alpha and beta naphthyl acetate hydrolysis [3.8- and 3.9-fold]). Examination of 3rd instar esterases by native PAGE identified increased intensity of several isoenzymes in the resistant population. Assays of cytochrome P450 activity (4-CNMA demethylation and aldrin epoxidation) did not identify elevated activity in resistant 3rd instars. Granular soil insecticides were applied at planting to corn, Zea mays L., in replicated field trials in 1997 and 1998 at the same Phelps County site as the source of resistant rootworms for the laboratory studies. In 1997, planting time applications of Counter 20CR, Counter 15 G (terbufos), and Lorsban 15 G (chlorpyrifos) resulted in the lowest root injury ratings (1-6 Iowa scale); 2.50, 2.55, 2.65, respectively (untreated check root rating of 4.55). In 1998, all insecticides performed similarly against a lower rootworm density (untreated check root rating of 3.72). These studies suggest that resistance previously documented in adults also is present in 3rd instars, esterases are possibly involved as resistance mechanisms, and resistance to methyl parathion in adults is also evident in larvae, but does not confer cross-resistance in larvae to all organophosphate insecticides.

COMPARISON OF SOIL INSECTICIDE APPLICATION METHODS IN A CONSERVATION TILLAGE SYSTEM FOR CONTROLLING CORN WIREWORMS ON FIELD CORN, 1999

COMPARISON OF SOIL INSECTICIDE APPLICATION METHODS IN A CONSERVATION TILLAGE SYSTEM FOR CONTROLLING CORN WIREWORMS ON FIELD CORN, 1999: This study was conducted at the Mountain Branch Experiment Station, Blairsville, GA, to evaluate the efficacy of various methods of applying soil insecticides for the control of corn wireworms. Each treatment was applied to the two middle rows of 25-ft long, 4-row plots. A RCB design with four replications was used. One untreated check was included in each replication. Seed was planted on 19 May using a four row Cole no-till planter. Granular insecticides were applied at planting using three methods: a 7-inch band application, a 7-inch T-band application, and precision placement of insecticide onto the planted hill using a jab planter for seed placement and a bazooka for insecticide application. All insecticide rates are specified as lb (AI)/acre based on 38-inch rows. On 4 Jun, 20 plants were selected at random in untreated rows and examined for insect injury and the presence of larvae. All plants had wireworm injury and 7 plants had late instar corn wireworm larvae present in the soil nearby. On 8 Jun, 26 Jun, and 19 Jul, wireworm plant damage ratings were assessed for wireworm damage by surveying all of the plants in the two middle rows of each plot for feeding holes, tillered plants, and severely stunted plants. The total number of damaged and undamaged plants was recorded. The middle two rows of each plot were mechanically harvested on 26 Oct using a Hage small plot one row combine. Whole kernel corn was weighed in lb in the field to determine yield.

CORN ROOT PROTECTION FROM CORN ROOTWORM WITH SOIL INSECTICIDES AND TRANSGENIC CORN, 1999

CORN ROOT PROTECTION FROM CORN ROOTWORM WITH SOIL INSECTICIDES AND TRANSGENIC CORN, 1999

CORN ROOT PROTECTION FROM CORN ROOTWORM WITH SOIL INSECTICIDES AND SEED TREATMENTS, 1998

CORN ROOT PROTECTION FROM CORN ROOTWORM WITH SOIL INSECTICIDES AND SEED TREATMENTS, 1998

CORN ROOT PROTECTION FROM CORN ROOTWORM WITH SOIL INSECTICIDES AND SEED TREATMENTS, 1999

CORN ROOT PROTECTION FROM CORN ROOTWORM WITH SOIL INSECTICIDES AND SEED TREATMENTS, 1999

The Effects of Four Insecticides on the Population Dynamics of the Rice Water Weevil, Lissorhoptrus oryzophilus Kuschel2

The rice water weevil, Lissorhoptrus oryzophilus Kuschel, has been managed for the past 30 yrs using the soil insecticide carbofuran. The recent cancellation of the registration for carbofuran in rice has necessitated a shift to management strategies involving other insecticides, including lambda-cyhalothrin, fipronil, and diflubenzuron. Efficacies and effects on population dynamics of three alternatives to carbofuran (lambda-cyhalothrin and diflubenzuron as foliar sprays and fipronil as a seed treatment) were compared in two water-seeded and one drill-seeded field trials. Applications of lambda-cyhalothrin, but not of diflubenzuron or fipronil, resulted in decreases in the densities of rice water weevil adults and eggs. All three insecticides suppressed larval densities to levels comparable to, or lower than, densities in plots treated with carbofuran. All three alternatives to carbofuran differed from carbofuran with respect to their effects on the population dynamics of weevil larvae. Lambda-cyhalothrin, diflubenzuron, and fipronil were more effective than carbofuran at preventing early larval infestation of rice roots, but were less effective at preventing later infestation of roots. Yields from plots treated with fipronil, diflubenzuron, and lambda-cyhalothrin were generally higher than yields from plots treated with carbofuran, probably because prevention of early injury to roots has a more beneficial impact than prevention of later injury. This study also provided evidence for the utility of early planting and delayed flooding for management of the rice water weevil.

The pyrethrins and related compounds. Part XLII:Structure-activity relationships in fluoro-olefin non-ester pyrethroids

A series of compounds containing fluorine atoms in place of hydrogen in olefinic non-ester pyrethroids has been synthesised using a route based on novel intermediates, ie 2-fluoroallyl acetates, which are coupled with aryl Grignard reagents, and tested against several insect species. In most cases, after introduction of fluorine at the olefinic position, the activity remains high in both the 1-aryl-1-(3-arylprop-2-enyl)cyclopropane and the (1-aryl-4-arylbut-2-enyl)cyclopropane series. In particular, the former series have potential as soil insecticides, because in tests against Diabrotica balteata, activities were high, and dose-transferability factors were increased by the introduction of fluorine. © 1999 Society of Chemical Industry

Effects of soil insecticide treatments on maize aphids and aphid predators in Catalonia

The effect on maize aphids and aphid predators of granular formulations of carbofuran and lindane applied at sowing was evaluated from plant emergence to flowering in a three-year study at two commercial farms. Plots treated with carbofuran showed lower total aphid and alate densities during the first week after plant emergence. Later, densities in carbofuran-treated plots were significantly higher than in lindane-treated or untreated plots. No differences in the presence of predators on plants were found, but at one farm catches of polyphagous ground-foraging predators in pitfall traps were greater in untreated plots, coinciding with lower aphid density on plants. Results indicate that the use of carbofuran, in our crop conditions, for controlling aphids and preventing MDMV was ineffective because aphid colonization and reproduction was not avoided, so allowing virus transmission, and ground-foraging predators were negatively affected. Lindane had no direct effect on aphids; and no indirect effects through its impact on predators were observed.

Strip Intercropping of Corn-Soybean in Irrigated and Rainfed Environments

A strip intercropping system of corn (Zea mays L.) and soybean [Glycine Max (L.) Merrill] has the potential to reduce soil erosion and increase the biological and economic efficiencies of a corn-soybean rotational system. The objective of this study was to evaluate grain production in a corn-soybean strip intercropping system under irrigated and rainfed conditions in eastern Nebraska. Corn and soybean were grown in alternating 20 ft. (eight-row) strips in a north-south orientation on a Sharpsburg silty clay loam (fine, smectitic, mesic Typic Argiudolls) at the University of Nebraska Agricultural Research and Development Center near Mead. A full-season corn hybrid was grown in strips in combination with soybean cultivars of different maturity groups. Yields of the two border rows of corn and soybean strips were machine harvested and compared with the middle four rows of each crop strip to determine border effects. Under irrigated conditions, corn yields in the outside two rows increased in 4 of 5 yr. A maximum yield increase of 28 bu/acre occurred in 1986, with a 5-yr average increase of 17 bu/acre (11%) in the corn borders. Under rainfed conditions, corn border row yield increases were less consistent, averaging 5 bu/acre. In 1989, a maximum corn yield increase of 19 bu/acre (23%) was obtained in the rainfed environments. Soybean yields were reduced in the outside two border rows compared with the middle four rows under both rainfed and irrigated environments. Yields from soybean rows adjacent to corn were reduced an average of 6 bu/acre over the 5-yr period. Land Equivalent Ratios (LER = land area needed in monoculture to equal production in one unit area of intercropping) averaged 1.00 and 0.96 for the irrigated and rainfed strip intercropping systems, respectively, suggesting no benefit under either condition for the multispecies systems. Although economics of the system are dependent on corn and soybean prices, results of these experiments indicate strip intercropping systems of corn-soybean show no consistent differences in systems yield or net returns compared with monoculture fields under the same conditions. Strip intercropping will then benefit by reducing erosion on soybean stubble.

An assessment of agrochemical leaching potentials for Tenerife

This paper reports an index-based regional-scale characterization of non-point source groundwater contamination potential for the agricultural areas on the Canary Island of Tenerife. The relative leaching potential for 24 pesticides was quantitatively assessed and ranked using the Leaching index (Li) for the soil, landcover, and recharge conditions in Tenerife. The uncertainty in the Li estimates, due to uncertainties in the soil, recharge, and chemical data, were accounted for using first-order uncertainty analysis. Several of the pesticides considered in this study were assessed to be potential leachers. The soil insecticide Carbofuran (2,3-dihydro-2,2-dimethyl-7-benzofuranyl- n-methylcarbamate) was found to have the greatest leaching potential for the soil, landcover, and recharge conditions across Tenerife.