Nematicide Application Research Articles

Impact of the root-lesion nematode Pratylenchus goodeyi and mulch on the East African Highland banana crop performance in Kibuye, Western Rwanda

AbstractThe effect of nematode root injuries on banana crop yield is very poorly known in higher parts of the East African highlands. This study assessed the impact of the root-lesion nematode, Pratylenchus goodeyi, on growth and yield of three banana cultivars (Musa spp. AAA-EA) in a field experiment involving nematicide and mulch applications at conditions of high altitude (about 1500 m). Plant growth, yield, root damage and nematode population densities were observed over three production cycles. Low to medium levels (≤50%) of root necrosis were associated with improved plant growth, whilst higher root necrosis (>50%) had no effect on plant growth. No significant reduction in bunch weight was associated with high root necrosis in any cycle and any of the three cultivars. Mulch significantly reduced root necrosis and P. goodeyi population densities. Bunch weight significantly increased in all mulched plots irrespective of root necrosis intensity. These results agree with those of earlier surveys in Rwanda that suggested little impact of P. goodeyi on banana yields. However, they challenge general perceptions and previous findings on the negative impact of root lesion nematodes on banana crop performance.

Factors influencing the survivorship of the burrowing nematode, Radopholus similis (Cobb.) Thorne in two types of soil from banana plantations in Martinique

The burrowing nematode, Radopholus similis (Cobb.) Thorne, causes the most damage to bananas. To minimize nematicide applications, cropping systems that use fallow, crop rotation and clean planting material have been developed in the French West Indies. In order to optimize the benefit of the intercropping period, we studied the survivorship of R. similis in different soil types and conditions. We monitored the survivorship of calibrated populations of R. similis in the laboratory on a Nitisol and on an Andosol, two soils derived from volcanic ashes and pumices. We studied water potentials ranging from 0 to −700 kPa on undisturbed soil and on soil previously frozen to get rid of living nematodes. Mortality of adult R. similis decreased regularly, and was fairly well described by Teissier's model. In the previously frozen soils, R. similis survived longer in wet soils (half-life of 21–46 days at 0 to −5 kPa) than in dry soils (half-life of less than 10 days between −80 and −250 kPa). In contrast, in undisturbed soils, R. similis survived longer in dry soils: half-lives ranged from 57 days at −273 kPa to 17 days at water saturation in the Andosol, and 36 days at −660 kPa to 14 days at water saturation in the Nitisol. These results are consistent with the absence of anhydrobiosis in R. similis, unlike Pratylenchus coffeae. P. coffeae survivorship curves over time do not follow a model derived from exponential decrease like Teissier's model. These results also show that the recommended one year host-free period required to sanitize soils cannot be shortened without risk, even if flooding the soil could improve it.

Root‐Lesion Nematodes Reduce Yield of Intolerant Wheat and Barley

Root‐lesion nematodes (Pratylenchus neglectus and P. thornei) are widely distributed and substantially reduce grain yields in wheat (Triticum aestivum L.)‐producing regions of the Pacific Northwest (PNW). The objective of this research was to determine if wheat and barley (Hordeum vulgare L.) cultivars differ in tolerance to these nematode species. Field experiments were conducted by comparing yields in untreated and nematicide‐treated plots over 3 yr at two locations infested with either P. neglectus or P. thornei Yield improvements from nematicide application ranged from 9 to 40% for spring cereals and 6 to 17% for winter cereals. Phenotypic tolerance responses differed (P < 0.01) among 45 cultivars of spring cereals but not among 22 and 45 cultivars of winter cereals. Tolerance ratings were assigned to spring cereals. This is the first report of wheat and barley tolerances to root‐lesion nematodes in North America. Variability within data sets was used to estimate that 40 and 56 comparisons (experiments × replications) would be required to assign tolerance ratings at the 95% confidence interval for spring and winter cereals, respectively. Cultivar reactions in these tests, production and economic statistics for Idaho, Oregon, and Washington, and surveys of Pratylenchus in these states were used to estimate that P. neglectus and P. thornei reduce region‐wide yields as much as 5% annually, equaling 361 Gg (361,000 metric tons) valued at $51 million. It was concluded that this yield‐based screening procedure was impractical for routine screening but added emphasis to the importance of these root parasites in regions with low precipitation.

Potential enhancement of degradation of the nematicides aldicarb, oxamyl and fosthiazate in UK agricultural soils through repeated applications

The potential for enhanced degradation of the carbamoyloxime nematicides aldicarb and oxamyl and the organophosphate fosthiazate was investigated in 35 UK agricultural soils. Under laboratory conditions, soil samples received three successive applications of nematicide at 25 day intervals. The second and third applications of aldicarb were degraded at a faster rate than the first application in six of the 15 aldicarb-treated soils, and a further three soils demonstrated rapid degradation of all three applications. High organic matter content and low pH had an inhibitory effect on the rate of aldicarb degradation. Rapid degradation was observed in nine out of the ten soils treated with oxamyl. In contrast, none of the fosthiazate-treated soils demonstrated enhanced degradation. The potential for enhanced degradation of aldicarb and oxamyl was demonstrated in nine out of 15 and nine out of ten soils respectively that had previously been treated with these active substances. Degradation of fosthiazate occurred at a much slower rate, with no evidence of enhanced degradation. Fosthiazate may provide a useful alternative in cases where the efficacy of aldicarb and oxamyl has been reduced as a result of enhanced degradation.

Nematode dispersion by runoff water: Case study of Radopholus similis (Cobb) Thorne on nitisol under humid tropical conditions

To minimize application of nematicides in banana fields, crop systems have been developed in the French West Indies that combine fallow or rotation crops and nematode-free in vitro plants. After two to four years, populations of the burrowing nematode Radopholus similis have developed enough to cause economic losses, leading banana growers to use nematicides. To understand how banana fields are recontaminated, we studied the dissemination of R. similis by water flow. At a 1-m scale, we analyzed the dispersion of R. similis under a rainfall simulator: we isolated a 1-m 2 study plot, placed a R. similis suspension on the upstream soil surface, and simulated a 60 mm/h rainfall for 72 min. We collected soil samples every 10 cm downstream after 12 min of rainfall, and subsequently at 20-min intervals, and extracted the nematodes using a Seinhorst elutriator and then a Baermann funnel. Our results showed that the nematode dissemination follows an inverse exponential law, and depends more on soil moisture at the beginning of rainfall than on the length of rainfall: in fresh soil, 69–80% of the R. similis recovered were found less than 10 cm downstream from the nematode inoculation line, whereas in wetted soil, 76–85% of the recovered individuals were collected in the outlet tub located downstream from the apparatus. This passive dissemination model partially explains the distance covered by individual nematodes but not the low percentage of motile nematodes recovered in the outlet tub (10% and 36% in fresh and wet soils) compared to the percentage of motile nematodes found in the soil (80% and 84% in fresh and wet soils). Indeed, water runoff is likely to disseminate R. similis over long distances only when soil moisture is close to field capacity.

오이 시설재배시 고구마뿌리혹선충의 경제적피해한계

고구마 뿌리혹선충(Meloidogyne incognita)의 시설재배 오이에 대한 경제적 피해한계를 조사하기 위하여 비닐하우스 내에 합판으로 만든 박스(<TEX>$30{\times}40{\times}15cm$</TEX>)를 묻고 박스 내 토양 <TEX>$100cm^3$</TEX>당 뿌리혹선충 유충의 밀도를 0, 10, 30, 100, 300, 600마리로 조정된 토양을 넣었다. 각 박스에는 '장수신토좌'에 접붙인 '슈퍼만촌'오이 23일 묘를 8월 1일 1포기씩 심고 11월까지 각 구당 오이 수확량을 조사하였다. 뿌리혹선충의 유충밀도와 수량과의 회귀식은 <TEX>$Y=0.82-0.04{\cdot}Log_{10}$</TEX>(Pi+1)로 방제 비용을 감안한 경제적 피해 허용 수준은 정식전 뿌리혹선충 유충의 밀도가 토양 <TEX>$1,000cm^3$</TEX>당 5마리이면 살선충제 입제 살포가 경제적이고, 유충의 밀도가 토양 <TEX>$1,000cm^3$</TEX>당 25마리 이상이면 훈증제를 처리하는 것도 고려해 볼 수 있다. 오이 시설재배시 뿌리혹선충의 피해를 방지하기 위해서는 최소한 정식 수개월 전에 미리 토양 선충 밀도를 조사해야 할 것이다. To determine the economic threshold level of Meloidogyne incognita on cucumber in greenhouse conditions, cucumber seedlings(Cucumis sativa L. cv. 'Super Manchon') grafted on 'Jangsushintozoa'(Cucurbita maxima x Cu. moschata) were planted in wooden boxes(<TEX>$30{\times}40{\times}15cm,\;L{\times}W{\times}D$</TEX>) under a plastic house in August 01 and harvested from Sep. 01-Oct. 30, 2006. The initial nematode population densities(Pi) in the wooden boxes were adjusted to 0, 10, 30, 100, 300, and 600 second-stage juveniles(J2)/100 <TEX>$cm^3$</TEX> soil. The relationship of total fruit yield to Pi level could be adequately described by a linear regression equation, <TEX>$Y=0.82-0.04{\cdot}Log_{10}$</TEX>(Pi+1). Initial nematode densities(Pi) before planting in excess of 5 J2/1,000 <TEX>$cm^3$</TEX> soil caused in total yields loss that is equivalent to the costs of granular nematicide application; Pi level in excess of 25 J2/1,000 <TEX>$cm^3$</TEX> soil caused in total yields loss that exceed the costs for application of fumigants at current control costs. We propose two different management strategies depending on nematode densities, (i) application of non-fumigant granular nematicides for M. incognita Pi level of 5 J2/1,000 <TEX>$cm^3$</TEX> soil and (ii) fumigant treatment with Pi level over 25 J2/1,000 <TEX>$cm^3$</TEX> soil. Soil samples to determine population density of Meloidogyne spp. for advisory purposes should be taken several months before planting time, which allows a period of time enough for implementing management procedures.

Nematode dissemination by water leached in soil: Case study of Radopholus similis (Cobb) Thorne on nitisol under simulated rainfall

New crop systems have been developed in the French West Indies that combine fallow or rotation crops with nematode-free vitro-plants to avoid the massive application of nematicides in banana fields. In these new banana fields, recontamination by the burrowing nematode Radopholus similis can then happen either by run-off or irrigation water. To understand these phenomena, we studied the vertical dissemination of R. similis by water leaching using soil cylinders and rainfall simulations. Steel drums were used to collect cylinders of soil (around 14.3 dm 3) with a backhoe. The soil cylinders were placed in an aspersion chamber, saturated with water, and a R. similis suspension was placed on the soil surface. Afterwards, rainfalls ranging from 12 to 540 mm were simulated. Nematodes were then extracted from different soil layers (0–5 to 20–25 cm depth) using either (i) a Seinhorst elutriator followed by a Baermann funnel or (ii) centrifugation–flotation combined with Meldola blue staining. Results showed that dissemination of R. similis at the scale of the decimetre in nitisoil is limited: less than 8% of the applied nematodes reached layers deeper than 10 cm after exceptional rainfalls that represent several times the poral volume of the soil. Dissemination below 25 cm depth seemed to be limited to very few individuals, from 0.1 to 0.2%. Among leached nematodes, the percentage of non-active and dead nematodes increased significantly with depth. It seems that R. similis have developed a behaviour to escape leaching. These findings question the generally accepted idea that water dissemination of plant-parasitic nematodes is mainly a passive phenomenon.

Preventing nematodes from spreading: A case study with Radopholus similis (Cobb) Thorne in a banana field

During the last decade, new crop systems have been developed in the French West Indies to avoid repeated applications of nematicides in banana fields. These combine fallow or rotation crops and nematode-free in vitro plants. In many fields, however, after 2–4 years, the burrowing nematodes Radopholus similis progressively re-infest banana fields, leading growers to re-apply nematicides. Among different hypotheses for re-infestation, we studied the possibility that nematodes were disseminated by runoff water. The study was conducted in an experimental field on plots that were defined by ditches or marked with flags and weeded or not, prior to replanting with in vitro plants. Results showed that 50–80 cm deep ditches efficiently prevent R. similis dissemination and that dispersion by water runoff is the major route of contamination. In contrast, weed management during the fallow period had little influence.

SIMBA, a model for designing sustainable banana-based cropping systems

Banana monocultures (Musa spp., AAA, Cavendish sub-group cv. Grande Naine) can have a detrimental impact on the environment. In these agro-systems, pesticide treatments can lead to surface and groundwater pollution, as is the case in the tropical insular conditions of the French West Indies. Using models to design alternative cropping systems is of growing interest but most of the research work has been concentrated on annual crops and most often in temperate climate. A specific model called SIMBA was built to assess environmental risks under a large range of cropping techniques and to help design more sustainable cropping systems. SIMBA simulates banana-cropping systems at field level over several cropping cycles. It includes sub-models that simulate soil structure, water balance, root nematode populations, yield, and economic outputs with a sound balance between representing the major phenomena well and keeping the model simple to reduce the parameterization costs in a large range of conditions. Agro-environmental indicators generated by the model make it possible to assess the major potential environmental impacts. The model has been developed and calibrated in Guadeloupe and Martinique and is used to draw up practical recommendations for farmers and for virtual experiments of agro-technological innovations or field management strategies. The structure of SIMBA is presented and a methodology is proposed for designing sustainable banana-based cropping systems using the model. SIMBA has been evaluated in a broad range of cropping systems in Guadeloupe by comparing model estimates to data collected in field experiments and surveys. Simulations lead to trends in rotation-based cropping systems characterized by systems that can be considered as intensive for profit evaluation, and combinations of frequent replanting, low nematicide application, no ploughing, and low fertilization level, for environmental evaluation. Simulations performed to optimize the replanting decision rule showed that relatively frequent replanting is good for profit while low frequency replantations (over four banana cycles) give a better environmental evaluation.

살선충제 침지처리에 의한 딸기잎선충 방제

Effects of different application of nematicides (fosthiazate 5% G, ethoprophos 5% G, and diazinon 34% EC) for the control of Aphelenchoides fragariae in strawberry were evaluated in a greenhouse experiments. Mother strawberry (Fragaria grandiflora) cv. Yeohong were dipped in solution of nematicides (fosthiazate or ethoprophos at 2.5 g a.i./liter in ) for 10 min. and planted in a greenhouse for dipping treatment. For the compare, mother strawberry were dipped in hot water for 10 min. without chemicals. For soil treatment, fosthiazate or ethoprophos at 3 kg a.i./ha were mixed into soil. For foliar spray, diazinon at 3.4 g a.i./liter was sprayed at foliage until runoff. At 40, 80, and 100 days after planting, runners were harvested from each treatment and the rate of nematode infestation and the number of nematodes per plant were examined. After 100 days of planting, mother strawberry plants dipped in fosthiazate solution (2.5 g a.i./liter, ) for 10 min. produced more number of healthy runners and reduced % of infected runner as much as 90% and also had fewer nematodes per runner. Fosthiazate was more effective than ethoprophos. Foliar application of diazinon was reduced A. fragariae populations only in early season. Hot water treatment and nematicide soil treatment were less effective.

Pesticide Residues in Heterogeneous Plant Populations, a Model-Based Approach Applied to Nematicides in Banana (Musa spp.)

Nematicides are widely used to control plant-parasitic nematodes in intensive export banana (Musa spp.) cropping systems. Data show that the concentration of fosthiazate in banana fruits varies from zero to 0.035 g kg-1, under the maximal residue limit (MRL=0.05 mg kg-1). The fosthiazate concentration in fruit is described by a Gaussian envelope curve function of the interval between pesticide application and fruit harvest (preharvest interval). The heterogeneity of phenological stages in a banana population increases over time, and thus the preharvest interval of fruits harvested after a pesticide application varies over time. A phenological model was used to simulate the long-term harvest dynamics of banana at field scale. Simulations show that the mean fosthiazate concentration in fruits varies according to nematicide application program, climate (temperature), and planting date of the banana field. This method is used to assess the percentage of harvested bunches that exceed a residue threshold and to help farmers minimize fosthiazate residues in bananas.

Improving root-knot nematode management on two soybean genotypes through the application of Bradyrhizobium japonicum, Trichoderma pseudokoningii and Glomus mosseae in full factorial combinations

The effects of soybean inoculation with arbuscular mycorrhiza fungus Glomus mosseae (200 spores/plant), the nodulating bacterium Bradyrhizobium japonicum (10 6 cells/plant) and the nematode antagonistic fungus Trichoderma pseudokoningii (6.8×10 7 spores/plant) were studied. Application of the microorganisms separately, in dual, or in triple combinations were assessed in the presence of the plant-parasitic nematode, Meloidogyne incognita under screen house (1000 second stage juvenile/plant) and field (1500 eggs/plant) conditions, with two soybean genotypes. The microorganism treatments were compared with application of a synthetic nematicide (Furadan 3G ® [a.i. carbofuran]), an untreated control without nematodes and a nematode-only control. Application of the microorganisms in full factorial combinations suppressed nematode reproduction in most cases and reduced nematode galling comparable to the nematicide treatment. The results provide evidence of the potential of beneficial microorganisms in providing equal or better protection against root-knot nematode damage, than the synthetic nematicide carbofuran.

Influence of Soil Physicochemical and Biological Properties on the Degradation and Adsorption of the Nematicide Fosthiazate

The degradation and adsorption of the organophosphorus nematicide fosthiazate were investigated in nine soils with various physicochemical and biological characteristics. Fosthiazate was more persistent in acidic soils (pH <6), with half-life (t1/2) values ranging from 53.3 to 57.7 days, compared to soils with higher pH (pH >7), with t1/2 ranging from 14.1 to 20.7 days. Application of antibacterial and antifungal antibiotics to soil samples resulted in a significant inhibition of fosthiazate degradation only in two of the three acidic soils. In contrast, soil autoclaving resulted in doubling the t1/2 of fosthiazate in all studied soils, suggesting that both microbial and abiotic processes contribute to fosthiazate degradation. Statistical analysis indicated a significant negative correlation (P < 0.01) between soil pH and t1/2. Fosthiazate was generally weakly adsorbed with Freundlich adsorption coefficient (Kf) values ranging from 1.23 to 2.74 mL/g. Fosthiazate concentration was strongly correlated with soil organic matter content with higher Kf values in soils with higher organic matter content (P < 0.01). The mean t1/2 and Kf values derived from the laboratory studies were used to parametrize the FOCUS groundwater (GW) models PRZM, PELMO, PEARL, and MACRO for nematicide application in potato and tomato crops. Predicted environmental concentrations produced by the models PEARL and MACRO suggested a potential risk for GW in several scenarios, unlike PELMO and PRZM, which predicted low risk for GW. These findings suggest that the environmental fate of fosthiazate is strongly influenced by soil characteristics and that this nematicide should be used with care in acidic, light soils with low organic matter content.

Modelling population dynamics of banana plant-parasitic nematodes: A contribution to the design of sustainable cropping systems

This article describes the biological background, the model-building methodology and some applications of SIMBA-NEM, a new model to simulate the population dynamics of two major plant-parasitic nematode species of banana, Radopholus similis and Pratylenchus coffeae. For each species, each generation is represented by one cohort. Cohorts of the same species form a chain representing the developmental stages of nematodes. A logistic function describes population growth in relation with: (i) an environmental carrying capacity ( K) that depends on available banana root biomass, (ii) an intrinsic growth rate ( c) and (iii) competition between nematode species. Soil water content and the quantity of nematicides used are considered to be the main variables influencing the intrinsic population growth rate of each species. SIMBA-NEM was calibrated and validated using datasets from banana cropping systems in Guadeloupe (French West Indies). By analysing the sensitivity of the model to the main parameters and performing simulations of validation for various cropping systems (banana monoculture with or without nematicide applications use and a banana/sugarcane rotation) we were able to test the ability of the model to predict nematode population dynamics under a range of conditions. SIMBA-NEM is able to predict long-term nematode population size, while taking interspecific competition into account. It also helped to define knowledge gaps in nematology and modelling. SIMBA-NEM was used to optimise the effect of nematicide applications. SIMBA-NEM can already be a very helpful tool for designing sustainable and more environment-friendly banana cropping systems. In the SIMBA global crop-modelling environment, SIMBA-NEM is a key sub-model which provides essential information concerning the sustainability of the simulated system and thus permits planning environmentally friendly cropping systems.

Response of cassava to nematicide application and plant-parasitic nematode infection in East Africa, with emphasis on root knot nematodes

Cassava (Manihot esculenta Crantz( is attacked by numerous species of plant-parasitic nematodes, among which, Meloidogyne spp. are the most damaging. However, data on the level of damage occurring under field and farm conditions are largely lacking. To examine the impact, upon cassava production, of plant-parasitic nematodes, field experiments were conducted at four sites in East Africa in Uganda (Serere and Sendusu( and Kenya (Mtwapa and Msabaha( during 2002 and 2003. We focused on Meloidogyne spp. (mainly M. incognita and M. javanica(, attacking two popular cultivars in each country. Nematicide (Nemacur® [fenamiphos]( was used against nematodes in control plots. Meloidogyne spp. were the most common nematodes encountered and caused galling damage at harvest at all sites, with Scutellonema spp. and Pratylenchus spp. being the next most commonly observed. The highest root densities of Meloidogyne spp. were recorded at Serere, while Mtwapa had the highest galling damage and intensity. At harvest, nematicide-treated plots had significantly lower densities of the most commonly occurring nematodes and fewer galls on feeder roots (galling intensity(. However, the root galling index score (damage( was not significantly lower compared with untreated plots. The majority of crop growth and yield variables measured at harvest across experiments were unaffected by nematicide application, but fewer storage roots suffered rot. The overall number of variables was minimized using Principal Components Analysis, which identified three major groups. A bivariate plot of the two larger groups across experiments showed that galling intensity, Pratylenchus spp. and Meloidogyne spp. density were negatively correlated with cassava yield (tonnes/ha( and marketable storage root number. Linear regression analysis showed that Meloidogyne spp. density at harvest was negatively associated with yield (tonnes/ha( for cv. Migyera and cv. SS4 in Uganda, but not for cv. Mtwapa1 or cv. Kibendameno (which was positively correlated( at Kenya sites. A strong negative correlation between marketable tuber number and Meloidogyne spp. for cv. Migyera was observed in Uganda, but not for cv. SS4. Meloidogyne spp. density and total nematode species density were each negatively correlated with non-marketable storage root number on both cultivars in Uganda, but not for either cultivar in Kenya.

Epidemiology and integrated control of Nacobbus aberrans on tomato in Mexico

Abstract Population densities, population fluctuations, yield loss and disease incidence caused by Nacobbus aberrans on tomato (Lycopersicon esculentum) were studied, using an epidemiological approach, in a field experiment that included three different control regimes: an integrated control (IC) scheme, which included fertilisation, nematicide (ethoprop) and chicken manure; a technical control (TC) scheme, based on the best local practices of fertilisation and use of carbofuran for nematode control; and a check treatment (AC), with no application of fertilisers or nematicide. At least three generations of N. aberrans occurred through the cropping season and the numbers of galls/plant and females/g of root through the crop season were used to define the area under a disease progress curve (AUDPC). The variables b−1 (Weibull's apparent infection rate), AUDPC and Yf (final disease incidence) indicated less crop damage under the IC scheme than under the other two schemes (TC and AC). The IC scheme resulted in increased plant height (41-49%), foliage dry weight (37-53%) and stem diameter (31-41%) compared with the TC and AC schemes. Tomato yields in IC surpassed those from TC and AC by 34 and 83%, respectively, while TC exceeded AC by 73%. The yield loss attributed to N. aberrans was 12, 29 and 83% in IC, TC and AC, respectively. The IC scheme improved commercial production by 20 and 81% in comparison to the TC and AC schemes. This was largely due to effective control of the initial inoculum density, which affects the first generation of the nematode population; control of this generation is essential for avoidance of yield loss. The first generation is completed during the period 0-60 dat (days after transplanting), i.e., during the critical stages of flowering, fruit initiation and fruit set (40, 50 and 60 dat). Data on plant performance taken every 10 days were used to derive a multiple point model for calculation of production loss.

Predicting Caterpillar Parasitism in Banana Plantations

This paper links ecological theory to the biological control of insect pests in banana plantations. Through an established predictive approach, ecological data on tritrophic interactions from natural systems were used to formulate simple recommendations for biological control in banana plantations. The specific goals were (1) to determine the most effective parasitoid enemies for biological control of lepidopteran larvae in banana plantations and (2) to examine the impact of nematicides on enemy populations. To assess percent parasitism, we reared 1,121 lepidopteran larvae collected from six plantations managed under two nematicide regimens. Attack by parasitoids in the families Tachinidae (Diptera), Braconidae, Eulophidae, and Chalcididae (Hymenoptera) closely paralleled rates reported for species with similar characteristics in lowland wet forests, and statistical models predicted the relative importance of these parasitoids as sources of mortality. We found that tachinid flies were the most important source of early instar larval parasitism in banana plantations, and their importance increased with more intensive nematicide applications. The statistical models that we derived from data on natural systems were useful in predicting which parasitoids would be important in banana and which larval characteristics they would preferentially attack. This approach could be used in other managed ecosystems where the identification of effective biological control agents is needed.

Seletividade de herbicidas aplicados em pré-emergência na cultura de cana-de-açúcar tratada com nematicidas

O objetivo do trabalho foi estudar a seletividade de herbicidas para a cultura da cana-de-açúcar quando aplicado em culturas tratadas com nematicidas. O experimento foi instalado em área pertencente à Usina São José, município de Borebi-SP, ano agrícola de 2000/01. A variedade de cana-de-açúcar utilizada foi a RB855113. Utilizou-se o delineamento experimental de blocos ao acaso em parcelas subdivididas, com quatro repetições. Cada parcela correspondeu a 27 linhas de 10,0 m, espaçadas em 1,0 m, sendo dividida em três subparcelas. As parcelas corresponderam aos tratamentos com os herbicidas, e as subparcelas, à aplicação ou não dos nematicidas carbofuran (2,10 kg ha-1) e terbufós 2,25 kg ha¹). Os herbicidas testados foram: tebuthiuron (1,12 kg ha-1), ametryne (1,75 kg ha¹), sulfentrazone (0,8 kg ha-1), metribuzin (1,92 kg ha-1), isoxaflutole (0,0525 kg ha¹), clomazone (1,25 kg ha¹), oxyfluorfen (0,36 kg ha-1) e azafenidin+hexazinone (0,1575 + 0,2025 kg ha-1), sendo todos aplicados em pré-emergência, além de uma parcela como testemunha. Os resultados obtidos evidenciaram que os herbicidas oxyfluorfen e azafenidin+hexazinone causaram os maiores níveis de fitotoxicidade na cana-de-açúcar, independentemente do uso dos nematicidas carbofuran e terbufós. Os herbicidas tebuthiuron, ametryne, sulfentrazone, metribuzin, isoxaflutole, clomazone, oxyfluorfen e azafenidin+hexazinone, aplicados em doses representativas das comercialmente utilizadas, mostraram-se seletivos à cana-de-açúcar, não afetando seu crescimento, sua produtividade e suas características tecnológicas. Os nematicidas não interferiram nos níveis de intoxicação provocados pelos herbicidas utilizados na cultura.

Control of potato cyst nematodes and economic benefits of application of 1,3‐dichloropropene and granular nematicides

SummaryThe two species of the potato cyst nematodes (PCN) Globodera pallida and G rostochiensis are the most problematic pests of the potato crop in the UK. There are no commercially available cultivars with full resistance to G. pallida and both crop rotation and granular nematicides are less effective at controlling this species than G. rostochiensis. In situations of very high PCN levels it may be possible to reduce populations and yield losses by using an autumn application of the soil fumigant 1,3‐dichloropropene (1,3‐D) followed by a spring application of a granular nematicide. Two field experiments were done to look at the integration of methods for the control of PCN. The Common Field experiment (G. rostochiensis infested) compared the use of 1,3‐D with the granular nematicides aldicarb, oxamyl and fosthiazate when growing the susceptible cv. Estima. The Four Gates experiment (infested with both PCN species but mainly G rostochiensis) compared the performance of cv. Santé (partially resistant to G. pallida, fully resistant to G. rostochiensis) with that of the susceptible cv. Estima when treated with 1,3‐D and oxamyl at full and half‐rates. The results of the experiments show that an integrated approach to nematode control on heavily infested sites, including granular and fumigant nematicides and cultivar resistance, can lead to significant decreases in nematode population densities and reduce yield losses. An economic evaluation of the experiments modelled the gross margins from the different nematicide treatments. In Common Field, the highest gross margins were achieved with the combined use of fumigant and granular nematicides. In Four Gates, there was a clear economic benefit for both cultivars from the use of 1,3‐D. In this experiment, oxamyl was of economic value to Estima but not to Sante and full‐rate oxamyl was of more benefit than half‐rate to Estima.

Evaluation of Crop Rotation and Other Cultural Practices for Management of Root‐Knot and Lesion Nematodes

Root‐knot [Meloidogyne incognita (Kofoid &amp; White) Chitwood] and lesion [Pratylenchus penetrans (Cobb) Chitwood &amp; Oteifa] nematodes are important pathogens that cause yield and quality losses for most vegetable and field crops in Maryland when they exceed certain threshold levels and if control measures are not applied. Chemical nematicides are the primary control tactic, but their use is both costly and raises environmental concerns. This study was conducted to evaluate the efficacy of crop rotation and other cultural practices for management of southern root‐knot nematodes (RKNs) and lesion nematodes. Three nonhost crops, a RKN‐resistant soybean [Glycine max (L.) Merr.] cultivar, and poultry litter/tillage (Year 1) and fallow (Year 2) were used as summer rotation crops/management options following production of nematode‐susceptible crops on two sites in Dorchester County, MD, on Downer and Hammonton sandy loam soils (coarse‐loamy, siliceous, mesic Typic and Aquic Hapludults), respectively. Sorghum sudangrass [Sorghum bicolor (L.) × S. arundinaceum (Desv.) Stapf var. sudanense (Stapf) Hitchc.], grown annually as a green manure crop following a nematode‐susceptible crop [potato (Solanum tuberosum L.) or cucumber (Cucumis sativus L.)], reduced the RKN population as effectively as the control treatment (soybean cultivar with no known RKN resistance and one nematicide application). Sorghum sudangrass and poultry litter/tillage/fallow were equally effective in managing the lesion nematode population. Annual inclusion of these practices was necessary to maintain the reduced population levels that were attained for these two nematode species. Finally, either summer or early‐fall sampling dates were determined to be more effective than a midspring sampling date for identifying threshold levels of these two pests.