Timing Of Pesticide Application Research Articles

Small-scale market gardeners’ knowledge, attitudes and practices regarding the use of chemical pesticides in the Kabare territory (South-Kivu) in Eastern D.R. Congo

Damage caused by pests and diseases is one of constraints on crop production for food security. Based on the use of questionnaire and interviews that were conducted in Kabare territory (South-Kivu), this study was carried out to (i) assess farmers practices, attitudes, and knowledge about pesticides use, and (ii) assess the human health and physical environment effects using pesticides. Data was collected from 300 small-scale farmers in study area. Results showed that majority of our respondents were men (59 %) rather than women (41 %) and local knowledge of pesticide use was low (60 %). Education level had a significant influence (p < 0.01) on level of knowledge about pesticide use, time and dose of treatment, method of control, and persistence time. In addition, education level influence significantly farmers' attitudes before and after pesticide treatment (p < 0.05). Pest management control, time of pesticide application, and packaging management method varied significantly with level of local knowledge (p < 0.01). Pesticides use by small-scale farmers has an effect on water, soil, and air quality. It also causes human pathologies such as vomiting, eye irritation, and even loss of life in event of heavy exposure. Inhalation and dermal exposure are main and most dangerous routes of pesticide exposure in our study area, which lacks protective strategies. Finally, use of pesticides disrupts biodiversity through the disappearance of pollinators, predators, parasitoids, and soil microorganisms. Therefore, broad continuity of this study with integration of other scientific aspects would effectively contribute to the improvement of environmental quality.

Long-term, landscape-level assessment of aquatic pesticide exposure to identify amphibian ontological traits affecting vulnerability.

Amphibians worldwide are threatened by habitat loss, some of which is driven by a changing climate, as well as exposure to pesticides, among other causes. The timing and duration of the larval development phase vary between species, thereby influencing the relative impacts of stochastic hydroregime conditions as well as potential aquatic pesticide exposure. We describe the stages of breeding through metamorphosis for eight amphibian species, based on optimal hydroregime conditions, and use a model of pesticide fate and exposure representative of central Florida citrus groves to simulate hydrodynamics based on observed weather data over a 54-year period. Using the Pesticide in Water Calculator and Plant Assessment Tool, we estimated daily wetland depth and pyraclostrobin exposure, with label-recommended application quantities. Species' timing and duration of larval development determined the number of years of suitable hydroregime for breeding and the likelihood of exposure to peak aquatic concentrations of pyraclostrobin. Although the timing of pesticide application determined the number of surviving larvae, density-dependent constraints of wetland hydroregime also affected larval survival across species and seasons. Further defining categorical amphibian life history types and habitat requirements supports the development of screening-level assessments by incorporating environmental stochasticity at the appropriate temporal resolution. Subsequent refinement of these screening-level risk assessment strategies to include spatially explicit landscape data along with terrestrial exposure estimates would offer additional insights into species vulnerability to pesticide exposure throughout the life cycle. Computational simulation of ecologically relevant exposure scenarios, such as these, offers a more realistic interpretation of differential agrichemical risk among species based on their phenology and habits and provides a more situation-specific risk assessment perspective for threatened species. Integr Environ Assess Manag 2024;20:1667-1676. Published 2024. This article is a U.S. Government work and is in the public domain in the USA.

Coffee berry borer (Coleoptera: Scolytidae) population dynamics across Hawaii Island's diverse coffee-growing landscape: optimizing location-specific pesticide applications.

A major challenge to area-wide management of coffee berry borer (Hypothenemus hampei Ferrari) (Coleoptera: Scolytidae) is understanding how a heterogeneous coffee-growing landscape affects coffee berry borer population dynamics across temporal and spatial scales. We examined coffee phenology, weather, coffee berry borer flight activity, infestation, coffee berry borer position within the fruit, and management across 14 commercial coffee farms from 2016 to 2018 on Hawaii Island to characterize variation among districts and elevations. Here we aim to determine whether the timing of pesticide applications might be optimized based on specific locations. We observed larger populations of coffee berry borer at low-elevation farms and in the Kona district compared to mid- and high-elevation farms and the Ka'u district. Temperature, relative humidity, and rainfall all differed significantly across districts and elevations. We also observed a trend of higher fruit production at low-elevation farms compared to high-elevation farms, and differences in the timing of fruit development. Infestation increased with higher pest pressure and air temperatures and reduced fruit availability early and late in the season. Lastly, the timing and number of management interventions varied among districts and elevations. Combining information on trap catch, infestation, coffee berry borer position, and plant phenology, we present an optimized pesticide spray schedule for each location and find that the number of sprays could be reduced by 33-75% in comparison to the existing integrated pest management recommendations while maintaining effective control. Implementing a coordinated area-wide approach refined by small-scale optimization will lead to improved management of coffee berry borer on individual farms and a reduction in pest pressure across the coffee-growing landscape.

Application timing as a mitigation tool for pesticide leaching to drains in northwest Europe

Study regionArtificially drained agricultural land in northwest Europe. Study focusThe use of application timing as a mitigation tool for pesticide leaching to drains was investigated by simulating pesticide fate after application every day in a pesticide-specific application window, using the agro-hydrological model DAISY. The simulations were carried out for six combinations of pesticide-crop-seasons using three synthetically generated climate series and 800 soil profiles. The simulated drain concentrations were transformed to normalized pesticide concentrations in a hypothetical adjacent stream. Each application day was then characterized by the maximum normalized hourly pesticide concentration in the stream, expressed as the maximum hourly toxic unit (mTU), occurring within 300 days after application. New hydrological insights for the regionThe result showed that if the pesticide was applied consistently every year at the best application day, pesticide leaching, in terms of the 90th percentile of mTU, could be reduced by up to 62% compared to a random application. If the pesticide application day was restricted to vary in a five-day period, the 90th percentile of mTU could be reduced by up to 21%. Thus, our study shows that there is a significant mitigation potential for reducing pesticide leaching to drains by tailoring the timing of pesticide application to weather conditions.

Typology for Decision Support Systems in Integrated Pest Management and Its Implementation as a Web Application

Decision support systems (DSSs) enable the optimisation of pesticide application timing to increase pesticide efficacy and thus reduce pesticide use without compromising yield quality and quantity. Limited access to information about available DSSs for use in integrated pest management (IPM) is a major barrier to the uptake of DSSs for IPM across Europe. To overcome this barrier, a typology for DSSs for IPM in Europe was developed, introducing a systematic approach to describe the ever-growing number of DSSs for IPM. The developed IPM-DSS typology was implemented in the free web tool “IPM Adviser”, where currently 79 IPM DSSs are described with over 50 attributes describing their structural and performance characteristics. The information about IPM DSSs, which was previously scattered on different websites and difficult to compare, is now standardised and presented in a uniform way, so that it is possible to compare different IPM DSSs on the basis of all the attributes described. The presented IPM-DSS typology implemented in the web tool IPM Adviser facilitates the dissemination and uptake of DSSs for IPM and thus contributes to the achievement of the EU targets for the sustainable use of pesticides.

Computer vision for plant pathology: A review with examples from cocoa agriculture.

Plant pathogens can decimate crops and render the local cultivation of a species unprofitable. In extreme cases this has caused famine and economic collapse. Timing is vital in treating crop diseases, and the use of computer vision for precise disease detection and timing of pesticide application is gaining popularity. Computer vision can reduce labour costs, prevent misdiagnosis of disease, and prevent misapplication of pesticides. Pesticide misapplication is both financially costly and can exacerbate pesticide resistance and pollution. Here, we review the application and development of computer vision and machine learning methods for the detection of plant disease. This review goes beyond the scope of previous works to discuss important technical concepts and considerations when applying computer vision to plant pathology. We present new case studies on adapting standard computer vision methods and review techniques for acquiring training data, the use of diagnostic tools from biology, and the inspection of informative features. In addition to an in-depth discussion of convolutional neural networks (CNNs) and transformers, we also highlight the strengths of methods such as support vector machines and evolved neural networks. We discuss the benefits of carefully curating training data and consider situations where less computationally expensive techniques are advantageous. This includes a comparison of popular model architectures and a guide to their implementation.

Honey bees and bumble bees may be exposed to pesticides differently when foraging on agricultural areas

In an agricultural environment, where crops are treated with pesticides, bees are likely to be exposed to a range of chemical compounds in a variety of ways. The extent to which different bee species are affected by these chemicals, largely depends on the concentrations and type of exposure. We quantified the presence of selected pesticide compounds in the pollen of two different entomophilous crops; oilseed rape (Brassica napus) and broad bean (Vicia faba). Sampling was performed in 12 sites in Ireland and our results were compared with the pollen loads of honey bees and bumble bees actively foraging on those crops in those same sites. Detections were compound specific, and the timing of pesticide application in relation to sampling likely influenced the final residue contamination levels. Most detections originated from compounds that were not recently applied on the fields, and samples from B. napus fields were more contaminated compared to those from V. faba fields. Crop pollen was contaminated only with fungicides, honey bee pollen loads contained mainly fungicides, while more insecticides were detected in bumble bee pollen loads. The highest number of compounds and most detections were observed in bumble bee pollen loads, where notably, all five neonicotinoids assessed (acetamiprid, clothianidin, imidacloprid, thiacloprid, and thiamethoxam) were detected despite the no recent application of these compounds on the fields where samples were collected. The concentrations of neonicotinoid insecticides were positively correlated with the number of wild plant species present in the bumble bee-collected pollen samples, but this relationship could not be verified for honey bees. The compounds azoxystrobin, boscalid and thiamethoxam formed the most common pesticide combination in pollen. Our results raise concerns about potential long-term bee exposure to multiple residues and question whether honey bees are suitable surrogates for pesticide risk assessments for all bee species.

The effect of climate variability in the efficacy of the entomopathogenic fungus Metarhizium acridum against the desert locust Schistocerca gregaria

Despite substantial efforts to control locusts they remain periodically a major burden in Africa, causing severe yield loss and hence loss of food and income. Distribution maps indicating the value of the basic reproduction number R0 was used to identify areas where an insect pest can be controlled by a natural enemy. A dynamic process-based mathematical model integrating essential features of a natural enemy and its interaction with the pest is used to generate R0 risk maps for insect pest outbreaks, using desert locust and the entomopathogenic fungus Metarhizium acridum (Synn. Metarhizium anisoliae var. acridum) as a case study. This approach provides a tool for evaluating the impact of climatic variables such as temperature and relative humidity and mapping spatial variability on the efficacy of M. acridum as a biocontrol agent against desert locust invasion in Africa. Applications of M. acridum against desert locust in a few selected African countries including Morocco, Kenya, Mali, and Mauritania through monthly spatial projection of R0 maps for the prevailing climatic condition are illustrated. By combining mathematical modeling with a geographic information system in a spatiotemporal projection as we do in this study, the field implementation of microbial control against locust in an integrated pest management system may be improved. Finally, the practical utility of this model provides insights that may improve the timing of pesticide application in a selected area where efficacy is highly expected.

Probabilistic modelling of the inherent field-level pesticide pollution risk in a small drinking water catchment using spatial Bayesian belief networks

Abstract. Pesticides are contaminants of priority concern that continue to present a significant risk to drinking water quality. While pollution mitigation in catchment systems is considered a cost-effective alternative to costly drinking water treatment, the effectiveness of pollution mitigation measures is uncertain and needs to be able to consider local biophysical, agronomic, and social aspects. We developed a probabilistic decision support tool (DST) based on spatial Bayesian belief networks (BBNs) that simulates inherent pesticide leaching risk to ground- and surface water quality to inform field-level pesticide mitigation strategies in a small (3.1 km2) drinking water catchment with limited observational data. The DST accounts for the spatial heterogeneity in soil properties, topographic connectivity, and agronomic practices; the temporal variability of climatic and hydrological processes; and uncertainties related to pesticide properties and the effectiveness of management interventions. The rate of pesticide loss via overland flow and leaching to groundwater and the resulting risk of exceeding a regulatory threshold for drinking water was simulated for five active ingredients. Risk factors included climate and hydrology (e.g. temperature, rainfall, evapotranspiration, and overland and subsurface flow), soil properties (e.g. texture, organic matter content, and hydrological properties), topography (e.g. slope and distance to surface water/depth to groundwater), land cover and agronomic practices, and pesticide properties and usage. The effectiveness of mitigation measures such as the delayed timing of pesticide application; a 10 %, 25 %, or 50 % reduction in the application rate; field buffers; and the presence/absence of soil pan on risk reduction were evaluated. Sensitivity analysis identified the month of application, the land use, the presence of buffers, the field slope, and the distance as the most important risk factors, alongside several additional influential variables. The pesticide pollution risk from surface water runoff showed clear spatial variability across the study catchment, whereas the groundwater leaching risk was uniformly low, with the exception of prosulfocarb. Combined interventions of a 50 % reduced pesticide application rate, management of the plough pan, delayed application timing, and field buffer installation notably reduced the probability of a high risk of overland runoff and groundwater leaching, with individual measures having a smaller impact. The graphical nature of BBNs facilitated interactive model development and evaluation with stakeholders to build model credibility, while the ability to integrate diverse data sources allowed a dynamic field-scale assessment of “critical source areas” of pesticide pollution in time and space in a data-scarce catchment, with explicit representation of uncertainties.

Foliar Photodegradation in Pesticide Fate Modeling: Development and Evaluation of the Pesticide Dissipation from Agricultural Land (PeDAL) Model.

Pesticide dissipation from plant surfaces depends on a variety of factors including meteorological conditions, the pesticide's physicochemical properties, and plant characteristics. Models already exist for describing pesticide behavior in agriculture fields; however, they do not account for pesticide-specific, condition-specific foliar photodegradation and the importance of this component in such models has not yet been investigated. We describe here the Pesticide Dissipation from Agricultural Land (PeDAL) model, which combines (a) multiphase partitioning to predict volatilization, (b) a new kinetics module for predicting photodegradation on leaf surfaces under varying light conditions based on location and timing, and (c) a generic foliar penetration component. The PeDAL model was evaluated by comparing measured pesticide dissipation rates from field experiments, described as the time for the pesticide concentration on leaves to decrease by half (DT50), to ones generated by the model when using the reported field conditions. A sensitivity analysis of the newly developed foliar photodegradation component was conducted. We also showed how the PeDAL could be used by applicators and regulatory agencies. First, we used the model to examine how pesticide application timing affects dissipation rates. Second, we demonstrated how the model can be used to produce emission flux values for use in atmospheric dispersion and transport models.

Abstract PO-125: Prenatal proximity to agricultural use of endocrine-disrupting pesticides and risk of testicular germ cell tumor (TGCT) among Latino and non-Latino adolescents in California

Abstract BACKGROUND. Incidence of testicular germ cell tumors (TGCTs) has increased steadily in the United States in recent years, especially among Latinos. TGCT initiation is believed to occur during fetal development and to be related to endocrine disruption; the increasing prevalence of in utero exposures to endocrine- disrupting chemicals may have contributed to the rise in the disease’s incidence. METHODS. This registry-based case-control study included 381 California-born patients diagnosed with TGCT at age 15-19 years from 1997-2011 (336 non- seminomas, 41 seminomas) and 762 controls matched on birth year and race/ethnicity. We assessed the agricultural application of 22 endocrine-disrupting pesticides (EDPs) using California’s Pesticide Use Reporting (PUR) database for an area within a 3km radius of participants’ birth address in the year prior to birth; 15 high-volume EDPs (those to which 50 or more participants were potentially exposed) were included in statistical analyses. We used logistic regression to calculate odds ratios (ORs) and 95% confidence intervals (CIs) for log2-transformed continuous pesticide levels, and to calculate attributable risk (AR) for dichotomous exposure (zero and low application vs. high application). Analyses accounted for the timing of pesticide application, histologic subtype, race/ethnicity, birth year, and neighborhood socioeconomic status (SES). RESULTS. Overall, 48% of cases and 45% of controls lived within 3km of an EDP application in the year before birth. Nearby pesticide applications were greater among Latinos than non-Latinos for 13 of 15 EDPs; the median [interquartile range (IQR)] for total EDP application was 29 kg [5- 135] vs. 11 kg [1-80]. Application was also greater for those born after 1990 (the period of time with complete PUR reporting) than before 1990 for 14 of 15 EDPs (median [IQR] for total EDP application: 54 kg [10-229] vs. 13 kg [0.7-70]). Analyses of individual EDPs showed an increased risk of TGCT associated with acephate (OR [95%CI]: 1.1 [1.0-1.2] and 1.3 [1.0-1.7] for continuous and binary exposures, respectively). In analyses stratified by ethnicity, risk remained elevated for acephate application among Latinos (n=614, OR [95% CI] for continuous exposure model: 1.1 [1.0-1.2]) and for carbaryl and copper sulfate in non-Latinos (n=504, OR [95% CI]: 1.2 [1.0-1.3] and 1.1 [1.0-1.3], respectively). Overall there were no differences by PUR reporting period (before and after 1990) and application timing (preconception and trimesters), yet risk appeared to be higher for non-seminomas and among high SES participants. The population AR for high levels of acephate was 5.4% among Latinos, and &amp;lt;1% prior to 1990 vs. 10% after 1990 for all subjects combined. In non-Latinos, the AR for carbaryl was 4.8% and 2.5% for copper sulfate. CONCLUSIONS. Acephate, an organophosphate insecticide, was associated with an increased TGCT risk, possibly contributing 5-10% to the prevalence of TGCT among Latinos in California. Citation Format: Scott J. Swartz, Libby Morimoto, Todd Whitehead, Robert Gunier, Joseph Wiemels, Xiaomei Ma, Catherine Metayer. Prenatal proximity to agricultural use of endocrine-disrupting pesticides and risk of testicular germ cell tumor (TGCT) among Latino and non-Latino adolescents in California [abstract]. In: Proceedings of the AACR Virtual Conference: Thirteenth AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2020 Oct 2-4. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2020;29(12 Suppl):Abstract nr PO-125.

Scientific report of EFSA on the 'repair action' of the FOCUS surface water scenarios.

The European Commission asked EFSA to undertake a ‘repair action’ of the FOCUS surface water report after the EFSA Pesticide Steering Network had been consulted. The main request was to introduce into all FOCUS surface water scenarios (both run‐off and drainage) a 20‐year assessment period instead of the current 12‐ or 16‐month assessment period. Because of the 20‐year assessment period, the way application dates are defined needed to be reviewed, reconsidering the functionality of the pesticide application timing currently used. Guidance on how substance parameters should be handled when correlated with soil properties has been provided. Foliar wash‐off calculated in MACRO and Pesticide Root Zone Model was aligned and the appropriateness of including rotational crop aspects was discussed. Processing time and how to use the results of the exposure assessment were considered.

Why farmers deviate from recommended pesticide timing: the role of uncertainty and information.

Precise timing of pesticide applications, as recommended by decision-support systems, can ensure crop protection, while maintaining efficient use of pesticides, yet farmers often deviate from recommended timing strategies. Here, we assess and explain farmers' choices to follow or not follow recommendations for the timing of fungicide applications against potato late blight in Switzerland. Based on daily fungicide application records as well as regional application recommendations and disease pressure, we found that 36% of applications took place earlier than recommended. Using regression analysis, we identified the exposure to economic risks of infection, susceptibility of the planted potato varieties to late blight infections, as well as yearly differences in disease occurrence as the most important determinants of farmers' application decision. Our results indicate that decisions to not follow application recommendations and apply early are linked to available information and uncertainty with respect to disease predictions. Based on our results, we make recommendations on how to account for farmers' uncertainty with regard to the timing of pesticide applications in the design of pesticide policies and agricultural decision-support systems. These include the use of new technologies and data, mandatory reporting and tailor-made taxes and insurance solutions. Although the focus of this article is on late blight in Switzerland, our analysis can easily be extended to other countries and important plant diseases like powdery mildew in grapevines or Fusarium head blight in winter wheat. © 2020 Society of Chemical Industry.

A reaction-diffusion population growth equation with multiple pulse perturbations

During the pest growth generations there exist a number of internal and external perturbations including birth pulses and pulse pesticide applications, which result in a complex growth pattern within each pest growth generation due to the variation of perturbation timings. In order to show how multiple pulse perturbations affect the dynamics of the pest population, we have extended the classical Fisher reaction-diffusion equation by involving instant birth and control perturbations. The main results indicate that the pulse perturbations have a remarkable influence on the existence and stability of a spatially homogeneous periodic solution. In particular, the birth rate and killing efficacy can affect the traveling wave and its spreading speed, while the timing of pesticide application does not make any effects on those threshold conditions. However, numerical investigations reveal that the timing of pesticide applications can significantly affect the spatial distributions of the pest population. Within each generation too early or too late pesticide application could result in a faster growth and wider spread of the pest, and the optimal timing of pesticide application is the middle of each generation provided that the efficacy of the pesticide is relatively low. Bifurcation analyses reveal that even generations and odd generations display a different spatial pattern, which depict some important issues related to the pest control and pest management, for example the different control strategies should be adopted for even and odd generations. To address how the spatial heterogeneity affects on the cost of the pest control, we further formulate the cost function to investigate the optimal pest control strategy, and the optimal spatial dependent killing rates which minimize the cost have been obtained numerically.

Sublethal Effects of Some Insecticides on Functional Response of Habrobracon hebetor (Hymneoptera: Braconidae) When Reared on Two Lepidopteran Hosts.

The effects of four commonly used pesticides, diazinon (EC 60%), phosalone (EC 35%), fipronil (Granular formulation 0.2%), and pyriproxifen (EC 10%), on functional response of Habrobracon hebetor (Say) (Hymenoptera: Braconidae) were investigated using two lepidopteran hosts, Ephestia kuehniella Zeller (Lepidoptera: Pyralidae) and Heliothis viriplaca (Hufnagel) (Lepidoptera: Noctuidae). Laboratory bioassays determined diazinon and fipronil as highly toxic insecticides for all developmental stages of the parasitoid, while the acute toxicity of phosalone and pyriproxyfen was moderate to very low depending on the life-stage studied. Larval, pupal, and adult stages of the parasitoid were exposed to sublethal concentrations (LC30) of insecticides, and the newly mated females were used to study functional response of the parasitoid to different host densities. With a single exception, a type II functional response was found for control and all insecticide treatments on all life stages and both host species. All insecticides tended to decrease the asymptote of the functional response curve and the maximum parasitism rate, probably by negatively affecting the searching efficiency (a') of the parasitoid. These results indicate that the control efficiency of parasitoids may be negatively affected by sublethal doses of pesticides, even though the type of functional response remains unchanged. As a potential solution, appropriate timing of pesticide application is required to avoid the antagonistic interactions with natural enemies under integrated management programs.

Predicting Pesticide Volatility Through Coupled Above- and Belowground Multiphysics Modeling

Pesticides are applied to agricultural fields to control unwanted pests but can volatilize and be transported downwind by wind currents to create the potential for non-target organism exposure. Volatilization rates change through the growing season due to pesticide application timing, meteorological differences, and the differential flux rates from soil and vegetation matrices. Field studies quantifying pesticide volatility are expensive and cannot capture the semi-infinite parameter combinations of soil, crop, management, and meteorological conditions encountered under regional agronomic practices. A numerical approach was used to simulate pesticide dissipation above- and belowground to augment field and laboratory experimental observations. Above- and belowground physics are coupled into a single numerical tool using the COMSOL Multiphysics® software package with the current emphasis on pesticide volatility into air from soil and vegetation and resulting near field neighboring air concentrations. Comparison of simulation results against experimental observations for an insecticide (chlorpyrifos) applied to potato and alfalfa fields shows good agreement (R2 0.68–0.98). Chlorpyrifos volatility from plant surfaces drives the overall volatility within the first several days post application. The maximum volatility flux rate simulated and observed were 0.79 and 0.66 μg m−2 s−1 for the alfalfa trial and 2.72 and 2.17 μg m−2 s−1 for the potato field, respectively. This coupled multiphysics tool [computational fluid dynamics (CFD), mass transfer coefficients, and variably saturated flow in soil] can be used to estimate volatility flux rates of pesticides when little or no prior knowledge is available and for extrapolating field study observations to different and diverse scenarios.

Travelling waves and paradoxical effects in a discrete-time growth-dispersal model

• The Beverton–Holt model with pulse control within each generation has been developed. • The traveling wave, speed and shape have been studied. • The effects of efficacy and timing of pesticide application on dynamics are studied. • The influence of dynamic complexity on pest control and spread are analyzed. • Threshold conditions for occurrence of paradoxical effects have been discussed. Integrodifference equations have been widely used to describe the spatiotemporal dynamics of a population. Here, we first extended the discrete Beverton–Holt model, to model the effects of an instantaneous control measure within each generation on a population’s growth. Then we investigated the effects of instantaneous killing rate and timing of pesticide application on a pest’s dynamics, together with the effects of a spatial factor on the existence of a travelling wave solution, its spreading speed and asymptotic stability, and the occurrence of paradoxical effects. The main results indicate that the instantaneous killing rate significantly influences the existence of a travelling wave and its speed of spread, while the timing of pesticide applications does not. In order to address how such dynamic complexities affect the above results, we included an interruption constant into the model which can generate chaotic dynamics. The results indicate that the pesticide efficacy not only affects the existence of a travelling wave and its speed of spread, but it can also produce paradoxical effects, i.e. low pesticide efficacy can result in an increase, not a decrease, of the stable population size, while high pesticide efficacy could inhibit the pests growth. Furthermore, different patterns of stable population sizes between odd and even generations can be produced. The results reveal that the pest control tactics should be designed according to the spatial characteristics and the pest generation.

Adsorbing vs. Nonadsorbing Tracers for Assessing Pesticide Transport in Arable Soils

Core Ideas Atrazine preferential flow shortly after application was governed by soil type. Injection of atrazine at depth enhanced preferential flow. Uranine realistically illustrated the rapid and significant atrazine breakthrough. In reserve, bromide mimicked early atrazine breakthrough only with moraine soil. Using dye tracers as pesticide surrogates might assist in making sustainable decisions. The suitability of two different tracers to mimic the behavior of pesticides in agricultural soils and to evidence the potential for preferential flow was evaluated in outdoor lysimeter experiments. The herbicide atrazine [6‐chloro‐N‐ethyl‐N′‐(1‐methylethyl)‐1,3,5‐triazine‐2,4‐diamine] was used as a model compound. Two tracers were used: a nonadsorbing tracer (bromide) and a weakly adsorbing dye tracer (uranine). Two soils that are expected to show a different extent of macropore preferential flow were used: a well‐drained sandy‐loamy Cambisol (gravel soil) and a poorly drained loamy Cambisol (moraine soil). Conditions for preferential flow were promoted by applying heavy simulated rainfall shortly after pesticide application. In some of the experiments, preferential flow was also artificially simulated by injecting the solutes through a narrow tube below the root zone. With depth injection, preferential leaching of atrazine occurred shortly after application in both soil types, whereas with surface application, it occurred only in the moraine soil. Thereafter, atrazine transport was mainly through the porous soil matrix, although contributions of preferential flow were also observed. For all the application approaches and soil types, after 900 d, &lt;3% of the applied amount of atrazine was recovered in the drainage water. Only uranine realistically illustrated the early atrazine breakthrough by transport through preferential flow. Uranine broke through during the first intense irrigation at the same time as atrazine. Bromide, however, appeared earlier than atrazine in some cases. The use of dye tracers as pesticide surrogates might assist in making sustainable decisions with respect to pesticide application timing relative to rainfall or soil potential for preferential flow.

Assessing recovery of stream insects from pesticides using a two-patch metapopulation model

Pesticides can exert lethal and sublethal effects on streams organisms. Field studies have shown that non-polluted upstream patches promote population recovery from such effects. Nevertheless, the dynamics and potential carryover effects on the upstream patch are largely unknown. We used a metapopulation model with 2 patches to simulate lethal and sublethal effects on the downstream population of an insect with one generation per year, which was structured into early and late instars aquatic life stages, and an adult terrestrial life stage. We examined the implications for the recovery time of a range of scenarios covering different pesticide effect combinations, migration and exposure types. We found that recovery time responded most strongly to a reduction in reproduction in terms of the reduction of the intrinsic growth rate during the early instar aquatic life stage. For 60 of 96 scenarios with pesticide exposure in consecutive years, no recovery occurred within one year if the intrinsic growth rate was reduced by 50% or more. Without migration between patches (32 scenarios), the polluted downstream population went extinct in 5 of these scenarios. Migration lead overall to slightly faster recovery, albeit this was scenario dependent, but also to a carryover of the pesticide effect from the polluted downstream to the non-polluted upstream patch (up to 25% reduction in the minimal population size). A sensitivity analysis revealed that recovery time was most sensitive to the parameters length of the intrinsic growth phase during early instar aquatic life stage and to migration mortality of the late instar aquatic larvae, and least sensitive to the adult emigration rate and timing of pesticide application. Our study highlights the important role of sublethal effects for population responses to pesticides and that migration buffers against effects, but also carries effects over to non-polluted patches.

Improvement of Management of Rhagoletis Cerasi in Bosnia and Herzegovina Based on a Phenological Model

AbstractEuropean cherry fruit fly (Rhagoletis cerasi) is the key pest of sweet and sour cherry throughout Europe. Pest management is usually based on pesticide application. The key of successful management is knowing the proper time of pesticide application, based on the phenological model. To develop a phenological model, a local population of the pest from the northern part of Bosnia and Herzegovina was studied. First adult appearance and population densities were monitored by yellow sticky traps. Soil and air temperatures were compared at two thermal thresholds, 5 °C and 7 °C. Air temperature was applied in the model since it is more suitable for farmers and is related to soil temperature. Both thermal thresholds can be used. The first adult flies were captured after 435 degree-days (dd) and the first cumulative 5% of the catch after 605 dd. These two times should be considered for time of application of pesticides. Regarding time for first egg hatch, the first larva burrowed into fruits at 730 dd. Cultivars that can be harvested beginning on the 730 dd calculate from 1 March are considered to have low risk of cherry fruit fly damage.