Dose and number of applications that maximise fungicide effective life exemplified by Zymoseptoria tritici on wheat - a model analysis

Two key decisions that need to be taken about a fungicide treatment programme are (i) the number of applications that should be used per crop growing season, and (ii) the dosage that should be used in each application. There are two opposing considerations, with control efficacy improved by a higher number of applications and higher dose, and resistance management improved by a lower number of applications and lower dose. Resistance management aims to prolong the effective life of the fungicide, defined as the time between its introduction onto the market for use on the target pathogen, and the moment when effective control is lost due to a build-up of fungicide resistance. Thus, the question is whether there are optimal combinations of dose rate and number of applications that both provide effective control and lead to a longer effective life. In this paper, it is shown how a range of spray programmes can be compared and optimal programmes selected. This is explored with Zymoseptoria tritici on wheat and a quinone outside inhibitor (QoI) fungicide. For this pathogen-fungicide combination, a single treatment provided effective control under the simulated disease pressure, but only if the application timing was optimal and the dose was close to the maximum permitted. Programmes with three applications were generally not optimal as they exerted too much selection for resistance. Two-application fungicide programmes balanced effective control with reasonable flexibility of dose and application timing, and low resistance selection, leading to long effective lives of the fungicide

Quantifying the hidden costs of imperfect detection for early detection surveillance

The global spread of pathogens poses an increasing threat to health, ecosystems, and agriculture worldwide. As early detection of new incursions is key to effective control, new diagnostic tests which can detect pathogen presence shortly after initial infection hold great potential for detection of infection in individual hosts. However, these tests may be too expensive to be implemented at the sampling intensities required for early detection of a new epidemic at the population level. To evaluate the trade-off between earlier and/or more reliable detection and higher deployment costs, we need to consider the impacts of test performance, test cost, and pathogen epidemiology. Regarding test performance, the period before new infections can be first detected and the probability of detecting them are of particular importance. We propose a generic framework which can be easily used to evaluate a variety of different detection methods and identify important characteristics of the pathogen and the detection method to consider when planning early detection surveillance. We demonstrate the application of our method using the plant pathogen Phytophthora ramorum in the UK, and find that visual inspection for this pathogen is a more cost effective strategy for early detection surveillance than an early detection diagnostic test

Self-adjointness of two-dimensional Dirac operators on corner domains

We investigate the self-adjointness of the two-dimensional Dirac operator D, with quantum-dot and Lorentz-scalar i-shell boundary conditions, on piecewise C2 domains (with finitely many corners). For both models, we prove the existence of a unique self-adjoint realization whose domain is included in the Sobolev space H1=2, the formal form domain of the free Dirac operator. The main part of our paper consists of a description of the domain of the adjoint operator D in terms of the domain of D and the set of harmonic functions that verify some mixed boundary conditions. Then, we give a detailed study of the problem on an infinite sector, where explicit computations can be made: we find the self-adjoint extensions for this case. The result is then translated to general domains by a coordinate transformation

The Origin of the Density Distribution of Disk Galaxies: A New Problem for the Standard Model of Disk Formation

We present new models for the formation of disk galaxies that improve upon previous models by following the detailed accretion and cooling of the baryonic mass, and by using realistic distributions of specific angular momentum. Under the assumption of detailed angular momentum conservation the disks that form have density distributions that are more centrally concentrated than an exponential. We examine the influence of star formation, bulge formation, and feedback on the outcome of the surface brightness distributions of the stars. Whereas the models are succesful in reproducing high surface brightness disks, they fail to produce exponential disks of low surface brightness. In addition, the models predict truncation radii in the gas that occur at too high surface density. This signals a new problem for the standard model of disk formation: if the baryonic component of the protogalaxies out of which disk galaxies form have the same angular momentum distribution as the dark matter, disks are too compact.Comment: 20 pages, 13 figures. To be published in MNRA

Geschiktheid van Staatsbosbeheer-terreinen voor groene buitenschoolse opvang, Locatieanalyse

De ambitie van Staatsbosbeheer is om een groot deel van haar plannen voor de jeugd te realiseren in achttien groene gebieden in dichtbevolkte delen van ons land, de zogenaamde Recreatie-om-de-stad (Rods)-gebieden. Recreatie om de stad is een jong, maar veelbelovend initiatief: de ambitie voor de achttien gebieden ligt hoog: de omvang moet uitbreiden van 2.500 naar 5.000 hectare, de gebieden moeten straks vrij toegankelijk zijn, goed bereikbaar én intensief en op uiteenlopende manieren te gebruiken zijn voor verschillende doelgroepen. Drie van de achttien Rods-gebieden fungeren de komende jaren als etalagegebied. Dat zijn het Diemerbos bij Amsterdam-Zuidoost, het Gagelbos aan de noordrand van Utrecht en de aangesloten gebieden de Balij en het Bieslandse Bos tussen Zoetermeer, Nootdorp, Pijnacker en Delft. Staatsbosbeheer is met name geïnteresseerd in de kansen voor groene BSO in de etalagegebieden

Quantitative resistance can lead to evolutionary changes in traits not targeted by the resistance QTLs

This paper addresses the general concern in plant pathology that the introduction of quantitative resistance in the landscape can lead to increased pathogenicity. Hereto, we study the hypothetical case of a quantitative trait loci (QTL) acting on pathogen spore production per unit lesion area. To regain its original fitness, the pathogen can break the QTL, restoring its spore production capacity leading to an increased spore production per lesion. Or alternatively, it can increase its lesion size, also leading to an increased spore production per lesion. A data analysis shows that spore production per lesion (affected by the resistance QTL) and lesion size (not targeted by the QTL) are positively correlated traits, suggesting that a change in magnitude of a trait not targeted by the QTL (lesion size) might indirectly affect the targeted trait (spore production per lesion). Secondly, we model the effect of pathogen adaptation towards increased lesion size and analyse its consequences for spore production per lesion. The model calculations show that when the pathogen is unable to overcome the resistance associated QTL, it may compensate for its reduced fitness by indirect selection for increased pathogenicity on both the resistant and susceptible cultivar, but whereby the QTLs remain effective