Practical experience with the use of Baking Powder (potassium bicarbonate) for the control of Apple Scab (Venturia ineaqualis)

In small plot trials, performed by several institutes in the past years, potassium bicarbonate proved to be a promising alternative to the use of copper for the control of apple scab in organic orchards. Feasibility, effectiveness, consequences, and side effects of the replacement of copper by bicarbonate under practical conditions are largely unknown. In 2007 Five Dutch organic apple growers compared a bicarbonate based scab management strategy with their standard spray program. The use of 5 kg potassium bicarbonate + 2 kg. wettable sulphur shortly before rain or during infection development, was the core of the strategy. It was concluded that the control of apple scab with the potassium bicarbonate strategy was as effective as the standard spray plan, provided lime sulphur was available tot cover extreme situations. The applications did not lead to any phytotoxic damage on leafs or fruits. Potassium bicarbonate tank mixed with a Mn leaf fertilizer however resulted in severe leaf drop, and necrotic spots on the remaining leafs. The use of potassium bicarbonate did not increase the potassium content of the fruits

Development of a dynamic population model as a decision support system for Codling Moth (Cydia pomonella L) management

In 2004 RIMpro-Cydia was developed as a dynamic population model that simulates the within-year biology of a local codling moth population. The model is meant to be used by growers and advisors to optimize the control of codling moth populations in organic and integrated managed orchards. The model is based on literature data and unpublished research data. Fractional boxcar trains are used to mimic the dispersion in the developmental processes. The model is run in real time on the data input of local weather stations, starting on 1 January. The output of the model was compared with the results of field observations in three years in an untreated orchard. In the years 2005 to 2007 the progress in egg deposition as predicted by the model was in general agreement with the field data. The start of the egg deposition period was predicted well. The end of the egg deposition period was predicted when in the field about 10% of the eggs was still to be laid. There was no consistency in the relation between cumulated pheromone trap catches and the cumulative egg deposition as calculated from the field data

Characterizing the Initial Phase of Epidemic Growth on some Empirical Networks

A key parameter in models for the spread of infectious diseases is the basic reproduction number $R_0$, which is the expected number of secondary cases a typical infected primary case infects during its infectious period in a large mostly susceptible population. In order for this quantity to be meaningful, the initial expected growth of the number of infectious individuals in the large-population limit should be exponential. We investigate to what extent this assumption is valid by performing repeated simulations of epidemics on selected empirical networks, viewing each epidemic as a random process in discrete time. The initial phase of each epidemic is analyzed by fitting the number of infected people at each time step to a generalised growth model, allowing for estimating the shape of the growth. For reference, similar investigations are done on some elementary graphs such as integer lattices in different dimensions and configuration model graphs, for which the early epidemic behaviour is known. We find that for the empirical networks tested in this paper, exponential growth characterizes the early stages of the epidemic, except when the network is restricted by a strong low-dimensional spacial constraint, such as is the case for the two-dimensional square lattice. However, on finite integer lattices of sufficiently high dimension, the early development of epidemics shows exponential growth.Comment: To be included in the conference proceedings for SPAS 2017 (International Conference on Stochastic Processes and Algebraic Structures), October 4-6, 201

Prevention and control of apple scab

Improved prevention and control of apple scab caused by Venturia inaequalis is aimed at without the use of copper containing products in the Repco-project. Substantial progress is made in selection of potential products against summer epidemics. A patent application is made for E73. New effective biocontrol agents are selected to reduce inoculum during winter. The product potassium bicarbonate has shown good efficacy and Repco contributes to the registration of this product in Europe. Earthworms tended to be stimulated to consume apple leaves treated with amino acids or beetpulp, especially when applied fresh under controlled environmental condi-tons

Reading comprehension level and development in native and language minority adolescent low achievers:Roles of linguistic and metacognitive knowledge and fluency

In a longitudinal design, we measured 50 low-achieving adolescents’ reading comprehension development from Grades 7 to 9. There were 24 native Dutch and 26 language minority students. In addition, we assessed the roles of (a) linguistic knowledge, (b) metacognitive knowledge, and (c) reading fluency in predicting both the level and growth of reading comprehension. Students improved in reading comprehension, the language minority students more so than the native Dutch students. We can explain the level of reading comprehension by linguistic and metacognitive knowledge, whereas most fluency-related predictors appeared to be of minor importance. We can hardly explain the growth in reading comprehension by the predictors. Nevertheless, we found a significant interaction indicating that growth in vocabulary explained growth in reading comprehension for the language minority students. This finding seems to suggest that language minority students profit from gains in vocabulary, more so than native students

Writing proficiency level and writing development of low-achieving adolescents: The roles of linguistic knowledge, fluency, and metacognitive knowledge

In a longitudinal design, 51 low-achieving adolescents' development in writing proficiency from Grades 7 to 9 was measured. There were 25 native-Dutch and 26 language-minority students. In addition, the roles of (i) linguistic knowledge, (ii) metacognitive knowledge, and (iii) linguistic fluency in predicting both the level and development of writing proficiency were assessed. Low-achieving students improved in writing proficiency, the language-minority students more so than the native-Dutch students. Regarding the level of writing proficiency, individual differences between low-achieving adolescents could be accounted for by receptive vocabulary, grammatical knowledge, and speed of sentence verification, suggesting that these are important components in low-achieving adolescents' writing. Regarding development in writing proficiency, grammatical knowledge predicted variation between lowachieving students. Explanations and educational implications of these findings are discussed

Gas vs dust sizes of protoplanetary disks: effects of dust evolution

The extent of the gas in protoplanetary disks is observed to be universally larger than the extent of the dust. This is often attributed to radial drift and grain growth of the mm grains, but line optical depth produces a similar observational signature. We investigate in what parts of the disk structure parameter space dust evolution and line optical depth are the dominant drivers of the observed gas and dust size difference. Using the thermochemical model DALI with dust evolution included we ran a grid of models aimed at reproducing the observed gas and dust size dichotomy. The relation between R_dust and dust evolution is non-monotonic and depends on the disk structure. R_gas is directly related to the radius where the CO column density drops below 10^15 cm^-2 and CO becomes photodissociated. R_gas is not affected by dust evolution but scales with the total CO content of the disk. R_gas/R_dust > 4 is a clear sign for dust evolution and radial drift in disks, but these cases are rare in current observations. For disks with a smaller R_gas/R_dust, identifying dust evolution from R_gas/R_dust requires modelling the disk structure including the total CO content. To minimize the uncertainties due to observational factors requires FWHM_beam 10 on the 12CO emission moment zero map. For the dust outer radius to enclose most of the disk mass, it should be defined using a high fraction (90-95%) of the total flux. For the gas, any radius enclosing > 60% of the 12CO flux will contain most of the disk mass. To distinguish radial drift and grain growth from line optical depth effects based on size ratios requires disks to be observed at high enough angular resolution and the disk structure should to be modelled to account for the total CO content of the disk.Comment: 18 pages, 27 figures, accepted in A&

Fruitmot in peer

Op appel ontstaat de meeste fruitmotaantasting in de loop van juni of juli. In jaren met een tweede generatie kan er in augustus nog schade bijkomen. Op peer (Conference) treedt in de meeste jaren nauwelijks vroege aantasting op, terwijl vanaf augustus de schade soms sterk toeneemt. Proeven bij PPO in Randwijk lieten zien hoe dit verschil ontstaat. Van fruitmoteieren die op vruchten van Elstar werden gelijmd, leverde grofweg een derde tot de helft een rups, en dus een aangetaste vrucht op. Bij Elstar veranderde de gevoeligheid van de vruchten voor aantasting gedurende het seizoen niet veel. Bij Conference wel: aan het begin van het seizoen overleefden veel minder rupsen dan later in de zomer. De proefresultaten zijn aanleiding om de bestrijdingsstrategie voor fruitmot op Conference aan te passen en rond begin augustus, als de vruchten extra gevoelig zijn, een fruitmotbestrijding uit te voeren

Observed sizes of planet-forming disks trace viscous evolution

The evolution of protoplanetary disks is dominated by the conservation of angular momentum, where the accretion of material onto the central star is driven by viscous expansion of the outer disk or by disk winds extracting angular momentum without changing the disk size. Studying the time evolution of disk sizes allows us therefore to distinguish between viscous stresses or disk winds as the main mechanism of disk evolution. Observationally, estimates of the disk gaseous outer radius are based on the extent of the CO rotational emission, which, during the evolution, is also affected by the changing physical and chemical conditions in the disk. We use physical-chemical DALI models to study how the extent of the CO emission changes with time in a viscously expanding disk and investigate to what degree this observable gas outer radius is a suitable tracer of viscous spreading and whether current observations are consistent with viscous evolution. We find that the gas outer radius (R_co) measured from our models matches the expectations of a viscously spreading disk: R_co increases with time and for a given time R_co is larger for a disk with a higher viscosity alpha_visc. However, in the extreme case where the disk mass is low (less than 10^-4 Msun) and alpha_visc is high (larger than 10^-2), R_co will instead decrease with time as a result of CO photodissociation in the outer disk. For most disk ages R_co is up to 12x larger than the characteristic size R_c of the disk, and R_co/R_c is largest for the most massive disk. As a result of this difference, a simple conversion of R_co to alpha_visc will overestimate the true alpha_visc of the disk by up to an order of magnitude. We find that most observed gas outer radii in Lupus can be explained using a viscously evolving disk that starts out small (R_c = 10 AU) and has a low viscosity (alpha_visc = 10^-4 - 10^-3).Comment: 19 pages, 17 figures, accepted in A&