Managing Crop Diseases with Fungicides

This guide contains a list of fungicides labeled for use in South Dakota at the time of publication. The list is dynamic and prone to frequent changes. It therefore should not be considered as a substitute for label information. Always read and follow label directions for approved uses of these products, and check with the South Dakota Department of Agriculture for up-to-date product registration information

Waddington’s Widget: Hsp90 and the Inheritance of Acquired Characters

Conrad Waddington published an influential model for evolution in his 1942 paper, Canalization of Development and Inheritance of Acquired Characters. In this classic, albeit controversial, paper, he proposed that an unknown mechanism exists that conceals phenotypic variation until the organism is stressed. Recent studies have proposed that the highly conserved chaperone Hsp90 could function as a “capacitor,” or an “adaptively inducible canalizer,” that masks silent phenotypic variation of either genetic or epigenetic origin. This review will discuss evidence for, and arguments against, the role of Hsp90 as a capacitor for morphological evolution, and as a key component of what we call “Waddington’s widget.

Stability Of Plasma Configurations During Compression

Magnetized Target Fusion (MTF) efforts are based on calculations showing that the addition of a closed magnetic field reduces the driver pressure and rise time requirements for inertial confinement fusion by reducing thermal conductivity. Instabilities that result in convective bulk transport at the Alphen time scale are of particular concern since they are much faster than the implosion time. Such instabilities may occur during compression due to, for example, an increase in the plasma-magnetic pressure ratio {beta} or, in the case of a rotating plasma, spin-up due to angular momentum conservation. Details depend on the magnetic field topology and compression geometry. A hard core z pinch with purely azimuthal magnetic field can theoretically be made that relaxes into a wall supported diffuse profile satisfying the Kadomtsev criterion for the stability of m = 0 modes, which is theoretically preserved during cylindrical outer wall compression. The center conductor radius and current must also be large enough to keep the {beta} below stability limits to stabilize modes with m > 0. The stability of m > 0 modes actually improves during compression. A disadvantage of this geometry, though, is plasma contact with the solid boundaries. In addition to the risk of high Z impurity contamination during the (turbulent) relaxation process, contact thereafter can cause plasma pressure near the outer surface to drop, violating the Kadomtsev criterion locally. The resultant m = 0 instability can then convect impurities inward. Also, the center conductor (which is not part of the Kadomtsev profile) can go m = 0 unstable, convecting impurities outward. One way to mitigate impurity convection is to instead use a Woltjer-Taylor minimum magnetic energy configuration (spheromak). The sheared magnetic field inhibits convection, and the need for the center conductor is eliminated. The plasma, however, would likely still have to be wall supported due to unfavorable {beta} scaling during quasispherical (3-D) compression otherwise. Use of a Field Reversed Configuration (FRC) substantially resolves the wall contact issue, but at the cost of introducing a new (rotational) instability. An FRC has an open magnetic field outside a separatrix which effectively diverts wall material. However, FRC particles diffusing across the separatrix have a preferred angular momentum, causing the FRC within to counter-rotate in response. When the FRC's rotational-diamagnetic drift frequency ratio {alpha} reaches a critical value of order unity, the FRC undergoes a rotational instability that results in rapid particle loss. The instability is exacerbated by cylindrical compression since {beta} {approx} R{sup -2/5} during this phase, assuming angular momentum conservation. A multipole magnetic field frozen into the solid liner during compression may stabilize this mode directly and/or by impeding spin-up without significantly perturbing the implosion's azimuthal symmetry

Photoevaporation of protoplanetary discs I: hydrodynamic models

In this paper we consider the effect of the direct ionizing stellar radiation field on the evolution of protoplanetary discs subject to photoevaporative winds. We suggest that models which combine viscous evolution with photoevaporation of the disc (e.g. Clarke, Gendrin & Sotomayor 2001) incorrectly neglect the direct field after the inner disc has drained, at late times in the evolution. We construct models of the photoevaporative wind produced by the direct field, first using simple analytic arguments and later using detailed numerical hydrodynamics. We find that the wind produced by the direct field at late times is much larger than has previously been assumed, and we show that the mass-loss rate scales as $R_{in}^{1/2}$ (where $R_{in}$ is the radius of the instantaneous inner disc edge). We suggest that this result has important consequences for theories of disc evolution, and go on to consider the effects of this result on disc evolution in detail in a companion paper (Alexander, Clarke & Pringle 2006b).Comment: 13 pages, 9 figures. Accepted for publication in MNRA

Protoplanetary disc evolution and dispersal: the implications of X-ray photoevaportion

(Abridged) We explore the role of X-ray photoevaporation in the evolution and dispersal of viscously evolving T-Tauri discs. We show that the X-ray photoevaporation wind rates scale linearly with X-ray luminosity, such that the observed range of X-ray luminosities for solar-type T-Tauri stars (10e28-10e31 erg\s) gives rise to vigorous disc winds with rates of order 10e-10-10e-7 M_sun/yr. We use the wind solutions from radiation-hydrodynamic models, coupled to a viscous evolution model to construct a population synthesis model so that we may study the physical properties of evolving discs and so-called `transition discs'. Current observations of disc lifetimes and accretion rates can be matched by our model assuming a viscosity parameter alpha = 2.5e-3. Our models confirm that X-rays play a dominant role in the evolution and dispersal of protoplanetary discs giving rise to the observed diverse population of inner hole `transition' sources which include those with massive outer discs, those with gas in their inner holes and those with detectable accretion signatures. To help understand the nature of observed transition discs we present a diagnostic diagram based on accretion rates versus inner hole sizes that demonstrate that, contrary to recent claims, many of the observed accreting and non accreting transition discs can easily be explained by X-ray photoevaporation. Finally, we confirm the conjecture of Drake et al. (2009), that accretion is suppressed by the X-rays through `photoevaporation starved accretion' and predict this effect can give rise to a negative correlation between X-ray luminosity and accretion rate, as reported in the Orion data.Comment: Figure 12 and 13 have been updated. In the original version the results from an unused model run were plotted by mistak

Best Management Practices for Corn Production in South Dakota: Corn Diseases in South Dakota

Corn diseases can be separated into 1) seed and seedling diseases, 2) root-infecting nematodes, 3) leaf diseases, 4) rusts, 5) stalk rots, and 6) ear and grain molds. Yield losses can result from diseases directly reducing yields or from harvestability, spoilage, or marketing and/or use issues associated with mycotoxin contamination. See Table 9.1 for corn disease management information. Attention to optimal seed quality, hybrid selection, seed treatments, weed and insect control, crop rotation, soil fertility, irrigation, and prompt harvest can reduce disease impacts. This chapter discusses aspects of recognizing and managing South Dakota corn diseases

Ice Lines, Planetesimal Composition and Solid Surface Density in the Solar Nebula

To date, there is no core accretion simulation that can successfully account for the formation of Uranus or Neptune within the observed 2-3 Myr lifetimes of protoplanetary disks. Since solid accretion rate is directly proportional to the available planetesimal surface density, one way to speed up planet formation is to take a full accounting of all the planetesimal-forming solids present in the solar nebula. By combining a viscously evolving protostellar disk with a kinetic model of ice formation, we calculate the solid surface density in the solar nebula as a function of heliocentric distance and time. We find three effects that strongly favor giant planet formation: (1) a decretion flow that brings mass from the inner solar nebula to the giant planet-forming region, (2) recent lab results (Collings et al. 2004) showing that the ammonia and water ice lines should coincide, and (3) the presence of a substantial amount of methane ice in the trans-Saturnian region. Our results show higher solid surface densities than assumed in the core accretion models of Pollack et al. (1996) by a factor of 3 to 4 throughout the trans-Saturnian region. We also discuss the location of ice lines and their movement through the solar nebula, and provide new constraints on the possible initial disk configurations from gravitational stability arguments.Comment: Version 2: reflects lead author's name and affiliation change, contains minor changes to text from version 1. 12 figures, 7 tables, accepted for publication in Icaru

Secular evolution of viscous and self-gravitating circumstellar discs

We add the effect of turbulent viscosity via the \alpha-prescription to models of the self-consistent formation and evolution of protostellar discs. Our models are non-axisymmetric and carried out using the thin-disc approximation. Self-gravity plays an important role in the early evolution of a disc, and the later evolution is determined by the relative importance of gravitational and viscous torques. In the absence of viscous torques, a protostellar disc evolves into a self-regulated state with disk-averaged Toomre parameter Q \sim 1.5-2.0, non-axisymmetric structure diminishing with time, and maximum disc-to-star mass ratio \xi = 0.14. We estimate an effective viscosity parameter \alpha_eff associated with gravitational torques at the inner boundary of our simulation to be in the range 10^{-4}-10^{-3} during the late evolution. Addition of viscous torques with a low value \alpha = 10^{-4} has little effect on the evolution, structure, and accretion properties of the disc, and the self-regulated state is largely preserved. A sequence of increasing values of \alpha results in the discs becoming more axisymmetric in structure, being more gravitationally stable, having greater accretion rates, larger sizes, shorter lifetimes, and lower disc-to-star mass ratios. For \alpha=10^{-2}, the model is viscous-dominated and the self-regulated state largely disappears by late times. (Abridged)Comment: 13 pages, 11 figures, accepted for publication in MNRA