X-ray Source Heights in a Solar Flare: Thick-target versus Thermal Conduction Front Heating

Observations of solar flares with RHESSI have shown X-ray sources traveling along flaring loops, from the corona down to the chromosphere and back up. The 28 November 2002 C1.1 flare, first observed with RHESSI by Sui et al. 2006 and quantitatively analyzed by O'Flannagain et al. 2013, very clearly shows this behavior. By employing numerical experiments, we use these observations of X-ray source height motions as a constraint to distinguish between heating due to a non-thermal electron beam and in situ energy deposition in the corona. We find that both heating scenarios can reproduce the observed light curves, but our results favor non-thermal heating. In situ heating is inconsistent with the observed X-ray source morphology and always gives a height dispersion with photon energy opposite to what is observed.Comment: Accepted to Ap

Bean leaf beetles: a current and historical perspective

In 2002, bean leaf beetle populations in Iowa reached their highest levels in 14 years (figure, left). In Iowa, this increase in beetle populations has been partly fueled by weather conditions that favor winter survival, such as mild temperatures (2001-2002: second mildest winter on record) or snow cover (2000-2001: snow cover for 99 consecutive days in central Iowa). The increase in beetle populations has followed the trend for warmer weather during the previous six winters (figure, right)

Bean leaf beetles and soybean planting date

Considering the enormous bean leaf beetle populations in recent years, many soybean growers are interested in options for managing this pest. Cultural control, such as planting date, could be very useful for managing bean leaf beetle. Studies conducted by Larry Pedigo and Mike Zeiss at Iowa State University (1998-1992) quantified the effects of soybean planting date on bean leaf beetle abundance, soybean pod injury, and soybean yield

Biological control of bean leaf beetles

Bean leaf beetles have few known natural enemies and even less is known about the use of these organisms to combat the beetle. Flies, mites, fungi, and nematodes attack bean leaf beetles. Below is a research summary of our current knowledge on the biological control of bean leaf beetle

Fall armyworm (Spodoptera frugiperda Smith) feeding elicits differential defense responses in upland and lowland switchgrass

Switchgrass (Panicum virgatum L.) is a low input, high biomass perennial grass being developed for the bioenergy sector. Upland and lowland cultivars can differ in their responses to insect herbivory. Fall armyworm [FAW; Spodoptera frugiperda JE Smith (Lepidoptera: Noctuidae)] is a generalist pest of many plant species and can feed on switchgrass as well. Here, in two different trials, FAW larval mass were significantly reduced when fed on lowland cultivar Kanlow relative to larvae fed on upland cultivar Summer plants after 10 days. Hormone content of plants indicated elevated levels of the plant defense hormone jasmonic acid (JA) and its bioactive conjugate JA-Ile although significant differences were not observed. Conversely, the precursor to JA, 12-oxo-phytodienoic acid (OPDA) levels were significantly different between FAW fed Summer and Kanlow plants raising the possibility of differential signaling by OPDA in the two cultivars. Global transcriptome analysis revealed a stronger response in Kanlow plant relative to Summer plants. Among these changes were a preferential upregulation of several branches of terpenoid and phenylpropanoid biosynthesis in Kanlow plants suggesting that enhanced biosynthesis or accumulation of antifeedants could have negatively impacted FAW larval mass gain on Kanlow plants relative to Summer plants. A comparison of the switchgrass-FAW RNA-Seq dataset to those from maize-FAW and switchgrass-aphid interactions revealed that key components of plant responses to herbivory, including induction of JA biosynthesis, key transcription factors and JA-inducible genes were apparently conserved in switchgrass and maize. In addition, these data affirm earlier studies with FAW and aphids that the cultivar Kanlow can provide useful genetics for the breeding of switchgrass germplasm with improved insect resistance

Recent bean leaf beetle and bean pod mottle virus research

Soybean growers face a dilemma when considering management options for bean leaf beetles and bean pod mottle virus. Rayda Krell recently completed a research program at Iowa State University that focused on immediate solutions for this pest problem. This article summarizes her research from which we suggest some short-term management options

Management decisions for bean leaf beetles and bean pod mottle virus

Yogi Berra said, If you come to a fork in the road, take it. Many soybean producers will be at that fork in a couple of weeks, trying to decide whether or not to spray overwintered bean leaf beetles, and determining how to manage bean pod mottle virus. The dilemma is that some overwintered bean leaf beetles may transmit bean pod mottle virus and not knowing where in Iowa the problem is most likely to occur, what percentage of beetles are transmitting the virus, or when to spray can greatly complicate management decisions

Revisiting an integrated approach to bean leaf beetle and bean pod mottle virus management

This article originally appeared in the 2005 ICM newsletter. However, the significance of the bean leaf beetle and bean pod mottle virus has not diminished in recent years. There is still the potential of economic damage from either or both pests. We have recently completed a three-year study that examines the complex issues of managing these two pests, but the data are still being analyzed. We also have identified potential field tolerance to virus disease. Growers are encouraged to query seed dealers regarding tolerance of varieties to virus disease. Ultimately, this will likely be the best management tool for disease control. In the meantime, we give you our best recommendations as we understand the situation in Iowa

Management of Soybean Aphids

The soybean aphid can be a serious pest of soybeans. This insect reached high numbers during the summer of 2001 in extreme northeast Iowa. Populations during 2002 were too low to cause economic damage; however, in 2003 infestations reached historically high populations and were above economic thresholds throughout most of Iowa. The soybean aphid has up to 15 to 18 generations annually. Overwintering eggs survive on buckthorn (Rhamnus). The nymphs hatch in the spring, and after winged female generations are born, they fly in search of soybeans. Throughout the summer, winged and wingless individuals are born. They feed on soybeans, and once crowded, the winged aphids fly in search of non-colonized soybeans. During the later stages of maturity, increased aphid mortality occurs due to the depletion of their food source, and surviving winged aphids migrate back to buckthorn. Aphid infestations that peak at the R1-R2 soybean growth stages may cause stunted plant growth with possible yellowing of leaves with reduced pod and seed counts. A black residue, sooty mold, grows on honeydew, a by-product excreted by aphids found on leaves, stems, and pods. Ants are usually present when ample honeydew is present. The objective of this experiment was to measure the performance of several insecticides for control of the soybean aphid

Evaluation of Management Tactics for Bean Leaf Beetles and Bean Pod Mottle Virus in Soybean

An increase in bean leaf beetles has caused an increase in bean pod mottle virus - a yield robbing plant pathogen in Iowa soybeans. The incidence of bean pod mottle virus is often positively correlated with bean leaf beetle populations. For example, the greatest increase in bean pod mottle virus infection occurs after the first generation of bean leaf beetles reaches peak population density (late July). However, soybeans are most affected when soybeans are infected as seedlings