Scott A. Isard

A Soil Moisture Climatology of Illinois

Abstract Ten years of soil moisture measurements (biweekly from March through September and monthly during winter) within the top 1 m of soil at 17 grass-covered sites across Illinois are analyzed to provide a climatology of soil moisture for this important Midwest agricultural region. Sod moisture measurements were obtained with neutron probes that were calibrated for each site. Measurement errors are dependent upon the volumetric water content with errors less than 20 percent when soil moisture is above 10 percent of soil volume. Single point errors in moisture measurements from the top 1 m of soil range from 6 percent to 13 percent when volumetric soil moisture is 30 percent of soil volume. The average depletion in moisture between winter and summer over the 10-year period for the top 2 m of soil in Illinois was 72.3 mm. Three-quarters of this decrease occurred above 0.5 m and only 5 percent occurred between the 1.0-m and 2.0-m depths. The average moisture decrease between winter and summer during a we...

Principles of the Atmospheric Pathway for Invasive Species Applied to Soybean Rust

Abstract Aerial transport alone is seldom responsible for the introduction of nonindigenous species into distant regions; however, the capacity to use the atmospheric pathway for rapid spread in large part determines the invasive potential of organisms once they are introduced. Because physical and biological features of Earths surface influence the routes and timing of organisms that use the atmospheric pathway, long-distance movement of aerobiota is largely regular and thus predictable. Soybean rust (Phakopsora pachyrhizi), potentially the most destructive foliar disease of soybean, recently invaded North America. The concepts presented in this article form the basis of the soybean rust aerobiology prediction system (SRAPS) that was developed to assess potential pathogen movement from South America to the United States. Output from SRAPS guided the scouting operations after the initial discovery of soybean rust in Louisiana. Subsequent observations of P. pachyrhizi in the southeastern United States provide validation of the modeling effort.

The Frequency and Intensity of Great Lake Cyclones

Abstract Cyclones are an important feature of the Great Lakes region that can have important impacts on shipping, lake temperature profiles, ice cover, and shoreline property damages. The objective of this research is to analyze the frequency and intensity of cyclones that traversed the Great Lakes region, the changes of these characteristics since 1900, the interrelationship of cyclone frequency and intensity, and their relationships to circulation patterns and regional temperature and precipitation. Significant increases in the number of strong (≤992 mb) cyclones over the twentieth century were found for the annual, cold season, November, and December time periods. In contrast, the frequency of all cyclones in the annual and warm season time series and the central pressure of all cyclones in the annual, cold, and warm season time series displayed significant decreases from 1900 to 1939. Relationships between cyclone frequency and intensity and between cyclone and anticyclone frequency and intensity sugg...

Regional-scale relationships between climate and strength of podzolization in the Great Lakes Region, North America

Abstract Along a 300 km transect in northern Wisconsin and the upper peninsula of Michigan, the areal coverage of Spodosols and spodic horizon development increases markedly from south to north. This study elucidated those aspects of climate that promote podzolization in this region, through an examination of the geographic correspondences between Spodosol development and soil climate. Climatic data (1951–1991) from 21 sites along this transect were processed by a hydrologic model developed to output data on (1) soil temperatures for 0.05 and 0.5 m depths for 20 minute intervals, including data on soil freezing, (2) snowpack thicknesses under forest cover, and (3) daily water fluxes, runoff, and soil water contents at several depths. Spodosols dominate the landscape in areas where soil frost and freeze-thaw activity are minimal and where soil temperatures rarely exceed 16–17°C. Podzolization is strongest where snowpacks are thickest — an association that holds at both regional and meso scales. Thick snowpacks inhibit soil frost and allow large fluxes of snowmelt water to infiltrate into already moist profiles. This type of flux (slow, steady, cold water) may be particularly effective in the podzolization process. In the southern part of the transect, where Spodosols are rare, snowmelt fluxes are 1/3 as large as in the northern “snowbelt” areas. The southern areas also have a small autumn infiltration peak that usually reaches to ≈ 0.3 m depth; this flux is absent in areas of strong podzolization. Mean soil water contents are low and fluxes of water into the soil are small along the entire transect during summer, underscoring the belief that the bulk of pedogenesis (i.e., translocation), in Spodosols in the study area, occurs during snowmelt.

The Effect of Solar Irradiance on the Mortality of Phakopsora pachyrhizi Urediniospores

Soybean rust, caused by Phakopsora pachyrhizi, may be the most important foliar disease of soybean. Within the last 10 years, the fungus has moved to many new geographical locations via spread of airborne urediniospores. The objective of this study was to determine the relationship between urediniospore viability and exposure to solar radiation. Urediniospores of P. pachyrhizi were exposed in Capitán Miranda, Paraguay, to determine the deleterious effects of sunlight. Concomitant total solar (0.285 to 2.8 μm) and ultraviolet (0.295 to 0.385 μm) irradiance measurements were used to predict urediniospore germination. Urediniospores exposed to doses of solar and ultraviolet (UV) radiation ≥27.3 MJ/m2 and ≥1.2 MJ/m2, respectively, did not germinate. The proportions of urediniospores that germinated, normalized with respect to the germination proportion for unexposed urediniospores from the same collections, were a linear function of solar irradiance (R2 = 0.83). UV measurements predicted normalized germination proportions equally well. Results of inoculation experiments with exposed P. pachyrhizi urediniospores supported the results of the germination trials, although the effects of moderate levels of irradiance varied. The relationship between urediniospore viability and exposure to solar radiation has been incorporated into the U.S. Department of Agricultures soybean rust aerobiological model that provides North American soybean growers with decision support for managing soybean rust.

Modeling evolution of behavioral resistance by an insect to crop rotation

Crop rotation has traditionally been a valuable method for managing pests, but now a serious insect pest of maize (Diabrotica virgifera virgifera LeConte [Coleoptera: Chrysomelidae]) has developed behavioral resistance to rotation. A simple model of adult behavior and population genetics can explain how this resistance may have developed. This general model indicates that evolution may be caused by selection on a single gene for adult movement and that behavioral resistance only develops at high levels of rotation (>80% of plant landscape). In less diverse landscapes, crop rotation selects for the expansion of host preferences (polyphagy) by adults. More diverse landscapes may delay the evolution of resistance to crop rotation depending on the fitness costs and the nature of the genetic system.

EFFECTS OF WINTER WEATHER CONDITIONS ON SOIL FREEZING IN SOUTHERN MICHIGAN

We examined climatic and (modelled) soil-temperature data from five winters in southern Michigan to ascertain the spatial variability in soil-freezing and freeze-thaw cycles at 5 cm. The five winters chosen for study (1951–1952, 1952–1953, 1953–1954, 1976–1977, and 1979–1980) represent the extremes of weather (e.g., cold and snowy, warm and dry) for the 1951–1980 period. We chose this study area because it lies on an ecotone between the cold, snowy climates of southern Canada and the warmer climates of the Ohio Valley where persistent snowpacks are rare, and because virtually no data on soil freezing exist for this area. Soil freezing in winter in southern Michigan is more dependent on snowpack persistence and thickness, especially in mid-winter, than on air temperatures. Here, even in warm winters, soils freeze to 5 cm, provided that snowpacks are thin or absent. Conversely, in even the coldest winters, soils rarely freeze where deep snows accumulate. Thus, freezing is least frequent, and in some years n...

Phytophthora Database: A Forensic Database Supporting the Identification and Monitoring of Phytophthora

Phytophthora spp. represent a serious threat to agricultural and ecological systems. Many novel Phytophthora spp. have been reported in recent years, which is indicative of our limited understanding of the ecology and diversity of Phytophthora spp. in nature. Systematic cataloging of genotypic and phenotypic information on isolates of previously described species serves as a baseline for identification, classification, and risk assessment of new Phytophthora isolates. The Phytophthora Database (PD) was established to catalog such data in a web-accessible and searchable format. To support the identification of new Phytophthora isolates via comparison of their sequences at one or more loci with the corresponding sequences derived from the isolates archived in the PD, we generated and deposited sequence data from more than 1,500 isolates representing the known diversity in the genus. Data search and analysis tools in the PD include BLAST, Phyloviewer (a program for building phylogenetic trees using sequences of selected isolates), and Virtual Gel (a program for generating expected restriction patterns for given sequences). The PD also provides a customized means of storing and sharing data via the web. The PD serves as a model that easily can be adopted to develop databases for other important pathogen groups.

Does Landscape Diversity Slow the Spread of Rotation-Resistant Western Corn Rootworm (Coleoptera: Chrysomelidae)?

Abstract A behavioral change in some western corn rootworm (Diabrotica virgifera virgifera LeConte) populations is threatening the effectiveness of crop rotation, a successful management strategy for controlling this pest. We created a set of simple meteorologic and behavioral models that can be used to predict the spread of the beetle infesting soybean (Glycine max (L.)) throughout the midwestern United States. We used data collected in Illinois, IN, MI, and Ohio to create maps of observations to evaluate the model. We displayed data on the maps using detection thresholds for western corn rootworm in soybean fields of 10 or 20 beetles per 100 sweeps and one or two beetles per yellow sticky trap per day. Counts greater than a detection threshold represent populations with a lack of fidelity to corn (Zea mays L.) and adapted to circumvent corn-soybean rotation. Some of the models invoked a landscape-diversity function that included the proportion of noncorn, nonrotated soybean vegetation on farmland in each county (i.e., extra vegetation). The best model for the period from 1997 to 2001 is based on heavy-storm data, with distance that beetles spread each year reduced by the proportion of extra vegetation in a county. This version is superior to a previously published model and to two new models that do not consider landscape diversity. Most of the models predicted spread at too high a rate between 1997 and 2001, compared with observations, but a few new models with rates of spread reduced by a landscape-diversity function matched the observations relatively well. Results suggest that the conclusions based on a linear model using proportion of extra vegetation as the key parameter are likely to be robust. Thus, we hypothesize that as the landscape diversity represented by the proportion of noncorn and nonrotated soybean vegetation in a geographic region increases, the rate of regional spread of the rotation-resistant western corn rootworm decreases over several years.

Soils Cool as Climate Warms in the Great Lakes Region: 1951–2000

Abstract We modeled soil temperatures at 50-cm depth, using 1951–2000 air temperature and precipitation data from 194 National Weather Service stations in Wisconsin and Michigan. The accuracy and bias of the physical model used in this study were validated by comparing its output data to 22,401 actual soil temperature readings taken from sandy soils at thirty-nine forested sites throughout northern Michigan; the model was shown to have almost no temperature bias. Although mean annual air temperatures across the region show no strong spatial or temporal trends over the fifty-year period, at many sites, especially in Wisconsin, wintertime air temperatures have been increasing slightly in recent years. Conversely, mean annual soil temperatures have been decreasing at most sites in the region, some by more than 0.5°C. Likewise, wintertime soil temperatures are also decreasing, especially at sites downwind from the Great Lakes—many of which are in snowbelt locations. Increasing wintertime air temperatures over the past fifty years coincide with (and probably have led to) more variable and thinner snowpacks, lessening their insulating impact and contributing to decreasing wintertime soil temperatures that our model show are occurring in the eastern and northern parts of the region. These findings illustrate the complex response of natural systems to slow atmospheric warming, and draw attention to the potential changes that are occurring in growing season characteristics, phenology, and spring runoff characteristics in the Great Lakes region.