Growth and Fecundity of Several Weed Species in Corn and Soybean

Do weeds that emerge later in the season justify additional control costs\u27? If crop yield is not reduced or few or no seeds arc added to the soil seed hank, then no control may he needed. Eight weed species were sown in corn (Zea mays L.) and soybean I Glycine max (L.) Mcrr.l (i) before crop emergence, (ii) at crop emergence, (iii) at V-1, and (iv) at V-2 stages of crop growth in 2002 and 2003. Weed seed was sown close to the crop row and thinned to 1.3 plants m 2• Weed growth and fecundity were influenced by species, time of planting, and year. Only barnyarclgrass (Echinochloa crus-galli L.), rcclroot pigwced (Amaranthus retniflexus L.), and vclvetlcaf (Abutilon theophrasti L.) survived to produce seed. Plants from the pre-emergence seeding had the largest canopy and produced the most seeds. Harnyardgrass had maximum canopy cover in early .July in corn and late .Inly in soybean hut only produced seed in corn. Rcclroot pigweecl and vclvctleaf had maximum canopy cover in late August or midSeptember, and some plants from most seeding elates survived and produced seed in both corn and soybean. However, plants that grew from seed sown at V-1 and V-2 crnp grnwth stages did not reduce yield or biomass of adjacent crop plants, had low fecundity, and may not warrant treatment. Control may be necessary, however, to prevent yield losses if weeds arc present at high densities or to prevent establishment of uncommon species

The longitudinal thickness of air-shower fronts

Linsely (1983) has proposed a technique for the detection and analysis of air showers at large distances from the shower axis based on a measurement of the shower front thickness and the assumption that this thickness is closely related to the core distance. Some of the problems involved with realizing such a technique were investigated, and some related observations are reported. The practical problems of how consistent the measurements of the shower front would be, how one would use the measurement, and how the rate of triggered events would depend on the minimum pulse width required are studied

Geostatistical Characterization of the Spatial Distribution of Adult Corn Rootworm (Coleoptera: Chrysomelidae) Emergence

Geostatistical methods were used to characterize spatial variability in western ( Diabrotica virgifera virgifera LeConte) and northern ( Diabrotica barberi Smith & Lawrence) corn rootworm adult emergence patterns. Semivariograms were calculated for adult emergence density of corn rootworm populations in fields of continuous corn and rotated (corn/soybean) corn. Adult emergence densities were generally greater for northern corn rootworms than for western corn rootworms. The spatial structures of the adult rootworm emergence were aggregated as described by spherical spatial models for western corn rootworm and exponential models for northern corn rootworm. Range of spatial dependence varied from 180 to 550 m for western corn rootworm and 172 to 281 m for northern corn rootworm. Semivariograrn models were used to produce contour density maps of adult populations in the fields, based on grid sampling of actual emerging adult populations

Cooperative orbital ordering and Peierls instability in the checkerboard lattice with doubly degenerate orbitals

It has been suggested that the metal-insulator transitions in a number of spinel materials with partially-filled t_2g d-orbitals can be explained as orbitally-driven Peierls instabilities. Motivated by these suggestions, we examine theoretically the possibility of formation of such orbitally-driven states within a simplified theoretical model, a two-dimensional checkerboard lattice with two directional metal orbitals per atomic site. We include orbital ordering and inter-atom electron-phonon interactions self-consistently within a semi-classical approximation, and onsite intra- and inter-orbital electron-electron interactions at the Hartree-Fock level. We find a stable, orbitally-induced Peierls bond-dimerized state for carrier concentration of one electron per atom. The Peierls bond distortion pattern continues to be period 2 bond-dimerization even when the charge density in the orbitals forming the one-dimensional band is significantly smaller than 1. In contrast, for carrier density of half an electron per atom the Peierls instability is absent within one-electron theory as well as mean-field theory of electron-electron interactions, even for nearly complete orbital ordering. We discuss the implications of our results in relation to complex charge, bond, and orbital-ordering found in spinels.Comment: 8 pages, 5 figures; revised versio

Efficiency of Pointing Dogs in Locating Northern Bobwhite Coveys

We studied the efficiency of pointing dogs in locating coveys of northern bobwhites (Colinus virginianus) using radiotelemetry from 1992-1997 on 2 private hunting plantations in southwest Georgia. During these 5 hunting seasons, 169 hunts generated data on 838 encounters with 254 separate radio-marked coveys. Pointing dogs located 53% of the available coveys, 25% of which were never seen by the hunters due to evasive behavior by the birds. An additional 12% of encountered coveys were seen by the hunters even though they were never located by the dogs. This resulted in the hunters seeing a total of just over half (53%) and shooting into approximately one-third (32%) of the total radio-marked coveys they encountered. An evaluation of false pointing was conducted by examining cases when dogs pointed radio-marked coveys that were never seen by the hunters. Most (58%) of these unproductive points were caused by coveys running away from pointing dogs, but were also attributed to wild flushes (28%) and pointed coveys that held tight and refused to flush (14%). The percentage of radio-marked coveys seen by hunters was highly variable from day-to-day (x = 53%, range = 0-100%), but fairly consistent between years (x = 53%, range = 40-63% ). Information obtained using pointing dogs appears to be more practical for measuring population trends than it is as a census technique

Survival of Northern Bobwhites on Areas With and Without Liberated Bobwhites

Increases in pen-raised quail releases are often implicated in the precipitous region-wide decline of wild northern bobwhites (Colinus virginianus). Therefore, we compared survival rates of wild radio-tagged northern bobwhites on a study area that received an influx of liberated pen-raised bobwhites from a neighboring property to those of wild bobwhites on a control area during 3 years in southwest Georgia. A total of 302 radio-tagged wild bobwhites were monitored on the wild-release (113) and wild-only areas (189) for a 22 week period from fall to spring each year during November 1993-April 1996. Fall-spring survival of wild bobwhites on the wild-only area (S = 0.43) was greater (P = 0.005) than that of wild bobwhites on the wild-release area (S = 0.18) for the 3 years combined. Losses to avian predation accounted for 38% and 58% of the fall population, respectively. Increased avian predation on the wildrelease area may have been attributed to avian predators attracted to the area

Effects of Supplemental Feeding on Home Range Size and Survival of Northern Bobwhites in South Georgia

We studied the effects of supplemental feeding on fall-spring covey home range size and survival of radio-marked northern bobwhites (Colinus virginianus) for 3 years in southwest Georgia. A total of 372 radio-marked bobwhites were monitored on 2 separate study areas for 25 weeks from fall-spring each year from November 1993 through May 1996. The traditional supplemental feeding program of bi-weekly broadcast spreading of whole grains from November through May was discontinued on one of the study areas during 1993-1994 and 1994-1995. Supplemental feed was distributed on both areas during fall-spring 1995-1996. During the 2 years of no feeding, fall-spring covey home ranges were larger (P = 0.04) on the unfed study area. During the first of these 2 years (1993-1994), fall-spring survival of birds without supplemental feed (S = 0.127) was lower (P = 0.005) than that of fed birds (S = 0.432). During the 1994-1995 season while covey home ranges of birds without supplemental feed were still slightly larger (P = 0.04), there was no difference (P = 0.76) in survival between bobwhites on the sites with and without supplemental feed. Coveys seen per hour hunted was significantly lower (P = 0.007) on the treatment (unfed) area during 2 years. During the year supplemental feed was distributed on both sites, there was no difference in home range size (P = 0.87), survival (P = 0.90), or hunting success (P = 0.82) between the 2 study sites. Supplemental feeding may reduce bobwhite movements and home range size thereby enhancing survival because of less exposure to predation. However, such an effect will probably vary among years in relation to prevailing weather and native vegetation conditions. The specific mechanisms through which supplemental feeding may effect bobwhite population performance remain unknown and require additional study

How Plankton Swim: An Interdisciplinary Approach for Using Mathematics & Physics to Understand the Biology of the Natural World

The authors have developed and field-tested high school-level curricular materials that guide students to use biology, mathematics, and physics to understand plankton and how these tiny organisms move in a world where their intuition does not apply. The authors chose plankton as the focus of their materials primarily because the challenges faced by plankton are novel problems to most students, forcing adoption of new perspectives and making the study of plankton exciting. Additional reasons that they chose plankton to focus on include their ecological importance, their availability to most teachers and students, the ease with which they can be collected and observed, and the current focus of some scientific researchers on their movement and behavior. These curricular materials include a series of inquiry-based, hands-on exercises designed to be accessible to students with a range of backgrounds. Many of these materials could be adapted for use by middle-school, and/or college-level students. In this article, the authors describe sample lessons, summarize what worked well, and flag obstacles they encountered while integrating mathematics and physics into the biology classroom