Browsing by Author "Michael G. Burton, Committee Member"

Filter results by typing the first few letters
Now showing 1 - 3 of 3
  • No Thumbnail Available
    The Association of Weed Species Richness and Abundance with Field Margin Type in Crop Fields
    (2004-05-13) Jelinek, Susan T; Cavell Brownie, Committee Member; Michael G. Burton, Committee Member; Nancy G. Creamer, Committee Co-Chair; J. Paul Mueller, Committee Co-Chair
    Natural vegetation on farms such as field margins, successional fallow fields, ditch systems, and neighboring forests provide increased biodiversity, structural diversity, habitat for wildlife and beneficial insects, and can act as protective buffers against agrochemical drift. Nevertheless, farmers frequently view these areas as potential sources of weeds, insect pests, and diseases. Objectives of this study were to examine weed species richness and abundance in cropland bordered by managed versus unmanaged field margins to determine if differences in weed infestation exist. Weed abundance and richness were measured in crop fields along permanent transects that extended from the field edge to the center of the crop fields. Presence/absence data for all plant species in the field margin were also recorded. Transect data from fields with margins of natural vegetation were compared to transect data from fields with managed margins using analysis of variance. There were no differences between log total abundance of weeds in crop edges adjacent to managed and unmanaged field margins (P=0.44). For both margin types, more weeds were found near the field edge than in the center of the field (1.37±0.08 to 0.52±0.07 and 1.39±0.07 to 0.41±0.06, for managed and unmanaged field margins respectively). Species richness was slightly higher along crop edges of managed field margins (7.35±0.32) than crop edges along unmanaged field margins (6.55±0.31). Across all sampling dates, a total of 105 plant species were identified in the field margins. Of these species, 42 (40% of all species) were found somewhere in a field when all sampling dates were pooled. Managed field margins had lower species richness than unmanaged field margins - less than half the mean number of species (5.8±0.28 versus 14.7±0.62 species, respectively). No association was found between plant species occurring in the field margin and in the crop field by generating 2 x 2 contingency tables via PROC FREQ and testing the association with Fisher's exact two-sided test. Using logistic regression via PROC GENMOD, margin type and weed presence in the field margin were not effective predictors of weed occurrence in the crop field. KEYWORDS: field margin, weed populations, crop edges, farm natural areas
  • No Thumbnail Available
    Biology and Control of Maryland Meadowbeauty (Rhexia mariana L.) in Blueberry (Vaccinium spp.) in North Carolina
    (2009-04-20) Roberts, Meagan Marykatherine; Katherine M. Jennings, Committee Chair; Michael G. Burton, Committee Member; David W. Monks, Committee Co-Chair
    North Carolina is the fifth largest producer of blueberries (Vaccinium spp.) in the U.S. with approximately 5,000 acres harvested in 2006. A study was conducted to determine if a positive correlation exists between the weed populations in field drainage ditches and weed populations in the field interior, and to inventory the weed species present in the ditches and the field interiors. Sixty-six species were inventoried over a two year period. A second study was conducted to define the seed biology of Rhexia mariana L., an aggressive perennial weed in blueberry, by determining temperature effects on germination, average seed number per capsule, seed number in the seed bank, and seed dormancy. Maximum seed germination was observed at day/night temperatures of 20/35C. Seed germination ranged from 47 to 86% and dormancy ranged from 14 to 53%. The number of seed capsules produced per infested area was different among locations and ranged from 500 to 1125 capsules/m2. Across locations, seed capsules produced an average of 74 seeds each. On average, 27 R. mariana seeds were present in each 273cm2 sample of soil. A single m2 of R. mariana infestation has the potential to produced 12,375 seed capsules and 915,750 seeds. Of those seeds, roughly 604,395 would be viable, 519,779 could germinate as freshly mature seeds, and an additional 84,615 seeds would be dormant. An estimated 1000 R. mariana seeds could germinate from 1m2 of the soil seed bank. A third study was conducted to determine the efficacy of flumioxazin on R. mariana and the tolerance of blueberry to flumioxazin. The data indicate that flumioxazin does not injure blueberry when applied PRE. Flumioxazin applied PRE in a single or a sequential application does not have a negative effect on blueberry yield, even at rates that exceed the registered rate. Control of R. mariana with a single application of flumioxazin at the registered rate of 0.42 kg ai/ha ranged from 83 to 100% at 60 days after treatment (DAT). Sequential applications of flumioxazin at 0.21 kg ai/ha per application resulted in control greater than 96% 30 d after the last of two applications. The data indicates that flumioxazin applied PRE at the registered rate of 0.42 kg ai/ha in a single application or 0.21 kg ai/ha in a sequential application in a 12 month period would give effective control of R. mariana. A final study was conducted in which a grower survey was used to determine the current weed management practices employed by blueberry growers in North Carolina. A 41-question survey was mailed to 241 blueberry growers in February 2008. A total of 58 valid responses were returned and were entered into the data set. Respondents represent 24% of the survey population. Thirty-eight percent of the survey population grows a combination of rabbiteye and highbush blueberry types. The highbush variety ‘Croatan’ was the most frequently planted variety in total hectacreage, and the rabbiteye variety ‘Premier’ was the most common variety of that blueberry type. Growers use a combination of mechanical cultivation, hand removal, and herbicides to control weeds in blueberry. Greenbriar species (Smilax spp.) were reported as those species that are increasing in severity, are the hardest to manage, and that interfere most with harvest. Sethoxydim and hexazinone are the most common herbicides used in non-bearing and bearing blueberries, respectively. Growers indicated that their greatest concern in weed management is crop safety to herbicides. Results from all four studies will aid in the development of a comprehensive weed management plan to address the specific needs of North Carolina blueberry producers.
  • No Thumbnail Available
    Japanese Stiltgrass (Microstegium vimineum): Population Dynamics and Management for Restoration of Native Plant Communities
    (2005-07-19) Judge, Caren Ann; Theodore H. Shear, Committee Member; Frank A. Blazich, Committee Member; Joseph C. Neal, Committee Chair; Michael G. Burton, Committee Member
    Japanese stiltgrass is a nonnative invasive grass that occurs in many habitats and is a management concern throughout the eastern United States. Experiments were conducted to address biological and ecological considerations for effective management of Japanese stiltgrass and restoration of native plant communities. Conventional management recommendations emphasize Japanese stiltgrass removal in autumn prior to flowering. Investigations of Japanese stiltgrass reproductive biology were conducted to assess biological considerations that impact such management strategies. Japanese stiltgrass was grown in long day growth chambers (26/22 C) and plants were moved 2, 6, or 10 wk after germination to short day growth chambers (26/22 or 22/18 C). All plants exposed to short days flowered, while under long days no plants flowered. No difference in inflorescence number or shoot dry weight was observed between the two temperature regimes. Japanese stiltgrass populations from North Carolina, Pennsylvania, and Virginia flowered similarly in response short day conditions. Furthermore, inflorescences from natural stands of Japanese stiltgrass were harvested four times; one raceme branch beginning to emerge through the leaf sheath, one raceme branch fully elongated and a second branch visible, fully expanded inflorescence, and in concert with natural dispersal. Following > 90 d storage, seed germination from each harvest averaged 13, 51, 95, and 100%, respectively, suggesting management designed to prevent seed production should be implemented before flowering. In forested areas, herbicides that selectively control Japanese stiltgrass while preserving native vegetation may be desired. The efficacy of three selective postemergence herbicides (fenoxaprop-P, imazapic, and sethoxydim) applied early, mid-, or late season were compared. The herbicides, averaged across application timings, controlled Japanese stiltgrass 83 to 89% and reduced seedhead production 79 to 94%. Seedling emergence was reduced 89, 70, and 78% in spring 2004 by fenoxaprop-P, imazapic, and sethoxydim, respectively, applied in 2003. Additionally, fenoxaprop-P or sethoxydim applied twice (4 wk interval) at half-label or full labeled rates controlled Japanese stiltgrass, providing 92% reduction in biomass and 97 to 98% seedhead reduction. Experiments were conducted to determine if Japanese stiltgrass seeds possess dormancy and if so, to determine conditions required to overcome dormancy and for successful germination. Mature Japanese stiltgrass seeds were collected in autumn 2002 and 2003, cold stratified moist at 4 C or stored dry at 21 C, 0 to 90 d. After storage, seeds were incubated in petri dishes in alternating or constant temperatures and exposed to 14 h or 0 h (total dark) photoperiod. Less than 1% of seeds stored 0 or 15 d germinated while > 95% of seeds stored 90 d germinated, suggesting primary innate dormancy upon natural dispersal. A three-year experiment was conducted in two forest sites to document the ecological impacts of conventional and alternative selective management on Japanese stiltgrass populations and native flora recruitment and establishment. Conventional management treatments included hand-pulling, mowing, or glyphosate (1.1 kg ai/ha) applied in autumn compared to hand-pulling or fenoxaprop-P (0.19 kg ai/ha) applied as needed throughout the season. All management treatments significantly reduced Japanese stiltgrass cover and seed bank over time compared to no management and decreases in relative Japanese stiltgrass cover and seed bank populations were greater in 2004 than 2003, after two seasons of management. However, selective management was more suitable than nonselective management or no management for recruitment and re-establishment of native plants and increasing overall species richness. Additionally, relative cover of other exotic plants decreased 6% over time, suggesting that removal of Japanese stiltgrass did not increase invasion of other exotic plant species.