Browsing by Author "Amos, Dan F."

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    Engineering properties of selected soils in the Virginia Piedmont
    Parker, Jack C.; Amos, Dan F.; Baker, James C. (Virginia Agricultural Experiment Station, 1983-10)
    The Piedmont Province i Virginia, running in a north-south direction, is approximately 50 miles wide along the Maryland border I ard broadens to the south until it encompasses approximately 150 miles along the North Carolina border. It cor prises at least one-third of the land area of the stat , with approximately 60% occupied by woodland and 40% by agriculture, primarily beef or dairy enterprises. Located in the Piedmont j:e the cities of Leesburg, Fairfax, Manassas, Warrenton, Culpeper, Charlottesville, Lynchburg , Bedford, Farmville, Martinsville, Danville and South Boston. I an McHargue, in his book Design With Nature, studied the Potomac River watershed and concluded that "the Piedmont is primaril suitable for urbanization with attendant agriculture and undifferentiated recreation" (McHargue 1969). Because of the development potential of the Piedmont and the intense pressures for future urbanization west of Washington, D.C., in the counties of Fairfax, Prince William and Loudoun; around Richmond in the counties of Hanover, Hen ico, Goochland, Powhatan, Amelia and Chesterfield; an in Albemarle, Amherst, Bedford, Campbell, Franklin, Henry and Pittsylvania counties, the need to intensively study the most widely distributed and potentially important Piedmont soils became apparent....
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    The etiology of the decline of eastern white pine (Pinus strobus L.) on Virginia landscapes: a survey of stress factors
    Weaver, Michael John (Virginia Polytechnic Institute and State University, 1982)
    A decline of eastern white pine, Pinus strobus L., has been observed for over 80 years in the eastern United States. The syndrome has not always been discussed as a decline but reported under a variety of names. Symptoms vary with time required for trees to die, but generally include chlorotic foliage, in many cases needle loss producing a tufted appearance, premature annual loss of needles, drooping of needles in some cases, shriveling of bark after a period of time, and eventual death after a period of months to years. An investigation into the causes of decline on landscape sites in Virginia included an indexing technique to compile and analyze, systematically, pertinent data from good and poor quality sites. Over 300 variables were studied from over 100 observations to narrow down the apparent causal factors for future investigation in a controlled environment. Observations were organized into two groups for analysis, one called the “decline habitat” and the other the “natural habitat”. Natural habitat observations consisted of trees from a site in the Jefferson National Forest (VA) and decline habitat observations consisted of trees from mostly western Virginia landscapes. After thorough study for a period of two years, a group of growth indicators were weighed against a group of site quality indicators. Growth quality indicators included: a height vs. age index, a 10-year compilation of tree ring increments and inter-branch whorl measurements converted to percent growth per year, and seasonal foliar color changes using a Munsell rating index. Site quality indicators centered around the soils with soil pH, clay content, amounts of compaction and soil disturbance as the most prominent factors derived from the study. Soil pH averaged 6.95 with a range of 5.9-8.1 for decline habitats; while the pH averaged 5.50 with a range of 5.0-6.0 for the natural habitat. Clay content averaged 37.05% for decline sites vs. 17.76% for the natural site for soils above and in the root zones of white pines. Clay content averaged 43.99% for decline sites vs. 17.95% for the natural site for soils beneath the root zones of white pines. Soils under decline habitat trees were highly compacted with measurements as high as 1806.1 psi to penetrate some decline habitat soils, while the natural habitat soils had little if any compaction, with readings of between 138 and 273 psi. Soil disturbance was not present in the natural site while present in most decline sites. The major cause of disturbance was construction and earth-moving activities around landscape sites. Important abiotic factors which worked in concert with soil factors included poor planting practices, competition with tree feeder roots from turfgrass, chemical pollutants, and mechanical damage by weather and man. Biotic factors were viewed as secondary agents attracted to already weakened trees after initiation of decline by the previously discussed factors. Separate studies of seasonal foliar color changes and the initial finding of the pinewood nematode in Virginia aided in identifying additional indicators of and contributors to decline.
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    Soilless media for seed germination and growth of tomato transplants, and for the rooting of certain herbaceous stem cuttings
    Ray, Frederick Harding (Virginia Polytechnic Institute and State University, 1974)
    Media containing Weblite were compared to various media for its effectiveness in germination, plant growth and rooting. The 2M media were compared by determining the percentage germination and the dry weight after U2 days of Lycopersicon esculentum cv Better Boy, grown to transplant size. These media were composed of various proportions and combinations of Weblite, vermiculite, Jiffy Mix, peat moss and sand. The available moisture, porosity,field capacity and permanent wilting point of these 2b media were determined. This information was compared with the results from the germination and growth study of tomato plants. Weblite was a constituent of the seven best media for germination. Tomato plants grown in media containing vermiculite had the highest dry weights. Chrysanthemum morifolium cv Sunny Mandalay stem cuttings were rooted in six media. These media were composed of various proportions and combinations of sand, peat moss, Weblite, and perlite. Their root system and foliage condition were evaluated 18 days later. Weblite was significantly better in rooting Chrysanthemums than the six other media.Dianthus caroyphyllus cv Caribe stem cuttings were rooted in nine media. These media were composed of various proportions and combinations of sand, peat moss, Weblite. perlite, and vermiculite. Their roots, stem and foliage condition were evaluated 26 days later. The best root system developed in media with vermiculite as its main constituent.
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    Survival and chemical control of Cylindrocladium spp. inciting root rot of black walnut seedlings
    Roth, Don Allen (Virginia Tech, 1978)
    Air drying of naturally infested soils (0.12 to 0.38% water or about -2,000 bars) resulted in no recovery of Cylindrocladium crotalariae microsclerotia, but rewetting soils to near field capacity for 1 to 4 wk before assay resulted in partial recovery from the air drying-induced decreased germinability. Numbers of germinable C. crotalariae microsclerotia (assayed at 26 C) decreased progressively over 4 wk when naturally infested soils were incubated at 6 C. No germinable microsclerotia were recovered when soils were incubated at -10 C. When soils incubated at -10 C and at 6 C were transferred to 26 C for 4 wk, the low-temperature effect was partially reversed. Incubation of naturally infested soils under field conditions over the winter months (November-February) indicated that a similar low-temperature phenomenon exists in nature. Germinability of axenic, laboratory-grown microsclerotia of C. crotalariae, C. floridanum, and C. scoparium incubated 4 wk at 6 C ranged from 0 to 91.3% (mean = 37.7%) of the initial germinability. Partial recovery of laboratory-grown microsclerotia from the lowtemperature effect, by incubation at 26 C, was demonstrated. Conductivity measurements of solutions bathing microsclerotia incubated at 6 C and 26 C for 4 wk indicated that chilling injury may account, in part, for decreased germinability of microsclerotia. Direct observation of washed conidia of C. scoparium on rewetted, non-sterile soils at 26 C indicated that peak germination (33-58%) occurred after 24 h incubation. Peak germination on continually moist soils was somewhat lower (18-26%) than on rewetted soils. Conidia did not germinate on continually moist soils at 6 C. Conidia germinated at a high level (93-95%) in axenic culture in the absence of exogenous carbon and nitrogen substrates. The inhibition of conidium germination on soils was due, in part, to the presence of fungistatic soil volatiles. Addition of low levels of carbon and nitrogen substrates nullified the inhibitory effect of soil volatiles. Germinability of C. scoparium, C. crotalariae, and C. floridanum conidia in artificially infested soils (assayed on a selective medium at 26 C) decreased progressively during incubation at 26 C from 1 wk to 4 mo. No germinable conidia were recovered after incubation of soils at 6 C for 4 wk. Control of Cylindrocladium root rot of black wainut seedlings with sodium azide at 224 kg/ha applied by the plowdown method was comparable to MC-33 at 504 kg/ha. Sodium azide at 67 kg/ha was only marginally effective in disease control. Reduction of Cylindrocladium microsclerotium populations, qualitatively assayed by the azalea leaftrap method, was found in soil samples from plots fumigated with sodium azide and MC-33. A small-spored Cylindrocladium sp. with clavate to papillate vesicles, identified as C. parvum, was consistently recovered from diseased roots and soil samples from a Virginia forest nursery. Percentage recovery from necrotic roots and soil samples collected from root zones of necrotic black walnut seedlings was appreciably higher for C. parvum than for C. floridanum or C. scoparium. In greenhouse tests, limited pathogenicity of C. parvum on black walnut seedlings was demonstrated.