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Ph. D. / incomplete_metadata

Integrated weed management involves the utilization of weed biology principles to develop effective and economical control strategies. This research involved investigations of herbicide-based weed management programs in potato (<i>Solanum tuberosum</i> L.) and winter wheat (<i>Triticum aestivum</i> L.) as well as investigations of the biological characteristics of smooth pigweed (<i>Amaranthus hybridus</i>), a troublesome species in many crops. Sulfentrazone is an herbicide registered for use in soybean [<i>Glycine max</i> (L.) Merr.] and tobacco (<i>Nicotiana tabacum</i> L.) that may also have potential for use in potato. In field experiments, potato tolerance to preemergence (PRE) applications of sulfentrazone at rates up to 0.21 kg/ha was similar to that from the registered herbicides metribuzin, metolachlor, or metribuzin plus metolachlor PRE. Potato generally did not tolerate sulfentrazone applications to foliage. Sulfentrazone effectively controlled common lambsquarters (<i>Chenopodium album</i> L.) at rates as low as 0.11 kg/ha and also controlled several annual grasses at higher application rates, but was slightly less effective on jimsonweed (<i>Datura stramonium</i> L.) and ineffective on common ragweed (<i>Ambrosia artemisiifolia</i> L.). Potato tuber yield and grade from sulfentrazone PRE applications was similar to yield of potato treated with registered herbicides. Laboratory research was also conducted to determine the mechanism of sulfentrazone selectivity between potato (a tolerant species), common lambsquarters (a sensitive species), and jimsonweed (an intermediate species). After 48 h root exposure to [14C] sulfentrazone, absorption by common lambsquarters was nearly two-fold that of jimsonweed and three-fold that of potato. Both weed species also exhibited nearly a two-fold increase in sulfentrazone translocation from roots to shoots compared to potato. Since the site of action of sulfentrazone, protoporphyrinogen oxidase, is located in shoot tissue, translocation to shoots is essential for sulfentrazone toxicity. Therefore, the proposed primary mechanisms of selectivity between these species are differential root absorption and differential translocation. Experiments were also conducted to investigate the potential of the experimental herbicide AE F130060 03 for Italian ryegrass (<i>Lolium multiflorum</i> Lam.) control in winter wheat. In laboratory research, foliar absorption of AE F130060 03 in Italian ryegrass was at least three times that in wheat. Additionally, herbicide metabolism was greater in wheat, particularly in wheat treated with the herbicide safener AE F107892. In field experiments, AE F130060 03 was as effective as diclofop-methyl for control of diclofop-sensitive Italian ryegrass and more effective than diclofop-methyl and all other herbicides tested for control of diclofop-resistant Italian ryegrass. Although wheat injury from AE F130060 03 was greater than from other herbicides, wheat recovered and yields were not affected. Postemergence AE F130060 03 applications controlled Italian ryegrass from emergence until the end of tillering, but applications made to four- to five-tiller Italian ryegrass resulted in the least amount of new Italian ryegrass emergence following application. To further define the utility of AE F130060 03 in winter wheat, ten wheat cultivars adapted to Virginia were evaluated for tolerance to AE F130060 03. Biomass production between cultivars was not influenced by AE F130060 03 application in the greenhouse, although slight yield decreases due to herbicide application were found in FFR 518, Coker 9663, AgriPro Patton, and VA98W593 under weed-free conditions in the field. Greenhouse, growth chamber, and field experiments were also conducted to investigate growth and seed production of one imidazolinone-susceptible (S) and five -resistant (R1, R2, R3, R4, and R5) smooth pigweed biotypes. Although the S biotype produced more total biomass than four of the five R biotypes, R4 displayed a more rapid growth rate at 3 to 5 wk after planting and a faster germination rate than S and all other R biotypes. Seed production in R4 was similar to S and greater than in all other R biotypes. Early rapid growth in R4 did not translate into increased biomass accumulation compared to S at the conclusion of the experiments. / Ph. D.

Tall fescue (Festuca arundinacea Schreb.) has great utility as a low maintenance turfgrass in the northern and transition zone regions of the United States. However, it is difficult to successfully maintain tall fescue of high quality over consecutive summers because of its susceptibility to the fungal pathogen Rhizoctonia solani, which causes the disease brown patch. Not only is brown patch aesthetically unpleasing in a stand of tall fescue but it can also thin out the turf and allow for the encroachment of undesirable weedy species. Cultivar selection, cultural practices, mixing turf species and timing of pesticide applications all can impact the epidemiology of brown patch in tall fescue. Research was conducted in tall fescue to quantify chitinase activity in different cultivars, elucidate the impact of mowing height and nitrogen fertility on brown patch and bermudagrass (Cynodon dactylon L.) encroachment, to evaluate seeding mixtures of tall fescue with hybrid bluegrass (Poa pratensis x Poa arachnifera) on diseases and weeds as well as measuring the impact of the herbicide bispyribac-sodium on brown patch. Chitinase activity was greater in the tall fescue cultivar that was less susceptible to brown patch. In the mowing-fertility studies, cutting tall fescue at 10 cm generally reduced brown patch and bermudagrass encroachment compared to 6 cm. Mixing hybrid bluegrass with tall fescue reduced disease and weed species infestations compared to tall fescue alone. Applying bispyribac-sodium earlier in April resulted in less brown patch and better weed control compared to application in May. Based on this research brown patch severity and subsequent weed species infestations can be reduced by selecting a tall fescue cultivar with a high basal level of chitinase, mowing it at 10 cm and mixing it with a hybrid bluegrass cultivar. / Ph. D.

Experiments were conducted with 'BigSur' broccoli (<i>Brassica oleracea</i> var. <i>italica</i> Plenck) at two sites in fall of 1993 and at two sites in the spring of 1994 on a Hayter loam in southwestern Virginia. Objectives were to determine the tillage main-plot (CT = conventional tillage, and NT = no-tillage) and weed-control subplot (C = no overseeding or preemergent herbicide; HB = oxyfluorfen; RC = red clover (<i>Trifolium pratense</i> L.); WC = Dutch white clover (<i>Trifolium repens</i> L.); and HV = hairy vetch (<i>Vicia villosa</i> Roth) effects on broccoli yield and weed suppression. At all sites, marketable broccoli yield was equal or higher in NT than CT and was unaffected by overseeded legume living mulches. Overseeded legumes suppressed weeds as well as the HB in three of the four sites. These data show that the NT systems used in these experiments can suppress weeds and produce high broccoli yields and that overseeded legume living mulches can be effectively established after transplanting to suppress weeds without reducing broccoli yield. / Master of Science

Coal has been and will continue to be an important energy source in the U.S. for the foreseeable future. Surface mining for coal is one of the methods employed to extract this resource from below the ground. The process of surface mining removes native topsoils and any native vegetation that was support by these native soils. In the Appalachian coal-producing region of the United States, the pre-mining landscape is predominantly forested. Prior to the Surface Mining and Reclamation Act of 1977 (SMCRA), surface mined lands were commonly reclaimed to forests. Subsequent to the passage of SMCRA, reforestation of surface mined lands has decreased. As a result, thousands of hectares of land that were forested prior to mining are being reclaimed using grasses and legumes. This is done in spite of the fact that the SMCRA requires that land be reclaimed to an "equal or higher land use." The decline of reforestation stems from two main issues, namely: (1) reclaiming land to pasture is an easy and low-risk way for mining companies to obtain bond release; and (2) SMCRA reclamation requirements have led to unfavorable conditions for tree establishment and growth. Recent interest has been shown in reverting these surface mined lands that have been reclaimed to pasture back to forests for reasons related to the environmental, economic, and carbon sequestration benefits that forests are believed to have when compared to pasture land. It is believed that forests can be established on existing reclaimed pasture land through the use of silvicultural treatments, that mature stands of trees growing on surface mines will respond to treatment similarly to stands growing on native soils, and that mature stands growing on relcaimed surface mines have different soil properties controlling their growth than those that have been found for younger stands. The purpose of this investigation was to understand the biological feasibility of restoring forests on post-SMCRA surface mined lands in the Appalachian coalfields reclaimed to pasture and to understand the productive potential and factors governing the productive potential of pre-SMCRA surface mines supporting mature forests in an attempt to show the benefits of reclaiming these lands with forests. A 3x3x3 factor random complete block design was used to assess first-year survival and growth of three species assemblages under three levels of silvicultural treatment intensity at each of three study sites having different site characteristics. The native hardwood species assemblage was found to have the best survival across all three sites, with 80 and 85% survival for sites with spoils derived from shale and oxidized sandstone, respectively. White pine generally had the lowest survival of all species and ranged from 27% across treatments on siltstone spoils to 58% across treatments on oxidized sandstone spoils. Hardwood and white pine grew little over the first year, ranging from -3.7 to 8.9cm in height compared to hybrid poplar, whose height growth ranged from 22.4cm to 126.6cm. Response to silvicultural treatment was variable by site and species, but weed control in combination with tillage generally resulted in the highest survival. Greatest height growth (126.6cm) occurred on the oxidized sandstone spoil, where hybrid poplar was treated with weed control plus tillage in combination with fertilization. Hybrid poplar was found to have the greatest growth after one year compared with the hardwood and white pine and also had the greatest height growth at each level of silvicultural intensity for all sites. This superior growth should give hybrid poplar an advantage over the others used to revert these grass lands back to forests, as the amount of height growth observed (>50cm over one year in the weed control plus tillage treatment at all sites) may be enough to ensure that these trees will not succumb to aggressive competing vegetation without further weed control. The results of this study show that based on first-year data, reforestation of these lands does appear to be biologically feasible, given the species and treaments used. In an attempt to quantify the productivity of a 26-year-old white pine stand established pre-SMCRA, a random complete block experiment was used to compare the response to a thinning that occurred in this stand at age 17. Site index of the stand was found to be 32.3m at base age 50, indicating that this is a very productive stand. Neither stand volume nor stand value was statistically different at age 26 between treatments with volumes and values ranging from 290m3ha-1 and $5639 ha-1 to 313 m3ha-1 and $5478 ha-1 for the thinned and unthinned treatments, respectively. The difference in mean breast-height diameter, however, was significant at age 26, and this was confirmed by a significant difference in a repeated measures analysis of annual diameter data for these treatments (P < 0.0001). Projection to age 30 revealed that both stand volume and value would be significantly higher in the thinned treatment by margins of 8.7 m3 ha-1 and $2457 ha-1. Regression analysis of soil data within the observed rooting depth of the trees from this stand indicated that nitrogen mineralization index, bulk density, sand percentage of the fine soil fraction, and percentage of oxidized sandstone in the soil profile were the most important variables in determining the stand's productive capacity (R2 = 0.7174). It was also found that of the five different spoil types encountered in the stand, the oxidized sandstone spoil had the most favorable physical and chemical properties for tree growth. Common root-restricting layers were found to have high soil density or increased levels of soluble salts. It has been shown that reclaimed surface mines can grow productive forests if the appropriate spoil materials are returned to the surface in sufficient depth. It has also been shown that surface mined lands reclaimed to pasture can be successfully reforested using silvicultural treatments to ameliorate unfavorable conditions for tree establishment and growth, though these treaments may not be cost-effective, and the success of these treatments was variable based on the soil characteristics of each site. / Master of Science

Field experiments were conducted at three Virginia locations in 1990 and 1991 to evaluate the effects of cover crop suppression method, nonselective herbicide, no-till cultivation, and herbicide banding on weed control, corn vigor, and corn yield. These factors were evaluated in experimental areas containing either a rye (Secale cereale) cover crop or in areas with no cover crop. In areas with a rye cover crop, the cover crop suppression methods evaluated were paraquat or mechanical suppression via mowing. In areas without a cover crop, paraquat was compared to a treatment without paraquat. Five selective herbicide treatments were evaluated within each level of the variable described above. These treatments included a control or no selective herbicides, a preemergence herbicide combination of atrazine plus metolachlor, and a postemergence herbicide combination of dicamba plus nicosulfuron. The preemergence and postemergence herbicides were applied either broadcast or banded over the crop row. The use of no-till, interrow cultivation was evaluated for each combination of the cover crop suppression method or nonselective herbicide and selective herbicide variables. Where a rye cover crop was present, paraquat significantly improved control of this species relative to mowing, and it provided significantly better control of most weed species and increased corn vigor and yield. In the absence of a cover crop, paraquat significantly improved weed control, but its effect on corn vigor and yield was dependent on weed pressure. Where weed pressure was moderate to heavy, paraquat significantly improved corn vigor and yield, whereas, it did not have a significant effect on these variables if weed pressure was low. In some situations, paraquat did not significantly improve late season weed control with broadcast selective herbicides, however, it provided quicker control of established weeds which significantly improved corn growth, especially in dry soil conditions. With or without a rye cover crop, cultivation did not significantly improve weed control, corn vigor, or corn yield when used with broadcast selective herbicides. Banded selective herbicides with cultivation provided weed control and corn vigor and growth equivalent to broadcast selective herbicides without cultivation if weed pressure was low. Where weed pressure is moderate to heavy, banded herbicides with cultivation did not perform as well as broadcast treatments without cultivation. Postemergence herbicides provided weed control and corn growth equivalent to preemergence herbicides, but use of effective nonselective herbicides at planting to control established weeds was critical. / Master of Science

Two studies were designed to test three herbicides and factors which influence their efficacy. In the first study four chemical combinations used for site preparation in southern pine, including triclopyr (3,5,6-trichloro-2-pyridinyloxyacetic acid), trichloropicolinic acid), dichlorophenoxy)acetic acid] picloram (4-amino-3,5,6- and 2,4-D [(2,4- were screened for the most effective control of selected hardwoods. The chemical combinations were tested on Piedmont and Coastal Plain physiographic sites and were examined for the optimum amount of time for chemical activity between application and slash disposal (site disturbance). Efforts were also made to use target-plant and environmental data to predict chemical efficacy. A combination of triclopyr and picloram at 2 and 1 lb ai/ac, respectively, each gave the best overall control of hardwood brush. The amount of time required to obtain the optimum chemical control, presumably related to translocation, was found to be six to eight weeks after application to the foliage. Chestnut oak (Quercus prinus L.) control was successfully predicted on the bases of plant tissue and environmental data. In a second study the effect of temperature and time on the distribution of foliar-applied triclopyr, picloram, and 2,4-D were observed in red maple (Acer rubrum L.). Detection of the herbicides in the stems and roots using gas chromatography revealed that triclopyr was less affected by temperature differences; however, overall more herbicide reached the roots of red maple growing in a 21° C than those growing in a 29° C temperature. Triclopyr concentrations in the roots reached a peak much earlier than picloram or 2,4-D which did not peak until 42 days after application. / M.S.

Intensive forest management techniques such as whole-tree harvesting and use of herbicides to control weeds can have an effect on nutrient cycling and nutrient pool sizes in the mineral soil. This study was conducted to measure differences in soil carbon (C), nutrient pools, or phosphorus (P) fractions associated with harvest-intensity (bole-only vs. whole-tree harvest) and weed-control treatments (initial weed control vs. five years of annual weed control) after ten years. Soil C, nitrogen (N), and P, and exchangeable calcium (Ca), potassium (K), magnesium (Mg), and Hedley P fractions were measured prior to treatment establishment and after ten years in two Douglas-fir (Pseudotsuga menziesii) plantations in the Pacific Northwest. We observed increases in most nutrient concentrations with initial weed control compared with annual weed control at Matlock, with opposite trends at Molalla. Exchangeable Ca and Mg content showed responses to weed control treatments. Harvesting treatments had no significant effects on soil C and nutrient pools at either site. Total P and many of the Hedley P fractions decreased over time, but these effects were ameliorated with the less-intensive initial-weed-control-only treatment at Matlock and the more-intensive annual-weed-control at Molalla. Ten-year responses suggest that harvesting intensity has not impacted potential for maintaining soil C and nutrient pools, with the exception of P, for long-term productivity. Knowledge of the on-site vegetative communities and their role in nutrient cycling is required to anticipate what effect weed control might have on nutrient pools through ensuing stand development. / Master of Science