The main objective of this project was to determine the possibility and feasibility of creating wildlife clearings through the use of herbicides as compared to conventional methods of bulldozing and hand clearing. The selected study area adjoining a series of 3 compartments designated as Broad Run Research Area, designed to study various methods of habitat manipulation. Twelve areas were selected for treatment and numbered consecutively. Two were abandoned; No. 1 because of its small size and No. 3 because of the value in its natural condition. A square clearing design was arranged in each of the remaining 10 areas. Four herbicides were selected for testing, each proposed clearing was divided into 4 equal sections in order to apply the 4 herbicides to each clearing; one per quarter-section. The 4 herbicides tested were Monuron, Fenuron, 2,4,5-T, and Ammonium sulfamate. Nonuron and Fenuron, in granular form, were applied around the base of each stem at rates of 5 and 10 grams per stem. Stems 0-4.9 inches d.b.h. received 5 grams and stems 5 inches d.b.h. and larger received 10 grams. Ammonium sulfamate and 2,4,5-T were applied to frills cut at waist height. The ax cute in 2,4,5-T treatment were spaced at 4 inch intervals, and in the ammonium sulfamate treatment were continuous and overlapping. These two chemicals were applied by the use of 2 gallon garden sprayers; ammonium sulfamate at a rate of 7lbs. of crystals dissolved in 2 gallons of water and 2,4,5-T at a rate of 12 lbs. active ingredient per 100 gals. of No. 2 diesel fuel. Frills were filled to overflowing. The granular herbicides were applied in June and July 1958 and the frill treatments were made in August of that year. Two stem counts by species were made on each entire area. The first was made immediately after treatment and the second after one complete growing season. The percent of kill was computed for each herbicide based on the stem counts. Herbaceous sample plots 1/100 acre in size, were established in 4 areas representing 4 topographical features. Two stem counts were made on each of these 4 areas. An incidental field study using 1,2, and 4-grams of Fenuron per stem revealed that most woody species can be controlled with 1 gram of active ingredient per stem. Openings were satisfactorily established with Fenuron and Monuron; a lower rate of application could have been used. Techniques used in frilling would have to be altered to obtain satisfactory results when using 2,4,5-T and ammonium sulfamate; complete frills are necessary for 2,4,5-T treatments and the ax cuts placed closer to the root collar in ammonium sulfamate treatments. Sight observations revealed the areas were being used by deer, rabbit, grouse, turkey, and woodcock. / Master of Science

Six combinations of grazing, tillage, and herbicides were studied during 2 yr in a randomized block design to determine alfalfa (Medicago sativa) survival, corn (Zea mays) plant populations and corn growth in an alfalfa-corn rotation. Alfalfa was overseeded with rye (Secale cereale) in autumn prior to planting corn in spring of each year. Treatments were 1) non-grazed control with standard chemical treatments for no-till establishment of corn, 2) grazing alfalfa, then grazing rye until corn planting followed by dicamba application, 3) alfalfa grazing plus glyphosate prior to corn planting, 4) treatment 3 plus grazing prior to rye jointing, and 5) alfalfa grazing plus autumn application of glyphosate, 6) alfalfa grazing plus autumn disking (no herbicides). Grazing until corn planting decreased (P<0.05) alfalfa stands and rye biomass, but increased (P<0.05) corn plant populations and soil bulk density compared to shorter grazing periods. Grazing prior to rye jointing increased (P <0.05) soil bulk density and corn plant populations, and decreased (P<0.05) rye biomass compared to no spring grazing. Autumn disking decreased (P<0.05) bulk density, but generally provided less (P<0.05) control of alfalfa compared to autumn application of glyphosate. Autumn disking and glyphosate application (Trts. 5 and 6) increased (P<0.05) rye biomass compared to no autumn treatment (Trts. 3 and 4). Applying glyphosate prior to corn planting (Trts. 3 and 4) improved (P<0.05) corn populations and growth compared to autumn glyphosate or disking (Trts. 5 and 6) and was similar to conventional no-till establishment (Trt. 1). Herbicides were necessary to completely kill alfalfa, but grazing reduced TNC in alfalfa roots and alfalfa plant persistence. / Master of Science

The effects of site quality, dormant and growing season harvests, and four even-aged regeneration treatments on natural hardwood and planted loblolly pine (Pinus taeda L.) are examined three years after clear felling and whole-tree harvesting upland hardwood stands in the Virginia Piedmont. Natural hardwood regeneration was dominated by stump sprouts, with seedlings and advanced regeneration playing a secondary role. Stump sprouts and seedlings plus advanced regeneration were significantly taller with a dormant season harvest. A growing season harvest resulted in significantly better survival and growth of loblolly pine after 2 growing seasons. A trend for more loblolly pine volume index growth on the poor site class was noted. Regneration alternatives included an herbicide stump treatment at time of harvest that significantly reduced stump sprout growth, 70%, and resulted in significantly better loblolly pine survival. This stump sprout control also favored hardwood seedling and advanced regeneration. One regeneration alternative included either a triclopyr basal bark spray or hexazinone soil applied spot treatment for releasing loblolly pine at age one. Both release treatments significantly reduced natural regeneration basal area and density when used two years after the herbicide stump treatment. Loblolly pine growth was significantly increased by both pine release treatments. Herbicide treatments were most effective, in terms of lower hardwood basal area and greater loblolly pine volume index, in growing season harvest treatment plots. / 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.

Fields studies conducted in 1987 and 1988 determined the weed control efficacy of ICIA-0051 and SC-0774 in conventional and no-till systems of corn (<i>Zea mays</i> L.) culture. Results of the preemergence and postemergence applications of ICIA-0051, across all treatments after 8 weeks, showed 85% control or better of triazine-resistant smooth pigweed (<i>Amaranthus hybridus</i> L.), while fall panicum (<i>Panicum dichotomiflorum</i> Michx.) control ranged from 43 to 87%. Giant ragweed (<i>Ambrosia trifida</i> L.) control ranged from 30 to 95%, while control of ivyleaf morningglory (<i>Ipomoea hederacea</i> (L.) Jacq.) was below 75% in the preemergence treatments and ranged from 89 to 99% in the postemergence treatments. In general, the addition of atrazine to the pre- and postemergence treatments of ICIA-0051 improved weed control. SC-0774 treatments gave 85% or better control of fall panicum, but inadequate broadleaf weed control (75% or worse). Soil mobility studies using soil thin-layer chromatography and soil leaching columns indicated that the movement of ICIA-0051 was highly negatively correlated with the organic/humic matter fraction. Although the mobility patterns were similar, ICIA-0051 was more mobile than SC-0774, which was more mobile than atrazine. A comparison of ICIA-0051 across soils indicated that the order of mobility was Appling loamy sand (Rf = 6.4) > Davidson clay (Rf = 5.6) > Bojac sandy loam (Rf = 5.0) = Frederick silt loam (Rf = 4.9) > Hyde silty clay loam (Rf = 1.1). Other soil properties such as the clay content and pH were not strongly correlated with ICIA-0051 movement. Results of the adsorption/desorption studies indicated that the organic/humic matter fraction was primarily responsible for the binding and retention of ICIA-0051 across the five soils investigated. Based on the K constants derived from the Freundlich equation, the order of adsorption was Hyde > Frederick > Davidson = Bojac > Appling. The desorption results indicated that ICIA-005l was not tightly bound to the soil particles, with losses between 20 and 50% of the amount adsorbed after two desorptions. Results of the greenhouse persistence study, using mustard (<i>Brassica kaber</i> L.) as a bioassay species, indicated that ICIA-0051 was more biologically available than atrazine. Similar to the adsorption and leaching results, the persistence of ICIA-0051 was highly positively correlated with the soils’ organic matter. Regardless of the rate used, crop injury decreased over time, although the highest rate (1 ppm of ICIA-0051) showed significant crop injury even after 6 months in several soils in the greenhouse studies. / Ph. D.

Response of barley (<i>Hordeum vulgare</i> L.) and wheat (<i>Triticum aestivum</i> L.) to root-applied chlorsulfuron (2-chloro N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl) amino] carbonyl] benzenesulfonamide), a herbicide for use in small grains, was investigated. The results showed that, although wheat roots take up more chlorsulfuron than barley roots, barley was less tolerant to chlorsulfuron and chlorsulfuron was more mobile in barley. This study indicated that difference in uptake or translocation cannot explain the differential response of the two species to root-applied chlorsulfuron. In an interaction study, significant chlorsulfuron antagonism on ryegrass (<i>Lolium multiflorum</i> Lam.) control by diclofop {(±)[-2-[4-(2,4-dichlorophenoxy) phenoxy) propanoic acid} was observed. Greenhouse experiments showed that the tolerance of corn (<i>Zea mays</i> L.) to chlorsulfuron and metsulfuron (2-[[[[(4-methoxy-6-methyl-l,3,5-triazin- -2-yl) amino] carbonyl] amino] sulfonyl] benzoic acid) was greatly increased by seed dressing with the herbicide safener NA (1,8-naphthalic anhydride). The soil behavior of chlorsulfuron was studied in the field, greenhouse and laboratory. In the field, corn adequately tolerated soil residues present 10 months following postemergence application of chlorsulfuron at 10 to 120 g/ha. However, at the same site and rates, residues from chlorsulfuron injured corn when sampled 2 months after application. In laboratory studies chlorsulfuron was moderately adsorbed by organic matter but showed low affinity to clay. R_f values calculated from soil thin-layer chromatography closely correlated with the mobility of chlorsulfuron leached with 16.8 cm of water over a 14-day period in hand-packed soil columns. In the soil thin-layer chromatography, chlorsulfuron mobility was positively and negatively correlated with pH and organic matter, respectively. The results indicated that chlorsulfuron could be mobile in low organic matter and non-acidic soils. The relationship of chlorsulfuron phytotoxicity to soil physical and chemical properties was also evaluated. Organic matter was inversely related to chlorsulfuron phytotoxicity while no such relationship to clay content was observed. The adsorption of chlorsulfuron decreased with increasing soil pH whereas desorption was greater at alkaline pH. / Ph. D.

Thifensulfuron is a new herbicide of the sulfonylurea class under development by E. I. Dupont de Nemours Company Inc. for postemergence broadleaf weed control in soybeans [Glycine max (L.) Merr]. Field studies evaluated the influence of adjuvants and chlorimuron upon the efficacy of thifensulfuron. Thifensulfuron applied alone provided smooth pigweed (Amaranthus hybridus L. #AMACH) control at application rates 12% of those of the similar herbicide chlorimuron. Nonionic surfactant or crop oil concentrate increased soybean sensitivity to thifensulfuron, but an adjuvant was required to obtain consistent seedling common lambsquarters (Chenopodium album L. #CHEAL) control. Chlorimuron and thifensulfuron combinations did not control ivyleaf morningglory [Ipomoea hederacea (L.) Jacq. #IPOHE]. Greenhouse studies evaluated soybean cultivar sensitivity to thifensulfuron. Seven popular Virginia soybean varieties and one national variety (Williams 82) were screened for tolerance to thifensulfuron. Differences in varietal sensitivity was verified. Soybean varieties Vance, Essex, Hutcheson, and York proved to be more sensitive to 9.1 g ha⁻¹ thifensulfuron than FFR 561, Williams 82, or Deltapine 105. No relationship between sensitivity to thifensulfuron and Essex parentage could be drawn. The selectivity of the sulfonylurea class of herbicides is reportedly based on differential metabolism of the herbicide between sensitive and tolerant weed and crop species. Laboratory studies were conducted utilizing thifensulfuron-sensitive and tolerant weed species, velvetleaf (Abutilon theophrasti Medic. #ABUTH) and spurred anoda [Anoda cristata (L.) Schlecht #ANVCR], respectively, as well as the relatively tolerant Williams 82 and sensitive Vance soybean. Absorption and distribution studies indicated that all species absorbed and translocated similar amounts of ¹⁴C 1, 3, and 5 days after application of the methyl ester of [¹⁴C-thiophene] thifensulfuron. Metabolism studies indicated that both tolerant spurred anoda and sensitive velvetleaf metabolized thifensulfuron at similar rates 3 days after treatment. Metabolism appears to be the major mechanism for the selectivity of thifensulfuron to soybeans. The mechanism for spurred anoda tolerance to thifensulfuron has yet to be determined. This research indicates that broadcast foliar applications of 4.5 g ha⁻¹ thifensulfuron with 0.125% v/v nonionic surfactant or 1% v/v crop oil concentrate can provide selective postemergence smooth pigweed and common lambsquarters control for soybean production in Virginia. Caution should, however, be taken in prescribing greater than 4.5 g ha⁻¹ thifensulfuron due to the variability in cultivar sensitivity to thifensulfuron. / Ph. D.

Herbicide safeners (protectants, antidotes) are used to protect crop plants from herbicide injury. Currently our understanding of the mechanisms involved in the protection of plants by safeners is not well defined; therefore, investigations were conducted to elucidate the mechanism(s) of action of the oxime ether safeners. Molecular comparisons of selected herbicide-safener combinations using computer-aided molecular modeling revealed that the chemical structures of safeners and herbicides are very similar at the molecular level; and, indicate that these compounds could bind at the same active site of the target protein or they may serve as inducers of metabolic enzymes which detoxify herbicides. Metolachlor at 10 μM and seed-applied CGA-133205 had no effect on germination while treatment with seed-applied oxabetrinil significantly reduced germination of grain sorghum. Results from experiments on ¹⁴C-acetate incorporation into lipids indicate that metolachlor and the oxime ether safeners influence lipid metabolism causing a redistribution of carbon in the lipid fractions of germinating sorghum roots. Results from studies with acetyl-CoA carboxylase indicate that this enzyme is not a target site for either metolachlor or the oxime ether safeners. Metolachlor and the oxime ether safeners enhanced glutathione levels in grain sorghum seedlings at 12 to 48 hr after imbibition was initiated with oxabetrinil being more stimulatory than metolachlor or CGA-133205. Glutathione reductase activity was also stimulated in safener-treated grain sorghum seedlings. Both safeners slightly enhanced nonenzymatic and enzymatic conjugation of metolachlor with reduced glutathione. Oxabetrinil conjugated enzymatically or nonenzymatically with reduced glutathione at a slow rate, but CGA-133205 did not. These data suggest that during the early stages of seed germination and seedling development of grain sorghum, safeners can enhance the detoxication of metolachlor by enhancing glutathione levels and enzymatic and nonenzymatic conjugation of metolachlor with glutathione. It appears that oxabetrinil and CGA-133205 are conferring protection to grain sorghum by increasing the rate of metolachlor metabolism. / Ph. D.

The successful regeneration of mature oak (<i>Quercus</i> spp.) forests is thought to be dependent on the presence of oak advance regeneration. However, the advance regeneration must be of sufficient size and density for oak to be competitive and become a dominant species after harvest. The presence of a dense midstory canopy of shade tolerant species has been implicated with the poor development of oak advance regeneration. Understory Vegetation Control was conducted in 1994 in average quality (SI₅₀ 17.7 - 21.9 m for upland oak) southern Appalachian forest stands to determine the effects on oak (<i>Quercus</i> spp.) and maple (<i>Acer</i> spp.) advance seedling abundance, growth, and development. Three study sites were located in southwest Virginia, and the following two treatments were implemented at each site: Understory Vegetation Control (UVC) and Control. Permanent sampling plots and individual seedlings were located to quantify the density, recruitment, and growth of advance regeneration. Competing vegetation was significantly reduced after one year by the UVC treatment, where the mean relative change in the sum of the heights of competing stems between 1 and 5 m in height was -15.9 percent for the UVC plots vs. 22.8 percent for the Control plots. Neither oak seedling recruitment nor height growth was enhanced by the UVC treatment after one year. Insufficient time has elapsed to allow for a growth response, or to determine if seedling recruitment will be enhanced by UVC. Several years may be required to determine if the UVC treatment can enhance the growth and competitive status of oak regeneration. / Master of Science

Chemical herbicides have been widely used in agriculture since the middle of the 20th century since they limit the competition of resources between crops and weeds. Herbicides are known to cause environmental degradation and to risk organisms and human health. Herbicides are chemical compounds that target weeds in different ways due to their chemical structures and concentrations. There is a growing concern with the usage of herbicides and the opposition to herbicides is growing due to the many risks the substances. There is an increased demand for sustainable options to chemical herbicides. Mechanical weeding has been used traditionally for weed management but has been forgotten due to the high efficiency of chemical herbicides. Precision agricultural technologies (PATs) can limit weeds mechanically. In this thesis PATs refer to robots equipped with AI, sensors, and other autonomous functionalities. This thesis studies how farmers perceive PATs and their ability to limit herbicides. The focus is on which factors need to be considered for farmers to adopt PATs for weed limitation, as well as what outcomes farmers expect from weeding tools. This research is a qualitative study conducted with semi-structured interviews with farmers. The most prominent themes were the business of agriculture, weed management, environmental perspectives, and perception of tools. These themes were used to find the farmers’ perceptions of PATs, and what outcomes a tool is expected to deliver. The theory of mediated activity (MAT) is used to analyse what the farmers want from their tools and how they perceive the PATs. Diffusion of innovation theory (DIT) is used to analyse the adaptability and willingness to adopt innovation, such as PATs. The key factors affecting adaptability are profit, efficiency, flexibility, and environmentally sustainable outcomes. These factors affect the farmers the most when adopting new tools and these are what the farmers are looking for in tools. To increase farmers' adoption of novel innovations they need to be presented with proof that the tools will bring the key factors. If PATs can offer the farmers the key factors the PATs can help to limit herbicide usage and therefore become a tool of sustainable transition.