No description available.

No description available.

The biomass of the submersed macrophytic vegetation in four hydrilla (Hydrilla verticillata Royle) infested lakes in central Florida was monitored for one year. Lake Orienta and Little Lake Fairview received 2,320 and 960 grass carp, respectively, while Clear Lake and Lake Mann did not receive grass carp. Hydrilla was eliminated in Lake Orienta within six months of stocking; the lake was stocked at 19 grass carp/mt hydrilla (45 fish/ha). Hydrilla was not eliminated from Little Lake Fairview which contained 9 grass carp/mt hydrilla (30 fish/ha). The growth of hydrilla was restricted in Little Lake Fairview which produced 0.380 mt hydrilla, dry organic wt., in contrast to Clear Lake and Lake Mann in which annual net primary production was 0.728 and 0.880 mt organic matter/ha, respectively. The rate of hydrilla growth was greater in the two unstocked lakes. Clear Lake produced 0.31 g/m2/day, dry organic wt., while the net primary productivity of hydrilla in Lake Mann averaged 0.38 g/m2/day. The net primary productivity of hydrilla in Little Lake Fairview was 0.14 g organic matter/m2/day. Three species (in addition to hydrilla) were common to Little Lake Fairview and Lake Mann and provided the only data upon non-target species. Pondweed (Potamogeton illinoensis Morong.) and stonewort (Nitella sp.) were more abundant and more widely distributed in Little Lake Fairview than in Lake Mann. The poor representation of pondweed and stonewort in Lake Mann was attributed to competitive pressure exerted by hydrilla which comprised 83%, by weight, of the annual mean biomass of submersed macrophytic vegetation. In comparison, hydrilla comprised 74% of the annual mean biomass in Little Lake Fairview. The effect of the grass carp in Little Lake Fairview may have been to ease the competitive pressure exerted by hydrilla, allowing pondweed and stonewort to remain well established. The percentage frequency of occurrence was concluded to be a poor criterion for measuring changes in the hydrilla population. Changes in biomass as great as 900% resulted in no change in the percentage frequency of occurrence of hydrilla in Lake Mann.

SC-0051 and SC-0774 are two experimental herbicides of undisclosed chemistry. A three year field study was conducted to evaluate SC-0051 and SC-0774 for weed control in conventional and no-till corn in Virginia. SC-0051 applied preemergence or postemergence, controlled common lambs-quarters (Chenopodium album L.), common ragweed (Ambrosia artemisiifolia L.) horseweed (Conyza canadensis (L.) Cronq.), common chickweed (Stellaria media (L.) Vill. and was safe to corn. SC-0051 did not control smooth pigweed (Amaranthus hybridus L.) or giant foxtail (Setaria faberi Herrm.). SC-0774 effectively controlled the rye (Secale cereale) cover crop and large crabgrass (Digitaria sanguinalis (L. Scop.) but did not control broadleaf weeds or giant foxtail. SC-0774 also caused considerable but temporary corn injury when applied at rates above 1.1 kg/ha. Combinations of SC-0051 and atrazine provided broad spectrum weed control and yields comparable to atrazine plus metolachlor. Field and laboratory studies were conducted to evaluate the effect of soil pH on the soil mobility of SC-0051 and SC-0774 in sandy loam soils. SC-0774 was applied to soils amended to high and low pH and samples were collected by depth throughout the growing season. A method was developed for extracting and quantifying SC-0774 from collected soil samples. Large crabgrass was also used as a bioindicator species for qualitative detection of SC-0774 residues. These studies showed that SC-0774 was significantly more mobile in high pH soil than in low pH soil. Also, the decreased mobility of SC-0774 at low soil pH lead to decreased corn injury but it increased the soil residual activity of this herbicide. Soil column studies with SC-0774 and SC-0051 showed that the soil mobility of both herbicides increased with increasing soil pH. These herbicides cause reductions in chlorophyll and carotenoid levels in susceptible species resulting in a bleached appearance. The mechanism of this bleaching action is not known. Studies were conducted which examined the effect of SC-0051 on the pigment content and quantity in the susceptible species soybean. High performance liquid chromatography was used to separate, quantify, and identify pigments present in extracts of bleached tissues. The bleaching herbicide norflurazon was also examined for comparison purposes. SC-0051 and norflurazon inhibited the biosynthesis of carotenoids while causing an accumulation of the carotene precursor phytoene and an additional, unidentified pigment that appears to be structurally related to phytoene. This indicates that SC-0051, like norflurazon, inhibits carotenoid formation by blocking the desaturation of phytoene to phytofluene. The uptake and translocation of ¹⁴C-SC-0051 into tolerant corn and susceptible soybean seedlings was examined under growth chamber conditions to investigate the basis for the selectivity of this herbicide. Herbicide uptake was similar in both species but the susceptible soybean translocated a higher percentage of the ¹⁴C-SC-0051 to the growing point of new tissues than did the tolerant corn. It is proposed that differential translocation plays a role in the crop selectivity of the herbicide SC-0051. / Ph. D.

Studies were conducted to determine the distribution of s-triazine resistant biotypes of common lambsquarters (Chenopodium album L.) and smooth pigweed (Amaranthus hybridus L.) in Virginia. Collections of seed were made from suspected triazine-resistant biotypes of common lambsquarters and smooth pigweed from counties in Virginia which had reported having triazine resistance problems. Triazine resistance was confirmed by measuring chlorophyll fluorescence in the presence of atrazine. For further confirmation of triazine resistance in collected common lambsquarters and smooth pigweed biotypes, greenhouse testing of whole plants and a sinking leaf disc assay were performed. Cross-resistance to another s-triazine, as-triazine, and substituted urea herbicide was also determined for s-triazine-resistant biotypes. These studies have shown triazine- resistant smooth pigweed to be present in 19 counties and common lambsquarters to be present in 8 counties in Virginia. s-Triazine resistant biotypes were found to be resistant to another s-triazine and as-triazine herbicide, but were susceptible to the substituted urea herbicide. Additional studies were initiated to determine the effects of different temperature regimes on triazine-resistant and -susceptible biotypes of common lambsquarters and smooth pigweed from different geographical locations. These studies were conducted at the North Carolina State University Phytotron facility in controlled environment growth chambers. Triazine-resistant common lambsquarters biotypes from Virginia, Maryland, and Switzerland as well as a smooth pigweed biotype from Virginia were examined. Triazine-susceptible biotypes of common lambsquarters and smooth pigweed were included as controls. Shoot height, weight, chlorophyll a and b content, and whole leaf fatty acid content of common lambsquarters and smooth pigweed were determined at 18°/14° C, 26°/22° C, and 36°/26° C. Measurements of shoot height were made at 30 and 63 days after planting. The shoot weight, chlorophyll a and b content, and fatty acid content was determined from plants harvested at 63 days after planting. These data indicate common lambsquarters biotypes from different geographical regions exhibited a differential response to temperature. There was no difference between triazine-resistant and -susceptible biotypes in response to temperature. Differences were detected between triazine-resistant smooth pigweed biotypes which indicated that the susceptible biotypes were more vigorous as indicated by shoot height and weight at lower temperatures than triazine-resistant biotypes of smooth pigweed. / M.S.

The purpose of this investigation was to study the behavior during electrolysis of the waste from the ammonia recovery still of the Solvay Process. Data was obtained to show the effect on chlorate formation of the variables; temperature, concentration of electrolyte, and current concentration. In all the experimental runs, observations were made of the weight of calcium scale formed on the cathode surface end of the anode consumption. The temperature studies were made at 25°C, 45°C., and 60°C. The concentration studies were made with waste varying in composition from the concentration given by T.P. Hou ⁽¹²⁾ for the product of the ammonia recovery still to a concentration three times as great. The current concentration studies were made at current concentrations of 2, 4, and 6 amperes per liter. Three runs were made at 8 amperes per liter. / Master of Science

Thesis (MSc)--Stellenbosch University, 2002. / ENGLISH ABSTRACT: The high cost of herbicides for weed control in crop fields in the Western Cape is a major cause of reducing farmers' net income. As chemical weed control became more difficult and expensive, it became necessary to focus on the technique of reducing weed impact, which does not only involve herbicide usage. Aspects such as tillage method, sowing date of crops, crop rotation, weed ecology and germination requirements, amongst other, may play a role in reducing weed impact. The first experiment was done to determine whether temperature and light had an effect on the germination of six selected weed species, namely Arctotheca calendula, Avena fatua, Bromus diandrus, Emex australis, Lolium temulentum and Raphanus raphanistrum. Seeds of the aforementioned weeds were collected from Langgewens during 2000 and stored at room temperature before being used in this study. The seeds were germinated in a germination cabinet at three temperature regimes namely 5 "C /15 "C, 10°C / 15°C and 10°C / 20°C. Most seeds showed a positive germination response at the 10°C / 15°C treatment, except for Emex australis and Lolium temulentum, which was believed to germinate throughout the year under favourable conditions. Among the germinated weed species, Avena fatua germinated best with a cumulative value of 90% as compared to Raphanus raphanistrum, which germinated least with a cumulative value of 12%. The second experiment was done to evaluate the effect of three growth regulators, namely gibberellic acid, hydroxylamine (auxin), and kinetin (cytokinin) to break dormancy and enable simultaneous germination of the six weed species mentioned above. Weed seeds were germinated in a germination cabinet at 20 °C using the test solutions of the aforementioned growth regulators. The germination was assessed after 3, 7, 10 and 14 days of incubation and the tetrazolium test for the viability of seeds was done for ungerminated seeds. The result obtained showed that no chemical/concentration proved to be successful in stimulating the germination of all species tested. As for example a high concentration of hydroxylamine increased germination of Emex australis to nearly 100% and inhibited germination of Raphanus raphanistrum to less than 12.5% at all hydroxylamine concentrations. The third experiment was conducted with the aim of determining the competitiveness of the six weed species mentioned above when grown together with wheat in order to decide when weed control will be cost-effective. An additive series experiment was conducted in a glasshouse. The influence of weed species on wheat plant height, tiller number at different growth stages, vegetative dry mass and gram mass was determined by using different varying weed densities. Weed densities, through reduction in number of tillers, reduced wheat grain yield. By increasing the density of wheat this competitive effect could be reduced. Different weed densities caused a significant difference in wheat plant height, tiller number, dry mass and grain mass. The results showed that species had a significant effect (p < 0.05) on wheat plant height during tillering, stem elongation and heading growth stages. Total wheat plant above-ground dry mass was significantly (p < 0.05) reduced by an increase in weed density. / AFRIKAANSE OPSOMMING: Die hoë koste van onkruiddoders vir onkruidbeheer in graangebiede van die Wes- Kaap is een van die hooffaktore wat graanprodusente se netto inkomste verlaag. Weens moeiliker en duurder chemiese onkruidbeheer en om die impak van onkruide te verlaag, het dit noodsaaklik geword om op die tegnieke te fokus wat nie die gebruik van chemikalieë insluit nie. Faktore wat in rol kan speel sluit bewerkingspraktyke, saaidatum van gewasse, wisselbou, ekologie en ontkiemingsvereistes van onkruide in. Die eerste eksperiment is gedoen om te bepaal of temperatuur en lig 'n effek het op die ontkieming van ses gekose onkruide, naamlik Arctotheca calendula, Avenajatua, Bromus diandrus, Emex australis, Lo/ium temulentum en Raphanus raphanistrum. Sade van die voorgenoemde onkruide is in 2000 op Langgewens versamel en by kamertemperatuur geberg voordat dit in hierdie studie gebruik is. Die sade is in 'n ontkiemingskabinet geïnkubeer by drie temperatuurreekse naamlik 5 oe / 15 oe, 10 oe / 15 oe en 10 oe / 20 oe. Die meeste sade het 'n positiwe ontkiemingsreaksie getoon na die 10 oe / 15 oe behandeling, met die uitsondering van Emex australis en Lolium temulentum, wat oënskynlik heeljaar salontkiem onder gunstige omstandighede. Avena fatua het die hoogste ontkiemingspersentasie oor alle spesies getoon met 'n kumulatiewe waarde van 90% en Raphanus raphanistrum die minste met 'n kumulatiewe waarde van 12%. Die tweede eksperiment is gedoen om die invloed van drie groeireguleerders, naamlik gibberelliensuur, hidroksielamien (ouksien) en kinetin (sitokinien), op die opheffmg van saadrus te ondersoek en om ook die gelyktydige ontkieming van bogenoemde ses onkruidspesies moontlik te maak. Onkruidsade is in 'n ontkiemingskabinet by 20 oe ontkiem deur gebruik te maak van toetsoplossings van bogenoemde groei-reguleerders. Die ontkieming van die sade is na inkubasie periodes van 3, 7, 10 en 14 dae geëvalueer en die tetrazoliumtoets VIr saadkiemkragtigheid is toegepas vir onontkiemde sade. Die verkreë resultate het getoon dat geen chemiekalie / konsentrasie die ontkieming van alle spesies suksesvol kon stimuleer nie. Hoë konsentrasies hidroksielamien het die ontkieming van Emex australis tot byna 100% verhoog en het die ontkieming van Raphanus raphanistrum geïnhibeer tot minder as 12.5% by alle hidroksielamien konsentrasies. Die derde eksperiment is uitgevoer met die doelom die kompetisievermoë van dieselfde ses onkruidspesies te bepaal as dit saam met koring groei en om te besluit wanneer onkruidbeheer koste effektief sal wees. 'n Additiewe reeks eksperiment wat uit vier herhalings bestaan het, is in plastiekpotte in 'n glashuis uitgevoer. Die invloed van die onkruidspesies op koring planthoogte, halmgetal by verskillende groeistadiums, droë massa en graanmassa is bepaal deur onkruiddigthede te gebruik. Onkruide het koring opbrengs verlaag deur die vermindering van halmgetal en hierdie kompeterende effek kon verminder word deur 'n toename in die plantestand van koring. Verskillende onkruiddigthede het 'n betekenisvolle invloed op koring planthoogte, halmgetal, droë massa en graanmassa gehad. Die resultate het getoon dat spesies 'n betekenisvolle effek (p< 0.05) op koring planthoogte, stem verlenging en aarverskyning gehad het. Die totale bogrondse droë massa van koring is betekenisvol (p< 0.05) verminder deur 'n verhoging in onkruiddigtheid.

Bibliography: leaves 125-141. / xiii, 141 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Addresses the poor control of major weed species under southern Australian winter conditions by the non-selective post-emergence herbicide, glufosinate in order to determine the best way to use it. Dose response experiments were performed under simulated southern Australian winter conditions, and demonstrated a variable glufosinate efficacy between Lollium rigidum and Avis sterilis. Glutamine synthetase assays showed that target site sensitivity did not influence these results. Spray retention experiments showed no influence from plant size or morphological features, while metabolic studies showed that only a small proportion of glufosinate was metabolised in both species. Tests of several populations of Raphanus raphanistrum showed that all populations, despite geographical origin, were poorly controlled by glufosinate, in both field and simulated conditions. Experiments conducted at higher temperatures showed enhanced glufosinate efficiency. Experiments with the use of co-herbicides, chelating agents, fertilizer salts and hormones were also carried out. Studies on the effect of the pH of the herbicide solution on cell uptake showed that uptake into the cell wall only was enhanced by reducing the buffer pH. Shows that the poor efficacy of glufosinate against these species is mainly due to poor translocation of the herbicide. / Thesis (Ph.D.)--University of Adelaide, Dept. of Applied and Molecular Ecology, 2003

No description available.

Selective application of herbicide in agricultural cropping systems provides both economic and environmental benefits. Implementation of this technology requires knowledge of the location and density of weed species within a crop. In this study, two image classification techniques (Artificial Neural Networks (ANNs) and Maximum Likelihood Classification (MLC)) are compared for accuracy in weed/crop species discrimination. In the summer of 2005, high spatial resolution (1.25mm) ground-based hyperspectral image data were acquired over field plots of three crop species seeded with two weed species. Image data were segmented using a threshold technique to identify vegetation for classification. The ANNs consistently outperformed MLC in single-date and multitemporal classification accuracy. With advancements in imaging technology and computer processing speed, these network models would constitute an option for real-time detection and mapping of weeds for the implementation of site-specific herbicide management. / xii, 106 leaves : ill. (col. ill.) ; 29 cm