The overall objective of this thesis was to improve our understanding of the light environment associated with two of the major deciduous competitors of commercial conifer seedlings in low elevation coastal British Columbia, and the physiological response of young conifers to specific environments and changes in the environment. Studies were conducted to investigate: 1) seasonal and herbicide-induced changes in the light regimes beneath the canopies of two brush species, 2) growth and physiology of seedlings of three conifer species in several different deciduous brush environments throughout the year, and 3) changes in the physiology and growth of suppressed conifer saplings when different methods and schedules were used to reduce shading from an overtopping red alder canopy. Seasonal changes in the light quantity and quality were documented within salmonberry (Rubus spectabilis Pursch) and below red alder (Alnus rubra Bong.) canopies. The prediction of light attenuation within salmonberry canopies using the Beer-Lambert law was good for foliated canopies using leaf area index, and defoliated canopies using stem area index. As salmonberry leaf area increased, the ratio of red to far-red light declined exponentially. Growth of grand fir (Abies qrandis (Dougl.) Forbes), western hemlock (Tsuga heterophylla (Raf.) Sarg.) and Douglas-fir (Pseudetsuga menziesii (Mirbel) Franco) seedlings decreased with increases in the canopy density of overtopping deciduous species. Physiological differences between conifer species and differences between overtopping canopy treatments declined in the autumn and winter. Based on the physiological measurements, suppression of the shade intolerant Douglas-fir seedlings was greatly reduced during the period that overtopping deciduous canopies were leafless. Animal damage reduces growth and probably increases the duration seedlings are under overtopping canopies. Suppressed Douglas-fir saplings released from overtopping by red alder canopies showed the greatest growth response when the alder canopies were removed in the spring; complete removal of the alder canopy during the summer had a predictably deleterious effect on the sapling physiology and growth. Herbicide injections resulted in a slower but predictable increase in conifer growth. / Forestry, Faculty of / Graduate

Phalaris arundinacea L. is an aggressive species that can dominate wetlands by producing monotypic stands that suppress native vegetation. In this study invasion windows were created for native species in monotypic stands of P. arundinacea with either fire or herbicide. Three native species groups, herbaceous plants, herbaceous seeds, and woody shrubs, were planted into plots burned or treated with herbicide in the early spring. Fire did not create an effective invasion window for native species; there was no difference in P. arundinacea root and shoot biomass or cover between burned and control plots (p ≥ 0.998). Herbicide treatment created an invasion window for native species by reducing P. arundinacea root and shoot biomass for two growing seasons, but that invasion window was fast closing by the end of the second growing season because P. arundinacea shoot biomass had nearly reached the shoot biomass levels in the control plots (p = 0.053). Transplant mortality, frost, and animal herbivory prevented the herbaceous species and woody seedlings from becoming fully established in the plots treated with herbicide during the first year of the experiment. Transplanted monocots had a greater survival than dicots. By the second growing season the herbaceous group had the greatest mean areal cover (5%), compared to the woody seedlings (3%) and seed group (0%). Long-term monitoring of the plots will determine whether the herbaceous transplants will compete effectively with P. arundinacea and whether the woody species will survive, shade the P. arundinacea, and accelerate forest succession.

Some of the factors influencing the performance of bromoxynil, 4(2,4-DB), or a companion crop for weed control in seedling alfalfa were studied in the greenhouse and at field locations in Farmington and Logan , Utah. The effect of application rate , stage of growth, temperature, and soil moisture on the phytotoxicity of bromoxynil and 4(2,4-DB) to alfalfa and weeds were studied. Alfalfa yields were increased by 4(2,4-DB) at all rates and stages of application. All rates and stages of bromoxynil treatment except the one-fourth pound per acre three to four trifoliate application resulted in alfalfa yields below that of the control. The use of a companion crop was not conducive to the growth and development of alfalfa although it did control the weeds . Bromoxynil at all rates and at both stages of application resulted in effective mustard control. Mustard control in the 4(2,4- DB) plots was excellent at the early stage of application but required three- fourths pound per acre for control at the later stage of weed growth . Pigweed control was rather ineffective in bromoxynil plots at Logan where moisture was optimum, but effective in plots at farmington where moisture was limited for 18-20 days following application. The density of the pigweed stand in bromoxynil treatments at Logan was attributed to an influx of weed growth following initial control of weeds . Control of pigweed by 4(2 , 4- DB) was in excess of 90 percent at the four to five leaf stage of weed growth.

Research was conducted in 2012 and 2013 to evaluate the use of saflufenacil in rice (Oryza sativa L.). Studies included a preemergence evaluation of different rates of saflufenacil in comparison to one rate of carfentrazone, a postemergence evaluation of saflufenacil at different rates and carfentrazone at one rate at different postemergence timings, an adjuvant evaluation to assess rice injury and weed control from different adjuvants when mixed with saflufenacil, a Clearfield program evaluation where saflufenacil was compared to other broadleaf herbicides in a Clearfield weed control program, and a cultivar tolerance evaluation where postemergence applications of saflufenacil were compared to carfentrazone on five different commercial rice cultivars.

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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.