Master of Science / Department of Agronomy / Dallas E. Peterson / During 2015 and 2016, five site years of research were implemented in double crop soybean after winter wheat at experiment fields in Kansas near Manhattan, Hutchinson, and Ottawa to assess various non-glyphosate herbicide treatments at three different application timings for control of Palmer amaranth (Amaranthus palmeri S. Wats.) and common waterhemp (Amaranthus rudis Sauer). Spring-post (SP) treatments with residual control of Palmer amaranth and waterhemp were applied in the winter wheat at Feekes 4 and resulted in less than 50% control of Palmer amaranth and waterhemp at the time of double crop soybean planting. Pre-harvest treatments were applied two weeks before winter wheat harvest. 2,4-D resulted in highly variable Palmer amaranth and waterhemp control whereas flumioxazin resulted in comparable control to PRE treatments that contained paraquat plus a residual herbicide. Excellent Palmer amaranth and waterhemp control was observed at 1 week after planting (WAP) double crop soybean with a preemergence (PRE) paraquat application; however, reduced control of Palmer amaranth and waterhemp was noted at 8WAP due to extended emergence. Palmer amaranth and waterhemp control was 85% or greater at 8WAP for most PRE treatments that included a combination of paraquat plus residual herbicides. PRE treatments that did not include the combination of paraquat and residual herbicides did not provide acceptable control. A second set of field experiments were established in 2015 and 2016 near Manhattan, Hutchinson, and Ottawa to assess residual Palmer amaranth and waterhemp control with very-long-chain-fatty acid (VLFCA) inhibiting herbicides. Acetochlor (non-encapsulated and encapsulated), alachlor, dimethenamid-P, metolachlor, S-metolachlor, and pyroxasulfone as well as the microtubule inhibiting herbicide pendimethalin were applied at three different field use rates (high, middle, and low) based on labeled rate ranges for soybean as PRE treatments in a non-crop scenario after the plot was clean tilled with a field cultivator. The experiment was conducted one time in 2015 and four times in 2016 at two different locations for a total of five site years of data. PRE applications were made June 1, 2015, near Manhattan. PRE applications in 2016 were made in April at locations near Hutchinson and Ottawa; the second run of the experiment was applied in June at the same locations on a different set of plot areas. At Manhattan pyroxasulfone, S-metolachlor, and dimethenamid-P resulted in the highest Palmer amaranth control at 4WAT. At Hutchinson, pyroxasulfone resulted in superior Palmer amaranth control compared to dimethenamid-P and pendimethalin at 4WAT and 8WAT. At Ottawa, acetochlor, S-metolachlor, and pyroxasulfone resulted in higher waterhemp control than alachlor and pendimethalin at 4WAT and 8WAT.

Morphological and anatomical effects of pyrazon, 5-amino-4-chloro-2-phenyl-3(2H)-pyridazinone, on Phaseolus vulgaris L. and Amaranthus retroflexus L. were studied after treatment of seeds or seedlings at various pyrazon concentration, exposure times and environmental regimes. Beans treated with pyrazon developed various chlorotic and necrotic symptoms on the unifoliate leaves. Chlorosis and necrosis were observed first on the leaf margins. Beans treated with pyrazon under a complete dark regime developed symptoms much later than those under an alternating light and dark regime. Pyrazon treated pigweed displayed symptoms similar to those on beans. Pyrazon induced abnormal chloroplasts and graded cellular collapse in the unifoliate leaves of beans and cotyledons of pigweed. The severity and/or extent to which morphological and anatomical symptoms developed were dependent upon herbicide concentration, exposure and treatment regime.

Cucumber (Cucumis sativus L.), pumpkin (Cucurbita maxima Duch. ex Lam.), and summer squash (Cucurbita pepo L.) are economically important crops in Virginia. Only a few herbicides are registered for weed control in these crops. Halosulfuron is a sulfonylurea herbicide which controls several broadleaf weeds and yellow nutsedge (Cyperus esculentus L.). Cucurbit crops have some tolerance to this herbicide. The efficacy of halosulfuron for control of several weed species and tolerance of four vine crops to halosulfuron were investigated in field and greenhouse studies in 1999, 2000, and 2001. In the field, halosulfuron was applied to cucumber, pumpkin, zucchini squash, and yellow summer squash at 4, 9, 18, and 27 g ai/ha preemergence (PRE) and postemergence (POST) in combination with clomazone at 174 g ai/ha plus ethalfluralin applied PRE at 630 g/ha. Crop injury, weed control, and crop yield was collected from the field studies. Weed control by halosulfuron was dependent upon application method. Halosulfuron applied preemergence controlled only common ragweed (Ambrosia artemisiifolia L.) and smooth pigweed (Amaranthus hybridus L.). Postemergence halosulfuron controlled common ragweed, smooth pigweed, morningglory species (Ipomoea spp.), yellow nutsedge, and rice flatsedge (Cyperus iria L.). All four crops treated with halosulfuron produced yields equal to or higher than the crops receiving clomazone and ethalfluralin alone or the hand-weeded check. In the greenhouse, tolerance of cultivars of each crop to halosulfuron was investigated with the same rates applied in the field. Cultivars responded similar to postemergence halosulfuron applications with respect to fresh and dry weights in all four crops. The response of several populations of acetolactate synthase inhibiting (ALS) resistant smooth pigweed to postemergence halosulfuron was also investigated. Halosulfuron activity against ALS-inhibitor resistant smooth pigweed was population dependent. In the greenhouse, postemergence halosulfuron at the same rates used in the field studies controlled yellow nutsedge. / Master of Science

A planta daninha Amaranthus palmeri é nativa dos Estados Unidos, porém foi pela primeira vez relatada no Brasil no ano de 2015. Embora comprovadamente com resistência múltipla aos herbicidas inibidores da ALS e da EPSPS, até o momento não foram investigadas as bases moleculares da resistência. Além disso, por causa da recente introdução da planta daninha no país, alternativas de manejo com culturas tolerantes a herbicidas necessitam ser estudadas. Sendo assim, os objetivos desse trabalho são de caracterizar a espécie de planta daninha introduzida no país, identificar os mecanismos de resistência aos herbicidas inibidores da ALS e da EPSPS presentes no biótipo, e propor abordagens de manejo em ambientes dos novos eventos transgênicos resistentes a herbicidas. Um bioensaio utilizando marcadores genéticos foi desenvolvido para confirmar que a população coletada no estado do Mato Grosso (BR-R) é A. palmeri, e não A. tuberculatus, outra espécie dióica do gênero Amaranthus. Os resultados de experimentos de curvas de dose-resposta e acúmulo de chiquimato indicaram que a BR-R possui alto nível de resistência, com DL50 de 4.426 e 3.400 g glyphosate ha-1 no primeiro e segundo experimento, respectivamente, mais que o dobro da dose típicamente recomendada para o controle da espécie e, adicionalmente, observou se acúmulo mínimo de chiquimato a concentração de 1 mM nos tecidos das plantas tratadas com o herbicida. BR-R também foi resistente a herbicidas dos grupos químicos das sulfoniluréias e imidazolinonas. O mecanismo de resistência ao glyphosate encontrado nesta população foi a super expressão gência, através do aumento no número de cópias do gene da EPSPS no genoma da planta BR-R, entre 50 e 179 cópias adicionais. Além disso, duas substituições de aminoácidos foram observadas na sequência da ALS, W574L e S653N, conferindo resistência tanto a sulfoniluréias quanto a imidazolinonas. No experimento utilizandos os herbicidas correspondentes às culturas geneticamente modificadas com novos traits de tolerância a herbicidas observou se, de uma forma geral, que as associações de herbicidas apresentaram níveis de controle mais satisfatórios. Assim, esta pesquisa confirma a introdução de da espécie A. palmeri no Brasil, assim como a resistência múltipla aos herbicidas inibidores da EPSPS e da ALS. Seu manejo é mais eficaz através da associação de herbicidas, garantindo assim o uso racional das novas tecnologias de culturas geneticamente modificadas com tolerância a herbicidas. / Palmer Amaranth (Amaranthus palmeri) is a weed species native to the United States, but it was reported in Brazil for the first time in 2015. Despite this population being resistant to EPSPS and ALS inhibitors, the molecular basis of its multiple resistance is unknown up to date. Because of this species introduction to Brazil, alternatives of management with the new herbicide-tolerant crops technologies need to be studied. The objectives of this research are to characterize the weed species introduced to Brazil, identify the mechanisms conferring resistance to ALS and EPSPS inhibitors herbicides, and to propose management approaches in environments with the new genetically modified herbicide-tolerant crops. A genotyping bioassay using genetic markers was developed to confirm that the species collected in the state of Mato Grosso (BR-R) is indeed A. palmeri and not A. tuberculatus, another dioceous species in the Amaranthus genus. Dose-response experiments and shikimate accumulation bioassay data indicate high level of resistance, with LD50 of 4,426 and 3,400 g glyphosate ha-1 in the first and second experiments, respectively, higher than the double rate tipically recommended to control it, and minimal accumulation in BR-R with 1 mM of glyphosate in treated plants in the leaf disks assay. BR-R also was resistanto to sulfonilurea and imidazolinone herbicides. The mechanism conferring resistance to glyphosate identified in this population was gene amplification, with increased EPSPS copy number - between 50 and 179 more copies in BR-R. Besides, two target-site mutations were identified in the ALS gene sequencing, W574L and S653N, conferring resistance to sulfonilureas and imidazolinones. The weed control experiment, overal, herbicide tank mixtures achieved higher levels of control. Therefore, this research confirms the introduction of A. palmeri to Brazil, as well as its multiple resistance to EPSPS and ALS inhibitor herbicides. Its control is more efficient with herbicide mixtures, which guarantees more susteinable use of the new herbicide-tolerant crop technologies.

As espécies de plantas classificadas no gênero Amaranthus são frequentemente encontradas infestando áreas agrícolas brasileiras, contudo existem poucos trabalhos que avaliaram as características biológicas e o controle destas espécies. Assim sendo, este trabalho foi conduzido com o objetivo de analisar a germinação, o crescimento e o desenvolvimento, estimar a área foliar, a competitividade e a susceptibilidade a herbicidas de cinco espécies de plantas daninhas do gênero Amaranthus As espécies de Amaranthus estudadas foram: A. deflexus (caruru-rasteiro), A. hybridus (carururoxo), A. retroflexus (caruru-gigante), A. spinosus (caruru-de-espinho) e A. viridis (caruru-de-mancha). O experimento que avaliou a germinação foi conduzido no Laboratório de Análise de Sementes e os demais em casa-de-vegetação do Departamento de Produção Vegetal da ESALQ/USP, Piracicaba - SP, no período compreendido entre março e dezembro de 2005. Com relação à germinação, constatou-se que variações na disponibilidade de luz e temperatura interferem em todas as espécies de Amaranthus, em que as maiores taxas de germinação foram obtidas em condição de fotoperíodo com alternância de temperatura (8h-luz-30°C / 16h-escuro-20°C). Em condições menos favoráveis, A. viridis e A. hybridus obtiveram maiores taxas de germinação que as demais espécies. Em geral, A. deflexus e A. spinosus foram as espécies de plantas daninhas que apresentaram os menores índices de velocidade de germinação. Sobre o crescimento e desenvolvimento, constatou-se que A. deflexus foi a espécie com ciclo vegetativo mais curto, menor acúmulo de massa seca e área foliar; por outro lado, A. retroflexus e A. hybridus foram aquelas que alcançaram os maiores valores para estas variáveis. A estimativa de área foliar demonstrou que a equação linear passando pela origem (Ar=a.(C.L)) foi adequada para ajustar a relação entre as medidas lineares do limbo e a área foliar real de todas as espécies. Com relação à competição, concluiu-se que a cultura do feijoeiro é melhor competidora que todas as espécies de plantas daninhas do gênero Aramanthus que foram utilizadas neste trabalho, quando cultivadas em igualdade de proporções. A. deflexus e A. viridis foram as espécies com a fenologia menos afetada pela competição com o feijoeiro; a competição intraespecífica foi a mais prejudicial à cultura do feijoeiro, o que sugere que os danos causados pelas plantas daninhas estão mais relacionados com as altas densidades em que estas ocorrem do que com a habilidade competitiva intrínseca das espécies. O controle químico obtido para as espécies de Aramanthus avaliadas neste trabalho demonstrou diferenças de susceptibilidade aos herbicidas aplicados em pósemergência, principalmente ao trifloxysulfuron-sodium e ao chlorimuron-ethyl, em que A. deflexus foi a espécie menos suscetível, seguido por A. spinosus, A. viridis, A. hybridus e A. retroflexus. / Plant species classified in the Aramanthus genus are frequently found infesting brazilian agricultural areas, although there are few researches that evaluated the biological characteristics and the control of these species. Therefore, this work was conducted with the objective of analyzing the germination, the growth and the development, estimating the leaf area, the competitiveness and the susceptibility to herbicides of five weed species of the Aramanthus genus. The species of Aramanthus studied were: A. deflexus, A. hybridus, A. retroflexus, A. spinosus and A viridis. The experiment that evaluated the germination was conducted in the Laboratory of Seed Analyses and the others in the greenhouse of the Crop Science Department of ESALQ/USP, Piracicaba - SP, in the period comprehended between March to December 2005. About the germination, it was established that variation in the availability of light and temperature interferes in all the species of Aramanthus and the highest levels of germination were obtained in condition of photoperiod with alternating temperature (8h-light-30°C / 16h-dark-20°C). In less favorable conditions, A. viridis and A. hybridus obtained higher germination levels than all the other species. In general, A. deflexus and A. spinosus were the weed species that presented the lowest rates of germination speed. About the growth and development, it was observed that A. deflexus was the species with shortest vegetative cycle, the lowest dry mass and leaf area accumulation; however, A. retroflexus and A. hybridus were the species which reached the highest values for these variables. The leaf area estimation showed that the linear equation crossing the origin (Ar=a.(C.L)) was adequate to adjust the correlation between the linear blade dimensions and the real leaf area for all the species. About competition, it was concluded that the crop of common bean is more competitive than all the weed species of the Aramanthus genus that were studied in this work, when grown in equivalent proportion; A. deflexus and A. viridis were the species which phenology was less affected by the competition with common bean; the intraspecific competition was the most damaging to the crop of common bean, what suggests that the damages caused by the weeds are more connected with its high density of infestation than the intrinsic competitive ability of the species. The control obtained for the Aramanthus species evaluated in this research presented differences of susceptibility to post-emergence applied herbicides, mainly to trifloxysulfuron-sodium and chlorimuron-ethyl, which A. deflexus was the least susceptible species, followed by A. spinosus, A. viridis, A. hybridus and A. retroflexus.

A planta daninha Amaranthus palmeri é nativa dos Estados Unidos, porém foi pela primeira vez relatada no Brasil no ano de 2015. Embora comprovadamente com resistência múltipla aos herbicidas inibidores da ALS e da EPSPS, até o momento não foram investigadas as bases moleculares da resistência. Além disso, por causa da recente introdução da planta daninha no país, alternativas de manejo com culturas tolerantes a herbicidas necessitam ser estudadas. Sendo assim, os objetivos desse trabalho são de caracterizar a espécie de planta daninha introduzida no país, identificar os mecanismos de resistência aos herbicidas inibidores da ALS e da EPSPS presentes no biótipo, e propor abordagens de manejo em ambientes dos novos eventos transgênicos resistentes a herbicidas. Um bioensaio utilizando marcadores genéticos foi desenvolvido para confirmar que a população coletada no estado do Mato Grosso (BR-R) é A. palmeri, e não A. tuberculatus, outra espécie dióica do gênero Amaranthus. Os resultados de experimentos de curvas de dose-resposta e acúmulo de chiquimato indicaram que a BR-R possui alto nível de resistência, com DL50 de 4.426 e 3.400 g glyphosate ha-1 no primeiro e segundo experimento, respectivamente, mais que o dobro da dose típicamente recomendada para o controle da espécie e, adicionalmente, observou se acúmulo mínimo de chiquimato a concentração de 1 mM nos tecidos das plantas tratadas com o herbicida. BR-R também foi resistente a herbicidas dos grupos químicos das sulfoniluréias e imidazolinonas. O mecanismo de resistência ao glyphosate encontrado nesta população foi a super expressão gência, através do aumento no número de cópias do gene da EPSPS no genoma da planta BR-R, entre 50 e 179 cópias adicionais. Além disso, duas substituições de aminoácidos foram observadas na sequência da ALS, W574L e S653N, conferindo resistência tanto a sulfoniluréias quanto a imidazolinonas. No experimento utilizandos os herbicidas correspondentes às culturas geneticamente modificadas com novos traits de tolerância a herbicidas observou se, de uma forma geral, que as associações de herbicidas apresentaram níveis de controle mais satisfatórios. Assim, esta pesquisa confirma a introdução de da espécie A. palmeri no Brasil, assim como a resistência múltipla aos herbicidas inibidores da EPSPS e da ALS. Seu manejo é mais eficaz através da associação de herbicidas, garantindo assim o uso racional das novas tecnologias de culturas geneticamente modificadas com tolerância a herbicidas. / Palmer Amaranth (Amaranthus palmeri) is a weed species native to the United States, but it was reported in Brazil for the first time in 2015. Despite this population being resistant to EPSPS and ALS inhibitors, the molecular basis of its multiple resistance is unknown up to date. Because of this species introduction to Brazil, alternatives of management with the new herbicide-tolerant crops technologies need to be studied. The objectives of this research are to characterize the weed species introduced to Brazil, identify the mechanisms conferring resistance to ALS and EPSPS inhibitors herbicides, and to propose management approaches in environments with the new genetically modified herbicide-tolerant crops. A genotyping bioassay using genetic markers was developed to confirm that the species collected in the state of Mato Grosso (BR-R) is indeed A. palmeri and not A. tuberculatus, another dioceous species in the Amaranthus genus. Dose-response experiments and shikimate accumulation bioassay data indicate high level of resistance, with LD50 of 4,426 and 3,400 g glyphosate ha-1 in the first and second experiments, respectively, higher than the double rate tipically recommended to control it, and minimal accumulation in BR-R with 1 mM of glyphosate in treated plants in the leaf disks assay. BR-R also was resistanto to sulfonilurea and imidazolinone herbicides. The mechanism conferring resistance to glyphosate identified in this population was gene amplification, with increased EPSPS copy number - between 50 and 179 more copies in BR-R. Besides, two target-site mutations were identified in the ALS gene sequencing, W574L and S653N, conferring resistance to sulfonilureas and imidazolinones. The weed control experiment, overal, herbicide tank mixtures achieved higher levels of control. Therefore, this research confirms the introduction of A. palmeri to Brazil, as well as its multiple resistance to EPSPS and ALS inhibitor herbicides. Its control is more efficient with herbicide mixtures, which guarantees more susteinable use of the new herbicide-tolerant crop technologies.

As espécies de plantas classificadas no gênero Amaranthus são frequentemente encontradas infestando áreas agrícolas brasileiras, contudo existem poucos trabalhos que avaliaram as características biológicas e o controle destas espécies. Assim sendo, este trabalho foi conduzido com o objetivo de analisar a germinação, o crescimento e o desenvolvimento, estimar a área foliar, a competitividade e a susceptibilidade a herbicidas de cinco espécies de plantas daninhas do gênero Amaranthus As espécies de Amaranthus estudadas foram: A. deflexus (caruru-rasteiro), A. hybridus (carururoxo), A. retroflexus (caruru-gigante), A. spinosus (caruru-de-espinho) e A. viridis (caruru-de-mancha). O experimento que avaliou a germinação foi conduzido no Laboratório de Análise de Sementes e os demais em casa-de-vegetação do Departamento de Produção Vegetal da ESALQ/USP, Piracicaba - SP, no período compreendido entre março e dezembro de 2005. Com relação à germinação, constatou-se que variações na disponibilidade de luz e temperatura interferem em todas as espécies de Amaranthus, em que as maiores taxas de germinação foram obtidas em condição de fotoperíodo com alternância de temperatura (8h-luz-30°C / 16h-escuro-20°C). Em condições menos favoráveis, A. viridis e A. hybridus obtiveram maiores taxas de germinação que as demais espécies. Em geral, A. deflexus e A. spinosus foram as espécies de plantas daninhas que apresentaram os menores índices de velocidade de germinação. Sobre o crescimento e desenvolvimento, constatou-se que A. deflexus foi a espécie com ciclo vegetativo mais curto, menor acúmulo de massa seca e área foliar; por outro lado, A. retroflexus e A. hybridus foram aquelas que alcançaram os maiores valores para estas variáveis. A estimativa de área foliar demonstrou que a equação linear passando pela origem (Ar=a.(C.L)) foi adequada para ajustar a relação entre as medidas lineares do limbo e a área foliar real de todas as espécies. Com relação à competição, concluiu-se que a cultura do feijoeiro é melhor competidora que todas as espécies de plantas daninhas do gênero Aramanthus que foram utilizadas neste trabalho, quando cultivadas em igualdade de proporções. A. deflexus e A. viridis foram as espécies com a fenologia menos afetada pela competição com o feijoeiro; a competição intraespecífica foi a mais prejudicial à cultura do feijoeiro, o que sugere que os danos causados pelas plantas daninhas estão mais relacionados com as altas densidades em que estas ocorrem do que com a habilidade competitiva intrínseca das espécies. O controle químico obtido para as espécies de Aramanthus avaliadas neste trabalho demonstrou diferenças de susceptibilidade aos herbicidas aplicados em pósemergência, principalmente ao trifloxysulfuron-sodium e ao chlorimuron-ethyl, em que A. deflexus foi a espécie menos suscetível, seguido por A. spinosus, A. viridis, A. hybridus e A. retroflexus. / Plant species classified in the Aramanthus genus are frequently found infesting brazilian agricultural areas, although there are few researches that evaluated the biological characteristics and the control of these species. Therefore, this work was conducted with the objective of analyzing the germination, the growth and the development, estimating the leaf area, the competitiveness and the susceptibility to herbicides of five weed species of the Aramanthus genus. The species of Aramanthus studied were: A. deflexus, A. hybridus, A. retroflexus, A. spinosus and A viridis. The experiment that evaluated the germination was conducted in the Laboratory of Seed Analyses and the others in the greenhouse of the Crop Science Department of ESALQ/USP, Piracicaba - SP, in the period comprehended between March to December 2005. About the germination, it was established that variation in the availability of light and temperature interferes in all the species of Aramanthus and the highest levels of germination were obtained in condition of photoperiod with alternating temperature (8h-light-30°C / 16h-dark-20°C). In less favorable conditions, A. viridis and A. hybridus obtained higher germination levels than all the other species. In general, A. deflexus and A. spinosus were the weed species that presented the lowest rates of germination speed. About the growth and development, it was observed that A. deflexus was the species with shortest vegetative cycle, the lowest dry mass and leaf area accumulation; however, A. retroflexus and A. hybridus were the species which reached the highest values for these variables. The leaf area estimation showed that the linear equation crossing the origin (Ar=a.(C.L)) was adequate to adjust the correlation between the linear blade dimensions and the real leaf area for all the species. About competition, it was concluded that the crop of common bean is more competitive than all the weed species of the Aramanthus genus that were studied in this work, when grown in equivalent proportion; A. deflexus and A. viridis were the species which phenology was less affected by the competition with common bean; the intraspecific competition was the most damaging to the crop of common bean, what suggests that the damages caused by the weeds are more connected with its high density of infestation than the intrinsic competitive ability of the species. The control obtained for the Aramanthus species evaluated in this research presented differences of susceptibility to post-emergence applied herbicides, mainly to trifloxysulfuron-sodium and chlorimuron-ethyl, which A. deflexus was the least susceptible species, followed by A. spinosus, A. viridis, A. hybridus and A. retroflexus.

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.

Landfills have served as the major sites for waste disposal in both developed and developing countries. Upon closure of a landfill site, the surface could be converted to a golf course, recreation park, playground, animal refuge, tennis court and industrial site. Even when closed, landfills still have the potential to contaminate the surrounding environment as a result of the migration of leachate from decomposing waste contained in the site. This study focused on assessing the impacts of a closed landfill on soils and plants at Lumberstewart closed landfill site in Bulawayo, Zimbabwe. Soil samples were collected at three different depths (0-30 cm, 30 - 60 cm and 60-90 cm) at the landfill and a control site. The soil samples were analysed for their texture, pH, electrical conductivity, organic matter content, cation exchange capacity and concentrations of Cd, Cu, Cr, Fe, Ni and Zn. Samples of jimson weed and pigweed growing at the closed landfill and the control site were collected from the same sites where soil samples were collected, and the concentrations of the same set of heavy metals in these weeds determined. Soil samples were digested using EPA method 3050B: Acid Digestion of Sediments, Sludge and soils whereas nitric acid and hydrogen peroxide was used for digestion of plant samples. Both plant and soil digests were analyzed for heavy metals concentrations using Flame Atomic Absorption Spectrometry (AAS). Soils from the landfill as well as the control site had a high content of sand with soil pH values which were alkaline. The electrical conductivity values of the soil samples were relatively low ranging from 0.39 to 1.67 dS/m, indicating low levels of salts in soils at the landfill. The concentrations of heavy metals at the closed landfill site were higher than the control site. Heavy metals concentrations in soils at the closed landfill followed the order Fe>Zn>Cu>Cr>Ni>Cd. Results indicated that Fe was exceptionally higher than the other metals with concentration values averaging 45690±17255 mg/kg. Cadmium on the other hand had the least concentration with values of 0.01±0.00 mg/kg. Values of Enrichment Factors of heavy metals around the soil at different depths indicated that the enrichment of heavy metals increased with depth at the landfill up to 30-60 cm after which a decrease was observed. Values for heavy metal Contamination Factor of soils around the landfill ranged from low concentration (CF<1) to very high concentration (CF>6). The Pollution Load Index (PLI) values for the soil at the Lumberstewart landfill indicated that all sites were polluted (PLI>1). Site 6 had significantly higher mean concentration of heavy metals in soils at the landfill whereas site 11 had the least. The concentrations of Cd and Ni in soils at the landfill were below permissible limits of South African National Norms and Standards (NNS) as prescribed by NEMA (2008) in South Africa whereas Cr, Cu and Zn in soils were above the NNS permissible limits. Heavy metal concentrations in soils at the landfill were above World Health (WHO) permissible limits except for Cd which was equal (0.01 mg/kg) to the permissible values of Cd in the soils at sites 5, 8, 9, 10, 11 and 12. Mean concentrations of heavy metals in jimson weed and pigweed were in the order Fe>Zn>Cu>Cr>Ni>Cd. The concentrations of Cd, Cr, Cu, Fe and Zn in both plants from all sites at the landfill were significantly higher than the control site. Heavy metal transfer coefficient for both plants indicated that heavy metal uptake was more species dependent than soil heavy metal concentration dependent. The results from this research indicate that though the Lumberstewart Landfill has been closed, it is still affecting the soils in the vicinity of the landfill. Plants and water around the Lumberstewart closed landfill could be at risk from heavy metal contamination. High concentrations of heavy metals observed in the soil could present a health risk to communities should they decide to use the landfill site for arable purposes. / Environmental Sciences / M. Sc. (Environmental Science)