Doctor of Philosophy / Department of Agronomy / J. Anita Dille / Integrated weed management (IWM) is an ecological approach to weed control that reduces dependence on herbicides through understanding of weed biology and involves using multiple weed control measures including cultural, chemical, mechanical and biological methods. The critical period of weed control is the duration of the crop life cycle in which it must be kept weed-free to prevent yield loss from weed interference. Eight experiments were conducted throughout Kansas between October 2010 and June 2012 to identify this period in winter wheat grown under dryland and irrigated conditions. Impact of henbit and downy brome density on winter wheat yields were evaluated on four farmer’s fields with natural populations and on a research station with overseeded populations. Henbit density up to 156 plants m-2 did not affect winter wheat yield, while downy brome at a density of 40 plants m-2 reduced yield by 33 and 13% in 2011 and 2012, respectively. In the presence of downy brome, winter wheat should be kept weed-free approximately 30 to 45 days after planting to prevent yield loss; otherwise, weeds need to be removed immediately following release from winter dormancy to prevent yield loss due to existing weed populations. Flumioxazin and pyroxasulfone are herbicides registered for use in winter wheat, soybean and corn for control of broadleaf and grass weeds. Flumioxazin and pyroxasulfone were evaluated for plant response to localized herbicide exposure to roots, shoots, or both roots and shoots utilizing a novel technique. Two weed species, ivyleaf morningglory and shattercane, as well as two crops, wheat and soybean, were evaluated for injury after localized exposures. The location and expression of symptoms from the flumioxazin and pyroxasulfone herbicides were determined to be the shoot of seedling plants. The utilization of preemergence herbicides in winter wheat is not a common practice, although application may protect winter wheat from early season yield losses as determined by the critical weed-free period. Kansas wheat growers should evaluate the presence and density of weed species to determine which weed management strategy is most advantageous to preserving winter wheat yield.

Submitted by Jorge Silva (jorgelmsilva@ufrrj.br) on 2018-08-22T18:44:56Z No. of bitstreams: 1 2017 - Thain? Alves dos Santos.pdf: 3011465 bytes, checksum: dfa12c411a3f74638a41876a450cb72d (MD5) / Made available in DSpace on 2018-08-22T18:44:56Z (GMT). No. of bitstreams: 1 2017 - Thain? Alves dos Santos.pdf: 3011465 bytes, checksum: dfa12c411a3f74638a41876a450cb72d (MD5) Previous issue date: 2017-02-20 / CAPES / The presence of exotic grasses in areas for reforestation is one of the main obstacles to the growth and survival of planted individuals, whether through competition for resources and / or allelopathy. Thus, the first study of this dissertation aimed to evaluate the effect of the presence of Urochloa brizantha on growth of tree species of the Atlantic Forest biome, in Serop?dica-RJ. The study included five experiments in a completely randomized design, each including one of the following species: Cedrela fissilis, Guazuma ulmifolia, Schinus terebinthifolius, Sapindus saponaria and Hymenaea courbaril. The treatments consisted of the presence or absence of U. brizantha in coexistence with the tree species. The experimental units consisted of vases containing 16 kg of soil. Monthly assessments of height, root collar diameter and seedling mortality were carried out. At 180 days post-planting the shoot and root dry masses of the tree and grass species were measured separately. The results showed strong interference of the grass on the growth of the forest species, with the shoot and root dry masses being the most affected growth variables. Among the species, C. fissilis presented high mortality when living with U. brizantha, reaching 83% of losses from the fifth month after planting. In the second study, the magnitude of competition for water, nutrients and allelopathy imposed by U. brizantha when in coexistence with Schinus terebinthifolius was evaluated. For this, a study was set up in greenhouse using as a principle the selective exclusion of competition for water, nutrients or the effect of allelopathy. The experimental units consisted of 18 kg vases with one molt of S. terebinthifolius. The experimental design consisted of a completely randomized complete factorial with three factors: (1) cohabitation or not with U. brizantha, planted in the density of 4 plants per vase; (2) supply of limiting nutrients (25% of the recommended dose) and non-limiting (200% of the recommended dose) and (3) limiting water supply (moisture maintained between wilt point at 50% field capacity) and non-limiting (humidity maintained between 60 to 80% of the field capacity). Monthly evaluations of seedling height and diameter were carried out. At 180 days, the dry masses of the shoot and root of the tree and grass species were measured. The results showed strong competition of the grass over the tree species. The presence of the grass decreased 30.5 cm the height, 1.58 mm the root collar diameter and 22.7 g and 9.5 g the shoot and root dry masses of S. terebinthifolius, respectively. The results indicated that competition for water is the main factor responsible for the reduction of S. terebinthifolius growth when living with U. brizantha, followed by competition for nutrients. The study did not allow to evaluate the existence of U. brizantha allelopathy on S. terebinthifolius, since it was not possible to concomitantly eliminate competition for water and nutrients in the proposed experimental model. The results of the two studies show the importance of the control of exotic grasses in reforestation projects with native species, for greater gains in growth and survival of introduced seedlings. / A presen?a de gram?neas ex?ticas em ?reas destinadas a reflorestamentos ? um dos principais entraves para o crescimento e sobreviv?ncia dos indiv?duos plantados, seja pela competi??o por recursos e/ou alelopatia. O primeiro estudo dessa disserta??o teve como objetivo avaliar o efeito da presen?a de Urochloa brizantha sobre o crescimento de esp?cies arb?reas do bioma Mata Atl?ntica, em Serop?dica-RJ. O estudo abrangeu cinco experimentos em delineamento inteiramente casualizado, cada um contendo uma das seguintes esp?cies: Cedrela fissilis, Guazuma ulmifolia, Schinus terebinthifolius, Sapindus saponaria e Hymenaea courbaril. Os tratamentos consistiram da presen?a ou aus?ncia de Urochloa brizantha em conviv?ncia com a muda da esp?cie florestal. As unidades experimentais constavam de vasos contendo 16 kg de solo. Foram realizadas mensalmente avalia??es de altura, di?metro do coleto e mortalidade das mudas. Aos 180 dias p?s-plantio mensurou-se a massa seca de parte a?rea e radicular da esp?cie arb?rea e da gram?nea, separadamente. Os resultados evidenciaram forte interfer?ncia do capim-braquiar?o sobre o crescimento das esp?cies florestais, sendo as massas seca de parte a?rea e radicular as vari?veis de crescimento mais afetadas. Dentre as esp?cies, C. fissilis apresentou alta mortalidade quando em conviv?ncia com U. brizantha, chegando a 83% de perdas a partir do quinto m?s ap?s o plantio. No segundo estudo foi avaliada a magnitude da competi??o por ?gua, nutrientes e alelopatia imposta por Urochloa brizantha quando em conviv?ncia com Schinus terebinthifolius. Para isso, um estudo foi montado em casa de vegeta??o utilizando como princ?pio a exclus?o seletiva da competi??o por ?gua, nutrientes ou do efeito de alelopatia. As unidades experimentais consistiram de vasos de 18 kg com uma muda de S. terebinthifolius. O delineamento experimental constituiu de um fatorial completo inteiramente casualizado com 3 fatores: (1) conviv?ncia ou n?o com U. brizantha, plantada na densidade de 4 mudas por vaso; (2) fornecimento de nutrientes limitante (25% da dose recomendada) e n?o-limitante (200% da dose recomendada) e (3) o fornecimento de ?gua limitante (umidade mantida entre ponto de murcha a 50% da capacidade de campo) e n?o-limitante (umidade mantida entre 60 a 80% da capacidade de campo). Foram realizadas mensalmente avalia??es de altura e di?metro do coleto das mudas. Aos 180 dias mensurou-se a massa seca da parte a?rea e radicular da esp?cie arb?rea e da gram?nea. Os resultados evidenciaram forte competi??o da gram?nea sobre a esp?cie arb?rea. O conv?vio com a gram?nea reduziu, em m?dia, em 30,5 cm a altura, em 1,58 mm o di?metro do coleto e em 22,7 g e 9,5 g as massas secas da parte a?rea e das ra?zes de S. terebinthifolius, respectivamente. Os resultados indicaram que a competi??o por ?gua ? o principal fator respons?vel pela redu??o do crescimento de S. terebinthifolius quando em conviv?ncia com U. brizantha, seguido pela competi??o por nutrientes. O estudo n?o possibilitou avaliar a exist?ncia de alelopatia de U. brizantha sobre S. terebinthifolius, visto que n?o foi poss?vel eliminar concomitantemente a competi??o por ?gua e nutrientes no modelo experimental proposto. Os resultados dos dois estudos executados evidenciam a import?ncia do controle de gram?neas ex?ticas em projetos de reflorestamento com esp?cies nativas, para maiores ganhos em crescimento e sobreviv?ncia das mudas introduzidas.

S-metolachlor is an effective herbicide used to control/suppress annual grasses, nutsedges and several broadleaf weeds in sweetpotato. However, a decline in storage root quality and yield has been reported under certain environmental conditions. Information is limited on the effect of S-metolachlor application followed immediately by rainfall on sweetpotato growth and development under different temperatures, as well as the optimum application time. Therefore, the objectives of this study were to evaluate sweetpotato responses to interactive effects of S-metolachlor, temperature and rainfall, and to determine S-metolachlor optimum application time. A sunlit, controlled environment experiment was conducted to investigate sweetpotato response to S-metolachlor and rainfall immediately after application under different temperatures. Sweetpotato slips were transplanted into sandy soil filled pots. Treatment combinations included five levels of S-metolachlor, 0.00, 0.86, 1.72, 2.58 and 3.44 kg ha-1, two levels of rainfall, 0 and 38 mm and three temperatures, 25/17, 30/22 and 35/27 °C, day/night. After POST application of S-metolachlor and rainfall, all plants were transferred to sunlit growth chambers that were maintained at their respective temperatures and ambient CO2 concentration for 60 days. In another experiment, S-metolachlor application time was varied to investigate sweetpotato growth and development. Two levels of S-metolachlor 0.0 and 1.0 kg ha-1 and three application times 0, 5 and 10 days after transplanting (DAT) were used and plants were harvested five times, 5, 10, 15, 20 and 80 DAT to estimate plant growth and development. Shoot, root and total plant biomass yields declined with increasing concentration of S-metolachlor across temperatures. In addition, storage root yield and quality decline was S-metolachlor rate dependent and aggravated by rainfall immediately after herbicide treatment across temperatures. S-metolachlor was more injurious on most plant component parameters in the optimum and high temperatures where plant growth was vigorous than in the low temperatures. S-metolachlor application at 0 and 5 days affected sweetpotato growth, including storage roots, but delaying until 10 days minimized the injury. These results can be used to weigh the risk of crop injury against the weed control benefits of S-metolachlor when making management decisions, and to determine application time based on weather information.

<p dir="ltr">Sweetpotato (<i>Ipomoea batatas</i> L.) is a staple crop that provides nutritional benefits to humans globally, but it is subjected to yield loss when competing with weeds, especially during the early stage of establishment. Despite increased organic sweetpotato production in the United States, growers face challenges with limited weed management options and often resort to time-consuming and costly cultivation and hand-weeding. To address this challenge, experiments were developed to determine (1) the effect of sweetpotato cultivar on the critical weed-free period, (2) the effects of in-row plant spacing and cultivar selection on weed suppression and sweetpotato yield, and (3) the impact of buckwheat and silage tarps for row-middle weed control. 1) In 2022, field research was conducted at the Samuel G. Meigs Horticulture Research Farm (Meigs), Lafayette, IN, and at the Southwest Purdue Agricultural Center (SWPAC), Vincennes, IN to estimate the critical weed-free period for ‘Covington’, ‘Murasaki’, and ‘Monaco’ in the Midwest. The experiment was a split-plot design, with weed-free interval treatments as the main plot factor and cultivar as the subplot factor. Weeds were removed by hand and allowed to establish and compete with the crop beginning at 0, 14, 21, 28, 35, or 42 days after transplanting (DAP). As weed-free interval increased from 0 to 42 DAP, predicted total yield increased from 19 kg ha^-1 to 20,540 kg ha^-1for Covington, 3 kg ha^-1 to 11,407 kg ha^-1 for Monaco, and 125 kg ha^-1to 13,460 kg ha^-1for Murasaki at the Lafayette location. A threshold of ≤10% total yield reduction was achieved by maintaining sweetpotatoes weed-free 24 DAP for Covington, 20 DAP for Murasaki, and 33 DAP for Monaco. 2) In 2022 and 2023, studies were conducted at Meigs, Lafayette, IN and SWPAC, Vincennes, IN to evaluate in-row plant spacing and cultivars for weed control and sweetpotato yield. The experiment was a split-split plot design, with in-row spacings of 20, 30, and 40 cm as the main plot factor, weeding frequency (‘critical weed-free period’ and ‘weed free’) as the subplot factor, and sweetpotato cultivar (‘Covington’ and ‘Monaco’) as the sub-subplot factor. However, in 2022, we evaluated only in-row spacing and weeding frequency because of poor establishment of Monaco. In-row spacing had no significant effect on weed densities at 4, 5, and 6 WAP. As in-row spacing increased from 20 to 40 cm, total sweetpotato yield pooled across both locations in 2023 decreased from 30,223 to 21,209 kg ha^-1 for Covington and 24,370 to 20,848 kg ha^-1 for Monaco, however, jumbo yield increased for both cultivars. Findings from this study suggest that an in-row spacing of 20 cm may provide greater yield than the standard spacing, 30 cm, for both Monaco and Covington cultivars and could reduce weed interference through more rapid sweetpotato canopy closure. 3) The experiment was a randomized complete block design, with three row-middle treatments [tarp, buckwheat, and cultivation] and four replicates. Row-middle treatments were established immediately after transplanting ‘Covington’ slips 30 cm apart into raised bed plots consisting of a single row 6 m long and 2 m apart on-center. Buckwheat was planted three weeks after transplanting (WAP) at a rate of 108 kg ha^-1 in row-middle. Row-middles for the tarp treatment were covered for the entire growing season. Weed density at 6 WAP was 184 plants m^-2 for the buckwheat, and 162 plants m^-2 for the cultivation treatments. Total yield was 11,050 kg ha^-1 for the buckwheat, 19,790 kg ha^-1 for the cultivation, and 17,810 kg ha^-1 for the tarping treatments. Tarping effectively suppressed weeds and produced sweetpotato yields comparable to cultivation indicating potential for organic growers. Buckwheat yields were lower than those from tarping and cultivation.</p>