Adoption of glyphosate-resistant crops has resulted in increased glyphosate usage and decreased use of residual herbicides thus resulting in weed pressure shifts. Weeds that display multiple-resistance to glyphosate and other herbicide modes of action have become a concern in many parts of the United States. Incorporation of multiple herbicide resistance traits into multiple cropping systems, may facilitate weed resistance to additional herbicides. Furthermore, controlling volunteer crop stands containing multiple herbicide-resistance traits may be problematic in herbicide resistant crops. These volunteer crops will compete with the currently growing crop qualifying them as a weed. Therefore, this research was conducted to determine control options for: failed glyphosate resistant corn stands, and volunteer glyphosate resistant corn stands in glyphosate resistant cotton. Furthermore, research was conducted to determine what densities of glyphosate-resistant corn will cause cotton yield loss and if time of removal of these densities impacts cotton yield loss.

Horseweed has been documented in 70 countries and 40 different crops around the world and is listed as being a problem weed in no-till production systems. Horseweed has developed resistance to many herbicide modes of action including glycine. Field experiments were conducted from 2004 to 2006 in the Mississippi Delta to evaluate the field emergence of horseweed and most effective treatment programs for its control. Field emergence of horseweed was observed occurring primarily in the fall of the year, September through early November, when temperatures were between 15.6 to 23.4 C with later flushes occurring from late January through early April with temperatures ranging from 5.2 to 16 C. Tillage in September followed by herbicide in March gave 100% control of horseweed across all locations. Glyphosate + 2,4-D and glyphosate + dicamba were the best glyphosate-based treatments and provided 90% or better horseweed control 4 WAT both years. Glufosinate-based burndowns provided 81 to 97% horseweed control and soybean yields were generally similar with all glufosinate-based programs.

No description available.

No description available.

No description available.

Broomrapes are achlorophyllous holoparasites of many economically important dicotyledonous crops. As weeds, they cause reductions in crop yield, adversely affect crop quality, and result in loss of cultivated land due to reduced crop alternatives. Few effective control measures exist for broomrapes. One of the most promising approaches is the use of low rates of glyphosate in hosts with tolerance to the herbicide. Recently, availability of glyphosate-resistant crops has provided an alternative in broomrape infested areas. Knowledge about the nitrogen status of broomrapes is essential for developing new control strategies. Broomrapes have two potential sources of amino acids. First, the haustorium aids in the translocation of amino acids from the host plant to the parasites. Second, broomrapes may be able to synthesize some amino acids themselves and obtain the rest from the host. However, the relative importance of these two modes of acquiring amino acids by broomrapes is not clear. Osmotic stress has been implicated as a possible reason for inhibition of broomrape germination by nitrogen. To date, there has been no attempt to correlate osmotic potential with nitrogen induced inhibition of broomrape germination. Optimum temperatures for conditioning and germination are different among broomrape species. Although temperature is known to influence germination in broomrape, its effect on subsequent development of the parasitic seedling has not been studied. Studies were conducted to determine the use of glyphosate in controlling broomrape in common vetch that is tolerant to low rates of glyphosate, and to compare this response with broomrape control in oilseed rape that has been genetically engineered for glyphosate resistance. Glyphosate dose response studies using a commercial formulation and patterns of absorption, translocation, and metabolism, using ¹⁴C-glyphosate, were determined for both host crops. Glyphosate significantly reduced the growth of broomrape at 0.18 and 0.36 kg ae ha⁻¹> in common vetch and 0.25 to 0.75 kg ha⁻¹ in oilseed rape. More than 25% of translocated ¹⁴C-glyphosate in both host crops accumulated in broomrape tubercles. Broomrape parasitism caused a redistribution of translocated ¹⁴C-glyphosate in the roots of both host crops. Glyphosate was metabolized up to 25% in common vetch, but remained intact in oilseed rape. Studies were conducted to analyze amino acid composition of both nonparasitized and broomrape-parasitized hosts and associated broomrape after hydrolysis and phenylisothiocyanate derivatization of amino acids. Results indicated that amino acid concentrations of leaves of parasitized carrot plants were lower than those of the leaves of nonparasitized carrot plants. Broomrape tubercles had equal or higher amino acid concentrations compared to those of the leaves of nonparasitized carrot plants. Levels of free alanine and arginine concentrations of broomrape callus were higher than those of any other tissue of either carrot or broomrape. The effect of glyphosate on the host-broomrape interaction regarding amino acid metabolism was examined. Glyphosate generally increased the amino acid concentrations in common vetch and oilseed rape plants, and broomrape attachments. The aromatic amino acids, phenylalanine and tyrosine, did not differ from this pattern. Concentrations of certain amino acids in broomrape were similar to those of parasitized common vetch and parasitized oilseed rape, whereas levels of several others, were higher in broomrape attachments compared to the host plants. <I>In vitro</I> studies were conducted to determine the influence of osmotic potential and temperature on broomrape germination. Osmotic potential significantly affected germination and radicle elongation of broomrapes. No correlation was found between osmotic potential and ammonium-induced inhibition of germination of broomrapes. Temperature significantly influenced germination and radicle elongation of all broomrape species tested. / Ph. D.

Double-crop production of corn (Zea mays L.) for grain following the harvest of small grain is not currently practiced in Virginia. Historical precipitation and evapotransportation data indicate that delayed corn planting could result in a higher probability of moisture during critical periods of crop development. Double-crop corn may also reduce economic risk as two crops would be harvested in the same year. Field experiments were conducted in three Virginia locations in 1998 and 1999 to determine the herbicide inputs required for double-crop corn production relative to those required in full-season no-till corn production. Experiments were conducted in a split-plot, randomized complete block design with cropping system as the main plot and herbicide treatment as the subplot. Herbicide treatments included combinations of nonselective herbicides for no-till establishment and/or preemergence residual herbicides and/or selective postemergence herbicides in both production systems. Glyphosate-tolerant corn was planted in all experiments and postemergence glyphosate treatments were also evaluated. In each experiment, dependent variables included weed control by species evaluated throughout the season, as well as weed biomass and corn yield evaluated at the end of the growing season. Generally, nonselective herbicides were not required in the double-crop system where atrazine was applied as a preemergence treatment, or where selective postemergence treatments were applied. Where a significant proportion of the infestation was comprised of perennial species, however, atrazine treatments were not sufficient in the double-crop system. Postemergence glyphosate treatments provided excellent broad-spectrum weed control in this situation. In heavy annual grass infestations, postemergence glyphosate treatments provided superior weed control to preemergence treatments alone, and equivalent weed control to treatments in which both preemergence and postemergence herbicides were applied. Corn yield response to weed control and cropping system variables varied significantly between the 1998 and 1999 growing seasons. Where adequate late-season rainfall was received, economic return from small grain and corn crops in the double-crop system was higher than the return in the full-season system, particularly in infestations where the double-crop system allowed significant reduction in herbicide input. / Master of Science

Master of Science / Agronomy / Mithila Jugulam / Common waterhemp (Amaranthus rudis) is a problematic weed species of cropping systems throughout the Midwestern states, including Kansas. Recently, waterhemp populations from Kansas were found to have evolved resistance to the widely used herbicide glyphosate as a result of amplification of the 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS), the enzyme target of glyphosate. The objectives of this research were to 1) perform glyphosate dose-response study and determine the relationship between relative EPSPS genomic copies and EPSPS gene expression in glyphosate-resistant waterhemp, and 2) characterize the genomic configuration and distribution of EPSPS copies using florescence in situ hybridization (FISH) in three glyphosate-resistant waterhemp populations. Waterhemp populations from eastern Kansas were screened with 868 g ae haˉ¹ (field used rate) of glyphosate, and genomic DNA and total RNA was isolated from the survivors to determine the EPSPS genomic copies and EPSPS gene expression relative to the acetolactate synthase (ALS) gene using qPCR. Furthermore, waterhemp specific EPSPS probes were synthesized to perform florescence in situ hybridization (FISH) on these glyphosate-resistant plants. Results of these experiments indicate a positive correlation between level of glyphosate resistance, EPSPS copies, and their expression. As expected, a negative correlation was found between shikimate accumulation and EPSPS copies. Sequencing of the EPSPS gene showed no presence of the proline 106 mutation, which is known to be associated with glyphosate resistance suggesting that an insensitive EPSPS enzyme was not involved in the mechanism of glyphosate resistance. FISH analysis of resistant plants illustrated presence of amplified EPSPS copies on two homologous chromosomes, likely near the centromeric region. . This is the first report demonstrating a positive relationship between EPSPS copies and expressions, as well as chromosome configuration of EPSPS copies in glyphosate- resistant waterhemp from Kansas.

Em 2015, o caruru palmer (Amaranthus palmeri) foi identificado pela primeira vez no Brasil, na região do núcleo algodoeiro do estado de Mato Grosso, em áreas normalmente cultivadas com rotação das culturas de algodão, soja e milho. Esta espécie possui reconhecida importância internacional, no entanto, não se conhece seu comportamento biológico nos sistemas de produção brasileiros. Ainda, também é desconhecido o grau de suscetibilidade do biótipo introduzido no país aos herbicidas, principalmente ao glyphosate e inibidores da ALS, que são os principais herbicidas utilizados para seu controle em outros países. Deste modo, este trabalho foi desenvolvido com o objetivo de caracterizar o crescimento e desenvolvimento do biótipo de A. palmeri originário do Estado do Mato Grosso, em condição de casa-de-vegetação; caracterizar o nível de resistência deste biótipo ao herbicida glyphosate (inibidor da EPSPS); verificar a existência de resistência múltipla EPSPS-ALS, bem como resistência cruzada entre os grupos químicos dos herbicidas inibidores da ALS; além de testar herbicidas alternativos aplicados em condição de pós-emergência da planta daninha. O biótipo brasileiro de A. palmeri teve rápido desenvolvimento fenológico, com início de emissão de inflorescências aos 50 dias após semeadura; o desenvolvimento fenológico de A. palmeri teve ajuste linear conforme equação y =0,8866.x; o biótipo teve acúmulo máximo de 45 g planta-1, com pico de crescimento absoluto aos 60 DAS; o crescimento da espécie foi considerado moderado quando comparado às espécies nacionais de Amaranthus, bem como aos dados internacionais de A. palmeri. Quanto aos herbicidas inibidores da EPSPS, pôde-se concluir com segurança tratar-se de biótipo resistente ao herbicida glyphosate. Ainda, constatou-se resistência múltipla aos inibidores da EPSPS-ALS. Considerando-se somente os inibidores da ALS, trata-se de população com resistência cruzada entre sulfoniluréias - triazolopirimidinas - imidazolinonas. Estas plantas foram adequadamente controladas pelos seguintes tratamentos herbicidas (g ha-1): fomesafen a 250, lactofen a 168, mesotrione + atrazina a 120 + 1.500, tembotrione + atrazina a 75,6 + 1.500, amônio glufosinato a 400 e paraquat a 400 g i.a. ha-1. O estádio de aplicação de 2 a 4 folhas, com até 5 cm de altura, é o mais indicado para o controle da planta daninha. / In 2015, Palmer amaranth (Amaranthus palmeri) was firstly identified in Brazil, at the cotton nucleus region of the State of Mato Grosso, in areas usually maintained under cotton, soybean and corn crop rotation. This species has recognized importance worldwide, however its biological behavior in Brazilian cropping systems is unknown. In addition, it is also unknown the degree of herbicide susceptibility of the biotype introduced in the country, mainly its susceptibility to glyphosate and ALS inhibiting herbicides, that are the main products used to control this species in other countries. Therefore, this work was developed with the objective of characterizing growth and development of the A. palmeri biotype collected in the state of Mato Grosso, Brazil, under greenhouse condition; verifying the resistance level of this biotype to glyphosate (EPSPS inhibiting herbicide); verifying the existence of EPSPS-ALS multiple resistance, as well as crusade resistance between chemical groups of ALS-inhibiting herbicides; testing alternative herbicides for post-emergence control of this weed. Brazilian biotype of A. palmeri had fast phenological development, with beginning of flowering at 50 days after seeding. Species phenology was adjusted to the linear equation y =0,8866.x. In average, the maximum dry matter accumulated was 45 g plant-1, with edge of absolute growth at 60 DAS. In conclusion, growth parameters of the Brazilian biotype of A. palmeri were considered moderated when compared to national species of Amaranthus, as well as with international data of A. palmeri. Regarding to EPSPS inhibiting herbicides, it was possible to conclude that Brazilian biotype of A. palmeri is glyphosate resistant. Therefore, multiple resistance to EPSPS-ALS inhibiting herbicides was also identified. Considering exclusively ALS-inhibiting herbicides, this population has sulfonilurea-triazolopirimidine-imidazolinone crusade resistance. Plants were adequately controlled with the following herbicides (g ha-1): fomesafen at 250, lactofen at 168, mesotrione + atrazine at 120 + 1,500, tembotrione + atrazine a 75.6 + 1,500, ammonium-glufosinate at 400 and paraquat at 400. Phenological stage of 2 to 4 leaves, with up to 5 cm of height, was the most indicated to Palmer amaranth control.

Em 1998 foi aprovado no Brasil o evento GTS 40-3-2 (Roundup Ready&trade; - RR), que confere tolerância ao herbicida glyphosate em soja. Outra tecnologia de tolerância a herbicida disponível para soja é a Liberty Link&reg; - LL (A2704-12 e A5547-127), que confere tolerância ao glufosinate. O evento DAS44406-6 (Enlist E3&trade; - E3) confere tolerância ao glyphosate, 2,4-D e glufosinate. Assim, objetivou-se com o presente estudo avaliar os efeitos de glyphosate no desempenho agronômico e índices de clorofila de soja E3 e RR, aplicado em diferentes estádios de desenvolvimento. Avaliar os efeitos de glufosinate no desempenho agronômico e índices de clorofila de soja E3 e LL, aplicado em diferentes estádios de desenvolvimento. Avaliar efeitos do herbicida 2,4-D colina, isolado e em associação com glyphosate ou glufosinate, no desempenho agronômico e índices de clorofila de soja E3, para a aplicação em pós-emergência (V4). Foram conduzidos três experimentos, repetidos nas safras 2016/17 e 2017/18, em Mogi-Mirim, SP. O experimento I constituído da aplicação de glyphosate (1.440 g e.a. ha-1), os tratamentos foram dispostos em arranjo fatorial 2X4 (evento X estádio de desenvolvimento). Para o fator evento foram utilizados E3 e RR. Para estádio, controle (sem aplicação), V4, V6 e R2. O experimento II da aplicação de glufosinate (460 g i.a. ha-1), os tratamentos foram dispostos em arranjo fatorial 2X4 (evento X estádio de desenvolvimento). Para o fator evento foram utilizados E3 e LL. Para estádio, os mesmo do experimento I. O experimento III foi constituido da aplicação 2,4-D, glyphosate e glufosinate no estádio V4 da soja E3. Foram avaliados os sintomas de injúria, índices de clorofila, e variáveis relacionadas ao desempenho agronômico. Não foram obsevadas reduções nos índices de clorofila e no desempenho agronômico da soja. Constatou-se a seletividade equivalente de glyphosate para soja E3 e RR, independente do estádio de desenvolvimento. Assim como, a seletividade equivalente de glufosinate para soja E3 e LL, independente do estádio de desenvolvimento. Também constatou-se a seletividade de 2,4-D colina isolado ou em associações com glyphosate ou glufosinate em soja E3. / In 1998 the GTS 40-3-2 (Roundup Ready&trade; - RR) event, which confers tolerance to glyphosate herbicide on soybean. Another herbicide tolerance technology available for soybeans is Liberty Link&reg; - LL (A2704-12 and A5547-127), which confers tolerance to glufosinate. The DAS44406-6 (Enlist E3&trade; - E3) event confers tolerance glyphosate, 2,4-D and glufosinate. Thus, the aim of this study was to evaluate the effects of glyphosate on agronomic performance and chlorophyll indexes of E3 and RR soybean, applied at different stages of development. To evaluate the effects of glufosinate on the agronomic performance and chlorophyll indexes of E3 and LL soybean, applied at different stages of development. To evaluate the effects of 2,4-D (choline), isolated and in association with glyphosate or glufosinate, on agronomic performance and chlorophyll indexes of E3 soybean, for post-emergence (V4). Three experiments were carried out, repeated in the 2016/17 and 2017/18 seasons, in Mogi-Mirim, SP. The experiment I consisted of the application of glyphosate (1.440 g e.a. ha-1), treatments were arranged in factorial arrangement 2X4 (event X development stage). For the event factor were used E3 and RR. For stadium, control (without application), V4, V6 and R2. The experiment II consisted of the application of glufosinate (460 g e.a. ha-1), treatments were arranged in factorial arrangement 2X4 (event X development stage). For the event factor were used E3 and LL. For stage, the same of experiment I. The experiment III was constituted of the application 2,4-D, glyphosate and glufosinate in the V4 stage of soybean E3. Were evaluated the crop injury, chlorophyll indexes, and variables related to agronomic performance. No reductions in chlorophyll indexes and agronomic performance of soybean were observed. It was found the equivalent of glyphosate selectivity to E3 and RR soybean, regardless of the development stage. As well as, the equivalent selectivity of glufosinate for E3 and LL soybean, regardless of development stage. Also the selectivity of 2,4-D isolated or in associations with glyphosate or glufosinate in E3 soybean.