Field and greenhouse research was conducted in 2009 and 2010 on herbicide applications enabled by the integration of Optimum GAT crop traits providing for resistance to glyphosate and certain ALS-inhibiting herbicides. The herbicide concepts were evaluated for control of several winter and summer annual weed species, as well as the effect of the resulting weed control on grain yield of Optimum GAT soybean. The combination of chlorimuron + rimsulfuron did not provide sufficient efficacy on the winter annual grass species little barley and annual bluegrass. Factors contributing the sub-lethal activity include: 1) a relatively low inherent sensitivity of the species to these herbicides, 2) a significant reduction in herbicide efficacy with increases in weed plant height, and 3) a lack of herbicide enhancement with more aggressive foliar adjuvants. The tank-mixture of glyphosate with chlorimuron + rimsulfuron was frequently necessary to achieve a maximum herbicide activity above 90% on annual bluegrass and little barley. Optimum GAT herbicide treatments including chlorimuron + rimsulfuron + flumioxazin in field experiments provided the greatest control of horseweed and common waterhemp in glyphosate-susceptible and -resistant populations. The addition of chlorimuron + rimsulfuron to glyphosate and 2,4-D improved horseweed control above glyphosate and 2,4-D applied alone even as weed height increased with applications made closer to soybean planting. However, removal of competitive vegetation with herbicide combinations including chlorimuron + rimsulfuron selected for emergence of ALS-resistant common waterhemp. Inclusion of flumioxazin with chlorimuron + rimsulfuron was beneficial for control of common waterhemp when applied 7 days before planting. However, chlorimuron + rimsulfuron + flumioxazin provided only 80% control of common waterhemp in a glyphosate-resistant population which demonstrates opportunity for improvement in herbicide concepts enabled by Optimum GAT. Grain yield of Optimum GAT soybean was greatest for herbicide treatments which provided effective weed management throughout the growing season which were the herbicide treatments applied the closest to soybean planting (7 days before planting). Optimum GAT herbicide concepts for corn include chlorimuron + thifensulfruon + tribenuron, chlorimuron + rimsulfuron, and rimsulfuron + tribenuron + mesotrione. These herbicides provided similar to slightly increased control of annual morningglory (Ipomoea spp.) in comparison to glyphosate alone. The addition of atrazine increased the consistency of control of annual morningglory for any herbicide treatment with additional residual activity at 28 days after treatment. Optimum GAT enabled herbicide concepts can improve control of some problematic weed species, including some glyphosate-resistant weed populations, compared to current herbicide tactics that rely primarily on glyphosate for weed control in commercial glyphosate-resistant soybean and corn. However, the integration of postemergence soybean herbicides beyond the ALS chemistry is necessary to provide a broader spectrum of weed control when considering the challenges of managing both glyphosate- and ALS-resistant weed species that are becoming more frequent in commercial fields.

Master of Science / Department of Agronomy / Johanna A. Dille / Palmer amaranth and horseweed are problematic weeds in no-till soybeans in Kansas. Integrating cover crops and herbicide programs could suppress weed populations. To determine the emergence pattern and survival of horseweed, a study was conducted across six locations in eastern KS in 2014-2015 and 2015-2016. Horseweed seedlings and leaf number per seedling were recorded at two-week intervals. Cumulative GDDs required to reach 50% horseweed emergence increased from north to south. Horseweed survival ranged from 4 to 90%, and majority of horseweed emerged in the fall. Field studies were conducted to determine effects of cover crops and herbicide programs on Palmer amaranth near Manhattan, KS in 2014-2015 and 2015-2016. Five cover crop treatments included no cover, fall-sown winter wheat, spring-sown oat, pea, and mixture of oat and pea. Cover crops were terminated in May with glyphosate and 2,4-D alone or with residual herbicides of flumioxazin and pyroxasulfone. By 10 weeks after termination in 2014-2015, Palmer amaranth biomass and density, averaged across cover crops. was 95 and 69% less with residual herbicides than without, respectively, and Palmer amaranth biomass was 98% less in winter wheat and 91% less in spring oat, averaged across termination methods, compared to no cover. Time to 50% Palmer amaranth emergence was delayed with winter wheat, spring oat, and spring oat/pea mix without residual herbicide. Soybean yields were greater with residual herbicide and greater with winter wheat or spring oat cover crop in 2014-2015. A field study was conducted to determine suppression effects of cover crop and herbicide programs on horseweed and Palmer amaranth near Manhattan, KS in 2015-2016. Three fall treatments included fall-sown rye, a residual herbicide tank mix of glyphosate, dicamba, chlorimuron-ethyl, tribenuron-methyl, and AMS, and no fall application. Four spring treatments included no spring application or three herbicide tank mixes: glyphosate, dicamba, and AMS alone or with flumioxazin and pyroxasulfone as early preplant, or as split applied with 2/3 preplant and 1/3 at soybean planting. Similar levels of horseweed suppression were observed when some control measure was used in fall or spring. Fall rye completely suppressed horseweed while the fall herbicide suppressed biomass by 93% and density by 86% compared to no fall application. Palmer amaranth suppression was observed when a spring herbicide application was used. In rye, total weed biomass was reduced by 97% or more across all spring treatments. Total weed biomass was reduced with a spring herbicide was used. Soybean yields were least when no herbicide treatment was used in the spring. An integrated program of fall cover crops or herbicide applications together with spring herbicide applications maintained soybean yields.

After termination, cover crop residue can suppress weeds by reducing sunlight, decreasing soil temperature, and providing a physical barrier. Experiments were implemented to monitor horseweed suppression from different cover crops as well as two fall-applied residual herbicide treatments. Results suggest that cover crops, other than forage radish in monoculture, can suppress horseweed more consistently than flumioxazin + paraquat or metribuzin + chlorimuron-ethyl. Cover crop biomass is positively correlated to weed suppression. Subsequent experiments were designed to determine the amount of weed suppression from different cover crop treatments and if carbon to nitrogen (C:N) ratios or lignin content are also correlated to weed suppression or cover crop residue thickness. Results indicate that cereal rye alone and mixtures containing cereal rye produced the most biomass and suppressed weeds more than hairy vetch, crimson clover, and forage radish alone. Analyses indicate that lignin, as well as biomass, is an important indicator of weed suppression. While cover crops provide many benefits, integrating cover crops into production can be difficult. Hairy vetch, a legume cover crop, can become a weed in subsequent seasons. Multiple experiments were implemented to determine germination phenology and viability of two hairy vetch cultivars, Groff and Purple Bounty, and to determine when viable seed are produced. Almost all germination occurred in the initial cover crop growing season for both cultivars. Both cultivars had <1% of viable seed at the termination of the experiment. These results indicate that seed dormancy is not the primary cause of weediness. / Master of Science in Life Sciences / Cover crops are grown in the time between cash crop production, such as corn or soybeans. These crops are not grown for profit but mainly for environmental benefits such as reducing erosion and increasing soil organic matter and water infiltration. Another benefit of cover crops is the ability to suppress weeds. Cover crops can suppress weeds while they are actively growing by competing for resources such as light, water, and nutrients. After the cover crops have been terminated, or killed prior to cash crop planting, the residue can form a mulch layer on the soil surface which acts to suppress weeds by reducing the amount of sunlight that reaches the soil surface, decreasing soil temperature, and providing a physical barrier to slow weed growth. Horseweed is a problematic weed for growers to control and the number of herbicide options that growers can utilize is decreasing due to herbicide resistance. This weed has small seed and multiple germination periods, which cover crops have the ability to target. Experiments were designed to compare horseweed suppression from different cover crop monocultures and mixtures with suppression obtained from two fall-applied residual herbicide programs. The cover crop species used were cereal rye, crimson clover, hairy vetch, and forage radish. The cover crops were planted and herbicides applied in the fall. Data collected included horseweed counts, visible suppression ratings, and horseweed biomass taken in the following corn or soybean growing season. All cover crop treatments suppressed horseweed as compared to the nontreated check, with the exception of forage radish alone. The fall-applied herbicides did not perform as well as the cover crops. Results indicate that integration of cover crops is a viable tactic for horseweed management. As cover crop biomass increases the level of weed suppression also increases. Experiments were implemented to measure the level of weed suppression and to determine if the composition of the cover crop residue is important in weed suppression. Monocultures and mixtures of the same four cover crop species listed above were grown prior to corn and soybean production. At cover crop termination, samples were taken to determine biomass, carbon to nitrogen (C:N) ratio, and lignin content. Cereal rye and mixtures containing cereal rye provided > 55% weed suppression 6 weeks after cover crop termination. Analyses also indicated that lignin, as well as biomass, is an important predictor of weed suppression after termination. While cover crops have many benefits, there can be some complications. Hairy vetch is a legume cover crop species that has the ability to suppress weeds but can also become weedy in subsequent crops. Experiments were performed to track germination and seed viability of two hairy vetch cultivars, Groff and Purple Bounty as well as determine when seeds are added to the soil seedbank. Over the course of the experiment, Groff had greater germination than Purple Bounty by 30% in the initial germination periods. Both cultivars had <1% of seed still viable at the end of the experiment. Also, both cultivars produce viable seed in mid-June. The results from these experiments indicate that seed dormancy is not the primary cause of weediness in hairy vetch and that if proper termination occurs prior to mid-June, seeds will not be added to the soil seedbank.

Field and labratory studies were conducted to determine the efficacy of saflufenacil alone and with mixture partners for burndown. Field studies were conducted in 2009 and 2010 to evaluate saflufenacil in mixtures with glyphosate, glufosinate, or paraquat for control of glyphosate-resistant (GR) horseweed prior to planting cotton. Saflufenacil and saflufenacil mixtures were applied 7 days before planting (DBP). Saflufenacil at 25 and 50 g ai ha-1 in mixture with all three non-selective herbicides provided similar GR horseweed control when compared to the current standard of glyphosate plus dicamba. Control of GR horseweed was also not different at the 25 and 50 g ai ha-1 of saflufenacil across all mixtures from the standard of glyphosate plus dicamba. Laboratory studies were initiated to determine the uptake and translocation of saflufenacil alone and when mixed with glyphosate and paraquat. It was found that glyphosate plus saflufenacil had a greater absorption of saflufenacil at 2 and 8 HAT. By 24 HAT there were not any differences between the amount of saflufenacil absorbed into GR horseweed between treatments. Translocation data also confirmed that the majority of saflufenacil stayed in the treated leaf at 72 HAT.

Thesis (Ph. D.)--Ohio State University, 2008. / Title from first page of PDF file. Includes bibliographical references (p. 96-107).

Submitted by IVANA PAULA FERRAZ SANTOS DE BRITO null (ivanapaulaf@yahoo.com.br) on 2016-12-12T11:21:38Z No. of bitstreams: 1 Tese_Ivana Paula Ferraz.pdf: 1609743 bytes, checksum: dabfed03ce3dbb1480947a22a52cddcd (MD5) / Approved for entry into archive by Felipe Augusto Arakaki (arakaki@reitoria.unesp.br) on 2016-12-13T12:19:57Z (GMT) No. of bitstreams: 1 brito_ipfs_dr_bot.pdf: 1609743 bytes, checksum: dabfed03ce3dbb1480947a22a52cddcd (MD5) / Made available in DSpace on 2016-12-13T12:19:57Z (GMT). No. of bitstreams: 1 brito_ipfs_dr_bot.pdf: 1609743 bytes, checksum: dabfed03ce3dbb1480947a22a52cddcd (MD5) Previous issue date: 2016-11-11 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / A sensibilidade de plantas daninhas a herbicidas frequentemente se apresenta variável, em função de diversos fatores. O herbicida amônio glufosinate tem ação de contato e inibe a atividade da enzima glutamina sintetase, causando dentre outros efeitos, o acúmulo de amônia nos tecidos foliares, sendo esse um bom indicativo da intoxicação das plantas. Desse modo, o objetivo desse trabalho foi identificar a resposta de plantas de Bidens pilosa e Conyza sumatrensis a diferentes doses do herbicida amônio glufosinate, e a variação da sensibilidade em populações das plantas e de suas progênies ao herbicida. Foram realizados três estudos, todos em casa-de-vegetação e repetidos em diferentes momentos. No primeiro estudo, dois experimentos de dose-resposta foram conduzidos, e foram aplicadas sete diferentes doses do herbicida amônio glufosinate (0, 50, 100, 200, 400, 800, e 1600 g ha-1), com quatro repetições, para cada espécie, sendo realizada análise de amônia e avaliações visuais de fitointoxicação. No segundo estudo, de variação de sensibilidade de B. pilosa e C. sumatrensis ao amônio glufosinate, 44 plantas de B. pilosa e 16 de C. sumatrensis foram aplicadas com a dose de 200 g ha-1 do herbicida, sendo nesse momento a região meristemática e folha mais nova de cada planta protegidas com saco plástico para que não recebessem o herbicida e possibilitasse a manutenção das plantas vivas. Dois dias após a aplicação (DAA) realizou-se a análise do teor de amônia, nas folhas expostas à aplicação, e as folhas protegidas foram mantidas nas plantas para que as mesmas se recuperassem do tratamento e produzissem sementes, utilizadas no estudo de sensibilidade de progênies. Ao atingirem o estádio reprodutivo os botões florais das plantas foram protegidos com sacos de papel para evitar a polinização cruzada e garantir a produção de sementes somente por autofecundação. No terceiro estudo, de variação da sensibilidade das progênies de B. pilosa e C. sumatrensis ao amônio glufosinate, progênies de sete das plantas anteriores foram também tratadas com 200 g ha-1 do amônio glufosinate. Foram quantificados os teores de amônia nos tecidos e porcentagens de controle foram avaliadas visualmente. A amônia foi extraída do tecido foliar fresco das plantas das duas espécies e quantificada por espectrofotometria. Foram realizadas avaliações visuais de controle aos 0, 3, 7, 14 e 21 DAA utilizando-se escala visual de notas variando de 0 a 100%. Os dados obtidos foram analisados pelo teste T e ajustados modelos de regressão não-linear. O estudo de dose-resposta demonstrou que o teor de amônia aumenta de forma assintótica com o aumento da dose do herbicida e que a porcentagem de intoxicação das espécies estudadas também aumenta de modo assintótico com o aumento tanto da dose do herbicida quanto do teor de amônia nos tecidos. O segundo estudo, de variação da sensibilidade, demonstrou haver variabilidade entre indivíduos de uma mesma população sensível ao herbicida, para as duas espécies analisadas; e o terceiro, de estudo das progênies, demonstrou que, para Bidens pilosa, as progênies das plantas com as diferentes capacidades de acumular amônia nos tecidos foram similares em termos de nível de acúmulo; no entanto, no caso de Conyza sumatrensis, as progênies de plantas com maior capacidade em acumulá-la, também exibiram maiores teores internos após o tratamento com glufosinate. Para as duas espécies, a variabilidade dos teores internos de amônia para cada progênie foi bastante alta, suplantando as diferenças médias entre as diferentes progênies, indicando pequena herdabilidade dessa característica. / The sensitivity of weeds to herbicide is often variable, due to several factors. The glufosinate-ammonium is a contact herbicide and inhibits the activity of the glutamine synthetase enzyme causing, among others, ammonia accumulation in the leaves, an indicator of the plants intoxication. The objective of this study was to evaluate the response of Bidens pilosa and Conyza sumatrensis to different doses of glufosinate ammonium and the sensitivity range of the plants and their progenies to the herbicide. Three studies were conducted, all in a greenhouse and repeated at different times. In the first study, two experiments were conducted to examine the dose-response curve, and the treatments were seven different doses of the herbicide glufosinate ammonium (0, 50, 100, 200, 400, 800, and 1600 g ha-1), with four replicates for each specie. In the second study, which examined the sensitivity range of B. pilosa and C. sumatrensis to glufosinate ammonium, 44 B. pilosa plants and 16 C. sumatrensis plants were sprayed with 200 g ha-1 of the herbicide. At the time of spraying, the meristematic region and the youngest leaf of each plant were protected with a plastic bag so that they would not receive the herbicide, thus keeping the plants alive. At two days after treatment (DAT), an analysis of the ammonium content on the sprayed leaves them was conducted. The protected leaves were kept on the plants enabling to recover from herbicide treatment and to produce seeds used to assess the sensitivity of B. pilosa and C. sumatrensis progenies to glufosinate ammonium. When the plants had reached the reproductive stage, the flower buds were covered with paper bags to prevent cross-pollination and guarantee that only self-pollination would take place. In the third study, the sensitivity range of the progeny of B. pilosa and C. sumatrensis to glufosinate ammonium was investigated; in this experiment, the progenies of seven of the previous plants were sprayed with 200 g ha-1 of glufosinate ammonium. It was measured the ammonium contents in the tissues and herbicide injury to plants was visually assessed. Ammonium was extracted from fresh leaf tissue immediately after leaf collection from the two species, and quantified per spectrophotometry. Evaluations of visual injury were conducted at 0, 3, 7, 14, and 21 DAT using a visual scale with grades ranging from 0 to 100%. The data were analyzed for t test (p≤0,05) and adjusted by non-linear regression models. The dose-response study showed that increase in ammonia content is related to the treatments used, being correlated to toxicity in the two species. The second study, the sensitivity variation showed that there was variability among individuals of the same population, for both species. The progenies study demonstrated that, Bidens pilosa, progeny plants with different capacities to accumulate ammonia in the tissues were similar in terms of buildup level; However, for Conyza sumatrensis, progeny plants with the greatest ability to accumulate it also exhibited higher internal levels after treatment with glufosinate. The variability of internal ammonia levels for each progeny was quite high, for both species, surpassing the average differences between different progenies, indicating low heritability of this characteristic.

Submitted by Maria Beatriz Vieira (mbeatriz.vieira@gmail.com) on 2017-04-06T15:22:02Z No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) dissertacao_andres_antonio_monge_vargas.pdf: 823114 bytes, checksum: f67f9c364ef84bc1b73e7ab74ddaf68c (MD5) / Approved for entry into archive by Aline Batista (alinehb.ufpel@gmail.com) on 2017-04-19T20:17:27Z (GMT) No. of bitstreams: 2 dissertacao_andres_antonio_monge_vargas.pdf: 823114 bytes, checksum: f67f9c364ef84bc1b73e7ab74ddaf68c (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Approved for entry into archive by Aline Batista (alinehb.ufpel@gmail.com) on 2017-04-19T20:18:36Z (GMT) No. of bitstreams: 2 dissertacao_andres_antonio_monge_vargas.pdf: 823114 bytes, checksum: f67f9c364ef84bc1b73e7ab74ddaf68c (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Made available in DSpace on 2017-04-19T20:18:49Z (GMT). No. of bitstreams: 2 dissertacao_andres_antonio_monge_vargas.pdf: 823114 bytes, checksum: f67f9c364ef84bc1b73e7ab74ddaf68c (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2015-08-04 / Sem bolsa / A buva (Conyza spp.) é uma planta daninha, disseminada em todo mundo, que ocorre em áreas agrícolas da América do Sul. Adaptada especialmente aos sistemas de semeadura direta, onde evoluiu junto com o uso de culturas geneticamente modificadas com resistência ao glifosato, originando biótipos resistentes a esse herbicida, agravando o problema de manejo e controle desta espécie. Diante disso, os objetivos da pesquisa foram: avaliar a dormência de buva, testando tratamentos pré-germinativos para superar a dormência das sementes em diferentes períodos de armazenamento; avaliar o efeito da temperatura de armazenamento na germinação e longevidade; e, determinar o efeito da profundidade de enterrio na longevidade do banco de sementes no solo. Para isso, foram conduzidos experimentos em campo e laboratório, utilizando-se sementes coletadas a partir de capítulos em fase final de maturação. As variáveis avaliadas, em percentagem (%), foram: primeira e segunda contagem de germinação, plântulas anormais, sementes: remanescentes, mortas, dormentes, viáveis e não viáveis. Os resultados demonstram que a semente de buva apresenta dormência primaria de tipo fisiológica, e que a embebição das sementes em água durante 24 horas ou o armazenamento a 25º C por 53 dias, são tratamentos eficientes para superar essa dormência. O enterrio da semente a 0,5 cm de profundidade, induzem as sementes a dormência secundária, quando armazenada a 10, 20 e 30º C, no entanto, quando armazenada a 20 e 30º C, a qualidade fisiológica é prejudicada. O banco de sementes de buva foi reduzido em 59 %, no período de um ano, ao mesmo tempo que o enterrio, independente da profundidade, podem induzir as sementes a dormência secundária. As sementes enterradas a maiores profundidades, apresentam longevidade e qualidade fisiológica superior. / Horseweed (Conyza spp.) is a worldwide disseminated weed, occurring in disseminated areas of South America. Specially adapted to no-till systems, where it evolved along with the use of genetically modified crops with glyphosate resistance, creating biotypes resistant to this herbicide, aggravating the problem of the management and control of this specie. Therefore, the research objectives were: to evaluate the horseweed seed dormancy, testing pre-germination treatments to overcome seed dormancy in different storage periods; to assess the effect of storage temperature on seed germination and longevity; and to determine the burial depth effect in soil seeds banks longevity. For this, field and laboratory experiments were conducted, using collected seeds from flowers in final maturation phase. The variables evaluated as a percentage (%) were: first and second count germination, adnormal seedlings, seeds: remnants, dead, hard, viable and non-viable. The results show that horseweed seed has primary physiological dormancy type, and soaking the seeds in water for 24 hours or storage at 25º C for 53 days are effective treatments to overcome this dormancy. The seed burial depth at 0,5 cm, induce secondary dormancy, when storage at 10, 20 and 30º C, however, at 20 and 30º C, physiological quality is affected. The horseweed seed bank was reduced by 59% in one year, while the burial, regardless of the depth, seeds can induce secondary dormancy. Seed burial at greater depths, have longevity and superior physiological quality.

<p>Acetolactate synthase (ALS) inhibitors are a widely used class of selective herbicides used to control grass and broadleaf weeds. The repeated use of ALS-inhibiting herbicides has selected for biotypes of weeds resistant to ALS inhibitors, especially in the weeds most problematic to growers in the Midwest. While ALS inhibitor use seems futile, new mechanisms of herbicide action are not predicted to be commercialized in the near future to solve this problem. This leads to the main objective of this research, determining what value ALS inhibitors provide in controlling populations of weeds with resistance to ALS inhibitors. </p> <p>Field experiments with soil-applied (PRE) applications of ALS inhibitors on horseweed (<i>Erigeron canadensis</i>) and tall waterhemp (<i>Amaranthus tuberculatus </i>var. <i>rudis</i>) exhibited higher efficacy than would be expected given the frequency of the ALS resistance trait in the population. Whereas control of these species with POST-applied applications was similar or less than the proportion of the population characterized as susceptible using molecular techniques. Soil-applied applications, therefore, resulted in relatively greater control than POST applications in populations with known ALS-inhibitor-resistance mechanisms.</p> <p>Greenhouse experiments showed that overall resistance ratios were higher for PRE applications of ALS inhibitors in horseweed, tall waterhemp, and Palmer amaranth (<i>Amaranthus palmeri</i>). However, GR₅₀ values decreased for both susceptible and resistant biotypes for the PRE applications compared to POST, suggesting the biologically effective dose of these herbicides is lower in soil residual applications. This research found that PRE applications of ALS inhibitors resulted in some level of control on horseweed and tall waterhemp classified as resistant to ALS inhibitors due to the higher efficacy of PRE herbicide applications.</p> <p>Genetic analysis assessing the amino acid substitutions that confer resistance to ALS inhibitors in tall waterhemp confirmed a difference in selection pressure between PRE and POST applications and between ALS active ingredients in tall waterhemp. Applications of chlorimuron PRE at 11 g ai ha^-1selected for 35% homozygous W574L genotypes and at 44 g ha^-1 selected for 70% homozygous W574L genotypes. An increase of homozygous W574L individuals along with a decrease in heterozygous individuals from 65 (11 g ha^-1) to 29% (44 g ha^-1) suggests that W574L is semi-dominant in tall waterhemp and that high labeled rates of chlorimuron applied PRE can partially overcome the heterozygous W574L-resistance mechanism. In horseweed, no difference in selection pressure was observed between application timing or between chlorimuron or cloransulam. A new mutation conferring ALS-inhibitor resistance in horseweed was discovered, a Pro197Leu amino acid substitution, with resistance ratios of 21X to chlorimuron and 8.6X to cloransulam. These resistance ratios are slightly less than those reported for the Pro197Ala and Pro197Ser amino acid substitutions in conferring ALS-inhibitor resistance in horseweed. </p> <p>Finally, a survey of 42 populations of tall waterhemp in Indiana counties with confirmed ALS-inhibitor resistant populations of tall waterhemp found that all populations contained at least 16% individuals with the W574L amino acid substitution, 35 populations contained at least 1% individuals with the S653N substitution, and 9 populations contained at least 1% individuals with the S653T substitution. Taking into consideration the three mutations tested, 8 of the 42 populations tested contained <50% ALS-inhibitor resistant individuals within the population. Using the same tall waterhemp populations as collected in the survey, Next-Generation Sequencing was used to determine if other amino acid substitutions conferring resistance to ALS inhibitors existed. Results from WideSeq revealed that 10 other amino acid substitutions in the ALS protein may be conferring resistance in tall waterhemp in Indiana: A122T, A122N, A122S, P197T, P197L, P197H, D376E, and G654F. Further research from this survey also suggests that metabolic resistance to ALS inhibitors is likely a contributor to resistance in tall waterhemp in Indiana.</p> <p>This research suggests that ALS-inhibiting herbicides, more specifically chlorimuron, would provide the greatest contribution to management of tall waterhemp. Chlorimuron would perform best when used in soil residual applications and in populations of tall waterhemp containing either individuals susceptible to chlorimuron or individuals heterozygous for ALS inhibitor resistance conferred by the W574L mutation. This research also demonstrates the specificity of the amino acid substitutions in the ALS protein and by weed species to realize the benefit of these herbicides for management of weeds resistant to ALS inhibitors. Molecular characterization of target site resistance to ALS inhibitors has traditionally been considered relatively simple. However, we found 11 new amino acid substitutions that confer resistance to ALS inhibitors in horseweed and tall waterhemp. The complexity of ALS inhibitor resistance calls for the use of methods such as NGS to detect all potential resistance mutations in a timely manner and for the use of tests detecting metabolic resistance. Overall, this research demonstrates that ALS inhibitors still provide some utility for management of weed populations classified as resistant to ALS inhibitors and that the resistance mechanisms in horseweed and tall waterhemp are more numerous than previously reported. </p>

No description available.