Acetolactate Synthase-inhibiting Herbicides Research Articles

Differences in sensitivity of F1 and F2 generations of herbicide tolerant sunflower volunteers to selected acetolactate synthase inhibiting herbicides

The aim of this work is to describe the differences in sensitivity of Clearfield, ExpressSun and non-herbicide tolerant (HT) sunflower cultivars to several acetolactate synthase inhibitor herbicides and to find out the differences in sensitivity in F1 and F2 generations of these cultivars. Non-HT sunflower was very sensitive to most of the tested herbicides, except for nicosulfuron (efficacy 43–75%). F2 generation of non-HT sunflower showed a low level of sensitivity to imazamox (efficacy 10–43%) and to nicosulfuron, tribenuron, thifensulfuron and rimsulfuron under dry conditions (efficacy 43–83%). Sensitivity of Clearfield sunflower (cultivar with tolerance to imidazolinone herbicides) to tested sulfonylurea varied according to used herbicide and weather conditions. The highest efficacy on Clearfield sunflower showed iodosulfuron (97–100%) > florasulam (88–100%) > foramsulfuron (40–98%) > thifensulfuron (12–99%) > rimsulfuron (37–99%) > tribenuron (0–87%) > nicosulfuron (0–78%). ExpressSun sunflower (cultivar with tolerance to tribenuron) was the most tolerant to all tested herbicides. The lowest efficacy on F1 generation showed tribenuron (0%) > imazamox (0–17%) > nicosulfuron (0–43%) > thifensulfuron (0–57%) > rimsulfuron (0–70%) > foramsulfuron (8–75%) > florasulam (75–96%) > iodosulfuron (87–98%). Sensitivity of F2 generation of ExpressSun to tested herbicide was usually higher as compared to F1 generation.

Resistance of Amaranthus retroflexus to acetolactate synthase inhibitor herbicides in Brazil

When in competition with cotton, Amaranthus retroflexus can cause high yield losses. Due to the limited availability of selective herbicides registered for post emergence control of this weed, the same herbicides have been used repeated times over the last few years, which may have selected resistant biotypes. Biotypes of A. retroflexus collected from the main areas of cotton cultivation in Brazil were submitted to dose-response trials, by applying the herbicides trifloxysulfuron-sodium and pyrithiobac-sodium in doses equivalent to 0, ¼, ½, 1, 2 and 4 times the recommended rates. Resistance to ALS inhibitors was confirmed in biotypes of A. retroflexus. Biotype MS 2 from Mato Grosso do Sul, was cross-resistant to both trifloxysulfuron-sodium and pyrithiobac-sodium, while biotype MS 1 was resistant to trifloxysulfuron-sodium only. Likewise, singular and cross resistance was also confirmed in biotypes from Goiás (GO 3, GO 4 and GO 6), in relation to trifloxysulfuronsodium and pyrithiobac-sodium. One biotype from Mato Grosso (MT 13) was not resistant to any of the ALS inhibitors evaluated in this work.

Cytochrome P450 CYP81A12 and CYP81A21 Are Associated with Resistance to Two Acetolactate Synthase Inhibitors in Echinochloa phyllopogon.

Previous studies have demonstrated multiple herbicide resistance in California populations of Echinochloa phyllopogon, a noxious weed in rice (Oryza sativa) fields. It was suggested that the resistance to two classes of acetolactate synthase-inhibiting herbicides, bensulfuron-methyl (BSM) and penoxsulam (PX), may be caused by enhanced activities of herbicide-metabolizing cytochrome P450. We investigated BSM metabolism in the resistant (R) and susceptible (S) lines of E. phyllopogon, which were originally collected from different areas in California. R plants metabolized BSM through O-demethylation more rapidly than S plants. Based on available information about BSM tolerance in rice, we isolated and analyzed P450 genes of the CYP81A subfamily in E. phyllopogon. Two genes, CYP81A12 and CYP81A21, were more actively transcribed in R plants compared with S plants. Transgenic Arabidopsis (Arabidopsis thaliana) expressing either of the two genes survived in media containing BSM or PX at levels at which the wild type stopped growing. Segregation of resistances in the F2 generation from crosses of R and S plants suggested that the resistance to BSM and PX were each under the control of a single regulatory element. In F6 recombinant inbred lines, BSM and PX resistances cosegregated with increased transcript levels of CYP81A12 and CYP81A21. Heterologously produced CYP81A12 and CYP81A21 proteins in yeast (Saccharomyces cerevisiae) metabolized BSM through O-demethylation. Our results suggest that overexpression of the two P450 genes confers resistance to two classes of acetolactate synthase inhibitors to E. phyllopogon. The overexpression of the two genes could be regulated simultaneously by a single trans-acting element in the R line of E. phyllopogon.

Differential sensitivity of locally naturalized Panicum species to 4-hydroxyphenyl pyruvate dioxygenase and acetolactate synthase-inhibiting herbicides

One of the possible reasons for the expansion of the alien panicoid grasses Panicum schinzii (Transvaal millet), Panicum dichotomiflorum (Fall panicum) and Panicum capillare (Witchgrass) in maize fields in Belgium might be a lower sensitivity to post-emergence herbicides acting against panicoid grasses, in particular those inhibiting 4-hydroxyphenyl pyruvate dioxygenase (HPPD) and acetolactate synthase (ALS). Dose-response pot experiments were conducted in the greenhouse to evaluate the effectiveness of five HPPD-inhibiting herbicides (sulcotrione, mesotrione, isoxaflutole, topramezone, tembotrione) and two ALS-inhibiting herbicides (nicosulfuron, foramsulfuron) for controlling naturalized Belgian populations of P. schinzii, P. dichotomiflorum and P. capillare. In another dose-response pot experiment, sensitivity of five local P. dichotomiflorum populations to HPPD-inhibitors and nicosulfuron was investigated. Finally, the influence of growth stage at time of herbicide application on efficacy of topramezone and nicosulfuron for Panicum control was evaluated. Large interspecific differences in sensitivity to HPPD-inhibiting herbicides were observed. Panicum schinzii was sensitive (i.e., required a three-fold lower dose than maximum authorized field dose to achieve 90% reduction in biomass) to tembotrione but moderately sensitive (i.e. required maximum field dose) to topramezone and poorly sensitive (i.e. required three-fold higher dose than maximum field dose) to mesotrione and sulcotrione. However, P. dichotomiflorum, a species that morphologically closely resembles P. schinzii, was sensitive to mesotrione and topramezone but moderately sensitive to tembotrione. Panicum capillare was sensitive to sulcotrione and topramezone, moderately sensitive to tembotrione and poorly sensitive to mesotrione. All Panicum species were sensitive to low doses of nicosulfuron and foramsulfuron. Naturalized Panicum dichotomiflorum populations exhibited differential herbicide sensitivity profiles. All species tested showed a progressive decrease in sensitivity to topramezone and nicosulfuron with seedling age. A satisfactory post-emergence control of Panicum species in the field will require appropriate choice of herbicide and dose, as well as a more timely application (i.e. before weeds reach the four leaves stage).Keywords: Bioassay, herbicide sensitivity, leaf stage, nicosulfuron, panicoid grasses, triketoneDifferentielle Sensitivitat von lokal naturalisierten Panicum-Arten gegenuber 4-Hydroxyphenylpyruvat-Dioxygenase und Acetolactat- Synthase hemmenden HerbizidenZusammenfassungEiner der moglichen Grunde fur die rasche Ausbreitung der standortfremden Unkrauthirsen Panicum schinzii (Glattblattrige Hirse), Panicum dichotomiflorum (Gabelastige Rispenhirse) und Panicum capillare (Haarastige Rispenhirse) in Maisfeldern in Belgien konnte eine geringere Empfindlichkeit gegenuber Nachauflaufherbiziden sein, insbesondere 4-Hydroxyphenylpyruvat-Dioxygenase (HPPD)- und Acetolactat-Synthase (ALS)-Hemmer. Dosis-Wirkungs-Experimente wurden im Gefasversuch im Gewachshaus durchgefuhrt, um die Wirksamkeit von funf HPPD-inhibierenden Herbizidwirkstoffen (Sulcotrione, Mesotrione, Isoxaflutole, Topramezone, Tembotrione) und zwei ALS-inhibierenden Herbizidwirkstoffen (Nicosulfuron, Foramsulfuron) gegen naturalisierte belgische Populationen von P. schinzii, P. dichotomiflorum und P. capillare zu beurteilen. In einem weiteren Dosis-Wirkungs-Topf Experiment wurde die Empfindlichkeit von funf lokal eingewanderten P. dichotomiflorum-Populationen gegenuber HPPD-Inhibitoren und Nicosulfuron untersucht. Schlieslich wurde der Einfluss des Blattstadiums zum Zeitpunkt der Herbizid-Anwendung auf Wirksamkeit von Topramezone und Nicosulfuron fur Panicum-Bekampfung ausgewertet. Grose interspezifische Unterschiede in der Empfindlichkeit gegenuber HPPD-inhibierenden Herbiziden wurden beobachtet. Panicum schinzii war empfindlich gegenuber Tembotrione aber masig empfindlich gegenuber Topramezone und leicht empfindlich gegenuber Mesotrione und Sulcotrione. Dagegen war P. dichotomiflorum empfindlich gegenuber Mesotrione und Topramezone aber masig empfindlich gegenuber Tembotrione. Panicum capillare war empfindlich gegenuber Sulcotrione und Topramezone, masig empfindlich gegenuber Tembotrione und leicht empfindlich gegenuber Mesotrione. Alle Panicum-Arten waren empfindlich gegenuber niedrigen Dosen von Nicosulfuron und Foramsulfuron. Eingeburgerte Panicum dichotomiflorum-Populationen zeigten differentielle Herbizid-Empfindlichkeitsprofile. Alle untersuchten Arten zeigten eine fortschreitende Abnahme der Empfindlichkeit gegenuber Topramezone und Nicosulfuron mit zunehmendem Blattstadium. Eine befriedigende Nachauflaufbekampfung von Panicum-Arten in Maisackern benotigt eine angemessene Wahl von Herbizid und Dosis sowie eine rechtzeitige Anwendung (das heist vor dem Vierblattstadium).Stichworter: Biotest, Blattstadium, Herbizidempfindlichkeit, Nicosulfuron, Triketone, Unkrauthirsen

A Novel Rice Cytochrome P450 Gene, CYP72A31, Confers Tolerance to Acetolactate Synthase-Inhibiting Herbicides in Rice and Arabidopsis

Target-site and non-target-site herbicide tolerance are caused by the prevention of herbicide binding to the target enzyme and the reduction to a nonlethal dose of herbicide reaching the target enzyme, respectively. There is little information on the molecular mechanisms involved in non-target-site herbicide tolerance, although it poses the greater threat in the evolution of herbicide-resistant weeds and could potentially be useful for the production of herbicide-tolerant crops because it is often involved in tolerance to multiherbicides. Bispyribac sodium (BS) is an herbicide that inhibits the activity of acetolactate synthase. Rice (Oryza sativa) of the indica variety show BS tolerance, while japonica rice varieties are BS sensitive. Map-based cloning and complementation tests revealed that a novel cytochrome P450 monooxygenase, CYP72A31, is involved in BS tolerance. Interestingly, BS tolerance was correlated with CYP72A31 messenger RNA levels in transgenic plants of rice and Arabidopsis (Arabidopsis thaliana). Moreover, Arabidopsis overexpressing CYP72A31 showed tolerance to bensulfuron-methyl (BSM), which belongs to a different class of acetolactate synthase-inhibiting herbicides, suggesting that CYP72A31 can metabolize BS and BSM to a compound with reduced phytotoxicity. On the other hand, we showed that the cytochrome P450 monooxygenase CYP81A6, which has been reported to confer BSM tolerance, is barely involved, if at all, in BS tolerance, suggesting that the CYP72A31 enzyme has different herbicide specificities compared with CYP81A6. Thus, the CYP72A31 gene is a potentially useful genetic resource in the fields of weed control, herbicide development, and molecular breeding in a broad range of crop species.

Reference Genes to Study Herbicide Stress Response in Lolium sp.: Up-Regulation of P450 Genes in Plants Resistant to Acetolactate-Synthase Inhibitors

Variation in the expression of numerous genes is at the basis of plant response to environmental stresses. Non-target-site-based resistance to herbicides (NTSR), the major threat to grass weed chemical control, is governed by a subset of the genes involved in herbicide stress response. Quantitative PCR assays allowing reliable comparison of gene expression are thus key to identify genes governing NTSR. This work aimed at identifying a set of reference genes with a stable expression to be used as an internal standard for the normalisation of quantitative PCR data in studies investigating NTSR to herbicides inhibiting acetolactate synthase (ALS) in the major grass weed Lolium sp. Gene expression stability was assessed in plants resistant or sensitive to two ALS inhibitors, subjected or not to herbicide stress. Using three complementary approaches implemented in the programs BestKeeper, NormFinder and geNorm, cap-binding protein, glyceraldehyde-3-phosphate-dehydrogenase and ubiquitin were identified as the most suitable reference genes. This reference gene set can probably be used to study herbicide response in other weed species. It was used to compare the expression of the genes encoding two herbicide target enzymes (ALS and acetyl-coenzyme A carboxylase) and five cytochromes P450 (CYP) with potential herbicide-degrading activity between plants resistant or sensitive to ALS inhibitors. Overall, herbicide application enhanced CYP gene expression. Constitutive up-regulation of all CYP genes observed in resistant plants compared to sensitive plants suggested enhanced secondary metabolism in the resistant plants. Comprehensive transcriptome studies associated to gene expression analyses using the reference gene set validated here are required to unravel NTSR genetic determinants.

Downy Brome (Bromus tectorum L.) and Broadleaf Weed Control in Winter Wheat with Acetolactate Synthase-Inhibiting Herbicides

A study was conducted for three seasons in northwest Kansas, USA to evaluate acetolactate synthase (ALS)-inhibiting herbicides for downy brome (Bromus tectorum L.) and winter annual broadleaf weed control in winter wheat. Herbicides included pyroxsulam at 18.4 g ai ha−1, propoxycarbazone-Na at 44 g ai ha−1, premixed propoxycarbazone-Na & mesosulfuron-methyl at 27 g ai ha−1, and sulfosulfuron at 35 g ai ha−1. The herbicides were applied postemergence in fall and spring seasons. Averaged over time of application, no herbicide controlled downy brome more than 78% in any year. When downy brome densities were high, control was less than 60%. Pyroxsulam controlled downy brome greater than or similar to other herbicides tested. Flixweed (Descurainia sophia L.), blue mustard [Chorispora tenella (Pallas) DC.], and henbit (Lamium amplexicaule L.) control did not differ among herbicide treatments. All herbicides tested controlled flixweed and blue mustard at least 87% and 94%, respectively. However, none of the herbicides controlled henbit more than 73%. Fall herbicide applications improved weed control compared to early spring applications; improvement ranged from 3% to 31% depending on the weed species. Henbit control was greatly decreased by delaying herbicide applications until spring compared to fall applications (49% vs. 80% control). Herbicide injury was observed in only two instances. The injury was ≤13% with no difference between herbicides and the injury did not impact final plant height or grain yield.

Comparison of Herbicides for Reducing Annual Grass Emergence in Two Great Basin Soils

Reducing seed germination and seedling emergence of downy brome (Bromus tectorum L.) improves the success of revegetating degraded shrubland ecosystems. While pre-emergence herbicides can potentially reduce these two processes, their impact on germination and emergence of downy brome and revegetation species in semiarid ecosystems is poorly understood and has not been comprehensively studied in soils with potentially contrasting herbicide bioavailability (i.e., residual plant activity). We designed a greenhouse experiment to evaluate the effects two pre-emergence acetolactate synthase–inhibiting herbicides (rimsulfuron and imazapic) on germination and emergence of downy brome and two revegetation grass species (crested wheatgrass [Agropyron cristatum {L.} Gaertn.] and bottlebrush squirreltail [Elymus elymoides {Raf.} Swezey]) that were grown in representative soils from salt desert and sagebrush shrublands. Pre-emergence herbicides significantly (P , 0.05) reduced seedling emergence and biomass production of downy brome and crested wheatgrass and increased mortality more so in sagebrush compared to salt desert soil, suggesting that these common Great Basin soils fundamentally differ in herbicide bioavailability. Also, germination and emergence of the two highly responsive species (crested wheatgrass and downy brome) were clearly more impacted by rimsulfuron than imazapic. We discuss these results in terms of how the specific soil physiochemical properties influence herbicide adsorption and leaching. Our results shed new light on the relative performance of these two promising herbicides and the importance of considering soil properties when applying pre-emergence herbicides to reduce germination and emergence of invasive annual grasses and create suitable seedbed conditions for revegetation. Resumen

Camelina mutants resistant to acetolactate synthase inhibitor herbicides

Camelina (Camelina sativa L.) is a low-input oilseed crop of recent interest for sustainable biofuel production. As a relatively new crop in modern agriculture, considerable agronomic and regulatory problems need to be overcome. A common and troublesome problem is sensitivity to residues of acetolactate synthase (ALS) inhibitor herbicides in soils. To develop resistance to those residues, camelina seed were mutagenized by exposure to 0.3% ethyl methane sulfonate and screened at the M2 generation for increased resistance to imazethapyr and sulfosulfuron. Five lines with resistance were identified and characterized. Four mutants, identified in a screen for imazethapyr resistance (IM1, IM6, IM10, and IM18), appeared phenotypically identical and were controlled by the same co-dominant gene. One mutant identified in a screen for sulfosulfuron resistance was phenotypically different but also appears to be controlled by a single co-dominant gene. Further analysis with the IM1 and SM4 mutants confirmed they had increased resistance to imazethapyr, sulfosulfuron, and flucarbazone, with the resistance in the SM4 mutant being the highest. Compared to the wild type, doses of approximately 200 times more imazethapyr, 30 times more sulfosulfuron, and seven times as much flucarbazone were required to reduce plant growth by 50%. Sequence analysis of ALS genes from the SM4 line identified at least eight different genes or alleles. An allele associated with the highest levels of resistance was created by a single base substitution creating an amino acid shift previously found to cause ALS inhibitor resistance in yeast and tobacco.

Registration of 34 Sorghum Germplasm Lines Resistant to Acetolactate Synthase–Inhibitor Herbicides

Sorghum [Sorghum bicolor (L.) Moench] germplasm lines designated KS201 through KS234 (Reg. No. GP‐684, PI 659520 to Reg. No. GP‐717, PI 659553) were developed and released by the Kansas Agricultural Experiment Station, Manhattan, KS in 2007. The donor of the herbicide resistance gene, Tailwind, was crossed to adapted‐seed and pollinator‐parent lines. The progenies were treated with the target herbicide, and resistant individuals were repeatedly backcrossed to the adapted parents. Backcrossing was performed until the undesirable wild characteristics from the donor parent were eliminated. Lines KS201 through KS218 are R lines and restore fertility in A1 cytoplasm system; lines KS219 through KS234 are B lines and do not restore fertility in A1 cytoplasm. All lines possess a unique genetic resistance to acetolactate synthase (ALS)–inhibitor herbicide families and are useful breeding materials for the development of commercial hybrids with ALS resistance. The lines are all of combine‐harvester height and reach 50% flowering 60 to 82 d after planting at Manhattan, KS. A majority of the lines are pigmented plant types and have variable grain color and seed sizes within the range common to existing public inbreds.

Evolution and diversity of the mechanisms endowing resistance to herbicides inhibiting acetolactate-synthase (ALS) in corn poppy ( Papaver rhoeas L.)

We investigated the diversity of mechanisms conferring resistance to herbicides inhibiting acetolactate synthase (ALS) in corn poppy ( Papaver rhoeas L.) and the processes underlying the selection for resistance. Six mutant ALS alleles, Arg 197, His 197, Leu 197, Ser 197, Thr 197 and Leu 574 were identified in five Italian populations. Different alleles were found in a same population or a same plant. Comparison of individual plant phenotype (herbicide sensitivity) and genotype (amino-acid substitution(s) at codon 197) showed that all mutant ALS alleles conferred dominant resistance to the field rate of the sulfonylurea tribenuron and moderate or no resistance to the field rate of the triazolopyrimidine florasulam. Depending on the allele, dominant or partially dominant resistance to the field rate of the imidazolinone imazamox was observed. Putative non-target-site resistance mechanisms were also likely present in the populations investigated. The derived Cleaved Amplified Polymorphic Sequence assays targeting ALS codons crucial for herbicide sensitivity developed in this work will facilitate the detection of resistance due to mutant ALS alleles. Nucleotide variation around codon 197 indicated that mutant ALS alleles evolved by multiple, independent appearances. Resistance to ALS inhibitors in P. rhoeas clearly evolved by redundant evolution of a set of mutant ALS alleles and likely of non-target-site mechanisms.

Widespread Occurrence of Herbicide-Resistant Italian Ryegrass (Lolium multiflorum) in Northern Idaho and Eastern Washington

Persistent use of herbicides has resulted in the selection of many herbicide-resistant weeds worldwide. A survey of 75 fields in the Palouse region of the inland Pacific Northwest was conducted to determine the extent of Italian ryegrass resistance to grass herbicides commonly used in winter wheat-cropping systems. Plants grown from collected seed samples were tested for resistance to diclofop, clodinafop, quizalofop, tralkoxydim, sethoxydim, clethodim, pinoxaden, triasulfuron, mesosulfuron, flucarbazone, imazamox, and flufenacet/metribuzin. Averaged across herbicide families within a herbicide group, some level of resistance was exhibited in 73, 31, and 31% of the populations to the aryloxyphenoxypropionates, cyclohexanediones, and phenylpyrazoline herbicides, respectively, and 39, 53, and 55% of the populations to the sulfonylureas, sulfonylaminocarbonyltriazolinone, and imidazolinone herbicides, respectively. Twelve percent of the populations showed some level of resistance to flufenacet/metribuzin. Cross-resistance to all acetyl coenzyme A carboxylase-inhibiting (group 1) herbicides was observed in 12% of the populations, whereas 25% of the populations were cross-resistant to all acetolactate synthase-inhibiting (group 2) herbicides tested. Of all the populations tested, 7% exhibited multiple resistance to at least one herbicide within all three groups tested. Only 5% of populations were completely susceptible to all 12 herbicides tested. These results indicate that herbicide-resistant Italian ryegrass populations are now common across much of the Palouse region in northern Idaho and eastern Washington.

Evaluation of Acetolactate Synthase-inhibiting Herbicides for Weed Control in Transplanted Bell Pepper

Field and greenhouse studies were conducted in 2001 and 2002 near Painter, VA, to determine the level of weed control and pepper (Capsicum annuum) tolerance to postemergence applications of the acetolactate synthase (ALS) inhibitors trifloxysulfuron, halosulfuron, sulfosulfuron, cloransulam, and tribenuron. Based on measurements of visual injury, heights, dry weights, and chlorophyll content of pepper, the safest ALS inhibitor to pepper was trifloxysulfuron followed by halosulfuron, cloransulam, sulfosulfuron, and tribenuron. In addition, trifloxysulfuron was the only herbicide that provided greater than 86% control of pigweed species (Amaranthus spp.) and carpetweed (Mollugo verticillata) in both years of the field study. Trifloxysulfuron was also the only herbicide evaluated that did not reduce pepper yield compared with the control in both years of the field study.

Evaluation of Acetolactate Synthase-inhibiting Herbicides for Weed Control in Transplanted Bell Pepper

Field and greenhouse studies were conducted in 2001 and 2002 near Painter, VA, to determine the level of weed control and pepper (Capsicum annuum) tolerance to postemergence applications of the acetolactate synthase (ALS) inhibitors trifloxysulfuron, halosulfuron, sulfosulfuron, cloransulam, and tribenuron. Based on measurements of visual injury, heights, dry weights, and chlorophyll content of pepper, the safest ALS inhibitor to pepper was trifloxysulfuron followed by halosulfuron, cloransulam, sulfosulfuron, and tribenuron. In addition, trifloxysulfuron was the only herbicide that provided greater than 86% control of pigweed species (Amaranthus spp.) and carpetweed (Mollugo verticillata) in both years of the field study. Trifloxysulfuron was also the only herbicide evaluated that did not reduce pepper yield compared with the control in both years of the field study.

Efficacy of imazamox in imidazolinone-resistant spring oilseed rape in Finland

Imidazolinonies (IMIs) are a group of herbicides inhibiting acetolactate synthase (ALS) activity. They control the growth of many broadleaved weeds and annual grass species. Herbicide resistance against imidazolinonies has been transferred in some crop species, for example in Brassica napus. IMI-resistant oilseed rape cultivars have been developed by a mutation in ALS. They have been on the market for a few years, especially in North America. To determine if imazamox, an imidazolinone herbicide, and IMI-resistant oilseed rape cultivars are suitable for cultivation in Finland, we conducted four herbicide trials in three locations. We found, that imazamox had no negative effect on yield or oil quality characters of IMI-resistant oilseed rape. Some transient chlorosis was observed immediately after the treatment, but it was not apparent after a few days. The effects of imazamox against the most troublesome weeds in oilseed field in Finland, Chenopodium album and Galium spurium, were very good. Imazamox had good or moderate effects on Stellaria media, whereas its effects on Viola arvensis, Lapsana communis and Fallopia convolvulus were insufficient. If the total weed number was high or the emergence of oilseed rape was slow, the application of imazamox increased the yield of oilseed rape compared to untreated control. Our results suggest that imazamox is a good alternative in controlling weeds for Finnish oilseed fields. Therefore, it would be beneficial to transfer the IMI-resistance into Finnish oilseed and turnip rape lines.;

Comparison of Broiler Performance and Carcass Yields When Fed Diets Containing Transgenic Maize Grains from Event DP-Ø9814Ø-6 (Optimum GAT), Near-Isogenic Control Maize Grain, or Commercial Reference Maize Grains

A genetically modified maize (Zea mays L.) line that contains the Optimum GAT trait (event DP-Ø9814Ø-6; 98140) was produced by integration of the gat4621 and zm-hra genes. The expressed GAT4621 and ZM-HRA proteins confer tolerance to the herbicidal active ingredient glyphosate and acetolactate synthase-inhibiting herbicides, respectively. The objective of this study was to compare the nutritional performance of 98140 maize grain to nontransgenic maize grain in a 42-d feeding trial in broiler chickens. Diets were prepared using grain from untreated 98140 plants and from plants treated with an in-field application of herbicides (98140 + Spray). For comparison, additional diets were produced with maize grain obtained from the nontransgenic near-isogenic control (control) and nontransgenic commercial reference Pioneer brand hybrids 33J56, 33P66, and 33R77. Diets were fed to Ross x Cobb broilers (n = 120/group, 50% male and 50% female) in 3 phases: starter, grower, and finisher containing 58.5, 64, and 71.5% maize grain, respectively. No statistically significant differences were observed in mortality, growth performance variables, or carcass and organ yields between broilers consuming diets produced with maize grains from unsprayed or sprayed 98140 and those consuming diets produced with near-isogenic control maize grain. Additionally, all performance and carcass variables from control, 98140, and 98140 + Spray test maize treatment groups were within tolerance intervals constructed using data from reference maize groups. Based on these results, it was concluded that 98140 maize grain (unsprayed or sprayed with a herbicide mixture) was nutritionally equivalent to nontransgenic control maize with comparable genetic background.

Two-Way Performance Interactions amongρ-Hydroxyphenylpyruvate Dioxygenase- and Acetolactate Synthase-Inhibiting Herbicides

There is little information available on performance interactions for tank mixtures of topramezone and acetolactate synthase (ALS)-inhibiting herbicides. Controlled-environment and field experiments were conducted in 2006 and 2007 to determine the interactions of topramezone when tank-mixed with ALS-inhibiting herbicides. Controlled-environment experiments were conducted on four annual grass species treated at the five- to six-leaf stage. Dose–response curves for large crabgrass, barnyardgrass, yellow foxtail, and green foxtail were generated for nicosulfuron or foramsulfuron alone and in combination with label rates of topramezone or mesotrione (with or without atrazine). Eight field experiments were conducted using registered rates of two ρ-hydroxyphenylpyruvate dioxygenase (HPPD)-inhibiting and three ALS-inhibiting herbicides alone and in combination. All herbicide treatments in the field were applied at the two- to three-leaf and five- to six-leaf stages of barnyardgrass, green foxtail, giant green foxtail, and witchgrass. In both the controlled environment and field experiments, antagonistic interactions were found to be species specific. In the controlled environment, nicosulfuron antagonized topramezone for the control of large crabgrass and barnyardgrass, but did not influence control of yellow or green foxtail. This antagonism was overcome with the addition of atrazine or an increased dose of nicosulfuron. Antagonism was not observed with tank mixtures of topramezone and foramsulfuron on the species tested under controlled-environment or field conditions. In the field, antagonism was not influenced by growth stage of the annual grasses. Antagonistic interactions were observed when topramezone was tank-mixed with nicosulfuron or nicosulfuron + rimsulfuron for the control of barnyardgrass and, to a lesser extent, giant green foxtail. Similar tank mixtures did not reduce control of green foxtail or witchgrass. HPPD-inhibiting herbicides are known to antagonize the activity of ALS-inhibiting herbicides for the control of annual grasses. This is the first report in the literature that an ALS-inhibiting herbicide can antagonize an HPPD-inhibiting herbicide. Thus, the chemistries of these herbicides exhibit a two-way antagonistic interaction.

Hybrid Kentucky Bluegrass Tolerance to Preemergence and Postemergence Herbicides

Field studies were conducted near Knoxville, TN, from 2003 to 2005 to evaluate the response of ‘Thermal Blue’, a new interspecific hybrid Kentucky bluegrass to commonly applied PRE and POST herbicides for weed management. Dithiopyr, oryzalin, oxadiazon, pendimethalin, prodiamine, quinclorac, and trifluralin applied at seeding injured hybrid bluegrass greater than 81% and reduced hybrid bluegrass cover greater than 57%. In a second study, established hybrid bluegrass was treated POST with acetolactate synthase–inhibiting herbicides including bispyribac-sodium, chlorosulfuron, foramsulfuron, halosulfuron, imazapic, imazaquin, metsulfuron, rimsulfuron, sulfosulfuron, and trifloxysulfuron at low and high rates (one and two times the suggested use rates in Kentucky bluegrass or other turfgrasses). By 5 wk after treatment (WAT), foramsulfuron at 88 g ai/ha and trifloxysulfuron at 35 g ai/ha injured hybrid bluegrass greater than 26% and reduced visually estimated quality and chlorophyll meter indices. However, hybrid bluegrass injury was no longer evident at 10 WAT. In a third study, established hybrid bluegrass was treated with clethodim, diclofop-methyl, fluazifop-p-butyl, and sethoxydim applied at low, medium, and high rates (0.5, 1, and 2 times the registered Kentucky bluegrass or other turfgrass use rates). Clethodim applied at 280 and 560 g ai/ha, fluazifop at 420 g ai/ha, and sethoxydim at 630 g ai/ha injured hybrid bluegrass 5 WAT. These treatments also reduced quality (to less than 5 on a scale of 1 to 9) and chlorophyll meter indices (24 to 37%) when compared to the untreated control. By 10 WAT, only clethodim at 560 g ai/ha caused injury (14%). By 10 WAT, hybrid bluegrass had recovered and injury was only observed in plots treated with clethodim at 560 g ai/ha. No differences in chlorophyll indices or quality were observed at 10 WAT for any POST graminicides.Nomenclature: Bispyribac-sodium, chlorosulfuron, clethodim, diclofop-methyl, dithiopyr, fluazifop-p-butyl, foramsulfuron, halosulfuron, imazapic, imazaquin, metsulfuron, oryzalin, oxadiazon, pendimethalin, prodiamine, quinclorac, rimsulfuron, sethoxydim, sulfosulfuron, trifloxysulfuron, trifluralin, Kentucky bluegrass, Poa arachnifera Torr. × P. pratensis L. ‘Thermal Blue’

A molecular assay for the proactive detection of target site‐based resistance to herbicides inhibiting acetolactate synthase in Alopecurus myosuroides

SummaryAcetolactate synthase (ALS) inhibitors are the most resistance‐prone herbicide group. Rapid resistance diagnosis is thus of importance for their optimal use. We formulate rules to use the derived cleaved amplified polymorphic sequence method to develop molecular tools detecting a change at a given codon, the nature of which is unknown. We applied them to Alopecurus myosuroides (black grass) to develop assays targeting ALS codons A122, P197, A205, W574 and S653 that are crucial for herbicide sensitivity. These assays detected W574L or P197T, or both substitutions, in most plants analysed from a field where ALS inhibitors failed after 3 years of use. Similar assays can easily be set up for any species. Given the rapidity of selection for resistance to ALS inhibitors, these assays should be very useful in proactive herbicide resistance diagnosis.

Aquatic Plant Management and The Impact of Emerging Herbicide Resistance Issues

Aquatic plants provide many benefits to the environment, but must be managed when growth reaches nuisance levels or when invasive plant species are released. Management tactics include biological, chemical, cultural, mechanical, and physical tools. Each specific management technique has advantages and disadvantages. In addition, the implementation of these techniques can become complicated because of the multiple users, managers, and stakeholders that may be present on large bodies of water. As an example, hydrilla is the most economically damaging aquatic weed in the United States. It reproduces through fragmentation, turions, and occasionally seed and can colonize a wide variety of aquatic environments. The most common management tactics for hydrilla include biological, chemical, and mechanical tools. Triploid grass carp have been the primary biological control agent, whereas fluridone has been the only systemic herbicide used. Because of heavy utilization of fluridone, biotypes have developed resistance to this herbicide in Florida. Although several acetolactate synthase-inhibiting herbicides are in development, herbicides with additional modes of action are needed for resistance management. Other aquatic plant management needs include additional control tactics for algae and additional extension resources for public education.Nomenclature: Fluridone, hydrilla, Hydrilla verticillata (L.f.) Royle, triploid grass carp, Ctenopharyngodon idella Val