Explore the vast range of titles available.

The evolution of weed biotypes resistant to multiple herbicide modes of action, here termed multiple herbicide resistance, is a growing problem around the world. We investigated two multiple herbicide resistant (MHR) wild oat (Avena fatua L.) populations from Montana and hypothesized that they would exhibit fitness costs compared with two herbicide‐susceptible (HS) populations. Dose‐response tests showed that the MHR populations were resistant to difenzoquat (a membrane disruptor), imazamethabenz (an acetolactate synthase [ALS] inhibitor), flucarbazone (an ALS inhibitor), and tralkoxydim (an acetyl‐CoA carboxylase inhibitor). In greenhouse studies, we assessed differences between MHR and HS populations in seed germination, photosynthetic parameters, plant growth, and reproduction. Seeds of one HS population germinated more at cold temperature (4.9°C) and less at high temperature (29.6°C) compared with the other populations. Plants of this HS population also had lower stomatal conductance (23%), intercellular CO2 concentration (7.5%), and transpiration (15.3%) than the other populations, but there were no differences in photosynthetic rates between any populations. Also, there were no differences in relative growth rate among all HS and MHR populations. The MHR populations initiated seed production several days sooner than the HS populations; however, HS populations produced 67% more tillers, and one HS population ultimately produced 43% more seeds than the MHR populations, indicating a potential fitness cost of resistance. With the exception of seed production differences, our results do not indicate a consistent fitness cost. More research is needed in field settings and with resource competition to further evaluate fitness costs in MHR populations.

A late-summer survey of herbicide-resistant (HR) weeds was conducted in Alberta in 2007, Manitoba in 2008, and Saskatchewan in 2009, totaling 1,000 randomly selected annually cropped fields. In addition, we screened 1,091 weed seed samples (each sample from one field) submitted by Prairie growers between 2007 and 2011. Of 677 fields where wild oat samples were collected, 298 (44%) had an HR biotype. Group 1 (acetyl CoA carboxylase inhibitor)-HR wild oat was confirmed in 275 fields (41%), up from 15% in previous baseline surveys (2001 to 2003). Group 2 (acetolactate synthase)-HR wild oat was found in 12% of fields (vs. 8% in 2001 to 2003). Group 8 (triallate, difenzoquat)-HR wild oat was identified in only 8% of fields (not tested in 2001 to 2003); the frequency of occurrence of group 1+2-HR wild oat was similar (8%, vs. 3% in 2001 to 2003). Group 1-HR green foxtail was found in 27% of 209 fields sampled for the weed (vs. 6% in 2001 to 2003). Group 2-HR spiny sowthistle was confirmed in all Alberta fields sampled (vs. 67% in 2001); common chickweed was found mainly in Alberta in 40% of fields (vs. 17% in 2001). Group 2-HR weed biotypes not previously detected in the baseline surveys included false cleavers mainly in Alberta (17% of fields) and Saskatchewan (21%), Powell amaranth in Manitoba (16% of fields), wild mustard (three populations in Saskatchewan and Manitoba), and wild buckwheat (one population in Alberta). No sampled weed populations across the Prairies were found to be resistant to herbicides from group 4 (synthetic auxins), group 9 (glyphosate), or group 10 (glufosinate). Based on the proportion of total field area at each site infested with HR weeds, it is estimated that 7.7 million ha (29% of annually cropped land) are infested with HR weeds (eight-fold increase from 2001 to 2003), in a total field area of 9.9 million ha (37%)—over a two-fold increase. Of 816 cases of HR wild oat identified from submitted samples, 69% were group 1-HR, 15% group 2-HR, and 16% group 1+2-HR. Additionally, there were 10 populations of group 1-HR green foxtail in Saskatchewan or Manitoba, and six populations of group 1-HR Persian darnel in southern Alberta and Saskatchewan. Various group 2-HR broadleaf weeds were identified, including 17 wild mustard populations mainly from Saskatchewan and 39 cleavers populations across the three Prairie provinces. Herbicide-use data from 2006 to 2010 indicated continued reliance on group 1 herbicides in cereal crops and group 2 herbicides in pulse crops. Nomenclature: Common chickweed, Stellaria media (L.) Vill. STEME; false cleavers, Galium spurium L. GALSP; green foxtail, Setaria viridis (L.) Beauv. SETVI; Persian darnel, Lolium persicum Boiss. & Hohen. ex Boiss. LOLPS; Powell amaranth, Amaranthus powellii S. Wats. AMAPO; spiny sowthistle, Sonchus asper (L.) Hill SONAS; wild buckwheat, Polygonum convolvulus L. POLCO; wild mustard, Sinapis arvensis L. SINAR; wild oat, Avena fatua L. AVEFA. Un estudio observacional sobre malezas resistentes a herbicidas (HR) se realizó al final del verano en Alberta en 2007, Manitoba en 2008 y Saskatchewan en 2009, para un total de 1,000 muestras aleatoriamente seleccionadas de campos cultivados anualmente. Adicionalmente, evaluamos 1,091 muestras de semillas de malezas (cada muestra proveniente de un campo) remitidas por productores de las Praderas entre 2007 y 2011. De 677 campos donde se colectó muestras de Avena fatua, 298 (44%) tuvieron un biotipo HR. Se confirmó Avena fatua HR grupo 1(inhibidores de acetyl CoA carboxylase) en 275 campos (41%), lo cual fue un incremento del 15% con base en estudios de referencia previos (2001–2003). Se encontró A. fatua HR grupo 2 (acetolactate synthase) en 12% de los campos (vs. 8% en 2001 a 2003). A. fatua HR grupo 8 (triallate, difenzoquat) fue identificada en solamente 8% de los campos (no se evaluó en 2001 a 2003). La frecuencia de presencia de A. fatua HR grupos 1+2 fue similar (8%, vs. 3% en 2001 a 2003). Setaria viridis HR grupo 1 fue encontrada en 27% de 209 campos muestreados por esta maleza (vs. 6% en 2001 al 2003). Se confirmó Sonchus asper HR grupo 2 en todos los campos muestreados en Alberta (vs. 67% en 2001); mientras que Stellaria media HR se encontró principalmente en Alberta en 40% de los campos (vs. 17% en 2001). Biotipos de malezas HR grupo 2 que no habían sido detectados en los estudios previos incluyeron Galium spurium principalmente en Alberta (17% de los campos) y en Saskatchewan (21%), Amaranthus powellii en Manitoba (16% de los campos), Sinapis arvensis (tres poblaciones en Saskatchewan y Manitoba) y Polygonum convolvulus (una población en Alberta). De las poblaciones de malezas muestreadas a lo largo de las Praderas, no se encontró ninguna que fuera resistentes a herbicidas del grupo 4(auxinas sintéticas), grupo 9 (glyphosate) o grupo 10 (glufosinate). Basándose en la proporción del área total de campos infestados con malezas HR en cada sitio, se estimó que 7.7 millones ha (29% de la tierra cultivada anualmente) están infestadas con malezas HR (un incremento de ocho veces desde 2001 a 2003), en un área total de 9.9 millones ha (37%)—más del doble de incremento. De 816 casos de A. fatua HR identificados en las muestras remitidas, 69% fueron HR grupo 1, 15% HR grupo 2 y 16% HR grupo 1+2. Adicionalmente, hubo 10 poblaciones de S. viridis HR grupo 1 en Saskatchewan o Manitoba, y seis poblaciones de Lolium persicum HR grupo 1 en el sur de Alberta y Saskatchewan. Varias malezas de hoja ancha HR grupo 2 fueron identificadas, incluyendo 17 poblaciones de S. arvensis predominantemente de Saskatchewan y 39 poblaciones de G. spurium a lo largo de tres provincias de las Praderas. Datos de uso de herbicidas de 2006 a 2010 indicaron que ha continuado la dependencia en herbicidas grupo 1 en cultivos de cereales y de herbicidas grupo 2 en cultivos de granos de especies dicotiledóneas.

Genetically modified crops are now grown worldwide and their area of cultivation is increasing yearly. Although transgenic crops offer benefits, several risks have been identified associated with their cultivation. One such risk is their potential for hybridization with wild species, and weed-related species, and the possible escape and subsequent introgression of the transgenes into these species. Transgenic wheat varieties are being successfully developed and field-tested, primarily on herbicide-tolerant wheat. If genetically modified herbicide-tolerant wheat is commercialized in the near future this may result in the escape of the inserted gene from the crop and its incorporation into closely related wild species. This fact could give a competitive advantage to the recipients. For risk assessment purposes it is necessary to determine the frequency of crop-wild transgene flow and the fertility of hybrids. Most wheat-wild hybridization studies have been conducted with the purpose of breeding with wheat acting as the female parent in crosses, but very limited information is available focused on hybrid production with wheat as the male parent. Here, we studied (1) the potential hybridization between wheat and the wild related Aegilops biuncialis , and (2) the fertility of the hybrids. Hybridization was quantified in crossing experiments over 5 years in a greenhouse using three wheat cultivars as pollen donors and emasculated plants of one A. biuncialis population as pollen recipients. Hybridization was estimated as the ratio of number of seeds set to the number of flowers pollinated in percentage terms. Our results show that hybrids between wheat and A. biuncialis are formed easily, with hybridization rates ranging from 8.5 to 75%. The fertility of the hybrids, measured as the number of seeds per spikelet (%), was also evaluated by self-pollination and by backcrossing. Most of the hybrids were self-sterile but 11 F 2 seeds were obtained from 191 A. biuncialis -wheat hybrids. However, backcrossing seeds were found in all BC 1 combinations at average rates of 3.7% (0–19.6%) for greenhouse experiments, and 4.6% (0–28.9%) for field experiments. In subsequent generations, although few plants were available, BC 1 F 1 exhibited a certain degree of fertility, up to 3.57% with the cultivar Chinese Spring. F 1 and BC 1 were also checked for resistance to the herbicide difenzoquat that was present in the parental wheat, while A. biuncialis was susceptible. Difenzoquat resistance was maintained in the F 1 hybrids and also in the derived BC 1 plants. This information on hybridization and fertility of the first A. biuncialis -wheat hybrid generations could be an initial step to assess the relative advantage of hybridization in the adaptive ability of A. biuncialis and hybrid derivatives and the impact thereof on the environment and agricultural system. This needs to be studied in depth when wheat and A. biuncialis share habitat.

Summary We report improved separation of the highly toxic contact herbicides paraquat, diquat, difenzoquat, mepiquat, and chloromequat by HPTLC. Quantification was based on a new derivatization reaction using sodium tetraphenylborate. Measurements were in the wavelength range from 440 to 480 nm or from 440 to 590 nm. An LED emitting very intense light at 365 nm was used for excitation. The quantification limits of paraquat and diquat in water, using improved solid-phase extraction, was in the low ng L -1 range. The linear range covered more than two orders of magnitude. Recovery was investigated for all the compounds, and was insufficient, ranging from 11 to 92%, but the method is inexpensive, rapid, and works reliably.

The levels and distribution of diquat, paraquat, and difenzoquat were determined by solid phase extraction (SPE) and high-performance liquid chromatography (HPLC) in water samples from irrigation channels, rivers, and lagoons taken during 1 year from three different marsh areas of the Valencian community. These areas are representative of the typical Mediterranean coastal ecosystems. All three compounds were detected. Diquat was found most frequently at all the sampling sites. Although the spatial distribution of diquat and paraquat showed a maximum concentration near the fields where they were originally applied, their location fluctuated due to irregular large spill and/or loading. The herbicide concentration tended to be highest during the summer (June, July, and August) because these are the months with the least rainfall and highest evaporation rates, when weeds grow best and pesticides are needed more often. The average concentration found for diquat was 0.09 g/L, with a maximum of 3.10 g/L. The average concentration for paraquat was 0.01 g/L, with a maximum of 3.95 g/L. Samples that were below the method detection limit are included in the mean calculation as zero. Difenzoquat was only detected in one sample at a concentration of 1.75 g/L.

The diversity of resistance among wild oat collected before and after commercial introduction of imazamethabenz, difenzoquat, diclofop, fenoxaprop-P, sethoxydim, and tralkoxydim was evaluated. Wild oat sampled in 1964 and 2000 from the Red River Valley of Minnesota and North Dakota were screened for resistance. Nearly 43% of the 1964 collections were susceptible (S) to all six herbicides, whereas only 9% were S by 2000. The frequency of resistance in 2000 compared with 1964 increased for all six herbicides, and 27 phenotype response groups to the six herbicides occurred in 2000 vs. 14 phenotype response groups for the 1964 collection. The proportion of resistant (R) plants increased faster for the aryloxyphenoxypropionate (APP) herbicides, diclofop and fenoxaprop-P, than for the cyclohexanedione (CHD) herbicides, sethoxydim and tralkoxydim. High diversity of resistance responses was observed in wild oat to acetyl-coenzyme A carboxylase–inhibitor herbicides, suggesting that there may be multiple APP herbicide– or CHD herbicide–specific resistance mechanisms in addition to those that confer cross-resistance. The trend of resistance response generally indicates that increased exposure to herbicides in wild oat may confer resistance to newly introduced but unrelated herbicides.

Selective on-line solid phase extraction (SPE) and liquid chromatography determination (HPLC) of diquat, paraquat and difenzoquat from environmental water samples has been accomplished with Graphitized Carbon Black (GCB) as both extraction and analytical columns. The method involved passing of 50 mL of water through a cartridge filled with Carbograph. In the elution step, the herbicides were transferred from the cartridge to the analytical column (Hypercarb) by mean of a gradient of pH 3 aqueous solution of tetramethylammonium hydroxide (TMAOH) and ammonium sulphate and methanol. Hypercarb columns were found to give a low probability of false positives for bypiridylium herbicides and are very selective for polar compounds. Recovery was better than 80 %. The breakthrough volume was studied with distilled water spiked with the herbicides at various concentration levels (from 0.1 to 20 μg L−1). The limits of quantification of the method were lower than 0.1 μg L−1. The total analytical method was applied to surface waters from Torreblanca Nature Park (Castelló, Spain).

Rates and application timings of postemergence herbicides for wild oat control in spring wheat and barley were evaluated at Crookston, MN, from 1994 to 1996. Diclofop, imazamethabenz, and fenoxaprop plus MCPA plus thifensulfuron plus tribenuron were applied to one- to three-leaf wild oat; and difenzoquat, imazamethabenz, fenoxaprop plus MCPA plus thifensulfuron plus tribenuron, and fenoxaprop plus 2,4-D plus MCPA were applied to four- to five-leaf wild oat at 1/2 ×, 3/4 ×, and 1 × rates. Wild oat response to herbicide rate and timing was similar in wheat and barley. Wild oat control with 1/2 × rates generally was less than that with 3/4 × rates, which was lower than or similar to that with 1 × rates. Wild oat biomass was often reduced less with 1/2 × rates than 1 × rates. However, reducing herbicide rates generally did not influence grain yields or net economic return. Grain yields and net economic return were generally greater in herbicide-treated plots than in the nontreated control.

In response to farmer complaints of poor triallate performance, wild oat seed was collected from 34 fields in Alberta in the fall of 1990. Screening trials in the greenhouse indicated that 15 of the populations were highly resistant to triallate applied at the equivalent of the recommended field rate (1.7 kg ha-1), whereas the other 19 populations were adequately controlled. All triallate-resistant populations were also highly resistant to difenzoquat applied at 1.7 kg ha-1 (equivalent to twice the recommended field rate). The effect of increasing rates of both herbicides on dry weight of five of the resistant and two of the susceptible populations was determined in greenhouse experiments. Triallate applied up to 3.4 kg ha-1 had little or no effect on the resistant populations, whereas the susceptible populations were controlled at 1.7 kg ha-1. At rates of 6.8 kg ha-1 or higher, there were differences among the resistant populations and among individuals within the populations in the response to triallate. Response of the resistant populations to increasing difenzoquat rates was variable between experiments, but in all cases the effect of difenzoquat on wild oat dry weight was considerably less in triallate-resistant than triallate-susceptible populations. Effects of increasing rates of triallate and difenzoquat on resistant and susceptible wild oat populations growing with barley in field experiments were generally similar to the responses in the greenhouse.