Annual Bromus Research Articles

Economics of herbicide weed management in wheat in Ethiopia

Effective use of herbicides for the control of annual grass and broadleaf weeds in wheat ( Triticum aestivum L.) was not a reality in Ethiopia, until in recent years. This study aimed at evaluating different post-emergence herbicides against annual grasses and broadleaf weeds in wheat for selection and incorporation into an integrated weed management (IWM) system. The study was conducted at Kulumsa Agricultural Research Centre main station, Bekoji and Lole farm fields. Treatments included herbicides, namely, Mesosulfron methyl+Idosulfuron methyl sodium (liquid) 1 lit ha -1 a.i. Pyroxsulam (liquid) 0.5 l ha -1 a.i. hand weeding twice (30-35 and 55-60 days after emergence (DAE)); and a weedy check. Among the annual grass weeds, Snowdenia polystachya, Avena fatua, Bromus pectinatus, Phalaris paradoxa and Setaria pumila ; and most broad leaf weeds like Polygonum nepalense, Guizotia scabra, Galinsoga parviflora and Gallium spurium were controlled with herbicide efficacy ranging from 75 to 100%. Mesosulfron methyl +Idosulfron methyl sodium, Pyroxulam and hand weeded twice plots outyielded the weedy check by 63, 58 and 53%, respectively. Maximum wheat grain yield (5,184 kg ha -1 ), biomass (12,808 kg ha -1 ), thousand kernel weight (48.55) and hectoliter weight (74.2) were obtained due to the application of Mesosulfron methyl+Idosulfuron methyl sodium. In addition, the herbicide had a yield advantage over Pyroxsulam, two hand weedings and the weedy check by 12, 21 and 63%, respectively. Application of Mesosulfron methyl + Idosulfuron methyl sodium (US$1,596.31 ha -1 ) had the highest net field benefit compared to Pyroxsulam (US$1,379.21 ha -1 ), two hand weeding (US$1,126.7 ha -1 ) and weedy check (US$574.1 ha -1 ) by 13.6, 29 and 64%, respectively. Moreover, the herbicide was also economically profitable to farmers, providing a marginal rate of return (MRR) of 1,737%. Sensitivity analysis (aMRR) also remained the most profitable even when the price of herbicide increased by 20%. Hence, Mesosulfron methyl +Idosulfuron methyl sodium at a rate of 1 lit ha -1 is thebest herbicide for the effective control of annual grasses and broad leaf weeds in wheat and can be used as one of the component in Integrated Weed Management Program (IWM) in wheat fields. Key Words : Idosulfuron methyl sodium, Mesosulfron methyl, Triticum aestivum

Low-Dose Glyphosate Does Not Control Annual Bromes in the Northern Great Plains

AbstractAnnual bromes (downy brome and Japanese brome) have been shown to decrease perennial grass forage production and alter ecosystem functions in northern Great Plains rangelands. Large-scale chemical control might be a method for increasing rangeland forage production. Although fall application has been shown to be the most effective and least likely to impact co-occurring native species, spring germination of downy brome may reduce the efficacy of fall-only herbicide application. We assessed the impact of a low glyphosate dose rate (210 g ha−1) applied to rangelands in fall or in fall and spring on nontarget species and on annual brome abundance at two sites in eastern Montana over 2 yr. We tested the following hypotheses: (1) nontarget effects are greater with spring herbicide application, (2) fall and spring herbicide application are necessary for effective downy brome control, and (3) fall herbicide application is sufficient to control Japanese brome. Few nontarget effects occurred; two dicotyledonous species exhibited small increases in response to herbicide. We found that that a single fall application reduced downy brome cover and seed bank density, but after the second fall application in the following year, downy brome did not continue to show a response to herbicide. After 2 yr of fall herbicide application, Japanese brome had denser seed banks in plots where herbicide had been applied. Blanket glyphosate application on rangelands is an unreliable method for controlling annual brome invasions in the northern Great Plains.

Site-Specific Effects of Exotic Annual Grass Control Integrated with Revegetation

Invasion by exotic annual grass species such as downy brome and Japanese brome has been implicated in ecosystem degradation in much of the western United States and strategies to restore lands dominated by these species are needed. We evaluated integration of herbicide and revegetation to restore old-field and rangeland sites dominated by annual brome species. In split-plot field studies, we compared three imazapic herbicide rates and eight seeding treatments at an old-field and a rangeland site. We evaluated brome, seeded species, and existing vegetation response to our treatments. Herbicide controlled annual brome at both sites, with > 95% decreases in brome biomass in plots treated with the high rate compared to non-sprayed controls. Control of annual brome persisted for two growing seasons at the old-field site and one season at the rangeland site. Annual brome abundance in non-treated control plots at both sites decreased by 80% between the first and second growing season. No seeded individuals established at the old-field site, but they persisted through two growing seasons at the rangeland site. Seeded species establishment at the rangeland site was impacted by both herbicide rate and seed mix, but no clear patterns emerged. Finally, while we controlled brome at both sites, existing desired vegetation increased only at the old-field site, where perennial grass biomass increased by about 30% in plots sprayed with both rates of herbicide. The differing responses of the existing and seeded plant communities across the two sites highlight the importance of integrating site-specific knowledge into restoration plans.

Evaluation of infection with endophytes in seeds of forage species with different levels of ploidy

Many C3 grasses establish mutualistic associations with endophytic fungi Neotyphodium spp. Lolium multiflorum Lam. natural diploid populations of the Pampa region present high levels of infection whereas commercial cultivars, mainly tetraploid, exhibit low or no infection. In the genus Bromus, no information is available about this association in polyploid populations. The incidence of Neotyphodium spp. endophytes in diploid and tetraploid commercial cultivars of L. multiflorum, as well as in natural hexaploid populations of genus Bromus, was analysed. Observed infection was higher in diploid populations of L. multiflorum than in tetraploid populations. No infection was detected in Bromus spp. Various factors such as the production and handling of commercial seeds, the interaction of endophytes with ploidy level, and the genetic manipulation of seeds are discussed as the possible causes for the differences observed between natural and improved annual ryegrass and brome populations, and between diploid and tetraploid annual ryegrass.

Suppression of annual Bromus tectorum by perennial Agropyron cristatum: roles of soil nitrogen availability and biological soil space.

Worldwide, exotic invasive grasses have caused numerous ecosystem perturbations. Rangelands of the western USA have experienced increases in the size and frequency of wildfires largely due to invasion by the annual grass Bromus tectorum. Rehabilitation of invaded rangelands is difficult; but long-term success is predicated on establishing healthy and dense perennial grass communities, which suppress B. tectorum. This paper reports on two experiments to increase our understanding of soil factors involved in suppression. Water was not limiting in this study. Growth of B. tectorum in soil conditioned by and competing with the exotic perennial Agropyron cristatum was far less relative to its growth without competition. When competing with A. cristatum, replacing a portion of conditioned soil with fresh soil before sowing of B. tectorum did not significantly increase its growth. The ability of conditioned soil to suppress B. tectorum was lost when it was separated from growing A. cristatum. Soil that suppressed B. tectorum growth was characterized by low mineral nitrogen (N) availability and a high molar ratio of [Formula: see text] in the solution-phase pool of [Formula: see text] Moreover, resin availability of [Formula: see text] explained 66 % of the variability in B. tectorum above-ground mass, attesting to the importance of A. cristatum growth in reducing N availability to B. tectorum. Trials in which B. tectorum was suppressed the most were characterized by very high shoot/root mass ratios and roots that have less root hair growth relative to non-suppressed counterparts, suggesting co-opting of biological soil space by the perennial grass as another suppressive mechanism. Greater understanding of the role of biological soil space could be used to breed and select plant materials with traits that are more suppressive to invasive annual grasses.

Pyrenophoric Acid, a Phytotoxic Sesquiterpenoid Penta-2,4-dienoic Acid Produced by a Potential Mycoherbicide, Pyrenophora semeniperda

A new phytotoxic sesquiterpenoid penta-2,4-dienoic acid, named pyrenophoric acid, was isolated from solid wheat seed culture of Pyrenophora semeniperda, a fungal pathogen proposed as a mycoherbicide for biocontrol of cheatgrass (Bromus tectorum) and other annual bromes. These bromes are serious weeds in winter cereals and also on temperate semiarid rangelands. Pyrenophoric acid was characterized as (2Z,4E)-5-[(7S,9S,10R,12R)-3,4-dihydroxy-2,2,6-trimethylcyclohexyl)]-3-methylpenta-2,4-dienoic acid by spectroscopic and chemical methods. The relative stereochemistry of pyrenophoric acid was assigned using 1H,1H couplings and NOESY experiments, while its absolute configuration was determined by applying the advanced Mosher's method. Pyrenophoric acid is structurally quite closely related to the plant growth regulator abscisic acid. When bioassayed in a cheatgrass coleoptile elongation test at 10(-3) M, pyrenophoric acid showed strong phytotoxicity, reducing coleoptile elongation by 51% relative to the control. In a mixture at 10(-4) M, its negative effect on coleoptile elongation was additive with that of cytochalasin B, another phytotoxic compound found in the wheat seed culture extract of this fungus, demonstrating that the extract toxicity observed in earlier studies was due to the combined action of multiple phytotoxic compounds.

Adaptive Restoration of River Terrace Vegetation through Iterative Experiments

ABSTRACT Restoration projects can involve a high degree of uncertainty and risk, which can ultimately result in failure. An adaptive restoration approach can reduce uncertainty through controlled, replicated experiments designed to test specific hypotheses and alternative management approaches. Key components of adaptive restoration include willingness of project managers to accept the risk inherent in experimentation, interest of researchers, availability of funding for experimentation and monitoring, and ability to restore sites as iterative experiments where results from early efforts can inform the design of later phases. This paper highlights an ongoing adaptive restoration project at Zion National Park (ZNP), aimed at reducing the cover of exotic annual Bromus on riparian terraces, and revegetating these areas with native plant species. Rather than using a trial-and-error approach, ZNP staff partnered with academic, government, and private-sector collaborators to conduct small-scale experiments to e...

Exposure to low water potentials and seed dormancy favour the fungus in the Pyrenophora semeniperda-Bromus tectorum pathosystem

In semi-arid regions of the United States, Pyrenophora semeniperda kills seeds of the winter annual Bromus tectorum. We report on pathosystem outcomes under manipulated water potential and temperature environments commonly observed within semi-arid environments for dormant and non-dormant seeds. We propose a range of outcomes for infected seeds. During summer, seeds remain dormant and are killed across a range of water potentials. During autumn, seeds survive by rapidly germinating or are killed if radicle emergence is delayed by intermittent hydration. In winter/spring, secondarily dormant seeds can be killed by the fungus. The only likely scenarios where seeds escape death include absence of infection (autumn, spring, or following autumn, germination) or infection in autumn when seeds germinate rapidly.

Effect of strain and cultural conditions on the production of cytochalasin B by the potential mycoherbicide Pyrenophora semeniperda (Pleosporaceae, Pleosporales)

The seed pathogen Pyrenophora semeniperda has demonstrated potential as a mycoherbicidal biocontrol for eliminating persistent seed banks of annual bromes on western North American rangelands. This pathogen exhibits variation in virulence that is related to mycelial growth rate, but direct laboratory tests of virulence on seeds often have low repeatability. We developed a rapid and sensitive high pressure liquid chromatography method for quantification of the phytotoxin cytochalasin B in complex mixtures in order to evaluate its use in virulence screening. All 10 strains tested produced large quantities of this metabolite in solid wheat seed culture, with production varying over a fourfold range (535–2256 mg kg−1). No cytochalasin B was produced in liquid potato dextrose broth culture, showing that its synthesis is strongly dependent on cultural conditions. In a Bromus tectorum coleoptile bioassay, solid culture extracts showed mild toxicity similar to the cytochalasin B standard at a concentration equivalent to 10−4 M cytochalasin B (72–95% of control), whereas at 10−3 M equivalent, the extracts exhibited significantly higher toxicity (8–18% of control) than the cytochalasin B standard (34% of control). This suggests the possible presence of other phytotoxic metabolites. Cytochalasin B production in solid wheat seed culture exhibited the predicted significant negative correlation with mycelial growth rate on potato dextrose agar, but the correlation was not very strong, possibly because cytochalasin B production and growth rate were measured under different cultural conditions.

Contrasting responses of heterotrophic and autotrophic respiration to experimental warming in a winter annual‐dominated prairie

Understanding how soil respiration (Rs) and its source components respond to climate warming is crucial to improve model prediction of climate-carbon (C) feedback. We conducted a manipulation experiment by warming and clipping in a prairie dominated by invasive winter annual Bromus japonicas in Southern Great Plains, USA. Infrared radiators were used to simulate climate warming by 3°C and clipping was used to mimic yearly hay mowing. Heterotrophic respiration (Rh) was measured inside deep collars (70cm deep) that excluded root growth, while total soil respiration (Rs) was measured inside surface collars (2-3cm deep). Autotrophic respiration (Ra) was calculated by subtracting Rh from Rs. During 3years of experiment from January 2010 to December 2012, warming had no significant effect on Rs. The neutral response of Rs to warming was due to compensatory effects of warming on Rh and Ra. Warming significantly (P<0.05) stimulated Rh but decreased Ra. Clipping only marginally (P<0.1) increased Ra in 2010 but had no effect on Rh. There were no significant interactive effects of warming and clipping on Rs or its components. Warming stimulated annual Rh by 22.0%, but decreased annual Ra by 29.0% across the 3years. The decreased Ra was primarily associated with the warming-induced decline of the winter annual productivity. Across the 3years, warming increased Rh/Rs by 29.1% but clipping did not affect Rh/Rs. Our study highlights that climate warming may have contrasting effects on Rh and Ra in association with responses of plant productivity to warming.

Growth and phenology of Dittrichia graveolens, a rapidly spreading invasive plant in California

Dittrichia graveolens is a rapidly spreading invasive plant in California. While populations are observed primarily in disturbed areas, there is concern it may expand into adjacent undisturbed areas, particularly grasslands and riparian corridors. In a field experiment conducted in two successive years, we compared plant growth and phenological development of fall, winter, and spring sown seeds. Plants establish equally well in disturbed upland sites in both above and below average precipitation years but the absence of late spring rainfall negatively affected total plant biomass. In a greenhouse experiment, we compared growth in four light environments (100, 50, 27 and 9 % available light). Total plant growth decreased exponentially with decreasing light. This suggests that D. graveolens is not competitive in low light environments, such as woodlands and riparian forests. All plants flowered in early- to mid-September, coinciding with flowering in field grown plants, suggesting that photoperiod is the primary signal for reproductive growth. Using a minirhizotron system, we measured root growth over time in D. graveolens and three common California annual grassland species, two non-natives, Centaurea solstitialis and Bromus hordeaceus, and the native forb Holocarpha virgata. Root growth of D. graveolens began later in the season than the other species, reaching depths >1 m by late May. Roots of C. solstitialis and H. virgata reached >1 m earlier in the season. The temporal difference in root growth suggests that D. graveolens may be less competitive for soil moisture with other early season annuals than other deep-rooted broadleaf species found in grasslands.

An aboveground–belowground assessment of ecosystem properties associated with exotic annual brome invasion

Exotic annual brome invasion has been well studied in western North American rangelands, particularly for Bromus tectorum L. invasion in sagebrush (Artemisia tridentata) grasslands. We examined both aboveground and belowground properties in native sagebrush grassland and adjacent areas dominated by exotic annual bromes (B. tectorum L. and Bromus japonicus Thunb.) to better understand the fundamental ecological differences between native and invaded areas. Field sites were located in north central Wyoming, USA, and plots were established in areas that had been historically subject to wildfire and either (1) recolonized by native sagebrush grassland vegetation or (2) invaded by exotic annual bromes. We employed measures of vegetation community structure as well as soil physical, chemical, and microbiological properties. Plots with greater than 20 % exotic annual brome cover had significantly less cover of all native vegetation functional groups resulting in lower richness and evenness than native plots. Invaded plots also had low diversity plant communities that were continuous and uniform across space. Soils beneath invaded plant communities had higher infiltration rates, higher levels of total nitrogen, and a lower C/N ratio than the native soils. Invaded soils also had 90–96 % lower abundance of all soil microbial groups measured by phospholipid fatty acid. We conclude that areas dominated by exotic annual bromes display different aboveground and belowground properties compared to the native community, and these changes possibly include spatial and temporal shifts in soil resources and organic matter processing.

Soil Seed Bank Responses to Postfire Herbicide and Native Seeding Treatments Designed to Control Bromus tectorum in a Pinyon–Juniper Woodland at Zion National Park, USA

AbstractThe continued threat of an invasive, annual brome (Bromus) species in the western United States has created the need for integrated approaches to postfire restoration. Additionally, the high germination rate, high seed production, and seed bank carryover of annual bromes points to the need to assay soil seed banks as part of monitoring programs. We sampled the soil seed bank to help assess the effectiveness of treatments utilizing the herbicide Plateau® (imazapic) and a perennial native seed mix to control annual Bromus species and enhance perennial native plant establishment following a wildfire in Zion National Park, Utah. This study is one of few that have monitored the effects of imazapic and native seeding on a soil seed bank community and the only one that we know of that has done so in a pinyon–juniper woodland. The study made use of untreated, replicated controls, which is not common for seed bank studies. One year posttreatment, Bromus was significantly reduced in plots sprayed with herbicide. By the second year posttreatment, the effects of imazapic were less evident and convergence with the controls was evident. Emergence of seeded species was low for the duration of the study. Dry conditions and possible interactions with imazapic probably contributed to the lack of emergence of seeded native species. The perennial grass sand dropseed outperformed the other species included in the seed mix. We also examined how the treatments affected the soil seed bank community as a whole. We found evidence that the herbicide was reducing several native annual forbs and one nonnative annual forb. However, overall effects on the community were not significant. The results of our study were similar to what others have found in that imazapic is effective in providing a short-term reduction in Bromus density, although it can impact emergence of nontarget species.

Perennial plant species from semiarid gypsum soils support higher AMF diversity in roots than the annual Bromus rubens

The arbuscular mycorrhizal fungi (AMF) communities composition regulate plant interactions and determine the structure of plant communities. In this study we analysed the diversity of AMF in the roots of two perennial gypsophyte plant species, Herniaria fruticosa and Senecio auricula, and an annual herbaceous species, Bromus rubens, growing in a gypsum soil from a semiarid area. The objective was to determine whether perennial and annual host plants support different AMF communities in their roots. The roots were analysed by nested PCR, cloning, sequencing of the ribosomal DNA small subunit region and phylogenetic analysis. Twenty AMF sequence types, belonging to the Glomus group A, Glomus group B, Diversisporaceae, Acaulosporaceae, Archaeosporaceae and Paraglomeraceae, were identified. Both gypsophyte perennial species, H. fruticosa and S. auricula had different compositions of the AMF community and higher diversity than B. rubens. This annual plant species shared the full composition of its AMF community with both perennial plant species. Seasonal variations in the colonisation of AM fungi could explain the observed differences in AMF community composition, but this is still a working hypothesis that requires the analysis of further data obtained from a higher number of both annual and perennial plant species in order to be fully tested.

Early Post-Fire Plant Establishment on a Mojave Desert Burn

Fire has become more extensive in recent decades in southwestern United States arid lands. Burned areas pose management challenges and opportunities, and increasing our understanding of post-fire plant colonization may assist management decision-making. We examined plant communities, soils, and soil seed banks two years after the 2005 Loop Fire, located in a creosote-blackbrush community in Red Rock Canyon National Conservation Area in southern Nevada’s Mojave Desert. Based on a spring sampling of 20, 0.01-ha plots, live + dead cover of the exotic annual Bromus rubens averaged nine times lower on the burn than on a paired unburned area. Perennial species composition shifted from dominance by late-successional native shrubs (e.g., Coleogyne ramosissima) on the unburned area, to dominance by native perennial forbs (e.g., Sphaeralcea ambigua, Baileya multiradiata )o n the burn. Species richness of live plants averaged 26% (100 m 2 scale) and 239% (1 m 2 scale) greater on the burn compared to the unburned area. Only 5% of Larrea tridentata individuals resprouted, compared to 64% of Yucca schidigera and baccata. Fire and microsite (interspace, below L. tridentata, or below Yucca) interacted to affect several 0–5 cm soil properties, with higher pH, conductivity, and total P and K on burned Yucca microsites. Bromus rubens density in 0–5 cm soil seed banks was four times lower on the burn, and its distribution among microsites reversed. Below-shrub microsites contained the most B. rubens seeds on the unburned area, but the least on the burned area. Intense fire below shrubs may have increased seed mortality, an idea supported by .3-fold decreases we found in emergence density after heating seed bank samples to 100uC. Our study occurred after a post-fire period of below-average precipitation, underscoring a need for longer term monitoring that characterizes moister years.

English

Annual bromes, primarily cheatgrass (Bromus tectorum) and Japanese brome (Bromus japonicus) are Eurasian winter annual plants that have come to be considered invasive. As such they are not included purposely in seed mixes used for mine reclamation. Examination of long-term vegetation monitoring data from reclaimed and reference areas at the Big Sky Mine in Rosebud County, MT offer insight into the dynamics of the presence of these weeds in a Northern Great Plains setting. Over the past 22 years, annual brome cover as a percent of total vegetation cover in the native open ponderosa pine (Pinus ponderosa) woodland vegetation at the Big Sky Mine has varied from as low as 0.3% in 2002 to as high as 50.7% in 1991. In reclaimed areas over the same period, annual bromes ranged from as little as 1.5 % to as much as 25.1 % of total vegetation cover. As of 2008 Native Reference Area vegetation was 37.0% annual bromes while reclaimed areas had declined to 6.5% annual bromes. Biomass production in reclaimed areas has exceeded reference area levels by 50 to 75% on most years. Precipitation in these adjacent areas can be presumed to have been very similar and grazing of both areas has been light to non-existent over the period. These data suggest that strong perennial herbaceous growth suppresses annual brome abundance especially during periods favorable precipitation. Native area vegetation periodically experiences outbreaks of annual bromes as drought stresses increase and then annual bromes decline as the competitive strength of the native perennials returns. High abundance of annual bromes is a symptom of reduced or lagging competitive strength of perennial plants: it is suggested that at least in the Northern Great Plains, annual bromes constitute a litmus test for community competitive strength, and are not of themselves a conquering invasion. Additional Keywords: Invasibility, reclamation biomass production, cheatgrass, downy brome, Japanese brome, invasive plants, cycles of invasions.

English

Phase II bond release is defined in Montana as replacement and soil tillage being completed and perennial vegetation establishing that is consistent with revegetation criteria (ARM 17.24.1116). Office of Surface Mining Reclamation and Enforcement (OSMRE) rules (30 CFR 800.40) define Phase II bond release as after revegetation has been established on the regraded mined lands in accordance with the approved reclamation plan. These definitions are similar, but not identical, and neither definition mandates quantitative measures that provide objective standards for judging success or failure. In the past, judgments have sometimes differed between various mine inspectors. This problem is exacerbated in years where high production of introduced opportunistic species, such as annual bromes (Bromus tectorum, B. japonicus) or yellow sweetclover (Mellilotus officinalis), may obscure the perennial vegetation. A method for determining the adequacy of vegetation establishment for Phase II bond release for surface coal mines in Montana is described. The method is designed to be quick, easy, and objective. It is used only for areas where questions or disagreements between regulatory personnel exist. The method assesses the percentage of 0.1 m 2 sample hoops that contain adequate perennial vegetation. We provide details for the method used in Montana, and we discuss potential adaptations for other geographic areas as well.

Introduction history and population genetics of the invasive grass Bromus tectorum (Poaceae) in Canada

The invasive annual Bromus tectorum (cheatgrass) is distributed in Canada primarily south of 52° N latitude in two diffuse ranges separated by the extensive coniferous forest in western Ontario. The grass was likely introduced independently to eastern and western Canada post-1880. We detected regional variation in the grass's genetic diversity using starch gel electrophoresis to analyze genetic diversity at 25 allozyme loci in 60 populations collected across Canada. The Pgm-1a & Pgm-2a multilocus genotype, which occurs in the grass's native range in Eastern Europe, is prevalent in eastern Canada but occurs at low frequency in western Canada. In contrast, the Got-4c multilocus genotype, found in the native range in Central Europe, is widespread in populations from western Canada. Overall genetic diversity of B. tectorum is much higher in eastern Canada than in the eastern U.S., while the genetic diversity in populations in western North America is similar between Canada and the U.S. The distribution of genetic diversity across Canada strongly suggests multiple introduction events. Heterozygous individuals, which are exceedingly rare in B. tectorum, were detected in three Canadian populations. Formation of novel genotypes through occasional outcrossing events could spark adaptive evolution and further range expansion across Canada of this exceedingly damaging grass.

Integrating prescribed burning and clopyralid for the management of yellow starthistle (Centaurea solstitialis)

Prescribed burning and the herbicide clopyralid are very effective tools for the management of yellow starthistle. However, repeated use of either can be impractical or can present other problems. The potential solution is the development of an effective integrated weed management strategy using a combination of the two approaches. In small plot studies (0.2 ha), we tested one of five possible treatments: (1) untreated control, (2) 2 consecutive yr of clopyralid (0.105 kg ha−1), (3) 2 consecutive yr of prescribed summer burning, (4) first-year clopyralid followed by second-year prescribed burning, and (5) first-year prescribed burning followed by second-year clopyralid. Treatments were made in 1999 and 2000 at three study sites in California (San Benito, Yuba, and Siskiyou counties). In 2001, the year following the final treatment, 2 consecutive yr of clopyralid or first-year burning followed by second-year clopyralid consistently reduced yellow starthistle cover in the following year by 92 to 100%. However, at the Yuba site, clopyralid alone increased medusahead and ripgut brome cover. Although 2 consecutive yr of burning was effective in Yuba, very high levels of starthistle infestation in San Benito were not completely burned in the second year because of the lack of available consumable fuel. Clopyralid treatment the first year followed by prescribed burning in the second year stimulated yellow starthistle germination and did not reduce the infestation. In a large-scale study conducted at two sites (13 and 81 ha) in southern Monterey County, we used a first-year burn followed by either 2 yr of clopyralid (0.158 kg ha−1) or a single year of clopyralid (0.210 kg ha−1) and a subsequent burn. Results were in close agreement with those found in the small-scale studies. In the year following the final treatment, control of yellow starthistle was greater than 99% when the burn was followed by 2 yr of clopyralid. In contrast, when a prescribed burn was used in the last year of the program, the level of control was not as good, probably because of the increased germination of the remaining soil seedbank. These results indicate that a first-year prescribed burn followed by a second-year clopyralid treatment can provide consistently good control of yellow starthistle, as well as reduced levels of noxious annual grasses, including medusahead and ripgut brome.

Effects of different cultivated or weed grasses, grown as pure stands or in combination with wheat, on take‐all and its suppression in subsequent wheat crops

Grass species were grown in plots, as pure stands or mixed with wheat, after a sequence of wheat crops in which take‐all (Gaeumannomyces graminis var. tritici) had developed. Annual brome grasses maintained take‐all inoculum in the soil as well as wheat (grown as a continuous sequence), and much better than cultivated species with a perennial habit. Take‐all developed more in wheat grown after Anisantha sterilis (barren brome) or Bromus secalinus (rye brome), with or without wheat, than in continuous grass‐free wheat in the same year, where take‐all decline was apparently occurring. It was equally or more severe, however, in wheat grown after Lolium perenne (rye‐grass) or Festuca arundinacea (tall fescue), despite these species having left the least inoculum in the soil. It was most severe in plots where these two grasses had been grown as mixtures with wheat. It is postulated that the presence of these grasses inhibited the development of take‐all‐suppressive microbiota that had developed in the grass‐free wheat crops. The effects of the grasses appeared to be temporary, as amounts of take‐all in a second subsequent winter wheat test crop were similar after all treatments. These results have important implications for take‐all risk in wheat and, perhaps, other cereal crops grown after grass weed‐infested cereals or after set‐aside or similar 1‐year covers containing weeds or sown grasses, especially in combination with cereal volunteers. They also indicate that grasses might be used experimentally in wheat crop sequences for investigating the mechanisms of suppression of, and conduciveness to, take‐all.