Multiple herbicide resistance in littleseed canarygrass (Phalaris minor): A threat to wheat production in India

Littleseed canarygrass (Phalaris minor Retz.), a troublesome weed of wheat in India, has evolved multiple herbicide resistance across three modes of action: photosynthesis at the photosystem II site A, acetyl‐coA carboxylase (ACCase), and acetolactate synthase inhibition. The multiple herbicide‐resistant (MHR) populations had a low level of sulfosulfuron resistance but a high level of resistance to clodinafop and fenoxaprop (ACCase inhibitors). Some of the populations had GR₅₀ (50% growth reduction) values for clodinafop that were 11.7‐fold greater than that of the most susceptible population. The clodinafop‐resistant populations also showed a higher level of cross‐resistance to fenoxaprop (fop group) but a low level of cross‐resistance to pinoxaden (den group). Although clodinafop and pinoxaden are from two different chemical families (fop and den groups), their same site of action is responsible for cross‐resistance behavior. The populations that were resistant to four groups of herbicides (phenylureas, sulfonylurea, aryloxyphenoxypropionate, and phenylpyrazolin) were susceptible to the triazine (metribuzin and terbutryn) and dinitroaniline (pendimethalin) herbicides. The P. minor populations that were resistant to the aryloxyphenoxypropionate and phenylurea herbicides were effectively controlled by the sulfonylurea herbicide, sulfosulfuron. In the fields infested with P. minor that was resistant to clodinafop, a sulfosulfuron application (25 g ha^?1) increased the wheat yield by 99.2% over that achieved using the recommended rate of clodinafop (60 g ha^?1). However, the evolution of multiple resistance against the four groups is a threat to wheat production. To prevent the spread of MHR P. minor populations, as well as the extension of multiple resistance to new chemicals, concerted efforts in developing and implementing a sound, integrated weed management program are needed. The integrated approach, consisting of crop and herbicide rotation with cultural and mechanical weed control tactics, should be considered as a long‐term resistance management strategy that will help to sustain wheat productivity and farmers' income.     

除草剂对小麦田雀麦的生物活性测定

为筛选防除雀麦Bromus japonicus的高效除草剂,采用室内生物测定法研究了13种除草剂对雀麦的除草活性及5种除草剂的田间药效试验。结果表明,在田间推荐剂量的低剂量下,氟唑磺隆、啶磺草胺、氟噻草胺、甲基二磺隆、异丙隆、磺酰磺隆、丙苯磺隆7种除草剂对雀麦具有很高的防除效果,21 d鲜重抑制率分别为88.30%、86.32%、83.97%、78.47%、76.76%、72.83%、71.39%,高剂量下的21 d鲜重抑制率达98.57%、95.36%、91.58%、91.46%、89.47%、82.48%、82.20%;其中氟唑磺隆各剂量下的防效较其它除草剂高。而嘧啶肟草醚、苯唑草酮、炔草酯、吡氟酰草胺、唑啉草酯、精噁唑禾草灵6种除草剂对雀麦防效较差。氟唑磺隆、啶磺草胺、氟噻草胺、甲基二磺隆、异丙隆5种除草剂的田间药效试验表明,氟唑磺隆对雀麦防效最高,高剂量下20 d株防效达85.04%,药后40 d株防效和鲜重防效分别达83.94%和84.17%,未见小麦有明显药害症状,建议田间推荐用量为21.00~42.00 g(a.i.)/hm~2。表明雀麦对不同除草剂的敏感性存在差异,在供试的13种除草剂中氟唑磺隆对雀麦防效最高,较为安全,为防除雀麦的理想除草剂。     

Weed control in wheat with pyroxasulfone and its combinations with other herbicides

Field and pot investigations were conducted to determine the effectiveness of pyroxasulfone alone and its combinations with other herbicides against diverse weed flora of wheat (Triticum aestivum L.) including multiple herbicide-resistant (MHR) littleseed canarygrass (Phalaris minor Retz.). Applications of pyroxasulfone 100–127.5 g/ha as pre-emergence (PE) or early post-emergence (EPOE) @ 63.75 g/ha at 21–23 days after sowing (1 day before irrigation) were highly effective for control of grass weeds namely P. minor and wild oat (Avena ludoviciana Dur.). It was poor for control of broad-leaved weeds (Medicago denticulata Willd. and Rumex dentatus L.). However, pyroxasulfone in tank-mix combination with metsulfuron 4 g/ha, triasulfuron 20 g/ha, and pyroxsulam 18 g/ha effectively controlled (96.5%–99.8%) the diverse weed flora and improved the wheat grain yield (69.5%–285.9%) over untreated weedy control. Also, the pre-mix of pyroxasulfone + pendimethalin applied as PE was superior to either of these applied alone for weed control and grain yield. Pyroxasulfone 100–127.5 g/ha had yield gain of 119.6%–125.4% and 10.1%–26% over untreated control and pendimethalin 800–1250 g/ha, respectively. In pot studies, straw burnt ash drastically reduced the pyroxasulfone efficacy against P. minor and A. ludoviciana. Pyroxasulfone was also effective in pot studies for control of MHR P. minor having resistance against acetyl-coA carboxylase (ACCase), acetolactate synthase (ALS), and photosynthesis at the photosystem-II site-A (PS-II) inhibitor herbicides (clodinafop, sulfosulfuron, and isoproturon, respectively). The studies indicate that pyroxasulfone as PE or EPOE can be an alternative grass weed control herbicide in wheat in particular for the control of MHR P. minor.     

Effects of some integrated management options on parthenium interference in sorghum

Parthenium is widely distributed across the uncropped areas of the tropics. It has slowly encroached into many crops and causes considerable yield loss. It heavily infests sorghum, which is widely cultivated by the resource‐poor farmers in Africa and Asia. Its interference and management in sorghum in these cropping systems is not well understood. Therefore, this experiment was undertaken to determine the appropriate parthenium management techniques to use in sorghum crops. All the studied weeds, in combination with parthenium, offered greater competition to sorghum than parthenium alone. Similarly, under a composite stand of weeds, parthenium was inferior in competitiveness to the other weeds until 60 days after sowing (DAS); by 90 DAS, it could accumulate a higher dry weight due to its consistent growth. A pre‐emergence treatment of atrazine (0.75 kg ha^‐1) with wheat straw mulch (5.0 t ha^?1) brought about a consistent and significant reduction in the parthenium growth and, consequently, increased the sorghum yield by 90.8%. Cowpea intercropping with and without pendimethalin (1.0 kg ha^?1) as a pre‐emergence treatment could not control parthenium between 0 and 60 DAS, but could reduce the parthenium growth during the later period of 60–90 DAS, which resulted in a significant increase in sorghum growth. These intercropping treatments increased the sorghum grain yield by 156.2% and 142.4%, respectively, over the unweeded control and by 18.5% and 12.1%, respectively, over the weed‐free control. These treatments also promoted a higher uptake of N, P, and K by the sorghum crop. Thus, cowpea intercropping was the most effective method for parthenium management vis‐à‐vis sorghum yield improvement, followed by cowpea intercropping with pendimethalin and then by atrazine as a pre‐emergence treatment with wheat straw mulch.     

Response of wild barley (Hordeum spontaneum) and winter wheat (Triticum aestivum) to sulfosulfuron: The role of degradation

Wild barley (Hordeum spontaneum) is one of the most troublesome weed species in winter wheat (Triticum aestivum) in Iran. Two bioassay experiments were conducted in order to study the response of wild barley and wheat to different herbicides and to study the efficacy of pre‐emergence (PRE), postemergence (POST), and PRE followed by POST applications of sulfosulfuron on wild barely. Moreover, the degradation of sulfosulfuron was studied by liquid chromatography coupled with tandem mass spectrometry (LC‐MS/MS). The results showed that wild barley was highly tolerant to clodinafop‐propargyl and its dry weight was reduced by only 15%, compared to the control, at the recommended dose (64 g ai ha^?1). Sulfosulfuron reduced the wild barley biomass by ≤50% at the highest dose (90 g ai ha^?1) in the first bioassay but by not more than 20% and 12% at the recommended dose (22 g ai ha^?1) in the first and second bioassay, respectively. Significant differences were found among the application methods of sulfosulfuron, with the POST application being the least effective method. In contrast to the POST application, wild barley was severely injured by the PRE application of sulfosulfuron, with an ED₅₀ dose of 7.3 g ai ha^?1. The degradation study showed that wild barley can metabolize sulfosulfuron that is applied POST, but at a lower rate than wheat. By 4 h after application, wild barley had metabolized 26% of the sulfosulfuron, compared to 46% by wheat. In conclusion, wild barley can metabolize the recommended dose of sulfosulfuron that is applied POST; thus, the PRE application of sulfosulfuron or other integrated methods should be considered for the effective control of wild barley in wheat.     

Weed Control Efficacy: Response of Chickpea to Pre- and Post-Emergence Herbicides

Lack of control options for cool-season broadleaf weeds is a major deterrent to autumn-sown chickpea. Weed control and chickpea tolerance to PRE (pre-emergence) and POST (post-emergence) application of isoxaflutole and oxyflurofen, PRE metribuzin, POST pyridate, and flumetsulam were investigated at three locations, including Kermanshah, Kurdistan, and Hamedan provinces during 2017–2018. Untreated and weed-free checks were added for comparison. Pyridate and PRE oxyflurofen 125?g ai ha^?1 caused the minor visual crop injury according to EWRS score (1–1.8), while the highest crop injury occurred with metribuzin (EWRS score 3.5–8.5) in whole locations. The most effective herbicides for weed reduction were pyridate (70–75%), PRE oxyfluorfen (69–76%), and POST oxyfluorfen (65–73%) at Kermanshah, PRE oxyfluorfen at 125 and 175?g ai ha^?1 (70–78%), POST oxyfluorfen (70–76%) and pyridate (70–78%) at Kurdistan, PRE oxyfluorfen at 125 and 175?g ai ha^?1 (88–96%), metribuzin (91–100%) and Pyridate (80–97%) at Hamedan. Pyridate and PRE oxyfluorfen at 125?g ai ha^?1 resulted in the highest chickpea grain yield at the three locations. In general, PRE oxyfluorfen (125?g ai ha^?1) was similar to pyridate in terms of efficacy in weed control and grain yield enhancement.

     

Littleseed canarygrass (Phalaris minor) resistance to clodinafop‐propargyl in wheat fields in north‐western India: Appraisal and management

Littleseed canarygrass (～canarygrass) evolved populations that are resistant to isoproturon during the early 1990s in north‐western India. Clodinafop‐propargyl (～clodinafop) was recommended for controlling these populations. It has been used extensively in wheat for the last several years. Recently, poor or no control of canarygrass by clodinafop has been observed in large areas, which could be related to cross‐resistance or multiple resistance. This study was designed to test whether resistance has evolved in canarygrass populations against clodinafop and to explore control of the resistant populations with sulfosulfuron and pinoxaden. Among the 311 canarygrass populations that were tested, 86, 55 and 34 showed variable phytotoxicity (0–99%) due to 0.030, 0.060 and 0.120 kg ha^?1 clodinafop, respectively. Based on the resistance index, 11 populations were “highly resistant”, 60 were “resistant” and the rest (240) were “susceptible” to clodinafop. Five and six clodinafop‐resistant populations showed slight resistance to 0.0125 kg ha^?1 sulfosulfuron and 0.025 kg ha^?1 pinoxaden, respectively. But, sulfosulfuron at 0.025 and 0.050 kg ha^?1 and pinoxaden at 0.050 and 0.100 kg ha^?1 controlled all the canarygrass populations. Clodinafop used for 4 years increased the chance of resistance evolving, whereas its rotation with sulfosulfuron reduced the chance of resistance evolving. This study showed that considerable canarygrass populations have evolved a low‐to‐high degree of resistance against clodinafop. The further use of clodinafop would lead to the spread of resistance in larger areas through the dispersal of resistant seeds. Clodinafop should be replaced with 0.025 kg ha^?1 sulfosulfuron or 0.050 kg ha^?1 pinoxaden. Besides, where canarygrass has not evolved resistance, the yearly rotation of sulfosulfuron with clodanafop or pinoxaden might delay the evolution of resistance.     

Nitrogen effect on competition between winter cereals and littleseed canarygrass

Field experiments were conducted in northern Greece during 1994, 1995, and 1996 to study the effect of nitrogen fertilization on competition between littleseed canaryglass (Phalaris minor Retz.) and wheat (Triticum aestivum L.), barley (Hordeum vulgare =distichum L.) or triticale (Triticosecale). The presence of 400P. minor plants per square meter until early March did not have an adverse effect on dry weight of any crop. However, their further presence significantly reduced dry weight of wheat and triticale, but not that of barley. Grain yield of wheat and triticale was reduced 48% and 47%, respectively, by season-long competition ofP. minor, whereas the corresponding reduction for barley was only 8%. Crop yield reduction due toP. minor competition resulted mainly from reduction in ear number and less from reduction in 1000-grain weight. Nitrogen fertilization (150 kg N ha⁻¹), compared with control (0 kg N), slightly increased yield of all crops grown without weed competition. The same treatment also increased dry weight and competitive ability ofP. minor against wheat and triticale, compared with that of control (0 kg N); the split application of nitrogen (50 kg N ha⁻¹ before crop sowing and 100 kg N ha⁻¹ in early March) caused a slightly greater increase inP. minor dry weight than did 150 kg N ha⁻¹ applied once before crop sowing. Dry weight ofP. minor grown with barley was not affected by nitrogen fertilization, but it was severely reduced compared with that ofP. minor grown with wheat or triticale. http://www.phytoparasitica.org posting April 22, 2003.     

Control of Solatium karsensis in grain sorghum

Solatium karsensis Symon, an Australian native perennial, has become an important weed in irrigated summer crops in far western New South Wales. A screening trial of 14 herbicides showed that atrazine was the most effective treatment, though 2,4-D also suppressed S. karsensis in grain sorghum (Sorghum bicolor L. cv. Rico) for the duration of the crop. Grain sorghum yields were higher in plots treated with atrazine at 2–5 kg (a.i.) ha^?1 than for any other herbicide treatment or the untreated control. Because the root system remained viable annual herbicide application would be necessary for the continued control of 5. karsensis.     

Non-target-site-based resistance to ALS-inhibiting herbicides in six Bromus rigidus populations from Western Australian cropping fields

BACKGROUND: Bromus rigidus is a common weed species that has increased in cropping fields owing to limited control options. During a random field survey in Western Australia, six B. rigidus populations that had survived in‐crop weed control programmes were collected. The study aimed to determine the resistance profile of these six populations. RESULTS: Based on dose–response studies, all six B. rigidus populations had a low‐level resistance to sulfosulfuron and sulfometuron (both sulfonylurea herbicides) while remaining susceptible to herbicides with other modes of action. ALS in vitro activity assays revealed no differences in enzyme sensitivity between susceptible and resistant populations, while the use of malathion (a cytochrome P450 inhibitor) in combination with sulfosulfuron caused the resistant populations to behave like the susceptible population. CONCLUSION: This study established that these six B. rigidus populations have a low‐level resistance to the ALS‐inhibiting sulfonylurea herbicides, but are able to be controlled by other herbicide modes of action. The low‐level, malathion‐reversible resistance, together with a sensitive ALS, strongly suggest that a non‐target‐site enhanced metabolism is the mechanism of resistance. Copyright © 2012 Society of Chemical Industry     

Grain sorghum response and Palmer amaranth control with postemergence application of fluthiacet-methyl

Palmer amaranth is a problematic weed in grain sorghum production in central United States. Due to limited herbicide options available and ever increasing herbicide-resistant weed species, there is a demand for new mode-of-action herbicides for use in grain sorghum. Fluthiacet-methyl is a relatively new active ingredient that inhibits the enzyme protoporphyrinogen oxidase in target plants. Field studies were conducted at three sites in central United States in 2010 and 2011 to evaluate crop response and Palmer amaranth control with postemergence application of fluthiacet-methyl in grain sorghum. Treatments included fluthiacet-methyl at 4.8 and 7.2 g active ingredient (a.i.) ha^?1 alone and tank-mixed with 2,4-D amine at 260 g acid equivalent (a.e.) ha^?1 or atrazine at 840 g a.i. ha^?1. Carfentrazone at 8.8 g a.i. ha^?1, atrazine at 840 g ha^?1, and a non-treated control were also included. Fluthiacet-methyl treatments caused 9–38% crop injury at 4 ± 1 days after treatment. Tank-mixing atrazine with fluthiacet-methyl seldom affected crop injury, while mixing 2,4-D with fluthiacet-methyl often reduced crop injury. Generally, injury caused by fluthiacet-methyl alone or in combination with atrazine or 2,4-D disappeared within 3 weeks after treatment. Grain yields were reduced in one trial, when 2,4-D mixed with 4.8 or 7.2 g ha^?1 of fluthiacet-methyl caused 18% and 13% plant lodging and 24% and 14% grain yield loss, respectively. Across site-years, fluthiacet-methyl alone at 4.8 or 7.2 g ha^?1 provided 55–95% control of Palmer amaranth. Greater Palmer amaranth control (≥75%) with fluthiacet-methyl alone was achieved when weeds were small or density was low at the time of spraying. Tank-mixing atrazine with fluthiacet-methyl increased Palmer amaranth control and sorghum yields considerably. Tank-mixing 2,4-D with fluthiacet-methyl also increased Palmer amaranth control, but to lesser extent and less consistently than with atrazine. Results indicated that fluthiacet-methyl has potential for use in grain sorghum to combat weeds resistant to acetolactase synthase-inhibitors, triazines, and synthetic auxin herbicides. Tank-mixing atrazine or 2,4-D with fluthiacet-methyl is desirable for effective Palmer amaranth control.     

Modelling the effects of sub-lethal doses of herbicide and nitrogen fertilizer on crop–weed competition

The effects of sub‐lethal dose of herbicide and nitrogen fertilizer on crop–weed competition were investigated. Biomass increases of winter wheat and a model weed, Brassica napus, at no‐herbicide treatment with increasing nitrogen were successfully described by the inverse quadratic model and the linear model respectively. Increases in weed competitivity (β₀) of the rectangular hyperbola and parameter B in the dose–response curve for weed biomass, with increasing nitrogen were also successfully described by the exponential model. New models were developed by incorporating inverse quadratic and exponential models into the combined rectangular hyperbola with the standard dose–response curve for winter wheat biomass yield and the combined standard dose—response model with the rectangular hyperbola for weed biomass, to describe the complex effects of herbicide and nitrogen on crop–weed competition. The models developed were used to predict crop yield and weed biomass and to estimate the herbicide doses required to restrict crop yield loss caused by weeds and weed biomass production to an acceptable level at a range of nitrogen levels. The model for crop yield was further modified to estimate the herbicide dose and nitrogen level to achieve a target crop biomass yield. For the target crop biomass yield of 1200 g m^?2 with an infestation of 100 B. napus plants m^?2, the model recommended various options for nitrogen and herbicide combinations: 140 and 2.9, 180 and 0.9 and 360 kg ha^?1 and 1.7 g a.i. ha^?1 of nitrogen and metsulfuron‐methyl respectively.     

Long‐term changes in weed occurrence,yield and use of herbicides in maize in south‐western Germany,with implications for the determination of economic thresholds

In 393 field experiments in Baden‐Württemberg region in south‐western Germany, herbicide efficacy, yield loss and crop tolerance of maize (Zea mays) were investigated between 1981 and 2011. The collected data served to determine changes in weed frequencies, in herbicide use, yield loss functions and economic thresholds (ETs). Over 60 weed species were reported. Chenopodium album and Galium aparine were the most frequent broad‐leaved weeds, the former becoming more frequent over time. Species of the genera Lamium, Polygonum, Veronica and Matricaria occurred in about every fifth trial. Alopecurus myosuroides and Echinochloa crus‐galli were the most frequent grass weeds; the former declining in frequency by 1.1% per year, the latter increasing by 1.5%. Results suggest a weed population shift towards thermophilic species. aceto‐lactate‐synthase and 4‐HPPD‐inhibitor herbicides became important in the 1990s. Pendimethalin and bromoxynil have been integral components of weed control since the 1980s. ETs, the point at which weed control operations provide economic returns over input costs, ranged between 3.7% and 5.8% relative weed coverage. Without weed control, no yield increase was found over 24 years. Yield increased by 0.2 t ha ^{? 1} year ^{? 1}, if weeds were controlled chemically. Despite intensive use of effective herbicides in maize, problematic weed species abundance and yield losses due to weed competition have increased in Baden‐Württemberg over a period of 30 years.     

Using chemical seed dormancy breakers with herbicides for weed management in soyabean and wheat

Variable dormancies result in periodicity in the germination of weeds and make weed control a repetitive practice. Under some conditions, repeated applications of selective herbicides can lead to the dominance of perennial weeds like Cyperus rotundus . Our hypothesis was that applying a chemical dormancy breaker (DB ) plus herbicide mixture would better control a mixture of weed species. Three experiments were designed to develop a cost‐effective DB treatment and to evaluate its dose with herbicides tank‐mixtures for effective weed management. KNO ₃ and gibberellic acid GA ₃ as dormancy breakers offered comparable effects, but KNO ₃ was more economical than GA ₃. KNO ₃ at a 6% concentration was more effective in promoting weed germination than a 3% concentration in soyabean. A combination of KNO ₃ (6%) and pre‐emergence pendimethalin 0.75 kg a.i. ha^?1 + imazethapyr 0.10 kg a.i. ha^?1 controlled annual weeds by 99% and reduced C. rotundus growth by 83%. This treatment gave significantly higher soyabean yield and net returns. Similarly, a tank‐mixture comprising of clodinafop 0.06 kg a.i. ha^?1 + metsulfuron 0.006 kga.i. ha^?1 was more effective against weeds than pre‐emergence tank‐mix application of pendimethalin 0.75 kg a.i. ha^?1 + carfentrazone‐ethyl 0.02 kg a.i. ha^?1 and isoproturon 0.75 kg a.i. ha^?1. The use of pre‐emergence tank‐mixture of pendimethalin 0.75 kg a.i. ha^?1 + imazethapyr 0.10 kg a.i. ha^?1 should exhaust seed/tuber bank if repeated and reduce the application cost of herbicides by 50% and the dose, residue and cost of pendimethalin by 25%.     

An integrated approach to control glyphosate‐resistant Ambrosia trifida with tillage and herbicides in glyphosate‐resistant maize

Glyphosate‐resistant Ambrosia trifida is a competitive and difficult‐to‐control annual broad‐leaved weed in several agronomic crops in the Midwestern United States and Ontario, Canada. The objectives of this study were to compare treatments for control of glyphosate‐resistant A. trifida with tillage followed by pre‐emergence (PRE) and/or post‐emergence (POST) herbicides in glyphosate‐resistant maize and to determine the impact of A. trifida escapes on maize yield. Field experiments were conducted in 2013 and 2014 in grower fields infested with glyphosate‐resistant A. trifida. Tillage prior to maize sowing resulted in 80–85% control compared with no tillage. Tillage followed by PRE application of saflufenacil plus dimethenamid‐P with or without atrazine resulted in 99% control compared with ≤86 and 96% control with PRE herbicides alone at 7 and 21 days after application respectively. Tillage or POST‐only herbicides resulted in 4–14 A. trifida plants m^?2, whereas a PRE and POST programme had <3 plants m^?2. Maize yield was greatest (13.1–14.2 tonnes ha^?1) with tillage followed by PRE and POST herbicide programme. The relationship between maize yield and late‐season density of A. trifida escapes showed a 50% maize yield reduction irrespective of control measures when A. trifida density was 8.4 plants m^?2. It was concluded that the combination of tillage with PRE and/or POST herbicides reduced A. trifida density and biomass accumulation early in the season and provided an integrated approach for effective management.     

Confirmed resistance to aryloxyphenoxypropionate herbicides in Phalaris minor populations in Iran

Phalaris minor (littleseed canary grass) is a major weed in wheat fields in some parts of Iran. Diclofop‐methyl, fenoxaprop‐P‐ethyl, and clodinafop‐propargyl are three acetyl coenzyme A carboxylase (ACCase)‐inhibiting herbicides that are commonly used to control this grass in wheat fields. Thirty‐four P. minor populations with suspected resistance to ACCase‐inhibiting herbicides were sampled from wheat fields in the provinces of Fars and Golestan in Iran. The dose–response assays that were conducted under controlled greenhouse conditions indicated that 14 populations were resistant to fenoxaprop‐P‐ethyl, seven populations were resistant to both fenoxaprop‐P‐ethyl and diclofop‐methyl, and three populations were resistant to fenoxaprop‐P‐ethyl, diclofop‐methyl, and clodinafop‐propargyl. These populations showed different levels of resistance to the applied herbicides, compared to the susceptible population. These results suggest that different mechanisms of resistance could be involved. The enzyme assay revealed that the existence of modified ACCase in the three most‐resistant populations (AR, MR4, and SR3) is responsible for the resistance of these populations.     

The implications of spatially variable pre‐emergence herbicide efficacy for weed management

BACKGROUND

The efficacy of pre‐emergence herbicides within fields is spatially variable as a consequence of soil heterogeneity. We quantified the effect of soil organic matter on the efficacy of two pre‐emergence herbicides, flufenacet and pendimethalin, against Alopecurus myosuroides and investigated the implications of variation in organic matter for weed management using a crop–weed competition model.

RESULTS

Soil organic matter played a critical role in determining the level of control achieved. The high organic matter soil had more surviving weeds with higher biomass than the low organic matter soil. In the absence of competition, surviving plants recovered to produce the same amount of seed as if no herbicide had been applied. The competition model predicted that weeds surviving pre‐emergence herbicides could compensate for sublethal effects even when competing with the crop. The ED50 (median effective dose) was higher for weed seed production than seedling mortality or biomass. This difference was greatest on high organic matter soil.

CONCLUSION

These results show that the application rate of herbicides should be adjusted to account for within‐field variation in soil organic matter. The results from the modelling emphasised the importance of crop competition in limiting the capacity of weeds surviving pre‐emergence herbicides to compensate and replenish the seedbank. © 2017 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.     

Real-time weed detection, decision making and patch spraying in maize, sugarbeet, winter wheat and winter barley

Information on temporal and spatial variation in weed seedling populations within agricultural fields is very important for weed population assessment and management. Most of all, it allows a potential reduction in herbicide use, when post‐emergence herbicides are only applied to field sections with weed infestation levels higher than the economic weed threshold; a review of such work is provided. This paper presents a system for site‐specific weed control in sugarbeet (Beta vulgaris L.), maize (Zea mays L.), winter wheat (Triticum aestivum L.) and winter barley (Hordeum vulgare L.), including online weed detection using digital image analysis, computer‐based decision making and global positioning systems (GPS)‐controlled patch spraying. In a 4‐year study, herbicide use with this map‐based approach was reduced in winter cereals by 60% for herbicides against broad‐leaved weeds and 90% for grass weed herbicides. In sugarbeet and maize, average savings for grass weed herbicides were 78% in maize and 36% in sugarbeet. For herbicides against broad‐leaved weeds, 11% were saved in maize and 41% in sugarbeet.     

Weed competition and control in sugarcane

Losses of about 40% in cane yields due to natural stands of weeds were found in experiments conducted in sugarcane var. Co 527 in the year of planting at Guneid Sugarcane Research Station, Sudan. Weed competition lowered millable stalks per metre row by 32%, stalk height by 24%, stalk thickness by 15% and number of nodes per stalk by 14%. Tillering was the growth phase most affected by weed competition. Cane yields were increased as number of hand weedings increased, but four weedings were not markedly better than three. The average yield (67·04 t ha^?1) obtained from four weedings was not significantly (P= 0·05) better than that of three weedings carried out at 3, 6 and 9 weeks after cane planting. Juice analysis components were also affected by weeds and a 15% reduction in sucrose recovery was recorded. Reductions in the other components were only 4–7%. Atrazine and diuron (3·3 kg ha^?1), metribuzin (2·4 kg ha^?1) and metribuzin (1·3 kg ha^?1) in tank mixture with diuron (1·5 kg ha^?1) gave excellent residual weed control of the dominant weed species, Ipomoea cordofana Choisy., Brachiaria eruciformis (Sm.) Griseb., Corchorus fascicularis Lam., Ocimum basilicum L. and Dinebra retroflexa (Vahl) Panz., for most of the first growing season. Excellent control of weeds achieved by the herbicide treatments resulted in comparable yields to frequently-weeded cane. These herbicides were not phytotoxic to sugarcane var. Co 527.     

麦田布顿大麦草的化学防除药剂筛选

布顿大麦草为麦田入侵杂草, 为尽早建立对该杂草的化学防除技术, 本研究采用室内盆栽法测定了布顿大麦草对21种除草剂的敏感性?结果表明:土壤处理剂41%氟噻草胺悬浮剂对布顿大麦草具有良好的防除效果, 42%氟啶草酮悬浮剂?60%丁草胺乳油?40%砜吡草唑悬浮剂?960 g/L精异丙甲草胺乳油对布顿大麦草的防除效果一般, 50%扑草净可湿性粉剂?50%异丙隆可湿性粉剂?45%二甲戊灵微囊悬浮剂?50%吡氟酰草胺可湿性粉剂防除效果不理想; 茎叶处理剂7.5%啶磺草胺水分散粒剂?12.5%烯禾啶乳油?41%草甘膦异丙胺盐水剂对布顿大麦草防除效果好, 5%咪唑乙烟酸水剂?8%炔草酯水乳剂?30 g/L甲基二磺隆可分散油悬浮剂?8%烟嘧磺隆可分散油悬浮剂?7%双唑草腈颗粒剂?70%氟唑磺隆水分散粒剂对布顿大麦草的防除效果一般, 5%唑啉草酯乳油?7.5%双环磺草酮颗粒剂?69 g/L精噁唑禾草灵水乳剂防除效果不理想?氟噻草胺?在推荐剂量492 g/hm2下, 处理21 d后对布顿大麦草的鲜重抑制率为75.40%; 啶磺草胺?草甘膦异丙胺盐?烯禾啶在推荐剂量14?1 500?187.5 g/hm2下, 处理21 d后对布顿大麦草的鲜重抑制率分别为73.96%?60.60%?65.07%?综合本研究结果及除草剂使用特性, 麦田布顿大麦草可采用氟噻草胺土壤封闭或者啶磺草胺茎叶喷雾处理进行有效防除; 油菜田布顿大麦草可采用烯禾啶进行防除; 非耕地布顿大麦草可采用草甘膦异丙胺盐进行防除?