Protoporphyrinogen IX-oxidizing activities involved in the mode of action of a new compound N-[4-chloro-2-fluoro-5-{3-(2-fluorophenyl)-5-methyl-4,5-dihydroisoxazol-5-yl-methoxy}-phenyl]-3,4,5,6-tetrahydrophthalimide

N-[4-Chloro-2-fluoro-5-{3-(2-fluorophenyl)-5-methyl-4,5-dihydroisoxazol-5-yl-methoxy}-phenyl]-3,4,5,6-tetrahydrophthalimide (EK-5385) is an experimental substituted bicyclic herbicide. Soil-applied EK-5385 showed good rice selectivity and potent herbicidal activity on barnyardgrass (Echinochloa crus-galli var. oryzicola) at rates of 3.9-250 g a.i./ha. Barnyardgrass was exhibited normal growth under dark condition, however, the growth of shoot and root was severely inhibited under light condition (14/10 h of light/dark, 50 μmol/m²/s of photosynthetically active radiation) when treated with EK-5385, oxadiazon, and oxadiargyl. IC₅₀ of EK-5385 and oxadiargyl to chlorophyll loss in cucumber cotyledons was approximately 0.3 and 0.7 μM, respectively. IC₅₀ of EK-5385 and oxadiargyl to carotenoids loss in cucumber cotyledons was about 0.26 and 0.1 μM, respectively. IC₅₀ concentration of EK-5385 and oxadiargyl on Protox activity was approximately 5.5 and 8 nM, respectively. Cellular leakage occurred without lag period from cucumber leaf squares treated with 1 μM of EK-5385 and oxadiargyl under light exposure.     

The role of altered acetyl-CoA carboxylase in conferring resistance to fenoxaprop-P-ethyl in Chinese sprangletop (Leptochloa chinensis (L.) Nees)

From paddy field observations in 2002 and 2004, fenoxaprop-P-ethyl resistance in Chinese sprangletop (Leptochloa chinensis (L.) Nees) has been studied using information collected from 11 sites in the Saphan-Sung district of Bangkok, Thailand. The resistant Chinese sprangletop was found in nine rice fields, whereas the susceptible Chinese sprangletop was found in only two rice fields. In greenhouse experiments, both fenoxaprop-P-ethyl-resistant and susceptible Chinese sprangletop from the same location were investigated for 50% growth reduction based on phytotoxicity, plant height and fresh and dry weight. The resistant Chinese sprangletop showed apparent resistance at 14-21 days after herbicide application at a rate of 21.1-337.6 g AI ha(-1). The resistance index of resistant Chinese sprangletop was 10-25 times higher than that of the susceptible Chinese sprangletop. In addition, Chinese sprangletop did not exhibit multiple resistance to oxadiazon, propanil and quinclorac. According to acetyl-CoA carboxylase (ACCase) assays, the level of ACCase specific activity in the resistant Chinese sprangletop was significantly higher than that in the susceptible Chinese sprangletop. Similarly, the ACCase activity of the resistant Chinese sprangletop was 10 times less sensitive to fenoxaprop-P-ethyl than that of the susceptible Chinese sprangletop, based on the I50 values. The present study of the mechanism responsible for resistance in the biotypes investigated indicated that there was a close association between the concentration-response at the whole-plant level and ACCase sensitivity to fenoxaprop-P-ethyl, and resistance to fenoxaprop-P-ethyl was conferred by a modified ACCase at the target site, as suggested by higher specific activity and less sensitivity to the herbicide.     

Herbicide-resistant barnyardgrass (Echinochloa crus-galli) in global rice production

Barnyardgrass (Echinochloa crus-galli (L.) Beauv.), an annual species of the family Poaceae, is a major weed problem in rice-producing countries throughout the globe. Synthetic herbicides can effectively control this grass in rice paddies, but the development of resistant biotypes after the continuous use of the same active ingredients has led to low herbicide efficacy and yield losses. In this review, a summary of resistant-barnyardgrass cases in global rice production is reported based on data from the International Herbicide-Resistant Weed Database. The first case of resistant barnyardgrass in rice paddies was to the photosystem-II inhibitor propanil in the late 1980s. Eighty-five (85) out of 116 cases in the period from 1986 to 2022 refer to resistant barnyardgrass (E. crus-galli var. crus-galli, E. crus-galli var. formosensis and E. crus-galli var. zelayensis) in 16 countries. Barnyardgrass has been found resistant to acetolactate synthase (ALS) inhibitors (34 cases), acetyl-CoA carboxylase (ACCase) inhibitors (23 cases), photosystem-II inhibitors (11 cases), auxin mimics/cellulose biosynthesis inhibitors (9 cases), very long chain fatty acid inhibitors (6 cases), and microtubule assembly inhibitors (1 case). The majority of all resistance cases reported to the active ingredients penoxsulam, bispyribac-sodium, and imazamox (ALS inhibitors), cyhalofop-butyl and fenoxaprop-ethyl (ACCase inhibitors), propanil (photosystem-II inhibitors), and quinclorac (auxin mimics/cellulose biosynthesis inhibitors). Although target-site resistance with specific mutations has been identified, non-target site resistance mainly through herbicide detoxification is also of great concern increasing the chance of multiple herbicide resistance evolution. Rotation of herbicides should be adopted concerning the modes of action used as well as the application methods to mitigate resistance evolution of this weed in rice paddies.     

Red rice (Oryza sativa L.) and barnyardgrass (Echinochloa spp.) biotype susceptibility to postemergence-applied imazamox

Pot experiments were conducted to evaluate the level of imazamox tolerance in five red rice ( Oryza sativa L.) and four barnyardgrass (three Echinochloa crus-galli (L.) Beauv. and one Echinochloa oryzoides (Ard.) Fritch) morphologically distinct biotypes collected from rice fields in northern Greece. The susceptibility of barnyardgrass biotypes to propanil was also studied. Red rice biotypes were not controlled by imazamox applied at 40 g ha⁻¹. In contrast, 80 g imazamox ha⁻¹ provided 56–84% red rice control (averaged across shoot number and fresh weight reduction). Not all barnyardgrass biotypes were susceptible to imazamox applied postemergence. However, propanil applied at 2.6 kg ha ⁻¹ controlled the E. crus-galli biotypes well, but propanil applied at rates of 2.6 and 5.2 kg ha ⁻¹ was not effective in reducing the shoot number and fresh weight of the E. oryzoides biotype. Propanil applied at 10.4 kg ha ⁻¹ reduced the shoot number and fresh weight of this biotype by 78 and 85%, respectively. In most cases, a linear equation ( y  = % of control, x  = g ha⁻¹) provided the best fit for regressions between red rice or barnyardgrass shoot number or fresh weight and imazamox rates. The results of this study suggest that postemergence application of imazamox is not effective against all red rice and barnyardgrass biotypes found in the rice fields of Greece and that significant variability regarding herbicide efficacy among biotypes might exist.     

Dissipation of tralkoxydim herbicide from wheat crop and soil under sub-tropical conditions

The persistence of tralkoxydim herbicide in wheat crop and in soil was evaluated under Indian sub-tropical field conditions at two application rates (400 g a.i ha ^?1 and 800 g a.i ha ^?1). At 400 g a.i ha ^?1, tralkoxydim persisted up to 28 days in soil but became non-detectable only after 45 days in the crop. However, at 800 g a.i ha ^?1, tralkoxydim residues persisted for 45 days in both soil and crop. The dissipation of the herbicide from both soil and crop appeared to occur in two phases at both rates of application. Each phase followed first-order kinetics. The values of DT₅₀ and DT₉₀ for both soil and crop are reported.     

五氯酚钠防除稻田杂草的试验

在旱秧田、水秧田、旱直播田和水直播田的试验中,播前施用五氯酚钠,每公顷5—20公斤,除草效果不够良好。但在插秧本田的试验中,插前每公顷施用五氯酚钠15—30公厅对防除稗草(Echinochloa crusgalli (L.) Beauv.)和球穗莎草(Cyperus globosus All.)的效果极为良好。以在插秧前一天,每公顷施用30公斤效果最好,对稗草和球穗莎草的防除效果分别达到92.7%和79.6%。插后处理,每公顷施用五氯酚钠15公斤,效果也较好。另外的试验,观察了五氯酚钠不同剂型:颗粒剂、混土、溶液等的防除效果。防除稗草用颗粒剂和混土处理要优于溶液处理;防除球穗莎草则以溶液处理为最好。各处理对水稻均无药害,所有用五氧酚钠处理区的产量均高于不除草区,但较两次人工除草的为低。本文讨论了在秧田和直播田用五氯酚钠防除稗草效果较差的原因。     

Influence of thiobencarb on nitrate reductase, nitrite reductase and DCPIP photoreduction in rice and Echinochloa crus-galli (L.) (barnyardgrass)

Summary. The influence of thiobencarb at 1500 ppm on levels of nitrate reductase, nitrite reductase and on 2,6-dichlorophenolindophenol (DCPIP) photoreduction was studied in rice ( Oryza sativa L.) and Echinochloa crus-galli (L.) (barnyardgrass) to understand the different sensitivities of these two plants to the herbicide. The herbicide treatment did not cause appreciable inhibition of nitrate reductase and nitrite reductase in rice leaf sections. In barnyard grass, the treatment strongly lowered nitrite reductase activity. DCPIP photoreduction by isolated chloroplasts of the treated rice leaves was not greatly affected. On the other hand DCPIP photoreduction by both mesophyll and bundle sheath chloroplasts from treated barnyardgrass was inhibited by 70%. Herbicide caused accumulation of nitrite in treated barnyard grass leaves when compared to rice. Thiobencarb phytotoxicity to barnyard grass may be due to impairment of the Hill reaction that in turn caused accumulation of nitrite in the leaf tissue.     

Herbicidal and biological characteristics of a new benzenesulfonylurea compound K-11451 under submerged paddy conditions

The new benzenesulfonylurea K-11451, an α-hydroxy-β-fluoropropyl- compound, applied at 3–9 g ha ⁻¹, controlled annual and perennial weeds grown in submerged paddy soil under greenhouse conditions. It effectively controlled barnyardgrass at growth stages varying from pre-emergence to the five-leaf stage. The compound inhibited acetolactate synthase, I₅₀ values for the enzyme isolated from barnyardgrass and rice being 56 and 67 nM , respectively. K-11451 inhibited the growth of rice when it was transplanted at a shallow depth (0–1 cm) and water leaching from the paddy soil was high (3–5 cm per day). With a water depth of 3 cm, the compound appeared to move readily down into the paddy soil and had the relatively short half-life of 15.2 days under submerged paddy conditions. A mixture of K-11451 + mefenecet + daimuron (9 + 250 + 250 g ha⁻¹) controlled almost all weeds in the paddy field without injury to rice, so that the combination could be used as a ‘one-shot’ herbicide in rice culture.     

Biochemical mechanisms of cross-resistance to aryloxyphenoxypropionate and cyclohexanedione herbicides in populations of Avena spp.

Aryloxyphenoxypropionate (APP) and cyclohexanedione (CHD) herbicides are used extensively in the UK to control grass weeds, including Avena spp. (wild-oats). Reports of resistance to APP and CHD herbicides are a particular concern for the agricultural community. In this study, the responses of four UK Avena populations were characterized towards the APP herbicides fenoxaprop-P-ethyl and fluazifop-P-butyl, and towards the CHD herbicides cycloxydim and tralkoxydim. An A. sterilis ssp. ludoviciana population (T/41) was found to be highly resistant to fenoxaprop-P-ethyl and fluazifop-P-butyl, but did not show cross-resistance to cycloxydim and tralkoxydim. In contrast, one A. sterilis ssp. ludoviciana (T/11) and one A. fatua population (Dorset) showed partial resistance to both APP herbicides and also showed cross-resistance to the CHD herbicide tralkoxydim, but not to cycloxydim. Before this study, the biochemical mechanisms that confer resistance to the APP and CHD herbicides in UK Avena populations were unknown. Results from the present study show that an enhanced rate of metabolism of fenoxaprop-P-ethyl was found to confer resistance in the two partially resistant Avena populations (T/11 and Dorset), and the presence of an insensitive form of the target enzyme, ACCase, was responsible for target site resistance to fenoxaprop-P-ethyl and fluazifop-P-butyl in the highly resistant population T/41. Cross-resistance to the CHD herbicide tralkoxydim in the T/11 and Dorset populations was not conferred by insensitive ACCase, and was most probably caused by enhanced metabolism. This is the first report that resistance to fenoxaprop-P-ethyl can be conferred by enhanced metabolism in Avena spp.     

Tolerance to acetolactate synthase and acetyl-coenzyme A carboxylase inhibiting herbicides in Vulpia bromoides is conferred by two co-existing resistance mechanisms

Vulpia bromoides is a grass species naturally tolerant to acetolactate synthase (ALS) and acetyl-coenzyme A carboxylase (ACCase) inhibiting herbicides. The mechanism of tolerance to ALS herbicides was determined as cytochrome P450-monooxygenase mediated metabolic detoxification. The ALS enzyme extract partially purified from V. bromoides shoot tissue was found to be as sensitive as that of herbicide susceptible Lolium rigidum to ALS-inhibiting sulfonylurea (SU), triazolopyrimidine (TP), and imidazolinone (IM) herbicides. Furthermore, phytotoxicity of the wheat-selective SU herbicide chlorsulfuron was significantly enhanced in vivo in the presence of the known P450 inhibitor malathion. In contract, the biochemical basis of tolerance to ACCase inhibiting herbicides was established as an insensitive ACCase. In vitro ACCase inhibition assays showed that, compared to a herbicide susceptible L. rigidum, the V. bromoides ACCase was moderately (4.5- to 9.5-fold) insensitive to the aryloxyphenoxypropionate (APP) herbicides diclofop, fluazifop, and haloxyfop and highly insensitive (20- to >71-fold) to the cyclohexanedione (CHD) herbicides sethoxydim and tralkoxydim. No differential absorption or de-esterification of fluazifop-P-butyl was observed between the two species at 48 h after herbicide application, and furthermore V. bromoides did not detoxify fluazifop acid as rapidly as susceptible L. rigidum. It is concluded that two co-existing resistance mechanisms, i.e., an enhanced metabolism of ALS herbicides and an insensitive target ACCase, endow natural tolerance to ALS and ACCase inhibiting herbicides in V. bromoides.     

双唑草腈的除草活性及对不同水稻品种和后茬作物的安全性

双唑草腈(pyraclonil)为原卟啉原氧化酶(PPO)抑制剂,为明确其在水稻田的应用前景,采用室内生物测定法研究了双唑草腈的除草活性及对不同水稻品种的安全性,通过大田试验作了进一步验证,并评价了双唑草腈对水稻及后茬作物的安全性。结果表明,双唑草腈对水稻田禾本科杂草稗草、阔叶杂草鸭舌草均有很好的除草活性。在室内试验中,该药剂对稻田稗草和鸭舌草的ED50分别为11.50g/hm~2和8.22g/hm~2,均高于对照药剂丙草胺对稗草和鸭舌草的活性;双唑草腈在3种水稻和稗草之间的选择性指数分别为4.15、3.44和3.73,高于对照药剂;田间试验结果显示,1.8%双唑草腈颗粒剂162、216、324g/hm~2处理在药后20、40d对稗草、鸭舌草、节节菜及异型莎草的株防效均在98%以上,显著优于对照药剂80%丙炔噁草酮可湿性粉剂和50%丙草胺乳油;双唑草腈对水稻以及三种主要后茬作物小麦、油菜和小白菜安全。研究表明双唑草腈具有很好的应用前景。     

Synthesis and herbicidal activity of new 3-(3-bromothiophen-2-yl)-5-(2,6-difluorobenzyl)oxymethyl-5-methyl-4,5-dihydroisoxazole as a paddy field herbicide

A new compound 3-(3-bromothiophen-2-yl)-5-(2,6-difluorobenzyl)oxymethyl-5-methyl-4,5-dihydroisoxazole was synthesized and the herbicidal activity was assessed under glasshouse and flooded paddy field conditions. This compound demonstrated good rice selectivity and potent herbicidal activity against annual weeds at 125 g ai ha⁻¹ under greenhouse conditions. Soil application of this compound showed the complete control of barnyardgrass to the 4th leaf stage at 250 g ai ha⁻¹. Field trials indicated that this compound, combined with pyrazosulfuron-ethyl, controlled annual and perennial weeds rapidly with good tolerance by transplanted rice seedlings from postemergence and soil application. This compound showed a low mammalian and environmental toxicity in various toxicological tests.     

Weed control in rose-scented geranium (Pelargonium spp)

Abstract: Field investigations were carried out during 1999 and 2000 to identify effective chemical/ cultural methods of weed control in rose-scented geranium (Pelargonium spp). The treatments comprised pre-emergence applications of oxyfluorfen (0.15, 0.20 and 0.25 kg AI ha(-1)) and pendimethalin (0.50, 0.75 and 1.00kg AI ha(-1)), successive hand weeding, hoeing and mulching using spent of lemon grass (at 5 tonnes ha(-1)) 45 days after planting (DAP), three hand-weedings 30, 60 and 90 DAP, weed-free (frequent manual weeding) and weedy control. Broad-leaf weeds were more predominant than grass and sedge weeds, accounting for 85.8% weed density and 93.0% weed dry weight in 1999 and 77.2% weed density and 93.9% weed dry weight in 2000. Unrestricted weed growth significantly reduced geranium oil yield, by 61.6% and 70.6% in 1999 and 2000, respectively. Pre-emergence application of pendimethalin (0.75-1.00 kgAI ha(-1)) or oxyfluorfen (0.25 kg AI ha(-1)), successive hand-weeding, hoeing and mulching and three hand-weedings were highly effective in reducing weed density and dry weight and gave oil yield comparable to the weed-free check. Application of oxyfluorfen (0.15 or 0.20 kg AI ha(-1)) and pendimethalin (0.50 kg AI ha(-1)) were less effective in controlling the weed species in geranium. None of the herbicides impaired the quality of rose-scented geranium oil measured in terms of citronellol and geraniol content.     

Antagonism of tralkoxydim activity in Avena fatua by metsulfuron methyl

In growth chamber experiments, tralkoxydim activity against Avena fatua was significantly reduced by addition of metsulfuron methyl to the spray solution. This was apparent particularly at low rates of tralkoxydim (e.g., 125 g a.i.ha^?1) and at high rates of metsulfuron methyl (8 or 12 g a.i. ha^?1). Metsulfuron methyl alone reduced A. fatua growth significantly, Chlorsul-furon, which did not reduce A. fatua growth at rates of up to 33 g a.i. ha^?1, caused only a slight loss in tralkoxydim activity. When applied in combination, metsulfuron methyl reduced the uptake of foliar-applied ¹⁴C-tralkoxydim 6 h after application, but did not affect uptake or translocation of ¹⁴C-tralkoxydim at subsequent sampling times. In in vitro assays, metsulfuron methyl at 10 or 100 nM in the assay medium had no effect on acetyl-coenzyme A carboxylase (ACCase) activity in A.fatua, nor did it interfere with the inhibition of ACCase by tralkoxydim. In addition, treatment of A. fatua plants with metsulfuron methyl at 4, 8 or 12 g ha^?1 did not reduce the level of extractable ACCase activity when the plants were harvested 24–96 h after spraying. Thus, no apparent physiological or biochemical basis for the antagonism of tralkoxydim was identified. The temporary growth inhibition induced by metsulfuron methyl may be of sufficient duration for most of the tralkoxydim to be metabolized to inactive products, thereby reducing tralkoxydim-induced injury. Antagonisme entre le metsulfuron-methyl et l'activité de la tralkoxydime sur Avena fatua Dans des essais en chambres climatiques, l'activité de la tralkoxydime contre Avena fatua a été significativement réduite par l'adjonction de metsulfuron-methyl dans la bouillie de pulvérisation. Ceci est particulièrement apparent à de faibles doses de tralkoxydime (ex. 125 g. m.a. ha^?1) et à de faibles doses de metsulfuron-methyl (8 à 12 g m.a. ha^?1). Le metsulfuron-methyl seul réduit la croissance d'Avena fatua. Le chlorsulfuron qui ne réduit pas la croissance d'Avena fatuaà des doses jusqu'à 33 g m.a. ha^?1 cause seulement une faible perte d'efficacité chez la tralkoxydime. Quand il est appliqué en mélange, le metsulfuron-méthyl a réduit l'absorption de la C14 tralkoxydime appliquée sur les feuilles 6 h après l'application, mais n'a pas affecté l'absorption et le transport de la C14 tralkoxydime aux autres temps d'échantillonage ultérieurs. Dans les essais in vitro, le metsulfuron-methyl à 10 ou 100 nm dans le milieu d'essai n'a pas eu d'effet sur l'activité de l'acetyl coenzyme A carboxylase (ACCase), ni n'a interféré avec l'inhibition de l'ACCase par la tralkoxydime. En outre, le traitement d'Avena fatua avec du metsulfuron-methyl a 4, 8 ou 12 g ha^?1 n'a pas réduit le niveau d'activité d'ACCase quand les plantes étaient récoltées de 24 à 96 h après l'application. Ainsi aucune base apparente physiologique ou biochimique pour l'antagonisme de la tralkoxydime n'a été identifiée. L'inhibition temporaire de la croissance induite par le metsulfuron-methyl peut être d'une durée suffisante pour que la plus grande partie de la tralkoxydime soit métabolisée en produits inactifs, et de ce fait réduit les effets induits par la tralkoxydime. Antagonismus von Metsulfuron-methyl auf die Wirkung von Tralkoxydim auf Avenua fatua In Phytotron-Versuchen wurde die Wirkung von Tralkoxydim auf Avena fatua durch Zugabe von Metsulfuron-methyl in die Spritzbrühe signifikant herabgesetzt, besonders bei niedrigen Tralkoxydim-Dosen (z. B. 125 g AS ha^?1) und bei hohen Metsulfuron-methyl-Dosen (8 oder 12 g AS ha^?1). Metsulfuron-methyl allein setzte das Wachstum von Avena fatua signifikant herab. Mit Chlorsulfuron, das das Wachstum von Avena fatua bis 33 g AS ha^?1 nicht verminderte, ließ sich die Wirkung von Tralkoxydim nur wenig beeinträchtigen. In Kombination reduzierte Metsulfuron-methyl die Blattaufnahme von ¹⁴C-Tralkoxydim 6 h nach der Applikation, aber bei späteren Probennahmen waren Aufnahme und Translokation von ¹⁴C- Tralkoxydim nicht beeinträchtigt. In In-vitro-Versuchen blieben 10 oder 100 mm Metsulfuron in der Versuchslösung ohne Wirkung auf die Aktivität der Acetyl-Coenzym-A-Carboxylase (ACCase) in Avena fatua, es wirkte auch nicht auf die Hemmung der ACCase durch Tralkoxydim. Auch eine Behandlung von Avena-fatua-Pflanzen mit 4, 8 oder 12 g AS ha^?1 Metsulfuron-methyl setzte nach 24 bis 96 h die ACCase-Aktivität nicht herab. So konnte keine offensichtliche physiologische oder biochemische Basis für den Antagonismus von Tralkoxydim gefunden werden. Die durch Metsulfuron-methyl induzierte zeitweilige Wuchshemmung kann lang genug sein, daß das meiste Tralkoxydim zu inaktiven Produkten abgebaut wird, so daß seine Wirksamkeit reduziert wird.     

Dissipation of the herbicide dithiopyr in soil and residues in wheat (Triticum aestivum L) grain under Indian tropical conditions

Dissipation of dithiopyr in soil was monitored after application to wheat crop as pre- or post-emergence applications at two rates, viz 100 and 200 g AI ha(-1). The level of dithiopyr in the soil was assessed by gas chromatography, and its disappearence was found to follow a first-order decay curve irrespective of rate or method of application. The half-life in soil ranged between 17.3 and 25.0 days and residues at harvest (150 days after application) ranged between 4.0 and 8.8% of amounts applied. Investigation of microbial degradation of dithiopyr was conducted in minimal salt and Czapek Dox media in which 80% of the compound degraded within 15 days. Residues were not detected in wheat grain at harvest.     

三株病原真菌对稗草生防潜力的研究

从稻田中采集自然感病的稗草标样,分离获得10余种病原真菌,经生测,链格孢菌、尖角突脐孢菌和内脐孢菌是3株很有希望的稗草生防潜力菌。对它们的生长及产孢特性、寄主范围及孢子悬浮液喷雾接种对水稻和稗草的致病性等进行了研究。结果表明,3个菌各有优缺点。链格孢菌对稗草致病力稍差,对水稻有轻度感染,但其产孢速度快,产孢量大;尖角突脐孢菌对稗致病力强,对稻无影响,但产生孢子慢,产生菌丝多;内脐孢菌对稗致病力强,对稻安全,菌落生长较慢,但产孢速度快,产孢量多,气生菌丝少。黑暗、空气充足有利于3菌株的生长及产孢。     

Allelic variation of the ACCase gene and response to ACCase-inhibiting herbicides in pinoxaden-resistant Lolium spp

BACKGROUND: The repeated use of acetyl‐coenzyme A carboxylase (ACCase) inhibiting herbicides to control grass weeds has selected for resistance in Lolium spp. populations in Italy. The efficacy of pinoxaden, a recently marketed phenylpyrazoline herbicide, is of concern where resistance to ACCase inhibitors has already been ascertained. ACCase mutations associated with pinoxaden resistance were investigated, and the cross‐resistance pattern to clodinafop, haloxyfop, sethoxydim, clethodim and pinoxaden was established on homo/heterozygous plants for four mutant ACCase alleles. RESULTS: Seven different mutant ACCase alleles (1781‐Leu, 1999‐Leu, 2041‐Asn, 2041‐Val, 2078‐Gly, 2088‐Arg and 2096‐Ala) and 13 combinations with two types of mutation were detected in the pinoxaden‐resistant plants. The 1781‐Leu allele appears to confer a dominant resistance to pinoxaden, clodinafop, haloxyfop, sethoxydim and clethodim at 60 g AI ha^?1. The 2041‐Asn and 2041‐Val alleles are associated with dominant or partially dominant resistance to FOPs, no substantial resistance to DIMs and a moderate resistance to pinoxaden. The 2088‐Arg allele endows a partially dominant resistance to clodinafop, sethoxydim and most likely to pinoxaden. In addition, non‐target‐site resistance mechanisms seem to be involved in pinoxaden resistance. CONCLUSION: Almost all the ACCase mutations selected in the field by other ACCase inhibitors are likely to confer resistance to pinoxaden. Although pinoxaden is sometimes able to control FOP‐resistant populations, it should not be considered as a sustainable ACCase resistance management tool. The presence of non‐ACCase‐based resistance mechanisms that could confer resistance to herbicides with different modes of action further complicates the resistance management strategies. Copyright © 2011 Society of Chemical Industry     

New 2-phenyl-4,5,6,7-tetrahydro-2H-indazole derivatives as paddy field herbicides

A series of 3-chloro-2-(4-chloro-2-fluorophenyl)-4,5,6,7-tetrahydro-2H-indazole derivatives containing various substituted isoxazolinylmethoxy groups at the 5-position of the benzene ring were synthesized and their herbicidal activities assessed under greenhouse and flooded paddy conditions. Among them, compounds having a phenyl or cyano substituent at the 3-position of the 5-methyl-isoxazolin-5-yl structure demonstrated good rice selectivity and potent herbicidal activity against annual weeds at 16-63 g AI ha(-1) under greenhouse conditions. Field trials indicated that these two compounds controlled a wide range of annual weeds rapidly with a good tolerance on transplanted rice seedlings by pre-emergence application. They showed a low mammalian and environmental toxicity in various toxicological tests.     

Resistance to ACCase-inhibiting herbicides and isoproturon in UK populations of Lolium multiflorum: mechanisms of resistance and implications for control

Herbicide-resistant Lolium multiflorum (Italian rye-grass) was first reported in the UK in 1993 and had been confirmed on 25 farms by 1999. In this study, resistance to five herbicides belonging to the aryloxyphenoxypropionate, cyclohexanedione and phenyl-urea classes was determined in six populations of L multiflorum from the UK under glasshouse and simulated field conditions. Glasshouse conditions tended to exaggerate the degree of resistance, but experiments performed in both environments detected resistance in four populations of L multiflorum. Four populations (Essex A1, Lincs A1, Wilts B1, Yorks A2) were resistant to diclofop-methyl, fluazifop-P-butyl, tralkoxydim and partially resistant to isoproturon, but only the population from Yorkshire (Yorks A2) showed resistance to cycloxydim. Biochemical analyses of acetyl coenzyme A carboxylase (ACCase) activity, oxygen consumption by thylakoids, diclofop metabolism and glutathione S-transferase activity showed that, in three of the resistant populations, an enhanced rate of herbicide metabolism conferred resistance. This is the first report world-wide of an enhanced metabolism mechanism of diclofop resistance in L multiflorum. In the Yorks A2 population, an insensitive ACCase was detected (target-site resistance) which also conferred cross-resistance to all of the other ACCase inhibitors investigated.     

Herbicidal activity on acetolactate synthase‐resistant barnyardgrass (Echinochloa crus‐galli) in Arkansas,USA

The intensive use of the acetolactate synthase (ALS)‐inhibiting herbicides, imazethapyr, penoxsulam and bispyribac‐sodium, in imidazolinone‐resistant (Clearfield) rice increases the risk of the evolution of ALS‐resistant barnyardgrass. In 2009, imazethapyr failed to control barnyardgrass that was collected from a field in Arkansas, USA, following the failure of the herbicide in 2008. A greenhouse experiment was conducted to confirm and document the level of resistance of the biotype against three ALS‐inhibiting herbicides that currently are labeled in rice. The level of control of the resistant biotype at the labeled rate of bispyribac‐sodium of 35 g ai ha^?1 was 10%, penoxsulam at 22 g ai ha^?1 was 0% and imazethapyr at 70 g ai ha^?1 was 25%. The level of mortality of the susceptible biotype was 100% with all the herbicides at the labeled rate. The dose needed to kill 50% of the resistant plants was 49 g ha^?1 of bispyribac‐sodium, 254 g ha^?1 of penoxsulam and 170 g ha^?1 of imazethapyr. For the susceptible biotype, bispyribac‐sodium at 6 g ha^?1, penoxsulam at 10 g ha^?1 and imazethapyr at 12 g ha^?1 killed 50% of the treated plants. Based on these findings, it was confirmed that a barnyardgrass population has evolved cross‐resistance to three ALS‐inhibiting herbicides in rice culture in Arkansas. Furthermore, an experiment was conducted to determine if the ALS‐resistant biotype could be controlled using other mechanisms of action. The results indicated that propanil, a photosystem II inhibitor, and quinclorac, a synthetic auxin, failed to control the resistant biotype at the labeled rates, whereas all the other evaluated herbicides provided effective control of both biotypes.