Degradation of the herbicide benzoylprop-ethyl in soil

The degradation of [¹⁴C] benzoyl prop ethyl (SUFFIX,^a ethyl N-benzoyl-N-(3,4-dichlorophenyl)-2-aminopropionate) in four soils has been studied under laboratory conditions. The major degradation product of benzoylprop ethyl at up to 4 months after treatment was its corresponding carboxylic acid (II). On further storage this compound became firmly bound to soil before it underwent a slow debenzoylation process which led to the formation of a number of products including N-3,4-dichlorophenylalanine (IV), benzoic acid, 3,4-dichloroaniline (DCA), which was mainly present complexed with humic acids, and other polar products. Although these polar products were not identified, they were probably degradation products of DCA, since they were also formed when DCA was added to soil. No 3,3′,4,4′-tetrachloroazobenzene (TCAB) was detected in any of the soils at limits of detectability ranging from 0.01-0.001 parts/million. Since N-3,4-dichlorophenylalanine (IV) and 3,4-dichloroaniline were transient degradation products of benzoylprop ethyl, the metabolism in soil of radiolabelled samples of these compounds was also studied. In these laboratory experiments the persistence of the herbicide increased as the organic matter content of the soil increased and the time for depletion of half of the applied benzoylprop ethyl varied from 1 week in sandy loam and clay loam soils to 12 weeks in a peat soil.     

The behaviour of residues of benzoylprop-ethyl and its breakdown products in wheat

Samples of wheat grain and straw have been analysed from trials with the wild oat herbicide benzoylprop-ethyl ( I ) in several countries. Following recommended commercial treatments (application of 1.0–1.6 kg ha^?1 at Feekes growth stage G-J), total residues of I and its hydrolysis product N-benzoyl-N-(3,4-dichlorophenyl)-DL - alanine (free and conjugated) were low and in the majority of instances they were < 0.01 mg kg^?1 in samples of grain from the UK, although rather higher residues were detected in some grain samples from other countries. Residues in straw were higher, but normally did not exceed 2 mg kg^?1, and were rather variable, possibly as a result of differences in agricultural practice.     

The fate of the herbicide benzoylprop-ethyl in crops grown in treated soils

The herbicide benzoylprop-ethyl (SUFFIX,^a ethyl (±)-2-(N-benzoyl-3,4-dichloro-anilino) propionate) is applied post-emergence for the control of wild oats (Avena spp.) in wheat. During application some falls onto the soil and in the present work the possible uptake of residues from the soil, particularly by rotation crops has been studied using radioisotope techniques under indoor and outdoor conditions. Soil application at 1 kg/ha gave lower residues in wheat in the year of application than were found in previous studies using overall foliar-soil application. In the radiochemical experiments soil residues did persist into the following year, but residues in potatoes and wheat grown in these soils, although generally below the limit of determination (0.005 mg/kg), were occasionally just above this level (0.006 mg/kg). On the results of the present work, residues in rotational crops from soils treated in the previous year are unlikely to reach the limits of normal analytical determination.     

咪唑啉酮类除草剂的应用及降解

咪唑啉酮类除草剂虽具有高效广谱的特点,但有较长的残留活性,长期使用会造成作物药害,并且会制约正常的作物轮作。因此,如何解决其残留问题已成为目前的重要课题。本文介绍了咪唑啉酮类除草剂的种类和特性,阐述了此类除草剂在杂草体内的作用方式、代谢机制、应用情况及其在土壤中的降解途径,并对该类除草剂的应用与降解研究进行了展望。     

Seed production of Raphanus raphanistrum following herbicide application during reproduction and effects on wheat yield

The influence of weather and agronomic factors on the activity of six selective herbicides applied at reproductive stages of development for the reduction in seed production of Raphanus raphanistrum in wheat was evaluated. The herbicides used in this way generally reduced seed production by between 80% and 100%. Triasulfuron and mixtures of triasulfuron + MCPA consistently provided the greatest reduction in seed production. This was greater when herbicides were applied at the bud and early flowering stages of R. raphanistrum and the efficacy of the herbicides increased as maximum temperature on the day of spraying increased over the range 14–24°C. An applied model developed from these results predicts the reduction in seed production of R. raphanistrum, for each herbicide, given the stage of weed development and maximum temperature on the day of its application. Wheat yield was significantly reduced as densities of R. raphanistrum increased, with predicted losses at low densities being approximately half of those reported in the literature. There was no consistent evidence that the late application of herbicides had any negative effect on wheat yield through crop injury, nor was there any indication of yield improvement. It is concluded that certain herbicides applied during the reproductive phase of development have considerable potential to reduce R. raphanistrum seed production in wheat crops. As part of an integrated strategy, such late post‐emergence application of selective herbicides to regulate seed production has a likely role for managing weed seedbanks, but little or no value for counteracting weed competition.     

The soil degradation of the herbicide florasulam

The route and rate of degradation of florasulam, a low‐rate triazolopyrimidine sulfonanilide herbicide, was investigated in six soil types under aerobic conditions at 20 or 25 °C. Degradation products were isolated and identified by mass spectroscopy. Florasulam was rapidly degraded by microbial action with an average half‐life of 2.4 days (range 0.7 to 4.5 days). The first step in the degradation pathway involved conversion of the methoxy group on the triazolopyrimidine ring to a hydroxy group to form N‐(2,6‐difluorophenyl)‐8‐fluoro‐5‐hydroxy[1,2,4]triazolo[1,5‐c]pyrimidine‐2‐sulfonamide. This metabolite degraded, with a half‐life of 10 to 61 days, via partial breakdown of the triazolopyrimidine ring to form N‐(2,6‐difluorophenyl)‐5‐aminosulfonyl‐1H‐1,2,4‐triazole‐3‐carboxylic acid. This was followed by cleavage of the sulfonamide bridge to form 5‐(aminosulfonyl)‐1H‐1,2,4‐triazole‐3‐carboxylic acid. Other degradation processes involved decarboxylation of the carboxylic acid metabolites and mineralisation to form carbon dioxide and non‐extractable residues. © 2000 Society of Chemical Industry     

The fate of the herbicide chlortoluron and its possible degradation products in soils

Chlortoluron hadàhalf-tire in soil of 4–6 weeks. The only metabolite identified was monomethyl chlortoluron, half-life 8 weeks. 3-Chloro-4-methylphenylurea hadàsimilar half-life but was not detected in soils treated with chlortoluron or monomethyl chlortoluron suggesting that 3-chloro-4-methylaniline was formed directly from monomethyl chlortoluron. This aniline hadàhalf-life of 1–2 days in soil, initial concentrations above 5 ppm yielding dimers and trimers predominantly C — N linked. Neither the aniline nor polymeric products were detected in chlortoluron treated soils, presumably because slow formation of the aniline was followed by rapid degradation which kept concentration low.     

The metabolism of the herbicide flamprop-methyl in wheat

The metabolism of the wild oat herbicide flamprop-methyl, methyl (±)-2-[N-(3-chloro-4-fluorophenyl)benzamido]propionate, in spring wheat grown to maturity has been studied under glasshouse and outdoor conditions. [¹⁴C]-Flamprop-methyl labelled separately in the halophenyl ring and the carbonyl of the benzoyl group was used. The major metabolite formed in plants was the corresponding carboxylic acid, II, which also occurred as conjugates. Other minor metabolites detected under glasshouse conditions only were the 3- and 4-hydroxybenzoyl analogues of flamprop-methyl and 3′-chloro-4′-fluorobenzanilide. The soil in which the plants were grown contained residues comprising mainly flamprop-methyl and II together with smaller amounts of unidentified polar material.     

麦田除草剂顶尖的应用技术研究

研究了15%顶尖可湿性粉剂在小麦田不同用药时间、不同剂量、不同对水量及混用对小麦田杂草的控制效果,探讨了顶尖在小麦田的使用技术。     

Field degradation of the herbicide metribuzin and its degradation products in a Manitoba sandy loam soil*

The degradation of the herbicide metribuzin (4-amino-6 r-butyl-3-(methylthio)-1, 2, 4-tnazin-5-(4H)one) applied at 1 and 2 kg/ha at times equivalent to pre-emergence (12 June), post-emergence (5 July), and pre-harvest (15 August), has been investigated in Almasippi very line sandy loam at Carman, Manitoba. Gas-liquid chromatographic analytical results showed that metribuzin degraded during the growing season, and that residue levels immediately prior to freeze-up (25 October) were in general less than 10% of applied metribuzin independent of application date, and were largely unchanged the following spring. The metabolites and photoproduct of metribuzin were present in maximum amounts near 13 July for the first two treatment dates, a time closely following maximum soil temperature readings, and these compounds in turn degraded almost completely by freeze-up. The following spring only very low levels were detected. Under the conditions described, metribuzin and its degradation products degraded to low levels and should not provide a carryover problem the next growing season.     

灭草肥的选配及其施用效果

通过室内稳定性与宜配性试验,从4种除草剂(丁草胺、克草胺、杀草丹、恶草灵)和4种化肥(尿素、过磷酸钙、碳酸氢铵、硫酸铵)的16种组合中筛选出2种比较理想的配方,即丁草胺、克草胺2种除草剂分别与尿素混配成2种灭草肥。2种配方灭草肥无论是现配现用还是配制后贮藏4个月再使用,对稻田稗草、野芹菜、鸭舌草、三菱草、节节草、水花生等防效均在98%以上。灭草肥处理的水稻有效穗数均比单施尿素处理有所增加,产量也有所提高。     

The degradation of the herbicide benzoylprop ethyl on the foliage of cereal seedlings

The breakdown of the herbicide benzoylprop ethyl [SUFFIX, ethyl N-benzoyl-N-(3,4-dichlorophenyl)-2-aminopropionate] has been examined in wheat, oat, and barley seedlings after application of ¹⁴C-labeled herbicide to the foliage.Within 15 days of the application the route and rate of the breakdown were similar in the plants of all three species. Some of the herbicide was present in the plants in a complexed form which could be extracted from the plant with organic solvents and converted back into the herbicide on treatment with hot acid. Evidence was obtained for hydrolysis of the herbicide in the plant to give its des-ethyl analog which conjugated with plant sugars. There was some evidence for a small degree of degradation of benzoylprop ethyl by debenzoylation to give products which also conjugated or complexed.There was no evidence for the formation of 3,4-dichloroaniline in the plants.     

淮北地区麦田除草剂对后茬大豆的药害症状及对策

淮北地区随着麦田除草剂使用面积的扩大,除草剂的残留对后茬大豆的药害发生面积逐年加大,危害程度逐年加重。本文分析了淮北地区麦田除草剂对后茬大豆的药害症状和产生原因,提出了具体的控制措施。     

乙草胺及其混配剂防除麦田硬草试验初报

随着麦、稻免耕和套播轻型栽培面积的不断扩大 ,加之单一使用茎叶处理除草剂 ,江苏省姜堰市麦田杂草草相发生明显变化 ,恶性杂草硬草成为防除重点。由于其抗性强 ,生产中应用异丙隆及骠马等除草剂 ,往往效果不够理想 ,达不到一次防除控害至收获的要求。为寻求一次性控制硬草的化除配方 ,2 0 0 2年秋我站进行了乙草胺与高渗异丙隆混用配方筛选和用药适期试验 ,现将有关结果初报如下。1　材料与方法1 1　试验药剂5 0 %乙草胺EC(大丰农药厂产 )、5 0 %高渗异丙隆WP(吴县宝带农药厂产 )、2 0 %乙·苄WP(江苏苏科农药厂产 )。1 2　试验处理1 2…     

In vitro sensitivity of wheat and oat mitochondria to the selective herbicide,diclofop-methyl

Compared to diclofop-methyl (methyl 2-[4-(2′,4′-dichlorophenoxy)phenoxy]propanoate), diclofop (the demethylated derivative) was a more potent inhibitor of polarographically monitored state 3 respiration of mitochondrial preparations isolated from shoots of dark-grown wheat (Triticum aestivum L. cv. Neepawa) and oat (Avena sativa L. cv. Terra) seedlings. Wheat and oat mitochondria demonstrated essentially similar concentration-response patterns for the uncoupler-like stimulation of state 4 respiration and the inhibition of state 3 respiration by diclofop, thereby intimating that differential mitochondrial sensitivity was not a selectivity factor between these species. Diclofop suppression of unconstrained oxygen utilization elicited by the respiratory uncoupler FCCP indicated that inhibition of state 3 respiration involved interference with some site(s) on the mitochondrial electron transport chain and not with energy transfer directly. Cytochrome c oxidase activity was not affected by diclofop, but succinate- and malate-PMS oxidoreductase activities were inhibited by diclofop. Enhanced rates of passive mitochondrial swelling in isotonic KCl medium in the presence of diclofop pointed to a direct influence on the permeability properties of the inner mitochondrial membrane and indicated that membrane disruption could have been a factor in the effects elicited by diclofop on mitochondrial respiration. However, it does not appear that specific interference with mitochondrial functionality is the primary mechanism of phytotoxicity in susceptible plants.     

Effects of the herbicide methabenzthiazuron on the physiology of wheat plants

Spring wheat (Triticum aestivum L. “Caribo”) was grown in vermiculite containing methabenzthiazuron (N-(benzothiazol-2yl)-NN′-dimethylurea) presowing. Effects of the herbicide on plant development and plant composition were analysed up to an age of 4 weeks. Inhibition of photosynthetic oxygen evolution represented the primary effect induced by the herbicidal treatment and led to a decreased concentration of soluble reducing sugars. Photosynthetic activity however recovered after 3 weeks and even increased above control values. Secondary effects following methabenzthiazuron treatment included a delayed chlorophyll breakdown, a decreased chlorophyll a/b ratio, enlarged chloroplasts, an increased concentration of soluble amino acids and of soluble protein, and an increased in vitro nitrate reductase activity. These responses are taken to indicate an increased photosynthetic and metabolic capacity in methabenzthiazuron treated wheat plants. Comparable results can be obtained with plants grown at low light intensities. It is concluded that the “physiological effects” observed in wheat plants after treatment with methabenzthiazuron are similar to a natural adaptation reaction to low light intensities. It is assumed that this adaptation reaction is caused by a low concentration of soluble reducing sugars. Experiments with plants growing at different light intensities indicated that effects due to herbicidal action were more pronounced at high light intensities. Measurements on daily fluctuations revealed a peak around noon for the sugar content and the nitrate reductase activities measured in vivo as well as in vitro. In vivo nitrate reductase activity in plants treated with 5 parts/million methabenzthiazuron was very low, presumably because of lack of sugars for the production of NADH. The protein concentration was increasing and the amino acids were decreasing during the day in herbicide treated plants, possibly indicating increased protein synthesis in the light in plants treated with methabenzthiazuron.     

The cyclization transformation of the sulfonylurea herbicide flupyrsulfuron in the soil of winter wheat crops

The synthesis of 1-(4,6-dimethoxypyrimidine-2-yl)-7-trifluoromethyl-1,2,3,4-tetrahydropyrido [2,3-d]pyrimidin-2,4-dione has been carried out in such a way that the dimethoxypyrimidine substituent was unambiguously in position 1 of the pyrido[2,3-d]pyrimidine ring. This regioisomer was obtained by cyclization with phosgene of 2-(4,6-dimethoxypyrimidin-2-ylamino)-6-trifluoromethylnicotinamide which had previously been ionized with sodium hydride. It was shown to be identical to the metabolite generated in the soil of winter wheat crops treated previously with the sulfonylurea herbicide flupyrsulfuronmethyl [(methyl 2-(4,6-dimethoxypyrimidin-2-ylcarbamoylsulfamoyl)-6-trifluoromethylnicotinate]. The position of the dimethoxypyrimidine substituent had not previously been assigned unambiguously to positions 1 or 3 of the pyrido[2,3-d]pyrimidine ring. The regioisomer was also identical to the cyclization compound generated chemically from flupyrsulfuron in a sterile water buffer at pH 9. The metabolism pathways of flupyrsulfuron in soil are discussed in the light these structure determinations and compared with the soil metabolism pathways frequently observed with other sulfonylurea herbicides.     

The analysis of crops and soils for the triazine herbicide cyanazine and some of its degradation products. II. Results

Crops and soils from field trials in 1967–1970 in several countries have been analysed for residues of the triazine herbicide cyanazine (‘BLADEX’

1 Shell Registered Trade Mark.

^a or ‘FORTROL’^a' 2-chloro-4-(1-cyano-1-methylethylamino)-6-ethylamino-1,3,5-triazine) and for its degradation products 2-chloro-4-(1-carbarmoyl-1-methylethylamino)-6-ethylamino-1,3,5-triazine ( II ), 2-chloro-4-(1-cyano-1-methylethylamino)-6-amino-1,3,5-triazine ( V ) and 2-chloro-4-(1-carbonyl-1-methylethylamino)-6-amino-1,3,5-triazine ( VI ). The time for the concentration of cyanazine in soils to fall to half the initial value was in the range 1.3 to 5 weeks with a mean value of 2.4 weeks. The rate of loss was not affected by sparse crop cover and there was some indication that the rate was greater under moist soil conditions. Residues of up to 0.5 part/million of ( II ) and up to 0.08 part/million of ( VI ) were detected in soils at 4 weeks from cyanazine application at 2 kg/ha. The residues of cyanazine and the degradation products declined rapidly and were 0.07 part/million or less at 16 weeks from treatment. Repeated annual applications did not lead to a detectable build up of residues in soil. Neither residues of cyanazine nor those of ( II ), ( V ) or ( VI ) could be detected in a wide range of crops harvested from soil treated in accordance with the likely recommendations and the limits of detectability were 0.01 to 0.04 part/million.