Herbicides monuron

TPNH) and oxygen to demethylate a number of closely related N,N-dimethylcarbamates (21). The same particulate system, however, exhibited a low order of activity on the urea herbicides monuron, diuron, and fenuron. Apparently, substitution of a nitrogen atom for the oxygen atom of the ester linkage to form the corresponding urea substantially decreased the velocity of the reaction. 

DIMETHYL-N -(4-CHLOROPHENYL)UREA 1,1-DIMETHYL-3-(p-CHLOROPHENYL)UREA HERBICIDES, MONURON KARMEX xMONURON HERBICIDE KARMEX W. MONURON HERBICIDE LIROBETAREX MONUREX MONURON MONUROX MONURUON MONUURON NCI-C02846 TELVAR TELVAR MONURON WEEDKILLER USAF P-8 USAF XR-41... 

Figure 26 In situ positive-ion FAB-MS/MS analysis of the phenylurea herbicide monuron.

Following the earlier work of Kirkland [125] on phenylurea herbicides, Sidwell and Ruzicka [126] applied liquid chromatography to the identification and determination of active ingredient contents of phenylurea herbicide formulations. Smith and Lord [118] have used liquid chromatography for the determination of Chlorotoluron residues in soil, but Diuron and Monuron interfered in their chromatographic system. 

Fig. 9.11 Typical chromatograms obtained from 5pl injections of soil extracts (a) unfortified and (b) fortified with uron herbicides at 2mg kg-1.1, Monuron 2monoLinuron 3 Metobromuron 4 Chlorotoluron 5 Diuron 6 Linuron 7 Chlorbromuron and 8 Chloroxuron.

Smith and Fitzpatrick [252] have also described a thin layer method for the detection in water and soil of herbicide residues, including Atrazine, Barban, Diuron, Linuron, Monuron, Simazine, Trifluralin, Bromoxynil, Dalapon, Dicamba, MCPB, Mecoprop, Dicloram, 2,4-D, 2,4-DB, Dichloroprop, 2,4,5-T, and 2,3,6-trichlorobenzoic acid. 

Herbicides 2,4-D, MCPA, Mecoprop, 4-(2,4-DB), TCA, Amitrole, Dalapon, Monuron, Chlorpropham, Endothal, Pyrazon, and DNOC. 

The urea herbicides do not inhibit seed-germination to any extent, or the growth of nonphotosynthetic tissue, nor do they interfere with dark-fixation reactions. Monuron-treated bean-leaves which were fed 14C02 in the light, however, decreased in sucrose content (as percent of ethanol-soluble materials) from 70 to 2% in 72 hours.185 Most of the carbon-14 label... 

Sugarcane Sower initiation is dependent on day length, temperature, age, moisture, and variety, and can be prevented by chemical applications at, or very close to, the date of floral initiation. The effective chemicals have been of two types (a) photosynthetic inhibitors, such as 3-(p-chlorophenyl)-1,1-dimethylurea (monuron), or (b) leaf-burning, contact chemicals. The very effective bipyridylium herbicides 6,7-dihydrodipyrido[l,2-a 2, r-c]pyrazidinium dibromide (diquat) and 1, l -dimethyl-4,4 -bipyridinium bis (methyl sulfate) (paraquat) combine the two properties, although the... 

Many other compounds have been included in studies on sucrose response. Most of these have been herbicides or enzyme poisons. None of the common herbicides had any positive effect on sucrose at rates up to that causing severe foliar injury. Earlier reports of response from 2-(2,4,5-trichlorophenoxy)propionic acid and 2,2-dichloropropionic acid could not be substantiated in British Guiana and Queensland. 27 Some compounds, such as 3-(p-chlorophenyl)-l,l-dimethylurea (monuron), (2,4-dichloro-phenoxy) acetic acid in soil, ethylenediaminetetraacetic acid, and leaf desiccants decreased sucrose and juice solids content. 20 Field trials with several chemicals in Trinidad showed enhanced sucrose at 14 to 28 days before harvest resulting from the application of 8 and 12 lb. (per acre) of... 

JJ Kikland. Trace analysis by programmed temperature gas chromatography. Simultaneous determination of monuron and diuron herbicide residues. Anal Chem 34 428-433, 1962. 

SE Katz. Determination of the substituted urea herbicides linuron, monuron, diuron, neburon and fenuron in surface waters. J Assoc Off Anal Chem 49 452-456, 1966. 

Research had confirmed that no parent simazine residues were found in treated com plants, and additional data on the dissipation pathway of simazine needed to be developed. Research also indicated that triazines interfered with the photosynthetic process on susceptible growing weeds, as evidenced by the appearance of chlorotic leaves. Steps were undertaken to elucidate simazine s dissipation pathway and herbicidal mode of action. In Basel, Dr. Gast (1958) showed that the accumulation of starch by common coleus (Coleus blumei Benth.) plants was inhibited from treatment with 2-chloro-4,6-bis-(alkyl-amino)-triazines due to the inhibition of sugar synthesis. At the same time, Moreland et al. (1958) found weed control activity could be reduced by supplying carbohydrates to the plants through their leaves and that simazine was a strong inhibitor of the Hill reaction in photosynthesis. Exer (1958) found that triazines inhibited the Hill reaction as strongly as urea of the CMU (monuron) type. 

Triazine (e.g., atrazine, simazine) and substituted urea (e.g., diuron, monuron) herbicides bind to the plastoquinone (PQ)-binding site on the D1 protein in the PS II reaction center of the photosynthetic electron transport chain. This blocks the transfer of electrons from the electron donor, QA, to the mobile electron carrier, QB. The resultant inhibition of electron transport has two major consequences (i) a shortage of reduced nicotinamide adenine dinucleotide phosphate (NADP+), which is required for C02 fixation and (ii) the formation of oxygen radicals (H202, OH, etc.), which cause photooxidation of important molecules in the chloroplast (e.g., chlorophylls, unsaturated lipids, etc.). The latter is the major herbicidal consequence of the inhibition of photosynthetic electron transport. 

In 1955 monuron was registered as the first preemergence herbicide in citrus (Day, 1955), followed by diuron and simazine. Simazine was recommended by the University of Florida as an excellent weed control tool for citrus beginning in 1962 (Kretchman and McCown, 1962). 

Pickett et al. (1992) reported that California citrus growers depend on herbicides for weed control. Simazine was rated as the most important herbicide used in citrus production. Abdel-Rehman et al (1994) reported that control of annual broadleaf weeds was most effective with simazine plus fluazifop and least effective with fhiazifop alone. Application of diuron or atrazine once at 1-4kg a.i./ha or twice at 1 + 1, 1 + 2 or 2 + 2kg a.i./ha, significantly reduced grasses and broadleaf weeds. Broadleaf weeds were controlled by 2-4kg a.i./ha of diuron and 2 + 2kg a.i./ ha of simazine at the 60-day sampling period (Singh et al, 1987). Perez (1976) reported that fluometuron, diuron, monuron, and simazine, all at 4.8kg a.i./ha, and bromacil at 4kg a.i./ha controlled weeds without injury to citrus on latosols, while simazine and diuron at 4.8 kg a.i./ha or bromacil at 4kg a.i./ha caused no injury to grapefruit after two applications on sandy soil. 

In the late 1950s, many herbicides were compared for preemergence weed control in pineapple. Many of these were triazines, which gave better weed control compared to monuron and diuron. 

Harris, C.I. (1966). Adsorption, movement, and phytotoxicity of monuron and. v-lriazinc herbicides in soil. Weeds, 14 6-10. 

Sheets (5), in reviewing the disappearance of substituted urea herbicides from soil, found that inactivation occurs under soil conditions favorable for the growth of microorganisms but takes place slowly or not at all in dry or autoclaved soil. Burschel and Freed (6), reviewing work relating to 2,4-D and amitrole as well as monuron, state that the data indicate that ultimate breakdown is caused by microbiological attack. 

Fig. 1.33. Top the resolution window diagram for the gradieni-elulion separation of a mixture of twelve phenylurea herbicides on a Separon SGX Cix. 7.5 nm. column (150 x 3.3 mm i.d.) in dependence on the initial concentration of methanol in water at the start of the gradient, A. with optimum gradient volume Mg = 73 ml. Column plate number N =. 5000.. Sample compounds hydroxymetoxuron (/). desphenuron (2), phenuron (.1). metoxuron (4). monuron (5), monolinuron (6). chlorotoluron (7), metobromuron (X), diuron (9), linuron (/O), chlorobromuron (//). neburon U2). Bottom the separation of the twelve phenylurea herbicides with optimised binary gradient from 24 to l(X)9f methanol in water in 73 min. Flow rate I ml/min.

Pig. 9.12. (a) Principle of immunoaffinity solid-phase extraction, (b) An example of on-line immunotrapping and RP-HPLC of 13 phenylurea herbicides spiked into water. Analytes 1, phenuron 2, metoxuron 3, monuron 4, methabenzthiazuron 5, chlortoluron 6, fluomethuron 7, isoproturon 8, difenoxuron 9, buturon 10, Unuron 11, chlorbromuron 12, difluzbenzuron 13, neburon [65]. (Reprinted with permission.)... 

Introduced in 1951 by du Pont in the USA monuron (CMU, 6) was the first urea herbicide. Diuron (DCMU, 7) was introduced by the same company in 1956. 

Monuron TCA, prepared by the reaction of monuron with trichloroacetic acid, is also a total herbicide with foliar action and can therefore also be used postemergence at rates of 10-15 kg/ha. Owing to its acid character, it is incompatible with alkaline substances. 

Isoproturon (Hoe 16 410 16) is a closely related analogue of monuron (6), containing an isopropyl group instead of the Cl atom of monuron in position 4. A period of 21 years separates the development of the two herbicides. This long time is indicative on the one hand of the difficulties of molecule development , and on the other hand of the fact that by changing the molecule of a well-known total herbicide, another herbicide of surprisingly new selectivity can be obtained. 

Bucha and Todd described the herbicidal properties of neburon (27) together with those of monuron, fenuron and diuron as early as 1951, but neburon, introduced only in 1955, did not gain widespread use. 

The selectivity of these compounds can be attributed to several factors. Because of their acyl group, their mode of penetration into the plants differs substantially from that of the other urea herbicides. The acyl group is slowly split off in the soil, resulting in diuron and monuron, and they exert their action in these forms. Owing to their poor solubility in water and strong adsorption on the soil, they remain in the upper 10 cm of the soil, and are not toxic to deep-rooted crop plants. 

A purely apoplastic movement of monuron is inconsistent with the fact that the site of phytotoxic action is within the chloroplast, and that to reach it the herbicide mtist penetrate the protoplasm and the plasmalemma surrounding the chloroplast (Ashton and Crafts, 1973). 

Urea herbicides, in addition to causing the degradation of photosynthetic tissues, inhibit root growth. Muzik et al. (1954), and Voderberg (1961) describe this action of CMU and monuron. 

Field tests with monuron, linuron and with diuron (Belasco and Pease, 1969 Maier-Bode, 1971) unequivocally showed that under natural conditions no azo compounds are formed in the soil in analytically detectable quantities neither could they be detected by gas chromatography (detectability 0.01 ppm) in cultured crops grown on soils treated with urea herbicides. 

In recent experiments mass spectrography has been used to identify 3-(2-hydroxy-4-chlorophenyl)-1,1-dimethylurea and 3-(2-hydroxy-4-chlorophenyl)-1 -methylurea in bean leaves as metabolites of monuron (Lee et al., 1973). This is, in the case of urea herbicides, experimental proof of the hydroxylating (oxidative) detoxication process, performed together with N-dealkylation by the microsomal oxidase enzyme system. 

Wallnofer et al. (1974) investigated the microbial degradation of some urea herbicides by Rhisopus japonicus and showed that this microorganism only demethylates monuron, fluometuron and monolinuron, while from buturon it splits off the l-methyl-2-propynyl group. 

---