Plants herbicides effects

This herbicidal mode of action of pyraflufen-ethyl is similar to those of other peroxidizing herbicides containing a diphenyl ether moiety. Herbicidal effects of pyraflufen-ethyl are revealed as yellowing and browning in the foliar portion, and then death of the whole plant with leaf burn. 

These results show that the 2,4-dichlorophenoxyacetic acid can remain stable, and exert its herbicidal effects, only during the initial lag phase before the rapid logarithmic phase of destruction takes place. This initial lag phase depends upon the previous treatment of the soil, particularly on whether it has already been exposed to 2,4-dichlorophenoxyacetic acid. Clearly, once a soil is enriched with 2,4-dichlorophenoxyacetic acid destroying organisms, the herbicide, if added to the soil, will have little or no value in the control of plants growing there. 

The plant-microbe symbiosis may help facilitate the effective use of inoculants. For example, developed (brady)rhizobial strains or root-colonizing pseudomonads may be more effectively introduced into a contaminated soil environment when they are applied in conjunction with theirplant host. Kingsley etal. (1994) showed that inoculation of soil with a 2,4-D-degrader protected germinating seeds from the herbicidal effects of residual pesticide. Thus, plants may be used to help restore treated soils that contain residual but biologically active compounds. 

The insecticidal usefulness of the amines is hindered hy their tendency to severely injure plants (phytotoxie effects) to which they may be applied. Advanlagc of this property, however, is taken by using some amine compounds us herbicides. Examples include henefin. niirahn. and trifluralin,... 

This method can be used to compensate for inhibition of a biochemical pathway which results in a deficiency of an essential metabolic product. Detailed variations of the method are provided by Dayan et al.7 and Amagasa et al.1 The inhibitor concentration should be no higher than that required for strong herbicidal effect. Metabolite concentrations should be below that which is phytotoxic. For example, certain amino acids such at methionine, are growth inhibitors at relatively low concentrations. So, in preliminary work, dose-response studies should be done with amino acids to find the maximum concentrations that do not inhibit growth. Then, seeds of test plants should be imbibed in solutions of the phytotoxin with and without metabolite solutions. Amino acids, tricarboxylic acid cycle intermediates, vitamins, nucleotides, and reducing agents have all been used in complementation studies to elucidate modes of action of a variety of phytotoxins. Examples of each of these is provided by Dayan et al.7... 

The herbicidal effects have been documented, and there has been some work published regarding the persistence of dichlobenil in the soil. Barnsley and Rosher (1) measured the persistence of dichlobenil under both tropical and temperate conditions, using plant bioassay to measure residues. They found that dichlobenil disappeared rapidly, within a few days, when it was applied to the soil surface but was not worked in. However, when the chemical was incorporated in the soil, it persisted... 

Herbicides have provided a more effective and economical means of weed control than mechanical cultivation. Together with fertilizers and improved varieties of plants, herbicides have made a immense contribution to increased yields and reduced costs. 

The herbicidal effect of paraquat is attributable to the formation of superoxide anion (02 ). Superoxide anion is very toxic compound and is formed by the reaction of oxygen with paraquat radical (paraquat ). Plants, algae, and cyanobacteria have ferredoxin-NADP reductase to form NADPH for the reduction of carbon dioxide (see below). The chemolithoautotrophs also have NAD(P) (NAD and NADP) reductase to form NAD(P)H for the reduction of carbon dioxide. Paraquat [mid-point redox potential at pH 7.0 (Emj 0) = -0.43 V] radical is produced when paraquat is reduced by the catalysis of ferredoxin-NAD(P) reductase or NAD(P) reductase, which catalyzes the reduction of many compounds with of around -0.4 V. Although the aerobic organisms (and even many anaerobic organisms) have superoxide dismutase (SOD) which detoxifies superoxide anion in cooperation with catalase [ascorbate peroxidase in the case of plants (Asada, 1999)], the anion accumulates in the organisms when it is over-produced beyond the capacity of SOD. 

There is a close relationship between the effect of various substances as auxins and their herbicidal effects, with some easily explained exceptions. 4-Phenoxybutanoic acids (e.g., MCPB) have no auxin effect, yet they are efficient herbicides in many plants, providing they are metabolically transformed to the corresponding acetic acid. Although MCPA is selective with toxicity mainly against broadleaves, MCPB has an even more narrow selectivity because broadleaved plants, which do not metabolize it to MCPA, are not killed. 

Fluazifop-butyl has a preemergence activity too, lasting about 3-6 weeks according to soil type. This activity is only 25-50% of the herbicidal effect of postemergence application. Its selectivity is believed to be due to rapid degradation followed by conjugate formation in broad-leaved plants (Plowman et ai, 1980). 

The lethal mechanism of the plant-killing effect of urea herbicides is not yet known. Though death by starving through the inhibition of photosynthetic processes seems to be a convincing explanation, it does not explain several experimental observations. 

Some of the urea herbicides are compounds with total action. The precondition of their total herbicidal effect is their presence during the germination or active growth stages of the plants in absorbable form with adequate quantity in the absorption zone of the roots. In the exertion of total action, one factor is the irreversible injury caused to the plant, the other the plant s inability to metabolise these herbicides into harmless compounds at a sufficient rate. 

Primary herbicidal effects are followed by secondary ones that show up before death of the plant cell. The 70-S ribosomes of wheat chloroplasts are decreased by bleaching pyridazinones in the light, but not in the dark ( 9) A prominent mode of action is observed upon the composition of fatty acids by, e.g., BAS 13338 (SAN 9785) (24, 5), which does not substcuatially interfere with carotenoid biosynthesis. Good direct inhibition of photosynthetic electron transport (I50 3 x 10 7m) is observed with the phenylpyridazinone BAS 100822 electron transport inhibition of other phenyl-pyridazinones is less than with BAS 100822 (28). 

Separation of primary herbicidal effects from the secondary, tertiary, or quaternary effects on plants is difficult. 

Plants synthesize all 20 common amino acids de novo. Glyphosate, a weed killer sold under the trade name Roundup, is an analog of phosphoenolpyruvate that specifically inhibits 3-enolpyruvylshikimate 5-phosphate synthase, a key enzyme of the pathway for chorismate biosynthesis. This compound is a very effective plant herbicide, but has virtually no effect on mammals. Why ... 

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