Herbicides Bentazon Research Articles

An analysis of the epicuticular wax of Chenopodium album leaves in relation to environmental change, leaf wettability and the penetration of the herbicide bentazone

SUMMARYThe fine‐structure, epicuticular wax and contact angle characteristics of Chenopodium album leaf surfaces have been examined with respect to the control of this weed by the herbicide bentazone. Epicuticular wax analysis and contact angle measurements suggest a relative impermeability to bentazone (BAS 35107H), that may be enhanced by the inclusion of the oil adjuvant Actipron (BP Oil Ltd) to the formulation. Under different regimes of light, temperature and relative humidity the chemical composition of the epicuticular wax layer remained relatively constant, whereas herbicide efficacy was greatly altered. These findings are discussed in relation to the mode of action and penetration of bentazone in this species.

Ultrastructural development of chloroplasts in radish seedlings grown at high- and low-light conditions and in the presence of the herbicide bentazon

The ultrastructure of chloroplasts from radish seedlings (Raphanus sativus L.) grown at high (24 klux; 250 W · m−2) and at low-light quanta fluence rates (1 klux; 15W · m−2) exhibits differences in many structural parameters. 1. The low-light (shade-type) chloroplasts are characterized not only by higher grana stacks and a higher stacking degree of thylakoids, but also by broader grana than the high-light (sun-type) chloroplasts. The latter are larger (length and width), possess large starch grains and contain more and larger plastoglobuli than the shade-type chloroplasts of the low-light plants, which are lacking starch. 2. The photosynthesis herbicide bentazon (10−4M) induces a shade-type adaptation (broader and higher grana stacks, higher stacking degree) particularly at high and to some extent also at low-light quanta fluence rates. The starch content and the number of plastoglobuli in the high-light bentazon chloroplasts is reduced as compared to the high-light controls.

Efeitos de doses e épocas de aplicação do bentazon na produção de duas cultivares de cebola (Allium cepa L.)

Em um solo aluvião eutrófico de classificação textural argilo siltoso, com 2,75% de M.O. foram estudados os efeitos de doses do herbicida bentazon (3 - isopropi l - 2,1,3 - benzotio-diazinona - (4) - 2,2 - dióxido) aplicado em pós-emergência. no controle de plantas daninhas dicotiledôneas na cultura da cebola. O delineamento experimental adotado foi um fatorial 2 x 5 x 2 + 4. constituído por duas cultivares: 'Baia Pe ri forme' e 'Texas Grano': cinco épocas de aplicação do produto: aos 10, 20, 30, 40 e 50 dias após a emergência das plantas daninhas: duas doses de bentazon: 0,46kg. i.a./ha e 0,96 kg. i.a./ha e quatro tratamentos adicionais: 'Baia Periforme' capinada e sem capina e 'Texas Grano'. capinada e sem capina. . As plantas daninhas predominantes no experimento foram: botão -de-ouro (Galinsoga parviflora Cav.), picão-preto (Bidens pilosa L.), amendoim-bravo (Euphorbia prunifoiia Jacq.(, mostarda (Brassica campestris L.), joá (Physalis angulata L.) fedegoso (Cassia tora L.(, serralha falsa (Emilia sonchifolia (L .) DC) e mentruz (Lepidium virginicum L. Nas condições em que foi realizado o ensaio, o herbicida bentazon nas duas doses aplicadas mostrou-se eficiente no controle das plantas daninhas até 60 dias após o transplante. Nas doses empregadas o bentazon não apresentou efeito fitotóxico sobre a produção das cultivares 'Baia Periforme' e 'Texas Grano'.

THE EFFECT OF BENTAZONE ON STOMATAL BEHAVIOUR IN CHENOPODIUM ALBUM L.

SUMMARYThe herbicide bentazone induces stomatal opening in epidermal strips of C. album in a light‐dependent response, over a temperature range of 9 to 29 °C. The relevance of these findings is discussed in relation to stomatal structure and the foliar penetration of the herbicide.

Physiological effects of photosystem II-herbicides on the development of the photosynthetic apparatus

Photosystem II-herbicides (bentazone*, diuron) not only block photosynthetic electron transport, but have additional effects on the cell metabolism of Raphanus seedlings. They induce the formation of shade-type chloroplasts with a different ultrastructure and prenyllipid composition. This is shown by higher grana stacks as well as by higher chlorophyll b and lutein amounts with reference to chlorophyll a, and lower levels of the plastidic prenylquinones (plastoquinone, phylloquinone, α-tocoquinone) and β-carotene as compared to the controls.The two herbicides bentazone and diuron change the labelling pattern of the chloroplast pigments from (3)H-mevalonic acid and 2-(14)C-acetate and also reduce the accumulation of anthocyanin (pelargonidin), which is a further indication of a shade-type growth response. The level of ubiquinone, an indicator for mitochondrial activity, is, however, increased.

The Mode of Action of Photosystem II-Specific Inhibitors in Herbicide-Resistant Weed Biotypes

Abstract This report reviews studies which provide evidence defining the mode of action and site of action of photosystem II (PS II) herbicides; the involvement of the secondary electron carrier on the reducing side of PS II (called B) is indicated as the target site for these compounds. These studies of the action of PS II-inhibitors were performed in chloroplasts of various weed species in order to define the mechanism which is responsible for herbicide tolerance at the level of chloroplast membranes in newly discovered triazine-resistant weed biotypes. Many species of triazine-resistant weed biotypes have been collected in North America and Europe. Where data is available, these plants have been found to share the following common features: a) they were discovered in areas where triazine herbicides had been used repeatedly, b) resistance to the triazines is extreme; it is not due to a minor shift in herbicidal response, c) no changes in herbicide uptake, translocation or metabolism - as compared to susceptible biotypes - can be detected, d) resistance is selective for only certain classes of photosynthetic herbicides, and, e) chloroplasts isolated from triazine-resistant weeds display high preferential resistance to the triazines in assays of photosystem II partial reactions. To focus on the mechanism which regulates preferential herbicide activity, we have characterized susceptible and resistant chloroplasts in the presence and absence of herbicides. Properties of the PS II complex of chloroplasts from several different triazine-resistant weed biotypes share the following traits: a) the herbicide binding site (as measured by direct binding of radiolabeled herbicides or by inhibition experiments) is modified such that the affinity for triazines is dramatically reduced. b) alterations in response to many PS II-herbicides occur such that the triazine-resistant chloroplasts are very strongly resistant to all symmetrical triazines, strongly resistant to assymmetrical triazinones, partially resistant to pyridazones and uracils, only slightly resistant to ureas or amides, and increasingly susceptible to nitrophenols, phenols and the herbicide bentazon (all as compared to susceptible chloroplasts), c) there is a change in the reaction kinetics of the electron transport step between the primary and secondary electron acceptors (referred to as Q and B ), and d) in two examples, specific small changes in a membranepolypeptide can be detected in the resistant thylakoids. We suggest that certain amino acids or segments of the apoprotein of B (the bound quinone which acts as the secondary electron carrier) are modified or deleted in these chloroplasts. Such a polypeptide change could affect both the redox poising of the Q-/B reaction pair, and the specific binding of herbicides.

Effect of Biocides on the Development of the Photosynthetic Apparatus of Radish Seedlings Grown under Strong and Weak Light Conditions

Abstract The influence of two biocides (bentazone, triadimefon) on the growth-response of radish seedlings (Raphanus sativus L.) was investigated with special emphasis on the development of sun or shade-type chloroplasts. 1. The fungicid e triadimefon causes strong-light growth-response and the formation of sun-type chloroplasts as seen from the changed chlorophyll a/b ratio and the carotenoid and prenyl-quinone com position. 2. The photosystem II herbicide bentazone, in turn, induces a shade-type adaption. It prevents the strong-light induced formation of sun-type chloroplasts, but has little influence on the chloroplast com position in weak light.

Rice Herbicide Trials in Brunei

Abstract Weed control trials in Brunei have primarily been directed at finding a suitable pre-emergence or early post-emergence herbicide for use in rice directly after transplanting and in conjunction with 2,4-D or MCPA about 30 days later. In 1975–6, the herbicides chloramben, nitrofen, butralin, butachlor and bentazone were applied just after transplanting for pre-emergence weed control. Chloramben at 1.76 kg a.i./ha showed markedly better weed control than the other chemicals used. Subsequently, in 1976–7 the suitability of this herbicide for pre-emergence weed control in swamp rice in Brunei was confirmed.

Herbicide-tolerant tobacco mutants selected in situ and recovered via regeneration from cell culture

SUMMARYThe herbicides Bentazone and Phenmedipharm kill the leaves of intact tobacco plants but do not affect callus cultures. Tolerant mutants were isolated by treating leaves of previously γ-irradiated haploid plants with herbicide then excising and culturing the green herbicide-resistant cell clones on the otherwise yellowed leaves. Among plants subsequently regenerated were a total of ten stable independently isolated mutants. Sexual crosses show these ten represent four Bentazone and two Phenmedipharm loci; all mutants were recessive to wild type.