Comparative effects of four herbicides on physiological aspects in Triticum sativum L.

Four herbicide (topik, puma super, granstar and derby) treatments at the recommended field dose (RFD) were applied for 5 weeks on wheat (Triticum sativum L. cv. Giza 168) crop. These selected herbicides are recommended to control two types (narrow and broad) of weeds in this crop. The growth parameter, oxidative stress defence system, nitrate reduction, proline level and protein contents were used to evaluate the toxic effect of these herbicides on wheat crop. The toxicity of herbicides used on this crop was as follows: puma super > topik > derby > granstar. The correlation between the herbicide concentrations and the activities of the antioxidant enzymes was monitored.     

In vitro studies on the effects of herbicides on the growth of rhizobia

AIMS: To study the possible adverse effect of herbicides on nodulation and nitrogen fixation in legumes by affecting the nitrogen-fixing rhizobia. METHODS AND RESULTS: Experiments were conducted to study the effect of four herbicides (terbutryn/terbuthylazine, trietazine/simazine, prometryn and bentazone) on the growth of nitrogen-fixing pea rhizobia (Rhizobium leguminosarum) in vitro by measuring optical density. Terbutryn/terbuthylazine, trietazine/simazine and prometryn had an adverse effect on the growth of rhizobia whereas bentazone was safe to rhizobia. CONCLUSIONS: The above herbicides could be used in pea at the recommended rates. SIGNIFICANCE AND IMPACT OF THE STUDY: The adverse effects of herbicides on rhizobia were observed at concentrations not normally expected to occur under field conditions. Further, previously observed adverse effects of these herbicides on nodulation and nitrogen fixation of peas were, possibly, not due to their effects in rhizobia but to their adverse effects on the plant growth itself.     

Comparative study of the effect of selected agrochemical products on Steinernema feltiae (Rhabditida: Steinernematidae)

The effect of three neurotoxic insecticides, three photosynthetic inhibitor herbicides and three enzymatic inhibitor herbicides on infective juveniles (IJs) of Steinernema feltiae Rioja (native) and ENTONEM® (commercial) strains were evaluated after a 48-h exposure at field tank concentrations and overnight treatment in mQ-water, using Spodoptera littoralis as target. Nematode survival was not affected by acetyl-cholinesterase inhibitors chlorpyrifos and pirimicarb, although chlorpyrifos seriously reduced their virulence. Both nematode strains showed differential sensitivity to cypermethrin, which affects the sodium channels of the nerve membrane, with the ENTONEM® strain being more tolerant than Rioja strain. However, these chemicals showed a strong sublethal effect on the nematode reproductive potential, limiting seriously their possible recycling in the field. Herbicides showed differential toxic effects on nematode survival. The commercial strain was tolerant to enzymatic inhibitor herbicides, whereas tribenuron and chlorsulfuron reduced Rioja strain survival. However, photosynthetic inhibitor herbicides severely affected survival of both nematode strains, with the Rioja strain being more sensitive. Sublethal effects on both nematode strains were observed only after exposition to terbutryn+chlortoluron+triasulfuron, increasing the time to kill insect larvae. These results are useful to optimize EPN dosages and to estimate their field recycling.     

The analysis of the effect of different herbicides on Johnson-grass in maize

The Johnson-grass (Sorghum halepense /L./Pers) is a perennial monocotyledon, its gen centre is in the Near East. Botanically this weed belongs to the monocotyledone class, Poaceae (Gromineae) family and within this, together with the maize to the Andropogonoideaei subfamily. At the time of the First National Weed Survey (1947-1953) it has not been found in Hungary. In the periods of the 2nd (1969-1971), 3rd (1987-1988) and 4th Survey it occupied the 94th, 18th and 10th place of importance, respectively. Because of its rapid multiplication and spreading after the second weed survey (1969-1971) and because of its very complicated and difficult control, the Plant Protection Division of our Ministry of Agriculture ranged it in 1974 into the category of "Dangerous weed". Johnson grass is the 6th most important weed in the world. A small plot field trial was carried out in Szabadszentkirtly (12th May 2006) in maize. The effect of pre- and post emergent herbicides was investigated against Johnson grass germinating from seed and sprouting from rhizome. The treatments were done in 4 repeats with Stomp 330 EC, Dual Gold 960 EC, Merlin WG, Wing EC, Guardian Max and Monsoon herbicides. The number of weeds germinating after spraying and the number of damaged weeds were counted and compared to the control plots 10 days after the treatments and then weekly. Parallel to the field trial, a "soil culture in pots" trial in glasshouse was also carried out in which the effect of the above mentioned herbicides was investigated against Johnson grass germinating from seed. During on experiments all the herbicides showed an excellent herbicide activity until the 2nd week of treatment, although the precipitation of the second week was only 8.4 mm. Under the given experimental conditions the best herbicide effect until the 4th week, in both experimental phases were given by Merlin WG.     

三种除草剂对外来入侵植物大狼耙草的防除效果

大狼耙草是危害生物多样性的一种恶性杂草。使用使它隆、二甲四氯、草甘膦3种除草剂对大狼耙草进行不同浓度、不同防治时期防除效果研究,结果表明:使它隆对大狼耙草平均致死率为92%,二甲四氯为85%,草甘膦为82%,但三者差异不显著;高、中、低3种浓度(使它隆分别为0.47、0.40、0.33g·L-1,二甲四氯分别为2.80、2.33、1.87g·L-1,草甘膦分别为5.18、3.89、2.59g·L-1)对大狼耙草致死率差异极显著,高浓度溶液防除效果较好;大狼耙草植株在幼苗期(植株高20cm)、生长盛期(植株高40cm)、花期(植株高60cm)3个防治时期致死率差异极显著,幼苗期防除效果理想。研究表明,在大狼耙草幼苗期使用0.47g·L-1浓度的使它隆防除效果最好。     

The effect of some herbicides on lactate dehydrogenase activity

The effect of herbicides N-(phosphonomethyl)glycine (glyphosate), 2-methyl-4-chlorophenoxyacetic acid (MCPA), 2-chloro-4-ethylamino-6-isopropylamino-1,3,5-triazine (atrazine) and the respective commercial preparations “Round-up”, “Aminex”, and “Zeazin”, on the activity of lactate dehydrogenase isolated from germinating soybean seeds and beef heart were compared. The main aim of the work was to compare the effect of the herbicides on lactate dehydrogenase isolated from animal and plant material. Simultaneously the effect of herbicides and the respective commercial preparations was compared. Substantial differences resulting from the two comparisons indicate differences in the structure of active centres of lactate dehydrogenase isolated from animal and plant material, and also a considerable effect of additives and surfactants in commercial preparations.     

The impact of synthetic nitriles on the morphology and viability of some bacterial species

The toxic effects of synthetic nitriles and nitrile herbicides on some bacterial species were estimated. Biotests based on bioluminescence revealed that aromatic nitriles including herbicides had the most significant toxic effect on bacteria, which differed from their effect on eukaryotic cells. It was shown that soil strains of nitrile-utilizing bacteria were resistant to high concentrations of the studied compounds. The minimal bactericidal concentrations for most of nitriles were 0.5 M or above. It was demonstrated that exposure to 0.1 and 1 mM bromoxynil solution resulted in a decrease in the linear parameters of the cells of all strains and sufficient changes in the cell surface of Gram-negative bacteria. It was proposed that the toxic effect of aromatic herbicides was caused not only by inactivation of an enzyme of the electron-transport chain but also by damage to the surface structures.     

Impact of agricultural practices on the Zea mays L. endophytic community

Agricultural practices are known to alter bulk soil microbial communities, but little is known about the effect of such practices on the plant endophytic community. We assessed the influence of long-term applications (20 years) of herbicides and different fertilizer types on the endophytic community of maize plants grown in different field experiments. Nested PCR-denaturing gradient gel electrophoresis (DGGE) analyses targeting general bacteria, type I or II methanotrophs, actinomycetes, and general fungi were used to fingerprint the endophytic community in the roots of Zea mays L. Low intraplant variability (reproducible DGGE patterns) was observed for the bacterial, type I methanotroph, and fungal communities, whereas the patterns for endophytic actinomycetes exhibited high intraplant variability. No endophytic amplification product was obtained for type II methanotrophs. Cluster and stability analysis of the endophytic type I methanotroph patterns differentiated maize plants cultivated by using mineral fertilizer from plants cultivated by using organic fertilizer with a 100% success rate. In addition, lower methanotroph richness was observed for mineral-fertilized plants than for organically fertilized plants. The use of herbicides could not be traced by fingerprinting the endophytic type I methanotrophs or by evaluating any other endophytic microbial group. Our results indicate that the effect of agrochemicals is not limited to the bulk microbial community but also includes the root endophytic community. It is not clear if this effect is due to a direct effect on the root endophytic community or is due to changes in the bulk community, which are then reflected in the root endophytic community.     

Capillary electrophoresis of herbicides. III. Evaluation of octylmaltopyranoside chiral surfactant in the enantiomeric separation of phenoxy acid herbicides

A chiral alkylglucoside surfactant, namely n-octyl-β-D-maltopyranoside (OM), was evaluated in the enantiomeric separation of phenoxy acid herbicides. The enantiomeric resolution of the phenoxy acid herbicides could be manipulated readily by adjusting the surfactant concentration, ionic strength, pH, the percent organic modifier and separation temperature. The optimum surfactant concentration needed for maximum enantiomeric resolution varied among the different analytes, and was an inverse function of the hydrophobicity of the phenoxy acid herbicides with the most hydrophobic solute requiring less surfactant concentration for attaining a baseline enantiomeric resolution. Due to the ionic nature of the phenoxy acid herbicides, increasing the pH of the running electrolyte increased the degree of ionization of the acidic herbicides thus decreasing their association with the chiral micelles and in turn their enantiomeric resolution. Increasing the ionic strength of the running electrolyte seems to enhance both the solubilization of the solute in the micelle and the chiral interaction of the solute with the micelle with a net increase in enantiomeric resolution. The percent of added methanol had a varying effect on the resolution of the various enantiomers in the sense that it enhanced the enantiomeric resolution for the most hydrophobic solutes while it decreased the enantiomeric resolution for the weakly hydrophobic ones. Thermostating the capillary column at subambient temperature improved enantiomeric resolution. © 1996 Wiley-Liss, Inc.     

Evaluation of herbicide combinations for livid amaranth (Amaranthus blitum) control in tuberous begonia (Begonia x tuberhybrida)

In the past years livid amaranth (Amaranthus blitum) is observed increasingly in begonia production fields. Control of weeds in begonia is generally done by a combined application of the soil herbicides isoxaben + simazin followed 10 days later by application of the contact herbicide bentazone. This treatment usually controls the weed population sufficiently with exception of amaranth. In 2003 a field trial was conducted to evaluate control of livid amaranth in tuberous begonia with isoxaben, simazin. S-metolachloor, phenmedipham + desmedipham and bentazone. These herbicides were used as combinations of soil treatment and contact herbicides. The results suggest that a soil treatment of isoxaben + S-metolachloor significantly reduces livid amaranth compared to isoxaben + simazin, without a pronounced negative effect on tuber yield. Application of phenmedipham + desmedipham however did not improve control of livid amaranth compared to bentazone.     

四种除草剂对根瘤菌、AMF等土壤微生物的影响

本文采用盆栽试验, 研究4种除草剂在大田常规剂量下, 对根际土壤微生物和土著根瘤菌、AMF与苗期大豆共生的影响。结果表明, 除草剂对V2期大豆根际土壤中真菌数量和V3期细菌数量的抑制作用显著, 对V2和V3期AMF的侵染率、V3期根瘤数量影响显著。除草剂对土壤中真菌数量的负面影响可能是抑制菌根形成的重要因素, 对菌根形成产生的抑制可能会进一步导致根瘤形成受到抑制。     

Impact of Agricultural Practices on the Zea mays L. Endophytic Community

Agricultural practices are known to alter bulk soil microbial communities, but little is known about the effect of such practices on the plant endophytic community. We assessed the influence of long-term applications (20 years) of herbicides and different fertilizer types on the endophytic community of maize plants grown in different field experiments. Nested PCR-denaturing gradient gel electrophoresis (DGGE) analyses targeting general bacteria, type I or II methanotrophs, actinomycetes, and general fungi were used to fingerprint the endophytic community in the roots of Zea mays L. Low intraplant variability (reproducible DGGE patterns) was observed for the bacterial, type I methanotroph, and fungal communities, whereas the patterns for endophytic actinomycetes exhibited high intraplant variability. No endophytic amplification product was obtained for type II methanotrophs. Cluster and stability analysis of the endophytic type I methanotroph patterns differentiated maize plants cultivated by using mineral fertilizer from plants cultivated by using organic fertilizer with a 100% success rate. In addition, lower methanotroph richness was observed for mineral-fertilized plants than for organically fertilized plants. The use of herbicides could not be traced by fingerprinting the endophytic type I methanotrophs or by evaluating any other endophytic microbial group. Our results indicate that the effect of agrochemicals is not limited to the bulk microbial community but also includes the root endophytic community. It is not clear if this effect is due to a direct effect on the root endophytic community or is due to changes in the bulk community, which are then reflected in the root endophytic community.     

不同除草剂的田间杂草防效及对糜子生长发育的影响

筛选糜子适宜除草剂来防范农田药害,是糜子高效安全生产和改善生态环境亟待解决的关键问题。本研究以粳性糜子品种‘榆糜2号'为材料,探究22种除草剂对糜子田间杂草的防除效果及对糜子生长发育的影响。结果表明: 1)喷施土壤封闭型除草剂谷友、丁草胺、莠去津、苄嘧·丙草胺和茎叶型除草剂苯唑·二甲钠、阔世玛、藤净、陶氏·优先、阔菲后,基本无药害作用,糜子幼苗生长正常,其余除草剂均对糜子有不同程度的药害影响;2)参试的22种除草剂在糜子田中对杂草均表现出一定的防除效果,总体而言,土壤封闭型除草剂的杂草防效相对优于茎叶型除草剂,但所有参试除草剂对糜子株高、功能叶片叶绿素含量、单株穗重均造成不同程度的影响;3)与人工除草相比,参试除草剂均导致糜子产量有不同程度的下降;但与不除草对照相比,部分除草剂有明显的增产增效作用。土壤封闭型除草剂中,谷友、丁草胺、莠去津、苄嘧·丙草胺的杂草防效较好,较不除草对照增产60%以上;茎叶型除草剂中,阔世玛、苯唑·二甲钠的杂草防效较好,较不除草对照增产50%以上。因此,在糜子出苗前可用38%莠去津或44%单嘧磺隆进行土壤封闭处理,或在出苗后喷施茎叶型除草剂3.6%二磺·甲碘隆或55%苯唑·二甲钠,农田杂草防效较好,且对糜子生长发育的负面影响较小。     

Nebenwirkungen von Herbiziden auf Nutzinsekten

Zusammenfassung An Larven und Imagines von drei Nutzinsektenarten:Trichogramma cacoeciae March. [Hym.: Trichogrammatidae], Chrysopa carnea Steph. [Planipennia: Chrysopidae] undEpistrophe balteata DeG. [Dipt.: Syrphidae] wurde im Biotest der Einfluss von fünf landwirtschaftlich wichtigen Herbiziden: Lasso, Ramrod, Semeron 25, Betanal und Bidisin forte, vorwiegend im Labor untersucht. Eine toxische Wirkung auf die Nützlinge war abh?ngig von dem geprüften Mittel sowie der Tierart. W?hrend sichChrysopa als unempfindlich gegenüber den Pr?paraten erwies, waren beiEpistrophe toxische Wirkungen unter dem Einfluss einiger Pr?parate festzustellen. Auf die hochempfindlichen Trichogrammen wirkten dagegen s?mtliche geprüften Herbizide mehr oder weniger sch?dlich. Somit sind wahrscheinlich auch im Freiland nach Applikation bestimmter Pr?parate Sch?digungen dieser Nützlinge zu erwarten.

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Summary The effect of 5 herbicides widely used in agriculture (active ingredients: alachlor, chlorfenpropmethyl, desmetryne, phenmedipham, propachlor) were studied, mainly in the laboratory, by measuring the reduction of beneficial capacity of three entomophagous insects showing quite different behaviour. The egg parasiteTrichogramma cacoeciae March. reacted very strongly in laboratory tests as well as in the field under the influence of the herbicides. Contact toxicity tested on residues on glass plates caused a reduction of the degree of parasitization leading to total mortality of the population, in contaminated cages for some preparations. Part of this effect was caused by the zero formulation examined simultaneously. In the study of the contact toxicity of the spray deposit on single leaves as well as on whole plants the strong effect onTrichogramma by some of the preparations was shown. This direct toxic effect should be discerned from a repellent effect which was probably more important in the field. In addition to this direct contact effect of spray deposits also systemic application caused an effect after transportation of herbicides through the soil and the plant. This was clearly demonstrated by a reduction of the degree of parasitization in comparison to untreated controls. The herbicides studied do not seem to have any influence onChrysopa carnea Steph. larvae. No effect was visible, neither in tests of contact toxicity or contaminated sandy soil nor in choice experiments on a repellent action of the residue or after topical application of the preparations. — Also after peroral application through an artificial food chain no influence of the preparations could be demonstrated. Only the overdosage of one herbicide increased the mortality rate of the test larvae. The adults showed also no repellent reaction against the herbicides tested in choice experiments. The syrphidEpistrophe balteata DeG., however, reacted in a more sensitive manner on the influence of herbicides. Both, in contact experiments of toxicity as well as in choice experiments for a possible repellent effect an influence on the larval stages of the herbicides examined was shown. The peroral intake over an artificial food chain had no effect on the larvae after systemic application of the herbicide. If, however, the same herbicide was sprayed directly on the plant, an increase of larval nortality was observed. Adults of this syrphid showed also reactions on herbicide residues. Females during egg deposition avoided surfaces previously treated by the herbicide (phenmedipham). In tests on a possible ovicidal effect of herbicides on the eggs of all 3 entomophagous species only one herbicide (chlorfenpropmethyl) reduced the rate of egg-hatching of syrphids quite clearly. In summing up it can be said that damages as observed depend on the species as well as on the herbicide applied and the type of application. Losses of sensitive entomophagous species in the field might well be possible according to the results obtained in experiments using certain herbicides.

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Gef?rdert von der Deutschen Forschungsgemeinschaft.     

Behaviour of Herbicides in Dicotyledonous Roots Transformed by Agrobacterium rhizogenes: I. SELECTIVITY

Mugnier, J. 1988. Behaviour of herbicides in dicotyledonousroots transformed by Agrobacterium rhizogenes. I. Selectivity.—J.exp. Bot. 39: 1045–1056. The effect of various herbicides on the growth of dicotyledonousroots transformed by the root-inducing transferred DNA of Agrobacteriumrhizogenes was studied. When a compound affected the growthof different root species differentially, the difference mightbe attributed to root uptake and metabolism of the herbicide.In general, metabolism of the herbicide led to inactivation(clopyralid, linuron, phenmedipham), but in certain instances,the change resulted in activation (quizalofop-ethyl). Visibleeffects on the root morphology were observed: dinitroanilinesand certain carbamates led to remarkable swelling of the roottips; norflurazon and diflufenican were effective bleachingagents in greening root cultures in Murashige and Skoog medium,whereas the presence of sucrose in the medium antagonized theeffect of triazine herbicides. Growth inhibition by sulphonylureascan be antagonized by addition of valine and leucine; asulaminhibition was antagonized by addition of folic acid but glyphosateinhibition was not significantly reversed by aromatic aminoacids. Bipyridinium and diphenyl ether herbicides, with certainexceptions, have rapid and devastating phytotoxic effects onroot growth. The phytotoxic effects of the herbicides on transformedroot growth is discussed with particular reference to theirmode of action in intact plants. Key words: Arobacterium rhizogenes, herbicides, root organ cultures     

Effects of Selected Herbicides on the Germination and Infection Process of Puccinia lagenophora,a Biocontrol Pathogen of Senecio vulgaris

The herbicides 2,4-D, glyphosate, linuron, and MCPP at rates of 1X (recommended field rate), 0.25X, 0.025X, and 0.0125X were evaluated in vitro for their effects on the rust fungus Puccinia lagenophorae, a biocontrol agent for the annual weed Senecio vulgaris. Herbicides applied at 1X and 0.25X completely prevented aeciospore germination. Glyphosate was toxic even at 0.0125X and 0.025X. Aeciospores germinated in linuron, 2,4-D, and MCPP at 0.025X and 0.0125X at rates similar to the water control. Abnormal germ-tube growth was observed with 2,4-D at 0.25X and 0.025X, with linuron at 0.025X, and with glyphosate at 0.0125X. Further in planta studies were perfomed with two inbred lines of S. vulgaris inoculated with aeciospores of P. lagenophorae and treated with water, linuron, and 2,4-D at 0.025X at different times of application. Quantitative analysis of the infection process revealed that both herbicides reduced spore deposition on the leaves and altered leaf morphology. The herbicides had no effect on disease severity at this low rate although linuron significantly reduced the formation of infection peg. Timing of herbicide application had no influence on the infection process, and the effect of the herbicides on fungal development did not differ between the two plant lines. Thus, the herbicides applied at 0.025X did not increase plant susceptibility to the rust fungus, and the rates of 1X, 0.25X, and 0.025X would prevent, inhibit, or delay fungal development. Therefore, joint application of P. lagenophorae with these herbicides to control S. vulgaris cannot be recommended.     

Circadian Response of Annual Weeds in a Natural Setting to High and Low Application Rates of Four Herbicides with Different Modes of Action

Four herbicides [glyphosate (GLYT), an amino acid synthesis inhibitor; glufosinate (GLUF), a glutamine synthetase inhibitor; fomesafen (FOME), a protoporphyrinogen oxidase inhibitor; and chlorimuron ethyl (CLIM), an acetolactate synthase inhibitor] were used to examine the influence of time of day of application on the control of a variety of annual broadleaf weeds in field studies conducted in Minnesota (five studies on GLYT and GLUF, three studies on FOME and CLIM). All herbicides were applied with an adjuvant at recommended high and low (half or quarter strength) rates every 3h between 06:00 and 24:00h local time. Visual ratings of percent weed control evaluated at 14d were analyzed by herbicide and application rate for each study and across studies for time-of-day effect by analysis of variance (ANOVA) and single cosinor. A circadian response to each herbicide was found, with greatest weed control observed between 09:00 and 18:00h. Increasing the herbicide application rate did not overcome the time-of-day effect (ANOVA: p≤0.008 for time-of-day effect for each herbicide and application rate). The least-squares fit of a 24h cosine was significant (p≤0.001) for each herbicide and application rate, with double amplitudes of 18–82% (units=% visual control) and estimated peaks (acrophases) near midday between 12:40 and 13:35h. Analysis of residuals obtained from multiple regression that included weed height, herbicide rate, temperature, and relative humidity as independent factors also found a significant time-effect by both ANOVA and cosinor for each herbicide and rate, with acrophases advancing significantly by 3 to 7h for GLYT and GLUF, but not for FOME or CLIM. These results suggest that the four herbicides, while belonging to different families with different modes of action, may reveal different peak times of efficacy when adjusting for environmental factors. Nonetheless, each displays similar circadian patterns when influenced by these factors under natural seasonal field conditions. The within-day rhythmic differences found in weed control are large enough to warrant consideration of the practical financial and environmental importance of the time-of-day that these and other herbicides are applied.     

Studies on plant growth-regulating substances XLVIII. The effects of3,5-diiodo-4-hydroxybenzoic acid on seedling growth in compact and loose soils

Effects of combinations of insecticides and herbicides on the growth and yield of cauliflower plants (cvs No. 110, Garant and Strong) were determined in two field experiments with seed drilled to give a stand of c. 300000 plants/ha. Granular formulations of chlorfenvinphos or fonofos were applied by the bow-wave method at 2 kg a.i./ha to control cabbage root fly (Delia brassicae). Weeds were successfully controlled with combinations of trifluralin, incorporated into the soil at 0·6 or 1·2 kg a.i./ha before drilling, and propachlor, applied pre-emergence at 2·2 or 4·4 kg a.i./ha. Fonofos, with and without herbicides, significantly lessened (P < 0·01) numbers of seedlings that would survive to harvest. Herbicides and chlorfenvinphos generally did not significantly affect the emergence of healthy seedlings of any cultivar. Combinations of herbicides and chlorfenvinphos were compatible for control of target species. Chlorfenvinphos reduced root damage by at least 50% but did not significantly increase (P > 0·05) the total or marketable weight of curds. Numbers of curds were not usually affected and consistent effects of treatments on maturation periods of the three cultivars were not detected.     

Circadian response of annual weeds in a natural setting to high and low application rates of four herbicides with different modes of actions

Four herbicides [glyphosate (GLYT), an amino acid synthesis inhibitor; glufosinate (GLUF), a glutamine synthetase inhibitor; fomesafen (FOME), a protoporphyrinogen oxidase inhibitor; and chlorimuron ethyl (CLIM), an acetolactate synthase inhibitor] were used to examine the influence of time of day of application on the control of a variety of annual broadleaf weeds in field studies conducted in Minnesota (five studies on GLYT and GLUF, three studies on FOME and CLIM). All herbicides were applied with an adjuvant at recommended high and low (half or quarter strength) rates every 3h between 06:00 and 24:00h local time. Visual ratings of percent weed control evaluated at 14d were analyzed by herbicide and application rate for each study and across studies for time-of-day effect by analysis of variance (ANOVA) and single cosinor. A circadian response to each herbicide was found, with greatest weed control observed between 09:00 and 18:00h. Increasing the herbicide application rate did not overcome the time-of-day effect (ANOVA: p≤0.008 for time-of-day effect for each herbicide and application rate). The least-squares fit of a 24h cosine was significant (p≤0.001) for each herbicide and application rate, with double amplitudes of 18-82% (units=% visual control) and estimated peaks (acrophases) near midday between 12:40 and 13:35h. Analysis of residuals obtained from multiple regression that included weed height, herbicide rate, temperature, and relative humidity as independent factors also found a significant time-effect by both ANOVA and cosinor for each herbicide and rate, with acrophases advancing significantly by 3 to 7h for GLYT and GLUF, but not for FOME or CLIM. These results suggest that the four herbicides, while belonging to different families with different modes of action, may reveal different peak times of efficacy when adjusting for environmental factors. Nonetheless, each displays similar circadian patterns when influenced by these factors under natural seasonal field conditions. The within-day rhythmic differences found in weed control are large enough to warrant consideration of the practical financial and environmental importance of the time-of-day that these and other herbicides are applied.     

Outdoor evaluation of herbicide resistant strains of Anabaena variabilis as biofertilizer for rice plants

Application of diazotrophic cyanobacteria, Anabaena variabilis, as biofertilizer for rice cultivation has a beneficial effect on crop productivity and maintenance of soil fertility. However, periodic applications of herbicides used to obtain high crop productivity are not only detrimental to weeds but to biofertilizer strains of cyanobacteria also. Therefore, research was undertaken to isolate four herbicide resistant strains (Arozin-R, Alachlor-R, Butachlor-R and 2,4-D-R) and a multiple herbicide resistant strain (MHR) of natural isolates of A. variabilis exhibiting resistance against these common rice field herbicides. The outdoor survivability of mutant strains and the productivity of rice crop (IR-36) were evaluated by inoculating the wild type and herbicide resistant mutant strains of A. variabilis in the presence and absence of recommended field dosages of test herbicides. No difference in survival and biofertilizer potentials of the herbicide resistant strains was observed in herbicide treated or in untreated conditions. Highest survivability (87%) was exhibited by MHR relative to other mutants. Highest growth and grain yield (76%) were recorded in plants treated with MHR as compared to uninoculated control rice plants. In conclusion, the mutant strains of A. variabilis had stable resistance to herbicides under outdoor conditions in flooded soils. Not only did the herbicide resistance strains increase growth of rice relative to the uninoculated pots, they were more beneficial for rice growth than the wild type strain. Responsible Editor: Richard W. Bell.