Field experiments to investigate long-term effects of repeated applications of MCPA, tri-allate, simazine and linuron: II. Crop performance and residues 1969–78

In four field experiments begun in 1963, each of four herbicides was applied to plots planted wilh the same crop each year. The annual treatments were: MCPA at 17 kg/ha to barley (Hordeum sativa Jess) and wheat (Triticum aestivum L.) at growth stage 15. tri-allate at 17 kg/ha pre-emergcnce to barley and wheat, simazine at l7kg/ha pre-emergence to maize (Zea mays L.) and linuron in two applications of 084 kg/ha pre- and post-emergence to carrots (Daucus carota L.). MCPA did not affect growth or yield of either barley or wheat. In general tri-allate also did not aftect the crops although wheat yield was depressed in 1978, wheat 1000 grain weight was reduced in 1972 and barley germination percentage was increased in 1973. Simazine did not influence the height, yield or appearance of maize. Linuron normally produced no effect on carrot yield, density and size. However, in 2 years when the post-emergence application was late, density but not yield was lower than in control plots. There was no accumulation of residues of any of these compounds in the soil. Rates of loss were similar to those predicted on ihe basis of laboratory experiments. In a fifth experiment these herbicides were applied twice per year (3 times in the case of linuron) at double the rales above on each occasion to bare plots. These applications ceased in 1968 (1969 for MCPA) but residues were monitored until 1972 except in the case of MCPA. Disappearance rates were similar to those in the cropped plots and residues were largely confined to the top 10 cm. The plots treated with MCPA had developed an enhanced ability lo degrade il prior to 1968. This persisted for 5 years after the final application.     

Residues of atrazine, simazine, linuron and diuron after repeated annual applications in a peach orchard

Annual applications of the herbicides atrazine, simazine, linuron and diuron at 45 kg/ha were made to the same plots for 9 consecutive years from 1963 to 1971 in a peach (Prunus persica (L.) Batsch.) orchard located on sandy loam soil near Harrow, Ontario. Soil samples from these plots were collected in late October for the last 3 years (1969–1971) and trees were cut down in December, 1969. Herbicide residues were determined by bioassays based on the fresh and dry weight of oats (Avena sativa L.) and in one year results were confirmed by chemical analysis. Significant accumulation of herbicides was not observed. The maximum residue levels measured in October over the 3 years of sampling were 7′3 kg/ha for diuron, 3–8 kg/ha for linuron, 1–6 kg/ha for simazine and 04 kg/ha for atrazine in the top 15 cm of the soil profile. Simazine and atrazine showed a rapid decrease in amount after treatment but diuron and linuron were degraded more slowly. Measurable residues of all herbicides were confined to the upper 15 cm of the soil profile and the majority of herbicide remained in the 0–5-cm soil layer. Oats were planted in the orchard plots from 1972 to 1974 to follow the disappearance of the herbicides. All herbicides caused highly significant yield decreases in 1972, atrazine causing the least (38%) and diuron the greatest (86%) reductions. Diuron reduced the yield of oats in 1973 and caused a highly significant decrease in the weight of young oat plants in 1974.     

Enhanced degradation in soil of tri-allate and other carbamate pesticides following application of tri-allate

Tri-allate degraded faster in soil from a site (T1) that had received 1·7 kg ha^?1 of tri-allate annually for 23 years than in soil from an adjacent site (TO) that had received no pesticide application. Soil from the untreated site, which had been removed to a glasshouse and treated three times per annum with tri-allate at 1·7 kg ha^?1 for 7 years (T2), also showed faster degradation. Soil previously treated with tri-allate showed an increased degradation rate for carbofuran and EPTC but not for aldicarb. A further experiment, 2 years after the last treatment with tri-allate, showed that the enhanced degradation effect was still present. Degradation rates were always in the order T1 > T2 > T0 for tri-allate, EPTC and carbofuran. Half-life for degradation was reduced for tri-allate and carbofuran by approximately 40% in the previously treated soils and for EPTC by approximately 80% when compared with the previously untreated soil.     

Control of Avena fatua and Fagopyrum tataricum with tank mixtures of linuron or linuron + MCPA and sequential applications of linuron, and post-emergence A. fatua herbicides

Linuron (0.21 and 0.28 kg/ha) and linuron + MCPA (0.21+0.56 kg/ha) in a tank mixture with field rates of barban, difenzoquat and flamprop-methyl reduced the phytotoxicity of these herbicides to Avena fatua. When linuron was applied immediately following or 6 days after the A. fatua herbicides no reduction in phytotoxicity to A. fatua occurred, suggesting that the antagonism may be occurring as a result of physical or chemical incompatability when the herbicides are mixed together. The possibility of obtaining broad-spectrum weed control with one trip over the field by applying linuron and one of these wild oat herbicides separately but at the same time using a double-boom, double-tank system deserves evaluation. When linuron was applied in a tank mixture (0.21 and 0.28 kg/ha), immediately after, or 6 days after diclofop-methyl (0.70 kg/ha), there was no reduction of A. fatua control, and wheat tolerance to the tank mixture was good. This tank mixture offers potential for control under field conditions of A. fatua and some broad-leaved weeds in one spray operation. Linuron + MCPA (0.21+0.56 kg/ha) in a tank mixture severely reduced A. fatua control with diclofop-methyl. No loss of phytotoxicity to Fagopyrum tataricum occurred when the A. fatua herbicides tested were tank mixed with linuron or linuron + MCPA. Lutte contre Avena fatua et Fagopyrum tataricum avec des mélanges extemporanés de linuron ou de linuron + MCPA et des applications successives de linuron et d'herbicides de postlevée actifs contre A. fatua     

The effect of repeated applications of 2,4-D and MCPA on their breakdown in soil

The effect of repeated applications of 2,4-D and MCPA in a long-term field experiment on their subsequent degradation was investigated. The herbicides had been applied annually since 1954, Comparisons were made with plots treated once and then retreated the following year. Repealed applications of the two herbicides resulted in a reduction in degradation lime from 10 weeks for 2,4-D and 20 weeks for MCPA after one application to 4 and 7 weeks respectively after 19 years of annual application. In spite of an increased capability of the soil microflora lo degrade 2,4-D and MCPA 9 months after a previous treatment. no change in numbers of organisms capable of utilizing the substances as carbon sources were found in treated plots as compared with the control. It is obvious that there is a cross adaptation between 2,4-D and MCPA. It seems most likely that two different ‘enrichment’ been induced, each capable of decomposing both herbicides, but with different efficiencies. Effet d'applications répétée de 2,4-D et de MCPA sur leur degradation dans le sol L'effet d'applications répétée de 2.4-D et de MCPA sur leur degradation uléerieure a étéétudié dans une expérience au champ de longue durée. Les herbicides ont été appliqués chaque année depuis 1954. Des comparaisons ont été effectuées avec des parcelles traiées une fois et traitées à nouveau l'année suivante. Les applications répétées des deux herbicides ont provoqué une réduction du temps de dégradation qui est passé de 10 semaines pour le 2,4-D et 20 semaines pour le MCPA après une seule application, à 4 et 7 semaines respectivement, après 19 années d'applications annuelles. En dépit d'une capacité accrue de la microflore du sol à dégrader le 2.4-D et le MCPA, neuf mois après un traitement préalable, aucun changement n'a été constaté dans le nombre des organismes capables d'utiliser les produits comme sources de carbone dans les parcelles traitées, par rapport au témoin. II est évident qu'il y a une adaptation croisée entre le 2,4-D et le MCPA. II apparait très probable que deux ‘enrichissements’ de Hores ont été induits, chacun d'eux étant capable de décomposer les deux herbicides mais avec des efficacités différentes. Die Wirkung wiederholter Behandlungen von 2.4- D und MCPA auf ihren Abbau im Boden Die Wirkung wiederholter Anwendungen von 2,4-D und MCPA auf ihren Abbau wurden in einem Freiland-Versuch untersucht. Die Herbizide wurden jährlich, sell 1954 ange-wendet. Es wurden Vergleiche mil Parzellen angcstellt, die zum erstenmal und im folgenden Jahr nochrnaK bchandelt worden waren. Die widerholien Behandlungen mit den beiden Herbiziden bewirkte elne Verringerung der Ab-bauzeit von 10 Wochen fur 2,4-D und 20 Wochen fiir MCPA nach einer Behandlung, auf 4 bzw. 7 Wochen nach 19 Jahren jahrlicher Anwendung. Trotz der erhohten Ffihigkeit der Bodenmikroflora 2,4-D und MCPA neun Monate nach einer vorhergehenden Behandlung abzubauen, war die Zahl der Organismen, die diese Herbizide als Kohlensloffquelle verwerten konnen, in den behandelten und unbehandelten Parzellen gleich gross. Zwischen 2.4-D und MCPA existiert ofVensichtlich elne Kreuz-Adaplalion. Sehr wahrscheinlich wurden zwei versehiedene ‘enrichment’-Floren induziert, von der jede in der Lage ist beide Herbizide, aber mit unterschiedlicher Effizienz, Hbzubauen.     

The effect of age on the availability of linuron and simazine residues in soil

Residues of linuron and simazine were measured by both bioassay and gas-chromatographic methods in soil from field plots that had been treated either 20 weeks (both compounds). 41/2 years (linuron) or 51/2 years (simazine) previously. There were no significant differences between the results obtained with the two methods; therefore the relationship between extractable herbicide and that available to plants was independent of the age of the residue. Hence‘bound’residues, if they existed in these plots, had no phytocidal significance.     

The degradation of simazine, linuron and propyzamide in different soils

Simazine, linuron and propyzamide were incubated in 18 different soils at 25°C and field capacity soil moisture content. The degradation of each herbicide followed first-order kinetics. The half-life of simazine varied from 20 to 44 days, that of linuron from 22 to 86 days and that of propyzamide from 10 to 32 days. The rate of linuron degradation was highly significantly correlated with soil organic matter content, clay content, soil respiration and the extent of herbicide adsorption by the soil. The rate of simazine degradation was significantly and negatively correlated with soil pH, but the rate of propyzamide degradation was not related with any of the soil factors examined.     

Kinetics of linuron and metribuzin degradation in soil

The disappearance of linuron and metribuzin was studied during laboratory incubation of soil samples which had been taken from several depths at three sites, and treated with the pesticides. Temperature and water content of the soils were varied. There was a tendency for the rate of loss to be slower in soil taken from deeper horizons than in surface soil but the differences were not large. In only ten out of forty experiments did the value 1 for the apparent order of reaction fall within 95% confidence limits. In the remaining experiments the apparent reaction order was greater than 1 with eight values higher than 4. For one soil, the reaction order for linuron was markedly lower for incubation at 22°C compared with incubations at 10°C. The results could be explained on the basis that the systems were complex, involving consecutive or competing reactions. An alternative possibility is that the apparent complexities were artifacts brought about by the inherent limitations of the laboratory incubation system.     

Effect of pH on the degradation of atrazine,dichlorprop, linuron and propyzamide in soil

The rates of disappearance of atrazine, dichlorprop, linuron and propyzamide were measured in two soils incubated at 22°C and 80% water holding capacity. Observations were made at four pH levels in each soil. Atrazine degradation was relatively insensitive to pH; it increased slightly with increasing pH in one soil and decreased in the other. The other compounds all degraded more slowly at low pH in both soils although dichlorprop had essentially disappeared in 14 days under all conditions, so that the effect of pH is not unlikely to be of practical interest. The ratios of the degradation rates of atrazine, linuron, and propyzamide varied with the soil and the pH.     

Persistence and movement of terbacil in peach orchard soil after repeated annual applications*

Terbacil (5-chloro-6-methyl-3-butyluracil) residues did not accumulate in peach orchard soil after seven consecutive annual spring applications of the herbicide at the rate of 4.5 kg/ha although carry-over of terbacil from year to year occurred. Terbacil was lost by degradation and leaching and the time required for a 50% decrease in surface soil concentration was 5–7 months in the sandy loam soil. The major part of the residues was found in the upper 15 cm of the soil profile and smaller amounts were detected to a depth of 60 cm. Terbacil leached readily in prepared columns of sandy loam soil in proportion to the amount of water added. The residual levels of terbacil in the orchard were phytotoxic to oats planted 3 years after the last application.     

Influence of repeated applications of nematicides on the soil fauna in begonia culture

At present most of the begonia growers around Ghent disinfect their fields annually or biennially to control nematodes, weeds, and also fungi. Investigations therefore were carried out on the influence of this annual application of nematicides on the soil fauna. Samples were taken in September from two adjacent experimental plots; one plot was disinfected for five consecutive consecutive years with 6 ml of DD per m², the other was used as a control. It was found that the annual disinfection of begonia fields with DD did not depress the saprophagic fauna and that earthworms, enchytraeids, mites and collembola were mainly in the upper 5 cm of the soil.Samenvatting We constateren dat tegenwoordig de meeste begoniakwekers jaarlijks of tweejaarlijks hun cultuurgrond ontsmetten met het doel aaltjes, onkruiden en ook wel schimmels te bestrijden.We hebben een aanvang gemaakt met de invloed van dit jaarlijks toedienen van nematiciden op de bodemfauna na te gaan. Hiervoor werden bemonsteringen in september uitgevoerd op, twee naast elkaar gelegen proefpercelen: het ene vijf opeenvolgende jaren met DD aan 6 liter per are ontsmet, het andere als getuige gehouden.We hebben vastgesteld dat het jaarlijks ontsmetten van begoniavelden met DD de saprofage fauna niet heeft gedrukt en dat de regenwormen, enchytraeiden, mijten en collembolen zich hoofdzakelijk in de bovenste 5 cm van de bodem bevinden.Research subsidized by the Institute for the Encouragement of Scientific Research in Industry and Agriculture (IWONL).     

Effect of concentration on the decomposition rates in soil of atrazine,linuron and picloram

The decomposition of atrazine, linuron and picloram when incubated with two soils at four levels of application was measured for periods of 3 or 4 months. The applicability of zero-order, half-order, first-order and Michaelis-Menten kinetics was considered. None of the equations described the breakdown rates adequately in spite of the apparent theoretical advantage for using an expression of the Michaelis-Menten type. In each case the rate of decomposition increased as the initial herbicide concentration decreased.     

Effects of repeated glyphosate applications on soil microbial community composition and the mineralization of glyphosate

Background: Repeated applications may have a greater impact on the soil microbial community than a single application of glyphosate. Experiments were conducted to study the effect of one, two, three, four or five applications of glyphosate on soil microbial community composition and glyphosate mineralization and distribution of ¹⁴C residues in soil. RESULTS: Fatty acid methyl esters (FAMEs) common to gram‐negative bacteria were present in higher concentrations following five applications relative to one, two, three or four applications both 7 and 14 days after application (DAA). Additionally, sequencing of 16S rRNA bacterial genes indicated that the abundance of the gram‐negative Burkholderia spp. was increased following the application of glyphosate. The cumulative percentage ¹⁴C mineralized 14 DAA was reduced when glyphosate was applied 4 or 5 times relative to the amount of ¹⁴C mineralized following one, two or three applications. Incorporation of ¹⁴C residues into soil microbial biomass was greater following five glyphosate applications than following the first application 3 and 7 DAA. CONCLUSION: These studies suggest that the changes in the dissipation or distribution of glyphosate following repeated applications of glyphosate may be related to shifts in the soil microbial community composition. Copyright © 2009 Society of Chemical Industry     

The kinetics of linuron and metribuzin decomposition in soil using different laboratory systems

Rales of linuron and metrihuzin breakdown in soil were studied in four laboratory systems: fresh soil incubated in polyethylene bags; air-dry soil resetted and incubated in polyethylene bags; complete soil cores; a perfusion apparatus. The apparent order of reaction. estimated using a power rate equation, varied from 0.45 to 2.90 and was not consistent with respect either to the compounds or the incubation methods. It is possible that diffusion controlled processes may be involved in producing this variation. The results of six of the eight experiments could be fitted to the first order rate equation (P= 0.01). When the first order model was statistically valid, half-life times were within 50% of the time for 50% disappearance calculated wiih the power rate expression but there were differences up to five-fold in the times for 90% disappearance, calculated by the two methods. It is suggested that decomposition experiments giving orders of reaction greater than I require verification in more than one experimental system     

Effect of cropping cycles and repeated herbicide applications on the degradation of diclofop-methyl, bentazone, diuron, isoproturon and pendimethalin in soil

A greenhouse study was conducted to investigate the ability of four crops (wheat, corn, oilseed rape and soybean) to influence the degradation of bentazone, diclofop-methyl, diuron, isoproturon and pendimethalin in soil. The present study showed that microbial biomass-carbon was significantly higher in planted soils than in bulk soil, especially with wheat and corn, after several cropping cycles. The biomass in corn and soybean planted soils was adversely affected by bentazone but recovered after three cropping cycles. In wheat-planted soils, diclofop-methyl application resulted in persistent increase of the amount of microbial biomass. Bentazone did not show accelerated degradation even after five successive treatments, differing from diclofop-methyl, for which two applications were sufficient to enhance significantly its rate of degradation. Enhanced degradation of diclofop-methyl was even more pronounced in wheat-planted soil. The rates of mineralisation of diuron, isoproturon and pendimethalin were not affected after the first cropping cycle, but were significantly increased in planted soils after five cropping cycles. The results confirm that plants may promote pesticide degradation in soil by stimulating biodegradation processes. In the case of diclofop-methyl, stimulation of accelerated degradation was observed.     

Adsorption and bioactivity of di-allate,tri-allate and trifluralin*

Studies were conducled to cstmiate the adsorption parameter k and the bioactivity (in terms of G R₅₀) of di-allate [S-2,3-dichloroallyl N, N-di-isopropyl (thiocar bamate)], iri-allate [S-2,3,3-trichloroallyl N, N -di-isopropyl (thiocar bamate], and [trifiuralin (2,6-dinitro N, N-dlpropyl-4-trifluoromelhylaniline) in a number of Saskatchewan soil. The k values ratiged from 5 for di-allate adsorption m Asquilh loamy sand to 315 for trifluralin adsorption on Melfort loam and were closely related to the soil organic matter content. The relative degree of adsorption was irifluralin > tri-allate >di-allaie. For each herbicide, the G R₅₀ values were positively correlated wich organic matter conienl atid wilh k. It was suggested that these nonionic herbicides may be amenable to a predictive approach for field application rates in different soils. Among herbicides for any one soil, however, there was not the same relationship between G R₅₀andk. since the G R₅₀ was least for trifluralin and there was no significant difference between di-allate and tri-allate.     

Metabolism of the herbicides chlorotoluron, diuron, linuron, simazine, and atrazine by CYP1A9 and CYP1C1 from Japanese eel (Anguilla japonica)

Through the use of a number of bioconversion experiments we demonstrated that P450 proteins (CYP1A9 and CYP1C1) from Japanese eel (Anguilla japonica) metabolized a number of herbicides and the drug phenacetin. We performed bioconversion experiments in which substrates were added directly to incubation medium. The resulting metabolites were extracted and analyzed by high-performance liquid chromatography. Proteins CYP1A9 and CYP1C1 metabolized 50 nmol of the drug phenacetin to yield 12.1 and 1.1 nmol of product (acetaminophen), respectively. Further incubation of CYP1A9 with 50 nmol of the herbicides chlorotoluron, diuron, linuron, simazine, or atrazine yielded 16.5, 18.5, 7.3, 1.6, or 0.8 nmol of product, respectively. CYP1C1 also metabolized linuron, diuron, and simazine yield 5.4, 4.6, or 0.7 nmol of product, respectively. Next, polyclonal antibody was isolated by immunizing with two conjugated-peptides (amino acid residues 272–290 and 294–310) of CYP1A9. This antibody did not recognize human CYP1A2 or CYP1C1. Western blotting using the antibody revealed one band in the livers of Japanese eel and tilapia (Oreochromis niloticus). Theses results suggest that CYP1A9 and CYP1C1 metabolize herbicides, and that CYP1A9 is an useful biomarker of contamination when detected with this antibody.     

Simulation of the persistence of atrazine, linuron and metolachlor in soil at different sites in the USA

The effects of soil temperature and soil moisture content on the rates of degradation of atrazine, linuron and metolachlor were measured in the laboratory in soil from different sites in the USA. Persistence of the herbicides was measured in the same soils in the field during the summers of 1978 and 1979. Weather records from the different sites for the periods of the field experiments were used in conjunction with appropriate constants derived from the laboratory data in a computer program to simulate persistence in the field. There was a general tendency for the model to overestimate the observed soil residues. For example, with atrazine, 40 of the 48 measured residues were lower than those predicted by the model; seven were more than 30% below and two were more than 50% below. With metolachlor, 16 of the 48 measured residues were more than 30% below those predicted and six were more than 50% below; almost identical results were obtained with linuron. When the model overestimated late-season residues by a large amount, the discrepancies between predicted and observed data were usually apparent from early in the experiment. Possible reasons for the discrepancies are discussed.