Enhanced degradation of some soil-applied herbicides

In a field experiment involving repeated herbicide application, persistence of simazine was not affected by up to three previous doses of the herbicide. With propyzamide, there was a trend to more rapid rates of degradation with increasing number of previous treatments. Persistence of linuron and alachlor was affected only slightly by prior applications. In a laboratory incubation with soil from the field that had received four doses of the appropriate herbicide over a 12–month period, there was again no effect from simazine pretreatments on rates of loss. However, propyzamide, linuron and alachlor all degraded more rapidly in the previously treated than in similar untreated soil samples. Propyzamide, linuron, alachlor and napropamide degradation rates were all enhanced by a single pretreatment of soil in laboratory incubations, whereas degradation rates of isoproturon, metazachlor, atrazine and simazine were the same in pretreated and control soil samples.     

Effects of application method on the performance of some soil-applied herbicides II. Field studies

Plots sown with a range of test species were treated with chlortoluron, nitrofen, propyzamide or terbutryne applied at several doses either by rotary atomizer (30 1 ha^?1), conventional hydraulic nozzle (250 1 ha^?1) or dribble bar (with orifices spaced at 2-cm intervals) (520 1 ha^?1). The performance of chlortoluron, propyzamide and terbutryne was similar with all the methods used, regardless of soil and weather conditions. Vertical movement in the soil was similar for each application method. Horizontal variability following dribble-bar application was measured for chlortoluron and was very large across short distances but weed control was as uniform as with the other application methods. In a further experiment, the phytotoxicity of chlortoluron applied by each of the three methods was less in a seed bed prepared by minimum tillage following straw burning than in a ploughed and cultivated seed bed. Activity following minimum tillage and straw baling was intermediate. This difference in phytotoxicity probably resulted from greater adsorption in the surface layers of the minimal cultivation treatments.     

Further studies of the enhanced biodegradation of some soil-applied herbicides

In field experiments to investigate the effect of repeated application of eight herbicides on their persistence in the soil, the rates of loss of metribuzin, metolachlor and isoproturon were shown to be unaffected by up to three previous doses of the same herbicide. With linuron, there was a small but significant enhancement of biodegradation by two or more previous applications. The persistence of monolinuron, propyzamide and metamitron was shorter in plots that had been treated once, twice or three times previously than in plots treated for the first time, but the effects were often small. In the case of napropamide, rates of loss were considerably increased by a single previous dose. In laboratory experiments with soil from the field plots, there was again no evidence of enhanced biodegradation of metribuzin, metolachlor or isoproturon. However, the rate of linuron degradation was enhanced by a single application. This effect was most marked after 12 weeks, but had disappeared by 57 weeks after initial treatment of the soil in the field. Considerable enhancement of monolinuron, propyzamide and metamitron degradation rates was also observed. The effects were again most pronounced after 12 weeks; however, with these compounds, they were still apparent more than 1 year later. Enhancement of napropamide biodegradation was most stable when assessed in laboratory incubations; the effects from a single pretreatment were still apparent more than 12 months later. Etudes complementaires de la degradation accélerée de certains herbicides appliques au sol Dans des essais de plein champ conduits pour etudier 1'influence d'applications répetées de 8 herbicides sur leur persistance dans le sol, les taux de perte de métribuzine, métolachlor et isoproturon n'ont pas été affectés jusqu'à 3 applications précédentes du même herbicide. Avec le linuron, il y a eu une faible mais significative augmentation de la dégradation aprés 2 ou 3 applications. La persistance du monolinuron, de la propyzamide et de la métamitrone éiait plus courte dans les parcelles déjà traitées une, deux ou trois fois que dans celles traitées pour la premiére fois, mais les effets étaient souvent faibles. Avec la napropromide, les taux ont été considérablement accrus aprés une seule application. Dans des essais de laboratoire avec du sol venant des parcelles de plein champ, il n'y a pas eu de nouveau d'accélération de la biodégradation pour la métribuzine, le métolachlor ou 1'isoproturon. Cependant, la dégradation du linuron a été renforcée par une seule application. Cet effet a été plus fort qu'aprés 12 semaines, mais a disparu 57 semaines aprés le traitement du sol au champ. Un accroissement important de la dégradation du monolinuron, de la propyzamide et de la métamitrone a étéégalement observé Les effets étaient de nouveau maxima aprés 12 semaines; cependant avec ces produits, ils étaient encore apparent une année plus tard. L'accé1ération de la biodégradation de la napropromide était la plus stable dans les observations de laboratoire; les effets d'une seule application étaient encore apparents plus de 12 mois plus tard. Weitere Untersuchungen zum beschleunigten Abbau von Bodenherbiziden In Feldversuchen zur Persistenz von 8 Herbiziden bei wiederholter Ausbringung ging bei Metribuzin, Metolachlor und Isoproturon nach 3-maliger Ausbringung desselben Herbizids die Verlustrate nicht zurück. Bei Linuron war der mikrobielle Abbau nach 2 oder mehr Vorbehandlungen nur leicht, aber signifikant erhöht. Die Persistenz von Monolinuron, Propyzamid und Metamitron war bei l-, 2- oder 3-maliger Vorbehandlung geringer als bei erstmaliger Behandlung, doch waren die Wirkungen oft klein. Bei Napropamid erhöhte sich die Verlustrate bereits nach einer Vorbehandlung beträchtlich. Auch in Laborversuchen mit Böden aus den Freilandparzellen konnte bei Metribuzin, Metolachlor und Isoproturon kein verstärkter mikrobieller Abbau nachgewiesen werden. Bei Linuron dagegen erhöhte sich die Abbaurate schon nach einmaliger Applikation. Diese Wirkung war nach 12 Wochen am deutlichsten ausgeprägt, verschwand jedoch nach 57 Wochen nach dem Behandlungstermin. Eine erheblich größere Abbaurate wurde auch bei Monolinuron, Propyzamid und Metamitron beobachtet, am deutlichsten nach 12 Wochen, aber auch noch nach mehr als l Jahr. Bei Napropamid war die Verstärkung der Biodegradation im Labor am bestRaUndigsten; die Wirkungen einmaliger Vorbehandlungen bestanden noch nach mehr als 1 Jahr.     

Effects of application method on the performance of some soil-applied herbicides. I. Glasshouse experiments

Chlortoluron, propyzamide, terbutryne and nitrofen were applied to the soil in pots with a rotary atomizer at 301 ha^?1, with a conventional hydraulic nozzle at 400 1 ha^?1 at several doses, or as discrete 2-μl drops applied with a microsyringe at 2-cm spacings. The test plants were Alopecurus myosuroides, Stellaria media, Chenopodium album, Avena fatua, perennial ryegrass and radish. Chlortoluron, propyzamide and terbutryne had the same activities following the rotary atomizer or conventional spray application but the rotary atomizer application of nitrofen was less effective against A. fatua than the conventional spray treatment. Chlortoluron, propyzamide and terbutryne showed appreciable activity applied as drops 2 cm apart at rates equivalent to 2 kg ai ha^?1, on plants growing equidistant from the drops, but nitrofen showed no activity under these circumstances. The activity of chlortoluron was investigated at different soil moisture contents; it was more active when applied to moist soil than to dry soil which was not wetted for at least 10 h. Application method did not affect this response     

Interactions between soil-applied herbicides in the roots of some legume species

The effects on plant growth of applying trifluralin or nitralin combination with simazine, atrazine, prometryne and linuron to the upper 5-cm root region of vetch (Vicia sativa L.), pea (Pisum sativum L.) and soybean (Glycine max) were investigated. Foliar injury due to herbicides of the second group was markedly reduced in each species by simultaneous treatment with trifluralin or nitralin both of which inhibited lateral root growth without affecting aerial plant growth or tap root extension growth. This inhibition of lateral root growth in roots treated with trifluralin or nitralin was associated with reduced uptake and subsequent transport to the foliage of ¹⁴C-labelled simazine in vetch and pea and ¹⁴C-labelled atrazine in soybean. This probably accounted for the reduction in simazine and atrazine phytotoxicity. In the presence of trifluralin or nitralin comparatively higher amounts of radioactivity were retained in the roots of pea and soybean and this reduced the amount of ¹⁴C available for transport to the foliage. This was not evident in vetch.     

Shoot zone uptake of soil-applied herbicides in some legume species

Localized placement of prometryne, linuron and diuron in the soil at the first or second shoot internodes of dwarf broad bean (Vicia faba L.) equally reduced aerial plant growth, whereas simazine and atrazine had no effect. Growth reduction also occurred when the first shoot internode of scarlet runner bean (Phaseolus multiflorus L.) in the soil was treated with all five herbicides, especially with diuron. Localized placement of these herbicides at the first or second shoot internodes of vetch (Vicia sativa L.) in the soil equally reduced aerial plant growth. Foliar injury to vetch due to placement of these herbicides in the shoot zone of the soil was markedly reduced by simultaneous treatment with trifluraiin or nitralin which prevented adventitious root development on the shoot without otherwise affecting plant growth. This lack of root development on the shoots treated with trifluraiin was associated with a marked decrease in ¹⁴C-labelled atrazine uptake, which probably accounted for the reduction in atrazine phytotoxicity. A similar explanation may account for the reduced phytotoxicity of the other herbicides in the presence of trifluraiin or nitralin.     

Effects of soil moisture content on the availability of soil-applied herbicides to plants

The phytotoxicities of atrazine, simazine, linuron, lenacil and aziprotryne were increased as the moisture content of the soil increased. Results from studies with ¹⁴C-labelled atrazine suggested that these differences could be related to differences in concentrations of herbicide accumulated by the plants. Total uptake of atrazine was directly proportional to water uptake, but a comparison of the amounts taken up with those supplied by mass-flow in the transpiration stream suggested that some exclusion factor was operative. It was concluded that herbicide transport within the soil-plant system was the main factor affecting phytotoxicity under the different soil moisture regimes. The significance of the results to herbicide behaviour under field conditions is discussed.     

Effect of trickle irrigation on soil-applied herbicides*

The effect of trickle irrigation on the activity, leaching and distribution in the soil of herbicides, was studied in a model specially constructed for simulating trickle irrigation in the field, and also under field conditions. The pattern of movement of a soil-applied herbicide in the soil under trickle irrigation paralleled, to some extent, that of the trickle water itself, but total herbicide movement was less than that of the water. Both water and herbicide distribution in the soil formed the shape of a hemisphere or cone under the trickle nozzle, the exact shape of which was determined by the soil characteristics (a narrow cone in a light soil and a wide cone in a heavy soil); cone size was determined by the amount of trickle water. Bioassays with susceptible test plants showed that effective weed control could be expected with either simazine or GS-14259 (2-t-butylamino-4-ethylamino-6-methoxy-s-triazine =‘Caragard') only in the areas wetted by the trickle nozzle. The results showed that the pattern of distribution in the soil of simazine and GS-14259 was similar, but there were quantitative differences in their final spread.     

Measurement of phytotoxicity of commercial and unformulated soil-applied herbicides

The relative potencies of analytical-grade lenacil (99% ai) and its commercial formulation, Venzar® (80% ai), technical-grade ethofumesate (96%) and its commercial formulation Nortron® (21% ai) were evaluated using oats (Avena sativa L. cv. Selma) as test plant. In all experiments the dose-response curves of the pure herbicide and its commercial product were parallel. The average potency of Venzar relative to lenacil, assayed twice in a sandy loam, was 0?80 and thus equal to the expected 0?80. The average potency of Nortron relative to ethofumesate, assayed in a sandy loam and a loamy sand, was 0?25 and close to the expected value of 0?21. The implication of using the technique of parallel-line assay in herbicide studies is discussed and its potential use in other contexts than the present one is suggested.     

Effect of soil compaction on phytotoxicity and persistence of soil-applied herbicides

Field and glasshouse experiments were conducted to study the effect of three levels of soil compaction on the activity of two soil-applied herbicides, atrazine and trifluralin, using oats as test species. The moderate and heavy compactions increased the bulk density by 24.7 and 35.1% respectively while the normal compaction had negligible effect on physical properties of the soil compared to the freshly cultivated ground. Initial phytotoxicity of both herbicide's was increased significantly by the heavy compaction treatment. Moderate soil compaction also enhanced the initial activity of atrazine but trifluralin activity remained unaffected from this treatment. Trifluralin was more persistent than atrazine and the residual activity of both herbicides was increased significantly as a result of both the moderate and heavy compaction treatments. Effet du compactage du sol sur la phytoloxicilé et la persistance des herbicides appliques sur le sol Des expériences au champ et en serre ont été effectuées pour etudier l'effet de trois degrés de compactage du sol sur l'activité de deux herbicides appliqués sur le sol, l'atrazine et la trifluraline, en utilisant l'avoine comme plante test. Le compactage modéré et le compactage intense ont accru la densite de la masse de 24,7% et 35,1% respectivement, alors que le compactage normal n'a eu qu'un effet négligeable sur les propriétés du sol compacté par rapport à un sol récemment cultivé. La phytotoxocité initiale des deux herbicides a été accrue significativement par le compactage intense. Le compactage modéré du sol a aussi augmenté l'activité initiale de l'atrazine mais celle de la trifluraline n'a pas été modifiée par ce degre de compactage. La triflura-line s'est montrée plus persistante que l'atrazine et l'activité résiduelle des deux herbicides a été significativement accrue à la suite du compactage modéré et du compactage intense. Die Wirkung von Bodenverdichtungen auf Phytotoxizität und Persistenz von Bodenherbiziden Es wurden Held-und Gewachshausversuche durchgeführt, indenen der Einfluss von drei unterschiedlich starken Bodenverdichtungen auf die Wirkung von auf den Boden appliziertem Atrazin und Trifluralin untersucht wurde. Als Testpflanze wurde Hafer verwendet. Durch eine mittlere und starke Ver-dichtung nahm das Boden-Volumengewicht um 24,7% bzw. um 35,1% zu. Eine normale Verdichtung hatte, verglichen mil einem frisch bearbeiteten Boden, nur eine geringe Wirkung auf die physikalischen Bodeneigenschaften. Durch die starke Verdichtung nahm die phytotoxische Wirkung beider Herbizide significant zu. Dieser Effekt trat auch bei der mittleren Boden-verdichtung auf, jedoch nur bei Atrazin; die Wirkung von Trifluralin blieb davon unbeeinflusst. Trifluralin erwies sich als persistenter als Atrazin, die Residualwirkung beider Herbizide nahm aber durch die starke und die mittlere Bodenverdichtung significant zu.     

Effects from simulated rainfall on shoot-zone uptake of herbicides

In glasshouse experiments, atrazine, simazine, lenacil and linuron applied to the soil surface were phytotoxic to turnip seedlings which had emerged from a depth of 1–5 cm when 3 mm artificial rainfall was applied at the time of seedling emergence or shortly afterwards. When rainfall was applied on 2 or 3 consecutive days, the herbicides were in general more phytotoxic. As the delay between emergence and commencement of surface watering increased, however, the response of the seedlings decreased. Studies with [¹⁴C]-atrazine showed that at emergence the seedlings contained a small amount of herbicide which increased considerably with surface watering. Relatively high concentrations were attained when rainfall was applied while the seedlings were small, but as the interval between seedling emergence and rainfall increased, the same uptake resulted in lower shoot concentrations, Atrazine extraction from the soil showed little movement from the surface 1.0 cm, suggesting uptake via the stem. The observed responses of the other three herbicides are explained by assuming the same pattern of uptake as that recorded for atrazine.     

Effects of some herbicides on soil enzyme activities

Effects of glyphosate, paraquat, trifluralin and atrazine on activities of dehydrogenase, phosphatase and urease in one soil were measured. Only glyphosate at 21.6 kg/ha was found to inhibit the enzyme activities and generally the results were not statistically significant. Enzyme activity associated with micro-organisms proliferating in soil supplemented with lucerne meal was similarly not affected by the herbicides. Interpretation of results from enzyme activity measurements in soils treated with herbicides is discussed. It is proposed that effects of natural stress can be used to judge the relative importance of herbicide induced change.     

植保无人机喷施对玉米田土壤处理除草剂的减量效应

在陇东旱塬条件下,以40%乙·莠SE为指示除草剂,测定了植保无人机喷施对玉米田土壤处理除草剂的减量效应。结果表明:通过植保无人机喷施,40%乙·莠SE的控草效果随施药量的减少呈逐渐降低的趋势,玉米果穗有效长度、果穗粗、穗粒数、百粒重、产量及纯收益均随施药量的减少呈先增后降的态势,当施用量降至2 400 mL/hm~2,即较推荐用量(4 500 mL/hm~2)减少用药46.67%时,对藜、狗尾草和总草的株防效仍分别高达93.31%、65.51%和86.40%,鲜重防效分别高达99.12%、78.61%和93.44%;对玉米穗部性状、产量及纯收益的影响程度亦降至较低或最低,其产量较人工除草和背负式喷雾器以药剂常用量喷施分别减产0.17%和增产5.61%,其纯收益较人工除草和背负式喷雾器以药剂常用量喷施分别增加652.08元/hm~2和1 076.85元/hm~2。可见,植保无人机喷施对玉米田土壤处理除草剂的减量效应显著,具有大面积推广应用的价值。     

Activities of mixtures of soil-applied herbicides with different molecular targets

The joint action of soil-applied herbicide mixtures with similar or different modes of action has been assessed by using the additive dose model (ADM). The herbicides chlorsulfuron, metsulfuron-methyl, pendimethalin and pretilachlor, applied either singly or in binary mixtures, were used on rice (Oryza sativa L.). The growth (shoot) response curves were described by a logistic dose-response model. The ED50 values and their corresponding standard errors obtained from the response curves were used to test statistically if the shape of the isoboles differed from the reference model (ADM). Results showed that mixtures of herbicides with similar molecular targets, i.e. chlorsulfuron and metsulfuron (acetolactate synthase (ALS) inhibitors), and with different molecular targets, i.e. pendimethalin (microtubule assembly inhibitor) and pretilachlor (very long chain fatty acids (VLCFAs) inhibitor), followed the ADM. Mixing herbicides with different molecular targets gave different results depending on whether pretilachlor or pendimethalin was involved. In general, mixtures of pretilachlor and sulfonylureas showed synergistic interactions, whereas mixtures of pendimethalin and sulfonylureas exhibited either antagonistic or additive activities. Hence, there is a large potential for both increasing the specificity of herbicides by using mixtures and lowering the total dose for weed control, while at the same time delaying the development of herbicide resistance by using mixtures with different molecular targets.     

Studies on the control of groundkeeper potatoes with the soil-applied herbicides chlorpropham,propyzamide and trifluralin

Chlorpropham, propyzamide and trifluralin were assessed in several trials, to test their potential for the control of groundkeeper potatoes (Solanum tuberosum L.). Chlorpropham was insufficiently active, but trifluralin and propyzamide at doses of 4 kg a.i./ha, or more, reduced and delayed the emergence of potato plants in the summer, after autumn/winter or spring applications. The highest dose (12 kg a.i./ha) prevented many tubers producing plants. Greatest activity was attained when the herbicides completely surrounded the tubers when active growth started in the spring. However, both residue and crop tolerance data indicated that the doses of trifluralin and propyzamide required to control the potatoes were so high that appreciable residues remained in the following summer. These damaged vegetable crops drilled in April and May, and affected cereals planted 12 months after application. Thus there is insufficient margin of selectivity between the doses required to control the potatoes and those tolerated by subsequent crops.     

Effects of some commercial herbicides on rhizobia and their symbiosis with peanuts

Four herbicides commonly used in Israel for controlling weeds in peanuts were evaluated under field and screenhouse conditions. Terbutryn (Terbutrex 50, w.p.), ethalfluralin (Sonalan 333, e.c.), dinitramine (Cobex 240, e.c.) and alachlor (Alapaz 480, e.c.), used at recommended levels, had no adverse effect on nodulation rate, nitrogenase activity, total nitrogen of peanut tops or pod yield, compared with control (inoculated but herbicide non-treated) plants. Studies were conducted to determine the relative toxicity in vitro of the herbicides on each of four Rhizobium strains used for commercial peat inoculant production. The results showed that at up to 94 μg g^?1 the herbicides has no inhibitory effect on the growth of rhizobia. The sensitivity of Rhizobium strains to different rates of the chemicals decreased in the order: dinitramine>alachlor>ethalfluralin>terbutryn. It was found that various strains differ in their sensitivity to the herbicides tested.     

Effects of some phenylurea herbicides on photosynthesis of two wheat varieties

Photosynthesis in the shoots of winter wheat (Triticum aestivum L.) was inhibited by certain phenylurea herbicides applied via the nutrient solution. Recovery from this inhibition after short treatments was used as a measure of the rate of inactivation of these herbicides in the leaf tissue of a variety tolerant to metoxuron (Caribo) and of a less tolerant variety (Manella). The introduction of chlorine atoms into fenuron greatly reduced the rate of inactivation in both varieties, whereas that of a methyl or butoxy group had little or no effect. Metoxuron was inactivated more readily than chlortoluron and both compounds were inactivated more rapidly in Caribo than in Manella.     

Collaborative studies of dose-response curves obtained with different bioassay methods for soil-applied herbicides

In a collaborative study by 12 laboratories the reproducibility of bioassay techniques was analysed by comparison and statistical treatment of the ED₅₀-values (μg herbicide/g soil). Commonlyused bioassay techniques were investigated; two direct seeding methods, a transplanting method and a shoot extension method. The herbicides studied were two photosynthesis inhibitors, atrazine and metribuzin using Lepidium sativum and Brassica rapa as test plants; two germination inhibitors, tri-allate and trifluralin using Avena sativa as test plant. The mean ED₅₀-value of atrazine in the direct seeding method was 0.18 with a variation from 0.12 to 0.29 and 0.12 (0.07–0.68) in the transplanting method. The values of metribuzin were 0.05 (0.02–0.11) and 0.03 (0.01–0.15) respectively. The values for triallate were 1.15 (0.50–2.60) in the direct seeding method and 1.10 (0.54–2.53) in the shoot extension method and for trifluralin 3.11 (0.72–18.31) and 1.33 (0.48–2.94) respectively. The reproducibility was best in the shoot extension method. No outliers (confidence intervals lying entirely outside the confidence interval of the overall mean) in the ED₅₀-values were observed with atrazine and metribuzin when using the direct seeding method, whereas with the germination inhibitors a high number of results (four with tri-allate, six with trifluralin) could be considered as outliers. A comparison of the use of fresh weight and dry matter showed good agreement between the ED₅₀-values they gave, with similar reproducibility.     

Influence of some 1,3,5-triazine herbicides on peroxidase activity in corn seedlings

The effect of some 1,3,5-triazine herbicides, on the rate of oxidative decarboxylation of tryptophan by peroxidase from corn seedlings, varied with the concentration. Atrazine was stimulatory in vivo at 10-⁶M but not at 10⁸ M or lower, whereas terbutryne was inhibitory at 10-⁶M but not at 10-⁸M or below. Prometryne inhibited enzyme activity at 10-⁶M and stimulated it at 10-¹⁰M and at 10¹²M, while simazine caused stimulation at 10-⁶M and inhibition at 10^?10M and 10^?12M. Atraton reduced enzyme activity at 10^?6M and 10^?8M but had no effect at 10^?10M and 10^?12M. When peroxidase activity was assayed in acetone-dried powders from seeds, harvested from fields that had received typical atrazine applications, the quantities of tryptophan consumed were significantly less than the quantity determined in the control powder. From the results obtained, by incorporating dealkylated and 2-hydroxy metabolites of atrazine at 10^?6M into the culture solutions, it seems possible that the inhibition observed may have been due to the presence of 4-amino-6-ethylamino-1, 3, 5-triazin-2-ol and/or 4, 6-diamino-1, 3, 5-triazin-2-ol residues in seeds from treated plots, even if, in previously reported experiments, analyses had not detected their presence.