VERTICAL DISTRIBUTION OF HERBICIDES IN SOIL AND THEIR AVAILABILITY TO PLANTS: SHOOT COMPARED WITH ROOT UPTAKE

Summary. Turnip, lettuce and ryegrass seedlings showed toxicity symptoms following shoot exposure to atrazine, linuron and aziprotryne at soil concentrations less than would be obtained from normal field applications. Responses following shoot exposure to simazine and lenacil were much less. Root exposure to all five herbicides caused seedling death at concentrations lower than those required for 'shoot-zone' toxicity. Pronamide and chlorpropham were tested against ryegrass only and at the concentrations examined were toxic only when localized in the shoot zone. Root exposure suppressed root growth, but the shoots were able to grow normally if the soil was kept sufficiently moist. Shoots contained more ¹⁴C-atrazine at emergence after shoot exposure compared with root exposure, but there was little subsequent uptake from the shoot zone. There was extensive uptake from the root zone after emergence. In the shoot-zone treatments, concentrations in the plant were high at emergence but were rapidly diluted by plant growth, whereas with root exposure, they increased throughout the experiments. The possible significance of these results to herbicide bebaviour under field conditions is discussed.
La distribution verticale des herbicides dans le sol et leur disponibilité pour les plantes: absorption comparée par la partie aèrienne et par les radnes     

The uptake of soil-applied chlorotriazines by seedlings and its prediction

¹⁴C-labelled atrazine or terbuthylazine was applied to the surface of soil columns 100 mm deep and the uptake by oat seedlings measured for up to 24 days after germination following two contrasting rainfall treatments. Attempts were made to predict measured uptake on the basis of mass flow theory given also measurements of transpiration rates, water, rooting and herbicide distribution profiles in the soil, and soil adsorption characteristics. Predictions over a tenfold range of uptake were close enough to suggest that the assumptions made to predict mass flow uptake were essentially correct. Discrepancies appeared to result principally from (i) shoot-zone uptake, and (ii) incorrect prediction of long-term herbicide adsorption in undisturbed soil. Greater attention to the effect of herbicide on transpiration rates and to the patterns of water uptake by roots should improve the accuracy of such predictions. The various factors that influence the mass flow uptake of chlorotriazines in the soil surface by seedlings are discussed as a basis for modelling herbicide uptake.     

Weed seedling herbivory by field cricket Teleogryllus emma (Orthoptera: Gryllidae) in relation to the depth of seedling emergence

This study aimed to determine whether seedling herbivory by the field cricket, Teleogryllus emma (Ohmachi et Matsuura), promoted the mortality of Italian ryegrass (Lolium multiflorum Lam.), a non‐native grass weed in Japan, whether the impact of seedling herbivory differed depending on the depth of seedling emergence and the influence of cricket density on seedling mortality. First, the seedlings at emergence depths of 0, 1 and 2 cm were exposed to the cricket for 2 days in plastic cups and the amount of seedling mortality by herbivory was calculated. The level of mortality of 60 seedlings that emerged from seeds on the soil surface was 92.4%, significantly higher than that of the seedlings that emerged from seeds at depths of 1 cm (10.8%) and 2 cm (9.6%). Second, the seedlings at the emergence depths of 0 and 1 cm were exposed to the crickets at four different densities (zero, one, two and three individuals per 5700 cm²) for 5 days in plastic containers and the amount of seedling mortality by herbivory was calculated. The level of mortality by herbivory of the seedlings that emerged from 100 seeds on the soil surface was higher (33.3–61.3%) than that of the seedlings that emerged from seeds at a depth of 1 cm (4.7–13.1%) in the containers with one‐to‐three crickets. The level of seedling mortality tended to increase with an increasing cricket density. These results suggest that seedling herbivory by crickets is an important factor in weed mortality, particularly in no‐till fields and in field margins, where the seeds are more prevalent near the soil surface.     

Herbicide Effects on Sugarcane Growth, Pythium Root Rot, and Pythium arrhenomanes

ABSTRACT Six herbicides were evaluated for their effects on Pythium root rot and growth of sugarcane in greenhouse experiments and on in vitro mycelial growth rate of Pythium arrhenomanes. Pendimethalin and atrazine were most inhibitory to mycelial growth, but neither reduced root rot severity. Asulam, atrazine, and metribuzin were not phytotoxic to sugarcane and did not affect root rot symptom severity in clay loam or silt loam field soils. Atrazine and metribuzin increased shoot number, and atrazine increased total shoot weight for treated plants in silt loam soil. Glyphosate, pendimethalin, and terbacil were phytotoxic to sugarcane. These herbicides increased root rot severity, but the extent to which growth reductions resulted from increased disease severity or from direct herbicide injury was not clear. Adverse effects on plant growth and root rot severity were greater in clay loam than in silt loam soil. The results suggest that sugarcane injury from some herbicides is compounded by increased severity of root rot.     

Co-uptake of atrazine and mercury by rice seedlings from water

The uptake of atrazine (ATR) by rice seedlings (Oryza sativa L.) from nutrient solution was investigated in the presence and absence of Hg²⁺ over a period of 96 h. Either ATR or Hg²⁺ was found phytotoxic to rice seedlings, as they inhibited the seedling growth. The seedlings showed about 50% biomass reduction when exposed to 1.0 mg/L Hg²⁺ alone in nutrient solution, and about 80% reduction when exposed to 12.0 mg/L ATR alone. Observed ATR and Hg²⁺ levels (in mg/kg) in seedlings are not related to biomass changes. When either ATR or Hg²⁺ was applied, the concentrations in seedlings increased largely in proportion to those in nutrient solution. The presence of Hg²⁺ at 0.1 and 1.0 mg/L in solution caused a small-to-moderate decline in ATR uptake by the seedlings, the effect being largely independent of the ATR concentration in nutrient solution (at 6.0 and 12.0 mg/L). The presence of ATR (at 6.0 and 12.0 mg/L) in the nutrient solution led to small-to-moderate irregular changes in the Hg²⁺ concentrations in rice seedlings. The overall results showed that there was no significant interdependence between the uptakes of ATR and Hg²⁺ by rice seedlings, which is in contrast to the enhanced ATR uptake noticed earlier with Pb²⁺ ion. Plant uptake of non-ionic organic compounds, such as ATR may be partly through water channels on the plasma membranes of plant cells.     

Emergence patterns of weed seedlings in relation to cultivation and rainfall

In experiments over 4 years, separate field plots were cultivated once only at 2-week intervals and the weed seedlings recorded weekly. Soil disturbance resulted in a flush of seedlings of which 90% appeared within 10 weeks after cultivation in early spring and within 3 weeks after cultivation in summer. Weekly emergence then returned to the level prevailing on undisturbed soil. The species composition of the seedling populations varied with the time of year at which the soil was disturbed. In each year there was a spring flush of seedlings, probably associated with rising soil temperature; subsequent flushes were coincident on cultivated and undisturbed soil and were related to the rainfall pattern. In each year there were periods when lack of soil moisture restricted emergence, and this appeared to be the over-riding factor determining seedling numbers. When cultivations were followed by long dry periods which prevented germination, the numbers of seedlings appearing when rain ultimately fell were no different from those when the soil was disturbed just before the rainfall.     

Uptake and phytotoxicity of chlorsulfuron in Zea mays L. in the presence of 1,8-naphthalic anhydride

The sites of uptake of chlorsulfuron in maize (Zea mays L.) were investigated at three different growth stages. Exposure of seedling roots, or shoots separately, to herbicide-treated sand over 4 days resulted in inhibition of both roots and shoots. Exposure of seedling roots to chlorsulfuron-treated soil over 21 days severely inhibited both roots and foliage, while separate shoot exposure also reduced both foliage and root growth. After plant emergence, exposure of the crown root node, growing point and lower stem to treated soil reduced foliage and root growth, but exposure of the shoot above the growing point caused only slight inhibition of foliage and had no effect on roots. The herbicide safener 1,8-naphthalic anhydride (NA) applied as a dust (10 g kg^?1 seed weight), or as a 50 mg 1^?1 suspension in water to maize seeds, reduced the root inhibition by chlorsulfuron in 4-day-old seedlings. NA completely prevented both foliage and root injury when chlorsulfuron was placed in soil in the shoot zone before emergence, or in the shoot zone below the soil surface after plant emergence. NA slightly decreased injury to foliage, but not to roots when chlorsulfuron was placed in soil in the root zone before emergence. NA seed treatment protected both roots and foliage against injury from foliarly applied chlorsulfuron. Plants were also protected when a suspension of NA in water was sprayed on the foliage seven days before chlorsulfuron. When a mixture of NA and chlorsulfuron was applied to foliage, root injury was reduced more than foliage injury.     

SHOOT ZONE UPTAKE OF SOIL-APPLIED HERBICIDES IN PISUM SATIVUM L.

Summary. The effects of localized herbicide placement at different internodes of pea ( Pisum sativum L. cv. Alaska) shoots below the soil surface after plant emergence were studied by removing the soil from around the shoots and replacing with herbicide-treated soil. The first internode proved insensitive to linuron, diuron, atrazine and simazine at 4·5 kg/ha, while treatment of the second and third internodes markedly reduced plant growth 4–6 days after treatment. Separate exposure of the first internode alone, and the second and part of the third together to ¹⁴C-labelled atrazine indicated no difference in herbicide metabolism. However, a two- to threefold increase in ¹⁴C uptake and movement to the foliar parts occurred when the second and part of the third internode was treated, as compared to first internode treatment. Thus the differential sensitivity of the internodes to atrazine, and possibly to the other herbicides, may be because the more mature first internode allows less uptake and subsequent movement to the foliar parts.
Absorption dans la zone des tiges des herbicides appliqués dans le sol chez Pisum sativum L.     

Effect of soil placement and shoot uptake of prometryne and terbutryne on peas

The effect of placing terbutryne in different soil layers with reference to different depths of sowing of peas was studied by measuring plant top growth. Increasing the depth of sowing resulted in greater plant injury by the same layer of herbicide-treated soil. Exposing the upper part of the emerging epicotyl (nearest the soil surface) to soil treated with terbutryne was more injurious than exposing the lower part of the epicotyl (nearest the seed). Uptake of ¹⁴C-labelled prometryne and terbutryne by pea seedlings during emergence and early growth was measured according to different soil-zone treatments. The absorbed amount of each herbicide decreased in the order: root system, lower epicotyl, upper epicotyl. Translocation of the herbicides to the foliage was higher from the upper than from the lower part of the epicotyl. Shoot and root uptake and translocation of prometryne were higher than of terbutryne.     

Chloris polydactyla (L.) Sw., a perennial Poaceae weed: Emergence, seed production, and its management in Brazil

Experiments were conducted to evaluate the plant emergence and seed production of Chloris polydactyla and the efficacy of herbicides for its control. The plants emerged mainly when the seeds were placed on the soil surface at ≤ 3 cm depth. Isolated plants produced a great amount of seeds. The pre-emergence herbicides, acetochlor, atrazine + simazine, s-metolachlor, alachlor, and trifluralin, were effective for C. polydactyla control. The postemergence herbicides, clodinafop-propargil, haloxyfop-methyl, clethodim, fluazifop- p -butil, tepraloxydim, sethoxydim, and quizalofop- p -tefuril showed satisfactory control of the plants at a 20 cm height with six leaves. During the flowering stage (85 cm plant height), only glyphosate was effective in controlling C. polydactyla .     

Burial depth and cultivation influence emergence and persistence of Phalaris paradoxa seed in an Australian sub-tropical environment

Emergence and persistence characteristics of Phalaris paradoxa seeds in no- and minimum-till situations and at different burial depths were studied in a sub-tropical environment. Three experiments were carried out using naturally shed seeds. In the first experiment, seedlings emerged from May through to September each year, although the majority of seedlings emerged in July. In the second experiment with greater seed density, cultivation in March of each year stimulated seedling emergence, altered the periodicity of emergence and accelerated the decline of seeds in the seedbank compared with plots that received no cultivation. The majority of seedlings in the cultivated plots emerged in May whereas the majority of seedlings in the undisturbed plots emerged in July. Emergence accounted for only 4–19% of the seedbank in both experiments over 2 years. Seed persistence was short in both field experiments, with less than 1% remaining 2 years after seed shed. In the third experiment, burial depth and soil disturbance significantly influenced seedling emergence and persistence of seed. Seedlings emerged most from seed mixed in the top 10 cm when subjected to annual soil disturbance, and from seed buried at 2.5 and 5.0 cm depths in undisturbed soil. Emergence was least from seed on the soil surface, and buried at 10 and 15 cm depths in undisturbed soil. Seeds persisted longest when shed onto the soil surface and persisted least when the soil was tilled. These results suggest that strategic cultivation may be a useful management tool, as it will alter the periodicity of emergence allowing use of more effective control options and will deplete the soil seedbank more rapidly.     

Aerial seed germination and morphological characteristics of juvenile seedlings in Commelina benghalensis L.

Seed germination, seedling emergence, and the morphological characteristics of juvenile seedlings of Commelina benghalensis L. were observed. For aerial seeds collected in September and October, seedling emergence peaked in April and June for large seeds and from June to August for small seeds, whereas seedling emergence for large seeds collected in November showed peaks in March and April under natural rainfall conditions, and in April and June under irrigation conditions. Seedlings from small seeds emerged intermittently over a longer period from April to August under both conditions. Aerial seeds of C. benghalensis germinated on wet filter paper on the second day after seeding (DAS) for large seeds and the fourth DAS for small seeds. The germination percentage for large seeds was higher than that for small seeds by the 14th DAS. The germination percentage for large aerial seeds showed no significant difference between light and dark conditions. However, the percentage for small aerial seeds was higher under light than under dark conditions. Seedlings from large aerial seeds emerged on the third DAS at 0–50 mm soil depths. The percentage of emergence at 0 and 1 mm soil depths increased until the 30th DAS, whereas those at soil depths of 5–50 mm showed no change after the 9th DAS. There was no emergence at a soil depth of 100 mm. Seedlings from small aerial seeds emerged on the 6th DAS at 0–1 mm soil depths, with the percentage increasing until the 30th DAS. Although seedlings at 5 and 10 mm soil depths also emerged on the 6th DAS, there was no change in the percentage after the 12th DAS. There was no emergence at soil depths of 20–100 mm. The hypocotyl and taenia (part of the cotyledon connected to the seed) in juvenile seedlings that emerged from soil depths of 50 mm were longer than those in seedlings emerging from a soil depth of 1 mm.     

VERTICAL DISTRIBUTION OF HERBICIDES IN SOIL AND THEIR AVAILABILITY TO PLANTS: TREATMENT OF DIFFERENT PROPORTIONS OF THE TOTAL ROOT SYSTEM

Summary. Uptake of atrazine and linuron by wheat seedlings was measured from different initial distributions of herbicide in the soil. Uptake of both compounds was proportional to the fraction of the total root system exposed to herbicide-treated soil. It was calculated that under the conditions of the experiments, this factor would offset the reduction in concentration of herbicide in the soil following incorporation of 1 kg/ha to 3, 6 or 9 cm, so that after the same time, the concentrations of herbicide in the plants in the different treatments would be similar.
La distribution verticale des herbicides dans le sol et leur disponibilité pour tes plantes: traitement de différentes fractions de l'ensemble du système racinaire total     

Atrazine soil metabolism in maize fields treated with organic fertilizers

The metabolism of atrazine in soil was studied in two maize fields located in regions with different soil types. Treatments were cow manure or pig slurry (50 tonnes each ha^-1) applied once either in March or in November before sowing, or green manure incorporated in March. Control plots were not treated with organic fertilizers. Atrazine at 0.75 or 1.0 kg a.i. ha^-1 was applied after sowing. In the 0-12 cm soil layer, the main atrazine metabolites found were deethylatrazine and hydroxyatrazine. Low concentrations of deisopropylatrazine and 6-chloro-1, 3, 5-triazine-2, 4-diamine were also observed. During the 4 months after sowing, the organic fertilizers decreased the rate of atrazine degradation, but subsequently there were no differences between treated and control plots. At harvest, the concentrations of atrazine and its metabolites were very low and similar in all plots. The organic fertilizers thus did not cause atrazine metabolites to accumulate in soil. In addition, atrazine and its metabolites were never detected below 12 cm in any of the plots.     

DIFFERENTIAL PHYTOTOXICITY OF ATRAZINE AND AMETRYNE TO BANANAS*

Summary. In field screening trials for bananas (Musa acuminata var. Dwarf Cavendish) in Hawaii, ametryne (2-methylthio-4-ethylamino-6-isopropylamino-s-triazine) was less phytotoxic to bananas than atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine). Sand culture experiments showed that both herbicides were equally injurious to banana plants. Differential degradation of the herbicides by the plants did not account for the phytotoxicity observed. Both herbicides were partly metabolized by the plant to their common hydroxyl derivative (hydroxyatrazine) and two other unidentified metabolites after 3 and 7 days of exposure to nutrient solution containing ¹⁴C-labelled ametryne and atrazine. Phytotoxicity was directly related to leachability of the herbicides and negatively related to adsorption capacity of each soil for the herbicides. Organic matter content seemed to be correlated to the response observed. It was postulated that phytotoxicity in the field may have been attributed to differential location of the herbicide in relation to the roots.     

莠去津在土壤中的残留动态和淋溶动态

利用HPLC法对土壤中莠去津的残留动态、淋溶动态进行了研究。结果显示,莠去津以有效成分2.25 kg/hm2和4.50 kg/hm2的剂量施用时,在土壤中的半衰期分别为19.1 d和18.1 d,即其半衰期与莠去津的施用浓度无关,属于典型的一级动力学反应。在120 d的玉米生长期中,土壤中莠去津在不断降解代谢的同时,逐渐向深层土壤中淋溶,多数莠去津持留在表层土壤中。施用莠去津27 d后,高浓度处理小区莠去津的淋溶深度超过30 cm,深度为10~15 cm处的土壤在施用后27 d莠去津的浓度最大。同一土壤深度,莠去津在高浓度处理小区的残留量要远高于低浓度处理小区。这些结果显示,减小莠去津的用量可以减少莠去津在土壤中的移动,表明低剂量施用莠去津是保护地下水免受污染的一种有效措施。影响莠去津的淋溶作用的主要因素包括使用量和土壤的理化特性。     

Residualwirkung von Chlortriazin-Herbiziden im Boden an drei rumänischen Standorten. I. Prognose der Persistenz von Simazin und Atrazin im Boden

Residual effects of chlorotriazine herbicides in soil at three Rumanian sites. I. Prediction of the persistence of simazine and atrazine Persistence of simazine and atrazine in the top 10 cm soil was measured at three sites in Rumania with variations in climate and soil conditions. Both herbicides were applied at 1 and 3 kg ai ha^?1 to uncropped plots and to plots cropped with maize (Zea mays L.). Rates of residue decline were independent of application rate and crop cover but varied between sites. The time for 50% loss of atrazine varied from 36 to 68 days and that of simazine from 48 to 70 days. Laboratory studies were made with atrazine to characterize degradation rates under standard conditions and to measure adsorption and leaching behaviour in the different soils. Weather records for the periods of the field experiments were used in conjunction with appropriate constants derived from the laboratory results, or from data in the literature, in a computer program to simulate persistence in the field. Results from the model were in reasonable agreement with the observed soil residues although there was a tendency to overestimate rates of loss on some occasions. The results suggest that the model of persistence was sufficiently accurate for practical purposes, and that its use could preclude the need for extensive analytical measurements of residues.     

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.     

The comparative behaviour of simazine and terbacil in soils

Adsorption of simazine (2-chloro-4,6-bisethyl-amino-1,3,5-triazine) was 2.2–4 times greater than that of terbacil (5-chloro-6-methyl-3-t-butyl-uracil) in the same soils and adsorption of both herbicides was 2–4 times greater in the topsoils than subsoils. Adsorption was inversely correlated with herbicide movement in a thick-layer chromatography system. One year after application of 3 kg/ha to field plots, simazine residues were highest near the soil surface, whereas terbacil residues increased with soil depth in the sandy and sandy loam soils. Total residues recovered from the upper 25 cm of soils was 5% or less of the simazine originally applied, and 10% or less of the applied terbacil. In an oat seedling bio-assay, the GR₅₀ values were generally 1.5–3 times higher for simazine than for terbacil in the same soils.     

Behavior of pyriftalid in soil and its phytotoxic activity on Echinochloa oryzoides seedlings emerging from various soil depths

The phytotoxic activity of pyriftalid ([RS]‐7‐[4,6‐dimethoxypyrimidin‐2‐ylthio]‐3‐methyl‐2‐benzofuran‐1[3H]‐one) on barnyard grass (Echinochloa oryzoides) seedlings emerging from various depths in the soil was investigated in relation to its behavior in the soil. The growth of the barnyard grass seedlings in the soil mixed with pyriftalid was inhibited, depending on the concentration of the herbicide in the soil water but not on the amount in the total soil. A topmost pyriftalid‐treated layer was formed by applying the herbicide to the soil surface under water‐leakage conditions. The concentration of pyriftalid in the soil water and the amount that was adsorbed on the soil solid decreased with time, but the decrease was more marked in the pyriftalid concentration in the soil water than in the amount that was adsorbed on the soil solid. The emergence time of barnyard grass in the soil was faster in the seeds that were located in the shallower soil layer, compared to the deeper soil layer. The growth inhibition of the barnyard grass seedlings emerging from the shallower soil layer was greater than that of the barnyard grass seedlings emerging from the deeper soil layer after the soil surface application of pyriftalid. It is suggested that the emergence timing from the different soil depths is an important factor affecting the herbicidal activity of pyriftalid when it is applied to the soil surface under paddy field conditions.