SHOOT ZONE UPTAKE OF SOIL-APPLIED HERBICIDES*

Summary. Studies were conducted to determine the effects of herbicide placement at different zones of maize (Zea mays L.) and pea (Pisum sativwm L.) shoots below the soil surface after emergence. Soil was removed from around the shoots and replaced with herbicide-treated soil. A wax barrier ensured separate exposure of the zones to treated soil. EPTC, chlorpropham, propham and sulfallate did not affect pea shoot growth, but in maize the shoot zone adjacent to the crown root node was extremely sensitive. Treatment in this area markedly reduced growth and severely inhibited the crown roots. The difference in susceptibility between these species may he due to the location of the growing point relative to the treated soil. Shoots of maize and pea were sensitive to diuron. In maize the shoot adjacent to the crown root node and the tissue of the first internode were the most susceptible. In pea the- uppermost shoot (beneath the soil surface) was the most sensitive. Trifluralin did not affect growth of maize and pea when placed in the shoot zone after emergence, although the crown roots of maize were severely inhibited. Naptalam, dalapon and 2,4-D did not affect growth of maize under similar conditions, and of these only 2,4-D reduced growth of pea. Zone d'abiorption des tiges pour les herbicides appliqués sur h sol     

SITE OF UPTAKE OF SOIL-APPLIED HERBICIDES*

Summary. We conducted studies to determine the effects on corn (Zea mays L, var. Indiana 654) and pea (Pisum sativum L. var. Alaska) of localizing various herbicides in the soil, using a double plastic pot technique which ensured separate exposure of the root and shoot zones of the plants to treated soil. Effects on corn and pea were similar in relation to site of uptake. 2,4-D-amine, naptalam, simazine, diuron and dalapon-sodium entered primarily through the roots. Some shoot entry and also severe inhibition of roots occurred in soil treated with 2,4-D and naptalam; these were noticed only to a slight extent with the other three herbicides. EPTC, chlorpropham and trifluraiin were most effective when applied to the shoot zone. Little effect on foliage growth was evident when the root zone alone was treated. However, roots in treated soil were severely inhibited by these three herbicides. Dinoseb displayed a contact type of action, injuring both shoots and roots. Treatment of both zones had an additive effect. Entry of chlorthal-methyl which was tested on a susceptible species, sorghum (Sorghum vulgare Pers.) was mainly through the shoot, with only a slight effect on top growth when roots alone were treated. Roots in treated soil were slightly inhibited. Localisation de l'absorption des herbicides appliqués sur le sol     

Studies on the rate of root growth of intact seedlings in a herbicide medium

Time-lapse cine photography was used to measure at 10-min intervals over 72 h the growth rate of pea and barley roots during separate exposure of the shoot + seed, root or entire seedling to eight herbicides. Times for commencement of root inhibition were determined at exposure to concentrations causing 50 % inhibition in 72 h. Root growth rate was normal in both species during shoot + seed treatment. Root inhibition commenced at the same time in a given species, when only the root or the entire seedling were treated with a particular herbicide. Except for dinoseb, times for commencement of root inhibition differed between pea and barley and between each herbicide. In pea these times ranged from 125 h with diuron to 23–7 h with diphenamid, and in barley from tl-1 h with diphenamid to 21–3 h with EPTC. Root growth ceased in only a few cases during the experimental period. EPTC, diphenamid, dinoseb, and trifluralin (on barley only) effectively inhibited root elongation, whereas diuron, simazine, paraquat, dalapon, and trifluralin (on pea only) had no direct effect on root growth at normal field rates of application. Etudes sur le taux de croissance des racines de plantules intactes dans un milieu herbicide Le cinéma avec prise de vue image par image, à des intervalles de 10 minutes, a été utilisé pour mesurer, pendant 72 heures, le taux de croissance des racines de pois et d'orge, soumises à l'action de huit herbicides, en traitant séparément soit l'ensemble pousse + semence, soit la racine, soit la plantule entière. On a déterminé les durées d'apparition de l'inhibition des racines, en utilisant des concentrations provoquant 50% d'inhibition en 72 heures. Le taux de croissance des racines fut normal chez les deux espèces pendant le traitement pousse + semence. L'inhibition des racines commença au méme moment chez une espèce donnée lorsque les racines seules ou la plante entière furent traitées avec un herbicide particulier. Les durées d'apparition de l'inhibition furent diffréntes pour le pois et pour l'orge et selon l'herbicide. Pour le pois, ces durées se situèrent entre 12,5 heures avec le diuron et 23,7 heures avec le diphénamide; pour l'orge, les durées furent comprises entre 11,1 heures avec le diphénamide et 21,3 heures pour l'EPTC. La croissance des racines ne cessa, durant la période expérimentale, que dans un petit nombre de cas. L'EPTC, le diphénamide, le dinosébe et la trifluraline inhibérent efficacement l'élongation des racines chez l'orge seulement, cependant que le diuron, la simazine, le paraquat, le dalapon et la trifiuraline n'eurent pas d'effet direct, chez le pois seulement, sur la croissance des racines aux doses normales d'appiication. Untersuchungen über das Wurzelwachstum von Keimpflanzen in einem Herbizidmedium Das Wachstum von Erbsen- und Gerstenwurzeln wurde über 72 Stunden in Abständen von 10 Minuten mit Hilfe der Zeitrafferphotographie gemessen, wobei jeweils Spross + Same, die Wurzel, Oder die ganze Keimpflanze, acht Herbi-ziden ausgesetzt war. Es wurde die Zeit bestimmt, die für eine 50%ige Hemmung des Wurzelwachstums während der 72 Stunden nötig war. Das Wurzelwachstum war bei Spross + Samen-Behandlung bei beiden Arten normal. Wenn nur die Wurzel oder die ganze Pflanze mit einem bestimmten Herbizid behandelt wurden, begann bei der jeweiligen Pflanzenart die Hemmung des Wurzelwachstums zur selben Zeit. Mit Ausnahme von Dinoseb, war der Zeitpunkt der Wurzelhemmung sowohl zwischen Erbse und Gerste und dem jeweiligen Herbizid unterschiedlich. Bei der Erbse bewegten sich diese Zeiten zwischen 12,5 Stunden mit Diuron bis 23,8 Stunden mit Diphenamid und bei der Gerste von 11.1 Stunden mit Diphenamid bis 21,3 Stunden mit EPTC. Nur in einigen wenigen Fällen hörte das Wurzelwachstum während des Versuchszeitraums auf. EPTC, Diphenamid, Dinoseb und Trifluralin (nur bei der Gerste) hemmten wirksam das Längenwachstum der Wurzeln, wogegen Diuron, Simazin, Paraquat, Dalapon und Trifluralin (nur bei der Erbse) keine direkte Wirkung auf das Wurzelwachstum bei normalen im Feld angewandten Aufwandmengen hatten.     

THE BASIS OF THE DIFFERENTIAL PHYTOTOXICITY OF 4-HYDROXY-3,5-DI-IODOBENZONITRILE*

Summary. Retention of the spray solution was shown to be a major factor in the selectivity of ioxynil. Retention was high on mustard plants with or without surfactant(Tween 20). Very little ioxynil was retained by barley and pea plants when no surfactant was included in the spray hut inclusion of 0.1 or 1.0% Tween 20 increased retention. With 1.0% the retention on pea plants approached that on mustard, and there was then little differential toxicity. With no surfactant in the spray, mustard plants retained twenty-six times more ioxynil than barley plants. Addition of 01 or 1.0% surfactant increased retention by barley and reduced the differential to eleven times and eight times respectively. By varying the angle of barley leaves to the spray it was shown that the normal upright position results in reduced interception of a vertical spray and reflection of the drops without surfactant. It was concluded that for a given species growth reduction by ioxynil is largely conditioned by the amount retained and that apart from influencing retention, Tween 20 has no major independent action. At equivalent retention levels barley was much less susceptible than mustard or pea. Plants of mustard, pea and barley were treated either on the leaves only or over the whole exposed surface of the plant lo assess the influence of morphology on the response to ioxynil. There was no difference in the response of barley, but treatment by dipping aerial shoots of mustard and pea produced an effect twice that from treatment of the leaves alone at the same level of retention. The increased response of mustard and pea to whole shoot treatment is considered to be due primarily to the exposed stem and bud tissues of these species. Les bases de la toxicilé différentielle du 4-hydroxy-3,5-di-iodobenzomtrite I. Infiuence de la rétention de la bouillie et de la morphologie de la plante     

Uptake patterns of soil-applied 45Ca and 32P in some legume species as influenced by differential trifluralin placement

The effect of localized placement of trifluralin on uptake patterns of soil-applied ⁴⁵Ca in vetch (Vicia sativa L.), pea (Pisum sativum L.) and soybean (Glycine max) and ³²P in vetch and pea was investigated in two soil zones in the roots and in the shoot zone before and after plant emergence. When trifluralin was in the upper root zone severe inhibition of lateral roots occurred as well as a marked decrease in uptake of ⁴⁵Ca and ³²P from this zone. Root growth in the lower zone was unaffected, but uptake of ⁴⁵Ca and ³²P was slightly reduced. Compensatory adventitious root growth as well as a marked increase in uptake of ⁴⁵Ca and ³²P occurred in the shoot zone. Neither root growth nor uptake of ⁴⁵Ca or ³²P in the upper root zone were affected by the presence of trifluralin in the lower root region. When trifluralin was placed in the shoot zone after plant emergence, adven-titious roots on the shoots were inhibited and uptake of ⁴⁵Ca and ³²P was reduced.     

EFFECT OF TEMPERATURE ON THE ACTIVITY AND PERSISTENCE OF AMITROLE AND 2,4-D

Summary. One leaf of each of several tomato plants 5–6 weeks old maintained at 55, 70 or 85° F was dipped in 0.05 M amitrole or 0.005 M 2,4-D solution. The treated leaf was removed 1 week later. Scions taken from untreated plants were grafted to the treated plants at intervals up to 4 months after treatment.
Amitrole-treated plants maintained at 55° F were killed within 1 month but those at 70 and 85° F recovered.
Plants treated with 2,4-D showed typical symptoms when maintained at 70 and 85° F but no symptoms at 55° F. Scions grafted on plants maintained at 55, 70 and 85° F for 60 days after 2,4-D treatments exhibited typical symptoms. Grafts made more than 60 days following the 2,4-D application did not exhibit symptoms except a slight malformation on the plants held at 55° F.
New growth on the scions grafted up to 103 days after amitrole treatment on plants which had been maintained at 70 and 85° F exhibited typical amitrole symptoms (i.e. white foliage) but scions grafted after this lime did not. New shoots developing from buds on the treated plants also produced green growth 115 days after treatment but produced white foliage prior to that time.
Effet de la température sur l'activi'ité et la persistance de l'aminotriazole et du 2,4-D     

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.     

SELECTIVE ACTION OF DIPHENAMID AND NAPROPAMIDE IN PEPPER (GAPSICUM ANNUUM L.) AND WEEDS

Summary. A comparison was made between diphenamid and napropamide with regard to phytotoxicity to pepper and weeds under glasshouse and field conditions. Diphenamid was considerably less phytotoxic than napropamide in inhibiting root elongation and shoot growth of pepper seedlings. Plant growth was reduced when the roots were exposed to either one of the herbicides, but growth of the shoot through treated soil was not adversely affected. Since diphenamid was found to be more leachable into soil, it might become more available to the roots and damage the crop plants. Graminaceous weeds were very sensitive to both herbicides, whereas several dicotyledonous weeds were more susceptible to napropamide. Selectivity of both herbicides at a late pre-emergence application to direct-seeded pepper was found satisfactory in two field experiments on different soil types.
Action sélective de la diphénamide et de la napropamide sur le piment et les mauvaises herbes     

EFFECT OF GROWTH REGULATORS AND HERBICIDES ON NORMAL AND WOUND PERIDERM ONTOGENY IN FRAXINUS PENNSYLVANICA SEEDLINGS*

Summary. IAA, GA, kinetin, 2,4-D and naptalam were applied at 100 or 1000 ppm in lanolin to wounds made at the top of the hypocotyl of Fraxinus pennsylvanica Marsh. seedlings. Formation of normal periderm was prevented in the hypocotyl below the wounded tissue by 1000 ppm IAA or naptalam and 100 or 1000 ppm 2,4-D. IAA or naptalam at 100 ppm and GA or kinetin at 100 or 1000 ppm retarded normal periderm development. Wound periderm development was prevented only by 1000 ppm 2,4-D. Wound-stimulated development of normal periderm in tissues near the wound was prevented by 1000 ppm kinetin and 100 or 1000 ppm 2,4-D. Anomalous growths which appeared morphologically similar to nascent roots developed in the wounded hypocotyl section of seedlings treated with 1000 ppm naptalam and 100 or 1000 ppm 2,4-D. Identical growths were found in unwounded portions of the hypocotyl of seedlings treated with 100 or 1000 ppm 2,4-D. The data emphasize differences in physiological control of normal and wound periderm development. Effets de substances de croissance et d'herbicides sur l'onlogénie du pérderme normal ou blessé dans des plantules de Fraxinus pennsylvanica.     

The influence of plant age on the movement of 2,4-D and assimilates in wheat

A quantitative study of the movement of 2,4-D and assimilates was made using radiocarbon-labelled materials. At the two-three leaf stage of wheat (cv Koga II) 2,4-D moved more slowly than assimilates, but the patterns of movement were very similar. At the five-six leaf stage of the cereal there were differences between 2,4-D and assimilates in the patterns of distribution from leaf 1 and from a leaf on a tiller. In both cases relatively less 2,4-D moved into roots than would have been predicted from knowledge of assimilate movement. Total amounts of 2,4-D reaching the roots did not differ significantly between growth stages but due to root growth, the concentration of radio-activity in the roots fell.     

THE EFFECT OF POST-EMERGENCE HERBICIDES ON THE VEGETATIVE AND REPRODUCTIVE GROWTH OF CENTROSEMA FUBESCENS BENTH. IN QUEENSLAND

Summary. 2,4-D-amine, 2,4-D ethyl ester, 2.4-DB-potassium. MCPA-sodium, diquat and a 1:1 mixture of 2,4,5-T butyl ester and 2,4-D ethyl ester were applied to the tropical pasture legume Centrosema pubescens Benth. (centro) grown either alone or with Panicum maximum Jacq. (guinea grass). Even at 0.5 Ib/ac (total) the 2,4,5-T/2,4-D mixture caused severe damage to seedling and mature centro. 2,4-D-amine, 2,4-D ethyl ester and 2,4-DB-potassium were less damaging and there were only slight differences in response to these. Diquat at 0.25 Ib/ac desiccated centro seedlings, but most plants survived and grew satisfactorily. There was some evidence that the growth of mature centro was depressed least when the herbicides were applied during vegetative quiescence.
Application just after the start of flowering altered the flowering pattern but did not reduce seed yields significantly. 2,4-D-amine at 0.75 and 1–5 lb/ac and 2,4-D ethyl ester at 1.5 Ib/ac decreased the percentage germination of abraded seed. Diquat 0.25 Ib/ac applied at the start of flowering caused significant increases in top growth and seed pod numbers, possibly the result of modification of the normal flowering pattern.     

THE MOVEMENT OF LABELLED 2,4-D IN YOUNG BARLEY PLANTS

Summary. After the 4- or 5-leaf stage in young barley plants, there is a decrease in the translocation of 2,4-D from the leaves to the root system. It is shown that there is no relation between this phenomenon and ear initiation, which occurs at this stage of development. Movement of 2,4-D out of leaves of the tiller in the axils of the 1st and 2nd leaves was also shown to be very small. There is some evidence for a'block'in the movement of 2,4-D in established grass plants.
La migration du 2,4-D marqué dans l'orge     

THE EFFECTS OF BENSULIDE ON THE GROWTH, MORPHOLOGY AND ANATOMY OF OAT ROOTS

Summary. Oat seedlings were grown by two different methods in various concentrations of bensulide. Root growth was inhibited, the roots were sometimes curved and root hairs were often present close to the root tip. Structural features of the treated roots included epidermal cells which were greatly elongated radially; short, pitied trachcary elements differentiated close to the root tip; and occasional lesions. One of the primary effects of bensulide appears to be inhibition of root growth, though it does not completely inhibit mitosis.     

CONTROL OF REGENERATION IN ROOTS OF THE DEEP-ROOTED WEED CHONDRILLA JUNCEA L.

Summary. A system was developed for testing the ability of herbicides applied to the shoots of the deep-rooted weed Chondrilla juncea to inhibit the regeneration of buds on serial sections along the root. Auxin herbicides known to inhibit regeneration when applied directly to root sections and with a potential for translocation or slow metabolic conversion to an active auxin were selected for testing. The most effective herbicides tested were picloram, N -(diethylaminomethyl)-2,4-dichlorophenoxyacetamide and 2,4-dichlorophenoxy-acet- O -methylhydroxamic acid. Each compound reduced bud formation along 40 cm of root. The inhibition of regeneration by the sodium salt of 2,4-D was decreased at temperatures above 25°C. The growth retardants chlormequat chloride, chlorphonium chloride and B-995 were tested as inhibitors of regenerated-bud growth and emergence when applied to shoots; only B-955 was inhibitory. Amitrole and tris-(laziridinyl) phosphine oxide inhibited bud formation and growth.
Suppression de la régénération par les racines de Chondrilla juncea L., mauvaise herbe à encrainement profond.     

STUDIEN ZUR VERTEILUNG VON 14C-MARKIERTEM 2,4-D IN VERSCHIEDEN EMPFINDLICHEN UNKRÄUTERN

Studies of the absorption and translocation of ¹⁴C-2,4-D in Chenopodium album L., Galinsoga parviflora Cav., Datura stramonium L. and Galium aparine L. in relation to their susceptibility gave the following results: In G aparine (resistant) there was little transport of 2,4-D applied to the leaves, and a probable relationship between resistance and the immediate binding of the 2,4-D in the treated leaf. D. stramonium (relatively resistant) transported 2,4-D in considerable amounts alter uptake through the leaf, while C. album (very susceptible) and G. parviflora (susceptible) were intermediate in respect of 2,4-D translocation. No relationship between susceptibility of these four species and 2,4-D uptake and translocation from the leaves could be established. After application to the root systems of the four species, 2,4-D was taken up and translocated in the shoot to varying extents. In G. aparine much 2,4-D was taken up and translocated. In contrast to leaf application, the herbicide was not immediately converted into a strongly-held immobile form. In C. album, G. parviflora and D. stramonium, however, no 2,4-D was translocated in the shoot. There was thus no correlation between susceptibility and shoot transport of 2,4-D in the four species studied. Distribution du 2,4-D marqué au ¹⁴C dans des espèces de mauvaises herbes présentant des sensibilités diverses     

Absorption and fate of imazapyr in leafy spurge (Euphorbia esula)

Imazapyr absorption, translocation, root release and metabolism were examined in leafy spurge (Euphorbia esula L.). Leafy spurge plants were propagated from root cuttings and [¹⁴C]imazapyr was applied to growth-chambergrown plants in a water + 28% urea ammonium nitrate + nonionic surfactant solution (98.75 + 1 + 0.25 by volume). Plants were harvested two and eight days after herbicide treatment (DAT) and divided into: treated leaf, stem and leaves above treated leaf, stem and leaves below the treated leaf, crown, root, dormant and elongated adventitious shoot buds. Imazapyr absorption increased from 62.5% 2 DAT to 80.0% 8 DAT. Herbicide translocation out of the treated leaf and accumulation in roots and adventitious shoot buds was apparent 2 DAT. By the end of the eight-day translocation period only 14% of applied ¹⁴C remained in the treated leaf, while 17% had translocated into the root system. Elongated and dormant adventitious shoot buds accumulated 3.2- and 1.8-fold more ¹⁴C, respectively, 8 DAT than did root tissue based on Bq g^?1 dry weight. Root release of ¹⁴C was evident 2 DAT, and by 8 DAT 19.4% of the ¹⁴C reaching the root system was released into the rooting medium. There was no metabolism of imazapyr in crown, root or adventitious shoot buds 2 DAT; however, imazapyr metabolism was evident in the treated leaf 2 and 8 DAT. Imazapyr phytotoxicity to leafy spurge appears to result from high imazapyr absorption, translocation to underground meristematic areas (roots and adventitious shoot buds), and a slow rate of metabolism.     

EFFECT OF 2,4-D AND PICLORAM ON TRANSLOCATION OF 14C-ASSIMILATES IN VITIS VINIEERA L.

Summary. High concentrations of 2,4-D and picloram interfered with the downward movement of ¹⁴c-assimilates infield-grown vines. The interference in translocation was appreciably greater with picloram than it was with 2,4-D, Although basipetal translocation was retarded, translocation within the treated shoots continued from the vegetative part to the clusters. Translocation of 2,4-D appeared to follow the same route as ¹⁴c-assimilatcs for the most part. Formative effects were absent on untreated grape shoots although the adjacent shoots treated with 2,4-D or picloram on the same cordons were killed; however, formative effects were evident on some of the stump sprouts which developed after the vines were harvested. The malformed leaves on the stump sprouts were twelve or more nodes from the base of the shoots, while ¹⁴c was in the more basal leaves.
Thompson Seedless (Sultanina) rootings treated with 20 000 ppm 2,4-D or picloram transported less ¹⁴C to the roots than did the controls. Treatment with either herbicide resulted in a marked increase in the labelling of the stems.
Effet du 2,4-D et du pichlorame sur la migration de métabolites marqués au ¹⁴C dans Vitis vinifera L.     

Allelopathic potential of wild onion (Asphodelus tenuifolius) on the germination and seedling growth of chickpea (Cicer arietinum)

Water extracts obtained from the roots, shoots, and fruits of mature wild onion ( Asphodelus tenuifolius ) plants and soil taken from an A. tenuifolius field were used to determine their allelopathic effects on the germination and seedling growth of chickpea ( Cicer arietinum ) in the laboratory. The roots, shoots, and fruits of A. tenuifolius were soaked individually in water in a ratio of 1:20 (w/v) for 24 h to prepare the extracts. Distilled water was used as the control. The germinated seeds were taken out from the Petri dishes and counted every day for 12 days. The seeds of chickpea were also sown in sand and in each of the controlled, normal soil and the soil taken from the A. tenuifolius -infested field in Petri dishes to record the length and weight of the roots and shoots 18 days after sowing. The mean germination time reached the maximum amount for the stem and fruit extracts. The fruit extract caused the most reduction in the germination index and the germination percentage of chickpea. The different wild onion organ extracts significantly reduced the root and shoot length and biomass of the chickpea seedlings compared with the distilled water. The fruit extract of wild onion proved to be the most detrimental to the root length, shoot length, and dry weight of the chickpea seedlings. The soil beneath the A. tenuifolius plants significantly reduced the emergence, root length, shoot length, shoot dry weight, and seedling dry weight but increased the root dry weight of the chickpea seedlings. It is suggested that A. tenuifolius releases phytotoxic compound(s).     

STUDIES ON HERBICIDE CONTENTS IN ROOTS OF SKELETON WEED (CHONDRILLA JUNCEA L.) FOLLOWING LEAF APPLICATIONS

Summary. The herbicides studied were 2,4-D, 2,4-DB, dicamba and orthoarsenic acid. Herbicide content in the roots was taken as an overall measure of penetration into and absorption by the leaves, and of translocation to the roots.
A significantly greater 2,4-D content resulted from foliar application at pH 3–5 than at higher values, though at pH 8–5 the inclusion of triethanolamine significantly increased the 2,4-D content. No evidence was obtained that a greater 2,4-D content should result from foliage applications of 2,4-DB than from 2,4-D. Dicamba gave a greater herbicide content than 2,4-D when applied at high concentration at 20° C but not at 25° C, probably because of less injury at the lower temperature.
Concentrations of Tween 20 up to 2% had no deleterious effect on the 2,4-D content; on the other hand 2,4-D content was lowered by 0–25% or more of cetyltrimethyl-ammonium bromide. Poor wetting is not the cause of the variable herbicide contents sometimes obtained.
Orthoarsenic acid, which has given better control of the weed than 2,4-D, was very poorly translocated; its effectiveness is due to its high intrinsic toxicity.
Etudes sur la teneur en herbicide des racines de Chondrilla juncea L. á la suite d'applications sur les feuilles     

CONTROL OF SONCHUS ARVENSIS (L.) WITH CHEMICALS

Summary. Pot experiments concerning the control of Sonchus arvensis with chemicals showed that the time of application of MCPA or 2,4-D has a dominant influence on the results obtained. Foliage applications at late rosette to early bud stage gave considerably better effects than did earlier or later applications as assessed by the. weight of roots, this assessment being considered the most reliable for final effects. Increasing the rates from 1 to 3 kg/ha was of less significance than the time of application. A good wetting ability of the spray solution is also essential for an effective control of this weed, which has very waxy leaves. The addition of a wetting agent to aqueous solutions of various salts of 2,4-D had a great and significant influence on the effects. This was not the case with 2,4-D acid in Carbowax. When wetter was added, there was no difference in the effects of the sodium, ammonium and triethanolamine salts. The latter were also slightly more effective than MCPA. 2,4-D-ester was much more effective than MCPA by foliage application. When the chemicals were applied to the roots through sub-irrigation pipes, however, MCPA was at least as effective as 2,4-D-ester. The maximum effect by this method of application was obtained at a somewhat later stage of development than by foliage application. By foliage application of MCPA and dinoseb or DNOC at various rates used alone or in mixture, an antagonism between the growth regulator and the contact herbicides was demonstrated as regards the reduction in root weight of S. arvensis . The scorching effects of dinitro compounds were, on the contrary, increased when applied in combination with MCPA. Amitrole at rates of 5, 7.5 and 10 kg/ha applied at late rosette stage gave a complete kill of S. arvensis.
La destruction du Sonchus arvensis L. à l'aide de produits chimiques