Effects of various classes of herbicides on four species of algae

Chlorella pyrenoidosa, Chlorococcum sp., Lyngbya sp., and Anabaena variabilis were cultured in Bold's basal medium. They were treated with 0.1, 1.0, and 10 μM concentrations of 2-chloro-2′, 6′-diethyl-N-(methoxymethyl)acetanilide (alachlor), 2-chloro-4-(ethylamino)-6-(tert-butyl-amino)-s-triazine (terbuthylazine), 2-sec-butyl-4,6-dinitrophenol (dinoseb), 1,1-dimethyl-3-(α,α,α-trifluoro-2,6-dinitro-N-propyl-p-toluidine) (profluralin), 2, 4-bis(isopropylamino)-6-(methylthio)-s-triazine (prometryne), and (2,4-dichlorophenoxy)acetic acid (2,4-D). Growth of all algal species tested was markedly reduced by the triazines. Alachlor, dinoseb, and fluometuron inhibited growth of some algae at higher concentrations while 2,4-D and profluralin did not inhibit growth at the concentrations tested. Photosynthesis was greatly inhibited by the triazines, even at the 0.1 μM concentration. Fluometuron was very toxic to the blue-green algae but had less effect on the green algae tested. Lyngbya was most susceptible to photosynthesis reduction by the herbicides. The concentrations of herbicides tested had little effect on respiration of the algae species. It appears that effects on algal growth were due primarily to inhibition of photosynthesis rather than to other metabolic processes.     

Triazine absorption by excised corn root tissue and isolated corn root protoplasts

Absorption of four triazine herbicide analogs [ametryn (2-(ethylamino)-4-(isopropylamino)-6-(methylthio)-s-triazine), atrazine (2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine), atratone (2-methoxy-4-(ethylamino)-6-(isopropylamino)-s-triazine), and hydroxyatrazine (2-hydroxy-4-(ethylamino)-6-(isopropylamino)-s-triazine)] was compared using excised corn (Zea mays L.) root segments and isolated corn root protoplasts. The tissue absorbed ametryn, atrazine, and atratone for only 20 min. Ametryn and atrazine permeated tissue to passive equilibrium with the ambient solution in 10 min. Atratone permeated to 65 and 82% of passive equilibrium in 10 and 30 min, respectively. In contrast, hydroxyatrazine concentration in tissue was only 15 and 70% of the ambient concentration at 30 min and 24 hr, respectively. However, hydroxyatrazine permeated frozen/thawed tissue to 90% of passive equilibrium in 10 min. Protoplast absorption of ametryn and atratone was complete in 10 sec; hydroxyatrazine absorption by protoplasts did not reach a plateau until 5 min. Protoplasts absorbed the triazines to greater than passive equilibrium. Three kinetically homogeneous pools were detected for ametryn, atrazine, and atratone, whereas elution of hydroxyatrazine produced four pools. The three pools for atrazine were confounded by metabolism of atrazine to hydroxyatrazine. Pools for the triazines could not be identified as the free space, cytoplasm, and vacuole as proposed previously for mineral ions. Although the plasma membrane impeded diffusion of hydroxyatrazine, all analogs penetrated into the symplast.     

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.     

N-Dealkylation of atrazine and simazine in Senecio vulgaris biotypes: A major degradation pathway

Separate populations of Senecio vulgaris were found that evolved partial tolerance to s-triazine herbicides and others that were totally resistant (plastid resistance). In plants from the susceptible, tolerant, and resistant populations, about one half of applied [¹⁴C]atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) was rapidly N-dealkylated to the des-ethyl and des-isopropyl products. These products were relatively inactive in inhibiting photosystem II and did not compete with atrazine. After 6 days, less than 25% of the applied [¹⁴C]atrazine was metabolized to water-soluble degradation products but they were not 2-hydroxy derivatives. Less than 2% of the applied atrazine was incorporated into methanol-insoluble residues. The results on metabolism do not explain the tolerance of Senecio to atrazine. However, our results show that N-dealkylation of the s-triazines is more active than previously reported.     

Root exudation of prometryn and its metabolites from Chinese celery (Apium graveolens)

Root exudates from Chinese celery (Apium graveolens) and Chinese cabbage (pak choi, Brassica chinensis) plants treated by prometryn, an herbicide, were qualitatively and quantitatively investigated and compared under hydroponic cultivation. Prometryn and its metabolites released into the nutrient solution were analyzed by ultra-performance liquid chromatograph coupled with orbitrap mass spectrometer to investigate whether this xylem-mobile herbicide is exuded from the roots. The results showed that celery and pak choi had different root exudation profiles. Celery metabolized prometryn to prometryn sulfoxide and released both compounds from the roots. In contrast, pak choi barely metabolized or actively released prometryn from the roots. The concentration of prometryn sulfoxide released from celery after 96 hr was 21 µg/L, which was nearly one-third that of released prometryn. Our results indicate that the root exudation and translocation of xylem-mobile herbicides could be significant in plants and are highly species dependent compared with phloem-mobile herbicides.     

Metribuzin metabolism in tomato: Isolation and identification of N-glucoside conjugates

Metribuzin [4-amino-6-tert-butyl-3-(methylthio)-1,2,4-triazin-5(4H)-one] metabolism was studied in tomato (Lycopersicon esculentum Mill. “Sheyenne”). Pulse-treatment studies with seedlings and excised leaves showed that [5-¹⁴C]metribuzin was rapidly absorbed, translocated (acropetal), and metabolized to more polar products. Foliar tissues of 19-day-old seedlings metabolized 96% of the root-absorbed [¹⁴C]metribuzin in 120 hr. Excised mature leaves metabolized 85–90% of the petiole-absorbed [¹⁴C]metrubuzin in 48 hr. Polar metabolites were isolated by solvent partitioning, and purified by adsorption, thin-layer, and high-performance liquid chromatography. A minor intermediate metabolite (I) was identified as the polar β-d-(N-glucoside) conjugate of metribuzin. The biosynthesis of (I) was demonstrated with a partially purified UDP-glucose: metribuzin N-glucosyltransferase from tomato leaves. A possible correlation between foliar UDP-glucose: metribuzin N-glucosyltransferase activity levels and differences in the tolerance of selected tomato seedling cultivars to metribuzin was suggested. The major polar metabolite (II) was identified as the malonyl β-d-(N-glucoside) conjugate of metribuzin.     

Comparative metabolism of atrazine and EPTC in proso millet (Panicum miliaceum L.) and corn

The purpose of this study was to examine the differential activities of proso millet (Panicum miliaceum L.) and corn (Zea mays L.) with respect to atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-S-triazine] and EPTC (S-ethyldipropyl thiocarbamate) metabolism. GSH-S-transferase was isolated from proso millet shoots and roots. When assayed spectrophotometrically using CDNB (1-chloro 2,4-dinitrobenzene) as a substrate, the shoot enzyme had only 10% of the activity of corn shoot enzyme while the root enzyme had 33% the activity of corn root enzyme. However, when proso millet shoot GSH-S-transferase was assayed in vitro using ¹⁴C-ring-labeled atrazine, it degraded the atrazine to water-soluble products at the same rate as the corn shoot enzyme. Incubation of excised proso millet and corn roots with [¹⁴C]EPTC indicated that uptake of EPTC was similar in both plants. However, proso millet metabolized the EPTC to water-soluble products at only half the rate of corn. Glutathione levels of proso millet roots were 35.9 μg GSH/g fresh wt, compared with 65.4 μg GSH/g fresh wt for corn. However, a 2.5-day pretreatment with R-25788 (N,N-diallyl-2-2-dichloroacetamide) elevated proso millet GSH levels to 62.7 μg GSH/g fresh wt. R-25788 did not elevate the activity of proso millet GSH-S-transferase, in contrast to its effects on corn. We conclude that differences in response to atrazine and EPTC in proso millet and corn are a result of their differential metabolism.     

Extended terbutryn persistence and herbicidal activity effected by superphosphate fertilizer

Microorganisms play a major role in the degradation and detoxification of most soilapplied pesticides. Any interference with soil microbial activity may affect the persistence as well as the effectiveness of the pesticide. The objective of this study was to investigate the effect of granulated superphosphate fertilizers on terbutryn (2-(tert-butylamino)-4-(ethylamino)-6-(methylthio)-l,3,5-triazine) degradation and on its herbicidal activity. Concentrations exceeding 1% of superphosphate in the soil slowed down terbutryn degradation; a concentration of 3% completely inhibited terbutryn degradation for nearly 60 days. When terbutryn was impregnated on the surface of superphosphate granules, the concentration of the fertilizer that inhibited terbutryn degradation was reduced from 3% to 0.1%. Bioassays with mustard seedlings confirmed the results obtained by chemical analysis of terbutryn. The decrease in the rate of terbutryn degradation was not specific to superphosphate. The inhibition of degradation could be attributed mainly to the concentration of the salt in the soil solution, expressed as electrical conductivity values, and not to the pH of the soil or to the type of the salt. Terbutryn was found to be quite stable on the surface of the superphosphate granule. At the concentrations tested, superphosphate did not affect root growth. The optimal weight of the impregnated granule for extending terbutryn activity was 125 mg, containing 0.2% terbutryn. A greenhouse experiment confirmed the findings that fertilizers could serve as potential inhibitors of terbutryn degradation.     

Uptake and translocation of [14C]asulam and [14C]bromacil by roots of maize and bean plants

The uptake and translocation of ¹⁴C-ring-labeled asulam (methylsulfanilcarbamate) and bromacil (5-bromo-3-sec-butyl-6-methyluracil), were compared after root application to maize (Zea mays L.) and bean (Phaseolus vulgaris L.). Autoradiographs showed the distribution of bromacil throughout these and other plant species, and the retention of asulam in the roots. The recovery of both compounds in quantitative radioassays was between 90 and 100%. The absorption of bromacil and asulam was rather similar. Absorption of bromacil increased up to 20% of the applied dose in bean plants after 2 days of exposure, and up to 11% in maize plants after 4 days. Absorption of asulam in bean plants was 22% of the applied dose after 2 days, and 8% in maize plants after 4 days. The pattern of distribution of bromacil and asulam was completely different. After 4 h of exposure of the roots about half of the absorbed bromacil had accumulated in the shoots, while two-thirds or more was translocated to the shoots after exposure periods of 1 to 4 days. Not more than one-eighth of the absorbed asulam was found in the shoots. In consequence, the bromacil content in the transpiration stream relative to that in the ambient solution was much higher than that of asulam. The leakage of asulam from bean and maize roots into herbicide-free nutrient solution was lower than that of bromacil. The reasons for these differences are not yet clear. There was only some metabolism of asulam in maize, but not in bean plants. No metabolites of bromacil were detected in the two plant species.     

Effects of chloroacetamides and phytosynthesis-inhibiting herbicides on growth and photosynthesis in sunflower (Helianthus animus L.) and Amaranthus hybridus L.

The effects of the chloroacetamide herbicides acetochlor, alachlor and propachlor and the pho-tosynthesis-inhibiting herbicides linuron, prometryn and terbutryn on sunflower (Helianthus annuus L.) and atrazine-sensitive and -resistant Amaranthus hybridus L. biotypes were investigated under laboratory conditions. Sunflower tolerated all three chloroacetamides in pre-emergence applications of 1.5–5.0 kg a.i. ha^?1 in growth assays. Sunflower also survived doses of 0.5–1.0 kg a.i. ha^?1 of linuron, prometryn and terbutryn, although growth reduction and chlorosis of treated plants was observed. These three herbicides inhibited photosynthetic electron transport in in vitro Hill reaction and fluorescence assays and, with terbutryn, photosynthesis recovered upon transfer of the leaves from herbicide solutions to water. The practical significance of these results for the control of weeds in sunflower cultivation in Spain are discussed. Effets d'herbicides chloroacétamides et d'herbi-cides inhibiteurs de la photosynthèse sur la crois-sance et la photosynthèse du tournesol (Helianthus annuus L.) et de Amaranthus hybridus L. Les effets des herbicides chloroacétamides acétochlor, alachlor et propachlor ainsi que des herbicides inhibiteurs de la photosynthèse linuron, prometryne et terbutryne, ont étéétudiés sur le tournesol (Helianthus annuus L.) et sur des biotypes sensibles et résistants d'Amaranthus hybridus L. en conditions de laboratoire. La croissance du tournesol n'était affectée par au-cun des trois chloroacétamides appliqués en prélevée (1,5–5,0 kg m.a. ha^?1). Le linuron, la terbutryne et la prometryne (0,5–1,0 kg m.a. ha^?1) occasionnaient des réductions de croissance et des chloroses sur le tournesol mais les plantes survivaient. Ces trois herbicides in-hibaient le transport d'électrons photosyn-thétique observé par des mesures de fluorescence et, in vitro par la réaction de Hill. Dans le cas de la terbutryne, la photosynthèse reprenait après transfert des feuilles des solutions d'herbicides dans 1'eau. La signification pratique de ces résultats pour la lutte contre les mauvaises herbes du tournesol en Espagne est discutée. Wirkung von Chloracetamiden und Photosyn-these-hemmenden Herbiziden auf Wachstum und Photosynthese der Sonnenblume (Helianthus annuus L.) und Amaranthus hybridus L. Die Wirkung der Chloracetamid-Herbizide Acetochlor, Alachlor und Propachlor und der Photosynthese-hemmenden Herbizide Linuron, Prometryn und Terbutryn auf die Sonnenblume (Helianthus annuus L.) und Atrazin-empfindliche sowie-unempfindl Amaranthus-hybridus-Biotypen wurde unter Laborbedin-gungen untersucht. In Wachstumstests tolerierte die Sonnenblume alle 3 Chloracetamide bei Vorauflaufanwendung von 1,5 bis 5,0 kg AS ha^?1. Auch Dosen von 0,5 bis 1,0 kg AS ha^?1 von Linuron, Prometryn und Terbutryn wurden vertragen, aber der Wuchs war beeinträchtig, und Chlorosen wurden beobachtet. Diese 3 Herbizide hemmten den photosynthetischen Elektronentransport bei Versuchen zur Invitro-Hill-Reaktion und Fluoreszenz, und bei Terbutryn stellte sich die Photosynthese nach Überführen der Blätter von der Herbizidlösung auf Wasser wieder ein. Die praktische Bedeutung dieser Ergebnisse für die Unkrautbekämpfung in Sonnenblumenkulturen in Spanien wird diskutiert.     

Potassium uptake in atrazine-treated roots of sensitive and resistan plants

The action of atrazine and its biodegradation products on the membrane transport of potassium in roots was evaluated in both sensitive and resistant plants. Excised roots of maize and oat showed inhibition of potassium uptake efficiency in the presence of 1.4 × 10^?4M atrazine and 1.4 × 10^?4M deethylated atrazine. Other biodegradation products such as 2-chloro-4-amino-6-ethylamino-1,3,5-triazine,2-chloro-4,6-,bisamino-1,3,5-triazine, and 2-chloro-4-amino-1,3,5-triazine showed no inhibitory effect on the K⁺ uptake capacity. Two maize hybrids showing different uptake efficiency were inhibited differently by atrazine. We suggest that atrazine and deethylated atrazine inhibited the K⁺ transport interacting directly with the plant cell membranes without discerning between resistant and sensitive plants.     

THE ABSORPTION,TRANSLOCATION AND METABOLISM CHARACTERISTICS OF 4-(2,4-DICHLOROPHENOXY)BUTYRIC ACID IN BIGLEAF MAPLE*

Summary. Detached leaves treated with 2,4-DB were used to demonstrate that the foliage of Acer macrophyllum Pursh. possesses the enzyme systems necessary for oxidation of the 2,4-DB side chain. Absorption and translocation studies showed that 2,4-DB was absorbed less but translocated more than some other phenoxy herbicides which have been tested on this species. Studies with excised stem phloem and excised roots showed that different plant tissues are not equally capable of decarboxylating 2,4-DB. An experiment with intact plants established that 2,4-DB was translocated unchanged, and that the primary product of the oxidation of 2,4-DB is 2,4-D. The results are discussed with respect to the translocation characteristics of this herbicide in bigleaf maple. Caractères de l'absorption, de la migration et du métabolisme de l'acide 4-(2,4-dichlorophénoxy) butyrique dans l'érable a grandes feuilles     

Phytotoxicity and detoxification of metribuzin in dark-grown suspension cultures of soybean

Differential resistance of soybean to metribuzin (4-amino-6-t-butyl 3-(methylthio)-as-triazin-5(4H)-one) was demonstrated in cell suspensions from resistant and susceptible cultivars. Whereas the herbicide had been reported to inhibit photosynthesis, the observations on achlorophyllous, dark-grown cultures indicated that phytotoxicity was not restricted to photosynthesis. The sites of light-independent herbicide activity were not identified, but the presence of these sites was demonstrated in both the herbicide-susceptible and herbicide-resistant cells. The mechanism to protect these sites was present in all cultures. The mechanism, enzymatic detoxification of the herbicide, was inoperative in the susceptible cultures due to accumulation of a substance which inhibited the enzyme. Resistant cultures metabolized that substance to an ineffectual form. Metribuzin selectivity was therefore determined according to the accessibility of the inhibitor to the enzyme responsible for resistance.     

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.     

The mechanism of bentazon selectivity

Absorption, translocation and metabolism of [¹⁴C]3-isopropyl-2,1,3-benzothiadiazin-4-one-2,2-dioxide (bentazon) by several plant species were investigated to determine the mechanism of bentazon selectivity.Marked selective phytotoxicities were observed between resistant rice (Oryza sativa L.) and susceptible Cyperus serotinus Rottb. when treated with bentazon. Absorption and transolcation of bentazon did not differ greatly between highly resistant rice and susceptible C. serotinus. However, a marked difference in bentazon metabolism occurred between the two species. In rice about 80% of the absorbed bentazon was metabolized within 24 h, and after 7 days about 85% was converted to a major water-soluble metabolite and unchanged bentazon was only 5%. In C. serotinus 50–75% of the radioactivity was unchanged bentazon after 7 days.Large amounts of water-soluble metabolites were detected in root-treated resistant plants such as barnyardgrass (Echinochloa crus-galli Beauv.), soybean (Glycine max Merr.) and corn (Zea mays L.), but only small amounts were present in such susceptible plants as Sagittaria pygmaea Miq. and Eleocharis kuroguwai Ohwi. Therefore, the mechanism of bentazon selectivity appears to be a difference between resistant and susceptible species in their ability to metabolize and detoxify bentazon.The major metabolite in rice was identified as 6-(3-isopropyl-2,1,3-benzothiadiazin-4-one-2,2-dioxide)-O-β-glucopyranoside, determined by GC-MS, NMR, IR and gas chromatography after hydrolysis with sulfuric acid or β-glucosidase.     

The mode of action of chlomethoxyfen

Chlomethoxyfen [5-(2, 4-dichlorophenoxy)-2-nitroanisole] has been widely used as a pre-emergence herbicide in rice in Japan, where it is known as chlomethoxynil. It is effective against many annual weeds and some perennials, including Eleocharis acicularis and Sagittaria pygmaea. The activity of chlomethoxyfen is only slightly affected by water movement because of its low water-solubility. It is more toxic to shoots than roots and is rapidly absorbed by roots, with limited translocation to upper parts of the plants. The demethylated derivative, which was presumed to be conjugated with plant materials, was identified as the major metabolite in plants. Several other metabolites were also detected in soils and animals. Chlomethoxyfen increases phenylalanine ammonia-lyase activity in plants under light conditions, resulting in the accumulation of the biphenyl-2-ol content. The biochemical basis of the light requirement of diphenyl ether herbicides is also discussed.     

Alternate pathways of metribuzin metabolism in soybean: Formation of N-glucoside and homoglutathione conjugates

Metribuzin [4-amino-6-tert-butyl-3(methylthio)-1,2,4-triazin-5(4H)-one] metabolism was studied in soybean [Glycine max (L.) Merr. Tracy]. Pulse treatment studies with seedlings and excised mature leaves showed that [5-¹⁴C]metribuzin was absorbed rapidly and translocated acropetally. In seedlings, >97% of the root-absorbed ¹⁴C was present in foliar tissues after 24 hr. In excised leaves, 50–60% of the absorbed ¹⁴C remained as metribuzin 48 hr after pulse treatment, 12–20% was present as polar metabolites, and 20–30% was present as an insoluble residue. Metabolites were isolated by solvent partitioning, and were purified by adsorption, ion-exchange, thin-layer, and high-performance liquid chromatography. The major metabolite (I) was identified as a homoglutathione conjugate, 4-amino-6-tert-butyl-3-S-(γ-glutamyl-cysteinyl-β-alanine)-1,2,4-triazin-5(4H)-one. Metabolite identification was confirmed by qualitative analysis of amino acid hydrolysis products, fast atom bombardment (FAB), and chemical ionization (CI) mass spectrometry, and by comparison with a reference glutathione conjugate synthesized in vitro with a hepatic microsomal oxidase system from rat. Minor metabolites were identified as an intermediate N-glucoside conjugate (II), a malonyl N-glucoside conjugate (III), and 4-malonylamido-6-tert-butyl-1,2,4-triazin-3,5(2H,4H)-dione (N-malonyl DK, IV) by CI and FAB mass spectrometry. Alternative pathways of metribuzin metabolism are proposed.     

Effect of different photosystem II inhibitors on chloroplasts isolated from species either susceptible or resistant toward s-triazine herbicides

In chloroplasts isolated from susceptible and atrazine-resistant Amaranthus retroflexus, the inhibition of photosynthetic electron transport by various classes of herbicides has been investigated. Resistance of mutant Amaranthus is not restricted to s-triazines but also extends to uracils, 1,2,4-triazine-5-ones, and ureas. For 1,2,4-triazin-5-ones and chloroplasts of both biotypes, a correlation between inhibition of photosynthetic electron transport and the partition coefficient could be established. In the case of phenolic herbicides only modestly decreased or even higher sensitivity of chloroplasts from the resistant biotype as compared to the susceptible one could be observed. These results are confirmed by binding of radioactively labeled herbicides to chloroplasts of both plants. Specific binding of atrazine or metribuzin to resistant chloroplasts is completely abolished, and that of diuron or phenisopham diminished as compared to susceptible chloroplasts. In contrast, binding of phenolic herbicides generally is enhanced in resistant chloroplasts. Photoaffinity labeling of thylakoids from both biotypes by 2-azido-4-nitro-6-[2′,3′-³H]isobutylphenol yields almost identical labeling patterns. These results are consistent with a recently proposed model (W. Oettmeier, K. Masson, and U. Johanningmeier, Biochim. Biophys. Acta679, 376 (1982) of two different herbicide binding proteins at the reducing side of photosystem II: a 32- to 34-kdalton protein responsible for binding of triazines, triazinones, ureas, and related herbicides and a photosystem II reaction center protein for binding of phenolic herbicides.     

STUDIES OF THE RESPONSE OF PLANTS TO ROOT-APPLIED HERBICIDES

Summary. Applications of several herbicides -were made to roots and to the bases of shoots of peas, cucumber, mustard and barley grown in soil, sand or water culture.
Localized applications (variation horizontal) of atratone and MCPA to roots of peas and barley in soil produced effects similar to those observed in water euluire, described in Pan I. Airatone killed the plants whether available to the whole or to only a portion of the root system whereas MCPA affected only the roots with which it was in direct contact, and growth continued when a portion of the root system was in herbicide-free environment.
In water culture, MCPA was more effective when applied to the lower (younger) roots with the upper (older) roots kept dry than when twice the concentration was applied evenly to the whole root system in water. When all the roots were kept wet the effect of application to the upper roots was greater than the effect of application to the lower roots. The response of plants to atratone was not appreciably altered whether applications were made to the upper or lower parts of the root system in water culture. Variations in water level had little effect.
Even when the herbicide solution was confined to the stem or hypocotyl, atratone and DNOC were little, if any, less effective than when applied to roots. MCPA, both as ester and sodium salt, was significantly less effective.
Partial replacement of solution in the root zone by sand and air did not reduce the activity of atratone at a given concentration. Similar replacement in the zone of the stem or hypocotyl greatly reduced the effectiveness of all herbicides. When sand of low water content was used, atratone and MCPA-sodium became quite ineffective via the stem, but DNOC and MCPA-ethyl ester remained active.
Études sur les réactions de certaines plantes á des herbicides appliqués aux racines II. Observations nouvelles sur l'effet de l'application localisée.     

Increased herbicidal activity of triazine herbicides by piperonyl butoxide

Piperonyl butoxide (PB) is a known Synergist which enhances the activity of insecticides by inhibiting their biotransformation to less active products. We have evaluated the possible use of PB as a herbicide synergist using triazine herbicides in sensitive, tolerant, and resistant plants. The effects of PB, triazine herbicides, and their combinations were examined in whole plants as well as in chloroplasts isolated from triazine-sensitive (S) and -resistant (R) weed biotypes. PB itself, applied postemergence (0.1–0.5%, v/v), was slightly toxic to the plants tested. However, foliar application of PB combined with atrazine, terbutryn or prometryn to maize seedlings significantly increased the phytotoxicity of the herbicides. Low rates of atrazine, prometryn, and terbutryn in a tank-mixture with PB, effectively controlled Solatium nigrum L. and Abutilon theophrasli Medik. PB enhanced atrazine efficacy in both S and R biotypes of Lolium rigidum Gaud. The synergistic effect of PB was evident also in vitro when atrazine and methabenzthiazuron were used to inhibit photosystem II electron transport in chloroplasts isolated from resistant weeds. These data demonstrate the potential of PB as a herbicide synergist and its possible utilization as an aid for improving the activity of triazine herbicides in sensitive, tolerant and resistant plants.