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.     

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.     

Lack of prevention of chlorsulfuron-induced inhibition by amino acids

The amino acids valine and isoleucine, which had been indicated by Ray (1984) as antidotes against growth inhibition of pea plants induced by chlorsulfuron, were ineffective in preventing the damage induced by chlorsulfuron on the plasma membrane of maize roots as measured by K⁺ uptake. In addition, in seedlings of two corn genotypes and three pea genotypes grown in culture solution containing chlorsulfuron, growth inhibition was not alleviated by valine and isoleucine. However, in agreement with Ray's results, acetolactate synthase, the key enzyme of the biosynthesis of valine and isoleucine, was inhibited in vitro by chlorsulfuron in both maize and pea. It is suggested that the chlorsulfuron mechanism of action involves several sites.     

局部根区水氮耦合对玉米幼苗养分吸收利用的影响

研究局部根区水分胁迫下不同氮形态与供应部位对玉米幼苗养分吸收利用的影响。氮设三种形态(50%NO3--N+50%NH4+-N;NO3--N;NH4+-N)。采用分根培养的方法,用聚乙二醇(PEG6000)模拟水分胁迫。PEG和氮只加入到分根装置的一侧根室,形成局部根区水分胁迫下水氮同区、水氮异区六个处理。收获时测玉米幼苗植株生物量和各养分浓度。结果表明,水氮同区比水氮异区更利于玉米幼苗生长,氮、磷、钾、钙、镁、铁总含量和增量都高于相应氮形态的水氮异区处理。不同氮形态相比,混合氮有利于促进玉米幼苗生长和增强氮的吸收能力;相对于铵态氮,硝态氮促进了钾、钙、镁、铁总量和增量的增加;养分利用效率基本上与其地上部分该养分浓度的高低呈负相关。     

Differential phytotoxicity of glyphosate in maize seedlings following applications to roots or shoot

The transport and differential phytotoxicity of glyphosate was investigated in maize seedlings following application of the herbicide to either roots or shoots. One-leaf maize seedlings (Zea mays L.) were maintained in graduated cylinders (250 mL) containing nutrient solution. Half of the test plants were placed in cylinders (100 mL) containing different ¹⁴C-glyphosate concentrations; the remainder received foliar appliation of ¹⁴C-glyphosate. After 26 h, the roots and the treated leaves were washed with distilled water, and the plants placed again in cylinders (250 mL) containing fresh nutrient solution for 5 days. Plants were weighed, and split into root, seed, cotyledon, coleoptile, mesocotyl, first leaf and apex. The recovery of ¹⁴C-glyphosate was over 86%. For both application treatments, the shoot apex was the major sink of the mobilized glyphosate (47.9 ± 2.93% for root absorption and 45.8 ± 2.91% for foliar absorption). Expressed on a tissue fresh weight basis, approximately 0.26 μg a.e. g⁻¹ of glyphosate in the apex produced a 50% reduction of plant fresh weight (ED₅₀) when the herbicide was applied to the root. However, the ED₅₀ following foliar absorption was only 0.042 μg a.e. g⁻¹ in the apex, thus maize seedlings were much more sensitive to foliar application of the herbicide.     

Alachlor placement in the soil as related to phytotoxicity to maize (Zea mays L.) seedlings*

Growth chamber studies were conducted to investigate the effects of alachor (2-choloro-2′,6′-diethyl-N- (methoxymethyl) acetanilide) on emerging seedlings of maize (Zea mays L.) planted 2.5 and 8.0 cm deep in a Plano silt loam soil. Alachlor was localized in the shoot zone, in the root zone, and in the shoot and root zones. Four days after emergence, seedlings were harvested and total shoot and root lengths used as measures of herbicidal effectiveness. The herbicide applied at a rate of 2.5 kg/ha caused a severe reduction in seedling height when placed in the shoot zone of seeds planted at the shallow depth. This injury was prevented when seeds were planted at the deeper level. When alachlor was placed in the root zone, there was no inhibition of shoot growth. When both shoot and root zones were exposed to the herbicide, severe growth inhibition again occurred. Roots were less sensitive to alachlor. A simple technique involving use of sand and activated charcoal barriers to effectively separate the shoot and root zones is described.     

Increased metabolism of a pyrrolidine urea herbicide in corn by a herbicide antidote

Corn, cotton, and sorghum plants were injured by high rates of 5328 (cis-2,5-dimeihyl-1-pyrrolidinecarboxanilide) when it was applied to the soil surface al planting time. The injury was severe al 35·84 kg/ha (eight times recommended dosage) and in corn resulted in complete inhibition of adventitious root development and reduced shoot and primary and secondary root growth. Treatment of the seeds with 0·5% Protect (1,8-naphthalic anhydride) prior to planting dramatically decreased the injurious effect of 5328 on corn, sorghum, and cotton. Using ¹⁴C-5328 in corn, it was shown that Protect did not alter herbicide uptake. However, the rate of conversion of the herbicide molecule in corn tissue lo water soluble, nonherbicidal metabolites was markedly enhanced in plants grown from Protect-treated seeds.     

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.     

Mode of action of naphthalic anhydride as a safener for the herbicide AC 263222 in maize

In hydroponic experiments, seed-dressing with the herbicide safener 1,8-naphthalic anhydride (NA), significantly enhanced the tolerance of maize, (Zea mays L., cv. Monarque) to the imidazolinone herbicide, AC 263222, (2-[4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl]-5-methylnicotinic acid). Uptake, distribution and metabolism studies where [¹⁴C]AC 263222 was applied through the roots of hydroponically grown maize plants showed that NA treatment reduced the translocation of radiolabel from root to shoot tissue and accelerated the degradation of this herbicide to a hydroxylated metabolite. Reductions in the lipophilicity and, therefore, mobility of this compound following hydroxylation may account for NA-induced retention of radiolabel in the root system. Hydroxylation of AC 263222 suggested that NA may stimulate the activity of enzymes involved in oxidative herbicide metabolism, such as the cytochrome P₄₅₀ mono-oxygenases. In agreement with this theory, the cytochrome P₄₅₀ inhibitor, 1-aminobenzotriazole (ABT), synergized AC 263222 activity and inhibited its hyroxylation in vivo. NA seed-dressing enhanced the total cytochrome P₄₅₀ and b₅ content of microsomes prepared from etiolated maize shoots. Isolated microsomes catalyzed AC 263222 hydroxylation in vitro. This activity possessed the characteristics of a cytochrome P₄₅₀ mono-oxygenase, being NADPH-dependent and susceptible to inhibition by ABT. Activity was stimulated four-fold following NA seed treatment. Differential NA enhancement of AC 263222 hydroxylase and the cytochrome P₄₅₀-dependent cinnamic acid-4-hydroxylase (CA4H) activity, suggested that separate P₄₅₀ isozymes were responsible for each activity. These results indicate that the protective effects of NA result from enhancement of AC 263222 hydroxylation and concomitant reduction in herbicide translocation. This may be attributed to the stimulation of a microsomal cytochrome P₄₅₀ system. © 1998 SCI.     

冠菌素对玉米苗期植株形态建成的调控效应

以玉米品种金海5号为材料,采用不同浓度植物生长调节剂冠菌素(COR)拌种和三叶期(V3)叶面喷施的方法,研究了COR对玉米苗期植株地上部和根系形态建成的影响,分析了其对叶面积、叶绿素含量和可溶性蛋白的调控效应。结果表明:不同浓度冠菌素对玉米幼苗形态建成的调控呈单峰曲线,即低浓度下促进幼苗生长,高浓度下抑制生长。用0.1 mg/L的COR拌种或叶面喷施处理,可促进玉米苗期植株株高和茎粗生长,增加单株叶面积,提高叶片叶绿素和可溶性蛋白含量,促进植株干物质积累。同时,COR可促进玉米苗期根系生长,增加根长和根表面积,进而可有效增加根系吸收能力。研究结果表明,适宜浓度的COR处理可以提高玉米幼苗光合性能,增强根系吸收能力,促进植株地上部和地下部的生长,有利于培育壮苗。     

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     

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     

UNTERSUCHUNGEN ÜBER AUFNAHME UND TRANSLOKATION VON 14C-MARKIERTEN HERBIZIDEN IN AGROSTEMMA GITHAGO L. UND TUSSILAGO FARFARA L.

Studies of the uptake and translocation of ¹⁴C-labelled 2, 4-D, MCPA and aminotriazole in Agrostemma githago L. and Tussilago farfara L. clarified the behaviour of the herbicides in both species. In A. githago, MCPA was more freely mobile than 2,4-D after application to the leaf; it was distributed in the plant more rapidly and in greater quantity. Similarly, following root uptake MCPA was transported in the shoot in greater amounts than was 2,4-D. There is a clear relationship between the susceptibility of A. githago to MCPA and the mobility of the herbicide in the plant. In T. farfara, 2,4-D and aminotriazole applied to the leaves were equally well absorbed and relatively rapidly translocated. During the period up to 72 h the amounts of herbicide in the plant increased to similar levels; after that, ¹⁴C activity in plants treated with 2,4-D fell slightly whereas there was further accumulation of aminotriazole. Following uptake through the roots, translocation and accumulation in the leaves were considerably greater with aminotriazole than with 2,4-D. The lack of accumulation of 2,4-D could be a factor in the resistance of T. farfara to this herbicidie. Recherches sur l'absorption et la migration d'herbicides marqués au ¹⁴ C dans Agrostemma githago L. et Tussilago farfara L.     

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.     

Uptake and fate of triticonazole applied as seed treatment to spring wheat (Triticum aestivum L.)

Following seed treatment of wheat (Triticum aestivum L.) with ¹⁴C-labelled triticonazole at a dose of 1·8 g kg^-1 seed, the uptake of radioactivity by shoots and roots was investigated from the two- to three-leaf stage up to the beginning of the booting phase, 80 days after sowing. Triticonazole equivalents taken up by wheat plants reached 5·7% and 14·6% of the applied dose in the shoots and the roots, respectively. Between the two- to three-leaf stage and the beginning of the booting phase, the concentration of triticonazole equivalents in the shoots decreased from 2·5 to 0·15 μg g^-1 fresh weight. This was attributed to uptake of triticonazole by roots not keeping pace with shoot growth and increased retention in the roots of triticonazole taken up. The main factor limiting the uptake of triticonazole by the roots may be the rapid growth of the uptake-active apical root parts out of the dressing zone which had formed in the soil. Distribution of triticonazole equivalents taken up by the main shoot showed a decreasing concentration gradient from the oldest to the youngest leaf. An increase in the seed treatment dose was investigated as a way to increase the concentration of triticonazole in the shoots, but its influence remained limited. © 1998 SCI     

Phytotoxicity and persistence of chlorsulfuron as affected by activated charcoal

Two bioassay procedures, using petri-dishes and pots, based on the root growth of pregerminated maize were used to study the residual phytotoxicity of chlorsulfuron under field conditions. Both bioassay procedures appeared to be equally reproducible and sensitive with residues of chlorsulfuron being detectable from 0·25 to 10·0 ng g^-1. The results indicated that persistence, movement and phytotoxicity increased with increasing rate of chlorsulfuron, but persistence of the herbicide was shorter in wet compared to dry field conditions. As little as 1 g a.i. ha^-1 of incorporated chlorsulfuron under warm and dry field conditions caused a stunting effect on maize plants (Hybrid F₁, Damon) and reduced yield by 53% compared to untreated control plants; while 5·0 and 10·0 g a.i. ha^-1 of incorporated chlorsulfuron killed all maize plants. However, under wetter field conditions, incorporated chlorsulfuron at 1·25, 2·5 and 5·0 g a.i. ha^-1 caused a stunting effect on maize plants (Hybrid F₁, ARIS) and decreased yield by 16, 57 and 92%, respectively, compared to untreated control. Incorporation of 50 kg ha^-1 of activated charcoal inactivated completely chlorsulfuron incorporated at 1·25 and 2·5 g a.i. ha^-1 and did not affect yield of maize compared to untreated control. Higher rates of activated charcoal such as 100 and 200 kg ha^-1 also inactivated chlorsulfuron applied at 1·25–5·0 g a.i. ha^-1 and did not affect grain yield of maize. Phytotoxicité et persistance du chlorsulfuron Deux méthodes d'essais biologiques, à savoir en boîte de Petri ou en pot, Basées sur la croissance des racines de maïs prégermé ont été utilisées pour étudier la phytotoxicité résiduelle du chlorsulfuron en conditions de plein champ. Les deux méthodes sont également reproductibles et sensibles à des niveaux de détection pour les résidus de chlorsulfuron de 0,25 à 10 ng g^-1. Les résultats montrent que la persistance et la phytotoxicité augmentent avec des doses croissantes de chlorsulfuron, mais la persistance est plus courte dans des conditions de plein champ humides que séches. Une dose aussi faible que 1 g de matiére active ha^-1 de chtorsulfuron incorporé en conditions chaudes et séches a causé un effet retard sur les plants de maïs (hybride F₁, Damon) et a réduit de 53% le rendement par rapport au témoin non traité; des doses de 5 à 10 g de matiére active ha^-1 de chlorsulfuron incorporé ont tué tous les pieds de maïs. Cependant, en conditions plus humides, le chlorsulfuron incorporéà 1,25, 2,5 et 5 g de matiére active ha^-1 a causé un effet retard sur le maïs (hybride F₁ ARIS) et a réduit le rendement par rapport au témoin non traité respectivement de 16, 57 et 92%. L'incorporation de 50 kg ha^-1 de charbon actif a complément inactive le chlorsulfuron incorporéà 1,25 et 2,5 g de matiére active ha^-1 et n'a pas eu de répercussion sur le rendement par rapport au témoin non traité. Des doses plus élevées de charbon actif comme 100 et 200 kg ha^-1 ont inactivé le chlorsulfuron appliquéà 1,25–5 g matiére active ha^-1et n'ont pas affecté le poids en grain du maïs. Ueber die Beeinflussung von Phytotoxizität und Wirkungsdauer von Chlorsulfuron durch Aklivkohle Zum Studium der Residualwirkung von Chlorsulfuron unter Feldbedingungen wurden zwei Bioassaymethoden, eine in Petrischalen, die andere in Töpfen, eingesetzt. Beide Methoden basierten auf dem Wurzelwachstum von vorgekeimtem Mais. Es zeigte sich, dass beide Versuchsverfahren in gleichem Masse reproduzierbar und empfindlich und in der Lage sind Rückstände von 0,25–10,0 ng g^-1 nachzuweisen. Mit steigender Chlorsulfurondosis wurde eine zunehmende Phytotoxizität, Persistenz und Mobilität des Herbizids festgestellt. Die Persistenz war unter feuchten Feldbedingungen kürzer als bei Trockenheit. Bis zu einer unteren Grenze von 1,0 g a.i. ha^-1 verursachte inkorporiertes Chlorsulfuron, unter trockenen und warmen Feldbedingungen an Mais (Hybride F₁, Damon) Wachstumshemmungen und Erntereduktionen von 53%, verglichen mit unbehandelten Kontrollpflanzen. Unter feuchteren Bedingungen, jedoch, hatten 1,25, 2,5 and 5,0 g a.i. ha^-1 eingearbeitetes Chlorsulfuron an Mais (Hybride F₁ ARIS) Wachstumshemmungen und Ernteverluste von 16, 57 und 92% zur Folge. Die Einarbeitung von 50 kg ha^-1 Aktivkohle inaktivierte 1,25 g und 2,5 g ha^-1 inkorporierles Chlorsulfuron vollständig und hatte keinerlei negative Auswirkungen auf die Maisernte, im Vergleich zu unbehandelten Kontrollen. Höhere Mengen von Aktivkohle, wie 100 und 200 kg ha^-1, inaktivierten auch Chlorsulfuronmengen von 1,25–5 g ha^-1 und hatten keinen Einfluss auf den Kömerertrag.     

Effect of benzoylprop-ethyl on uptake, transport and metabolism of 32P in Avena fatua L. and Triticum aestivum L.

The effect of benzoylprop-ethyl on plant weight, root uptake, transport and metabolism of ³²P in wild oat and wheat plants was examined 4 h, 1,3 and 9 days after treatment. The fresh weight of wild oat plants was significantly reduced, due to herbicide action only, by day 9 after treatment. By day 3, shoot weight was decreased while root weight was significantly increased by 47%. No significant changes in plant weight were caused by benzoylprop-ethyl in wheat plants. Uptake of ³²P by treated wild oat plants decreased by 39% compared with the control, by day 9, after an initial increase; uptake of ³²P was not significantly influenced in wheat plants. By day 1 transport of ³²P to the shoots was significantly reduced in wild oat plants by 34%, whereas in wheat plants it was significantly increased by 35%. Metabolism of ³²P was already hampered in wild oat plants 4 h after treatment. The content of ³²P was reduced on the first two sampling dates in both the roots and shoots of treated plants in all fractions except in DNA in the shoots. On day 3, this decrease was apparent especially in organic, lipidic and nucleic acid fractions in the shoots; incorporation of ³²P into lipidic and RNA fractions was significantly inhibited on day 9 in both the roots and shoots of treated wild oat plants. Wheat plants responded most strongly to benzyoylprop-ethyl on day 1 after treatment, when ³²P incorporation into all fractions except DNA was hampered. Differences between treated and control wheat plants gradually levelled off on days 3 and 9 after treatment.     

Model Predictions and Field Measurements of Chlorsulfuron Leaching under Non-steady-state Flow Conditions

Model simulations of chlorsulfuron (1-(2-chlorophenylsulfonyl)-3-(4-methoxy-6-methyl-1,3,5-triazin-2-yl)urea) leaching in a loamy soil were made with the mechanistic dual-porosity model MACRO. Comparisons were made with a data set obtained in a lysimeter experiment in which leaching was measured during an 11-month period after applying chlorsulfuron at two rates (4 and 8 g ha⁻¹). In this experiment, peak concentrations appeared c.6 months after pesticide application, reaching levels of 14 and 21 ng litre⁻¹ in the low- and high-dose treatments, respectively. These peak concentrations appeared after c.70 mm of accumulated leachate, implying that some of the herbicide was displaced through the soil columns by non-equilibrium flow processes. Model calibration was limited to parameters related to evapotranspiration, water uptake by roots and degradation rates in the subsoil. With this minimum amount of calibration, the model successfully described the leaching pattern of chlorsulfuron, provided that the two-flow domain option in the model was used. Running the model in one-flow domain resulted in considerable underestimates of leaching of chlorsulfuron over the short-term (<1 year). The degradation rate in the subsoil was also found to be critical. It had to be increased about fivefold to match measured chlorsulfuron concentrations in leachate. At such concentrations, 0·012 g ha⁻¹ of chlorsulfuron (0·3% of that applied) was predicted to leach through the soil profile during the 11-month simulation period when the lower dose of the compound was applied.     

Comparison of chlorsulfuron and metsulfuron for control of Allium vineale L.

The response of natural and planted stands of Allium vineale L. to chlorsulfuron and metsulfuron was determined in field experiments in Illinois, U.S.A., in 1982 and 1983. In natural stands very low rates of either herbicide controlled A. vineale. Chlorsulfuron, applied in the spring at 20 g ha^?1, reduced aerial bulblet production by 99% but when it was applied in the fall it reduced aerial bulblet production by only 59%. All rates of metsulfuron (5–20 g ha^?1), at both times of application, effected better than 94% reduction in plant density and yield of aerial bulblets. In a glasshouse experiment, plants derived from aerial bulblets were more susceptible to chlorsulfuron than plants derived from soft offset bulbs. Soft offset bulbs were, therefore, used to establish a uniform stand of A. vineale in the field. In this experiment, non-linear regression analysis showed that metsulfuron was two to three times more active than chlorsulfuron. GR₉₅ values calculated from the computed regression equations show that metsulfuron and chlorsulfuron, applied in April at 5 and 15 g ha^?1, respectively, reduced aerial and underground bulb production by 95%.     

Physiological responses of maize and sorghum to four different safeners for metazachlor

The ability of the herbicide safeners, BAS-145138 (1-dichloroacetyl-hexahydro-3,3,8a-trimethyl-pyrrolo(1,2a)pyrimidin-6(2H)-one), dichlormid (N,N-diallyl-2,2-dichloroacetamide), flurazole (phenylmethyl ester), and MG-191 (2-dichloromelhyl-2-methyl-1,3-dioxolane) for preventing metazachlor injury to maize (Zea mays L.) and sorghum (Sorghum bicolor L.) seedlings were compared with their effects on ¹⁴C-metazachlor metabolism to a glutathione (GSH) conjugate, effects on non-protein thiol contents (mainly GSH) and effects on Glutathione S-transferase (GST) activity in these two species. Sorghum shoot growth was reduced by 41% and maize shoot growth was reduced by 54%, by metazachlor concentrations in vermiculite nutrient culture of 0·6 μM and 7·5μM, respectively. In this system, all four compounds had significant activity as safeners for metazachlor in both sorghum and maize seedlings. BAS-145138 and flurazole were the most effective safeners in maize and sorghum, respectively. In the absence of safeners, the rate of non-enzymatic conjugation of metazachlor and GSH was much greater than the enzymatic rate. However, the rate of enzymatic conjugation of metazachlor with GSH was increased by safener treatment in both maize and sorghum. Safener effectiveness was highly correlated with increases in ¹⁴C-metazachlor uptake and metabolism in both species. Safener effectiveness was more highly correlated with safener effects on GST activity in maize or sorghum when ¹⁴C-metazachlor was used as the substrate than when the non-specific CDNB (1-chloro-2,4-dinitrobenzene) was used as the substrate. Safener effectiveness was also strongly correlated with safener effects on GSH levels in sorghum, but not in maize, possibly because of the greater importance of non-enzymatic conjugation of metazachlor with GSH in sorghum as compared to maize.