Effects of formulation and environment on absorption and translocation of clopyralid in Cirsium arvense (L.) Scop. and Polygonum convolvulus L

The patterns of absorption and translocation of ¹⁴C clopyralid commercially formulated as the acid, monoethanolamine salt, potassium salt, 2-ethylhexyl ester and 1 -decyl ester were compared in Cirsium arvense and Polygonum convolvulus grown under three environmental regimes. Plants were grown under a 35% or 65% RH regime in silica sand maintained at 33% w/w moisture or under a water stress regime at 65% RH. Approxi mately 26,39,86,93 and 100% of the applied ¹⁴C-activity from the 2-ethylhexyl ester, acid, monoethanolamine salt, 1-decyl ester and potas sium salt, respectively, were recovered 72 h after application to glass cover slips placed in the growth room. However, loss of applied ¹⁴C-activity after application of the five formulations to both plant species was significant only for the 2-ethylhexyl ester. Regardless of environmental regime, the acid was the most readily absorbed formulation. In contrast to the acid, the salts and esters were less readily absorbed. When the data were expressed as a percentage of absorbed radioactivity, there was no significant difference in translocation when the acid, monoethanolamine salt and potassium salt were compared. However, significantly smaller quantities of the absorbed 2-ethylhexyl and 1-decyl ester were exported from the treated leaf. These results indicate that once absorbed, the esters do not readily partition out of the cuticle, whereas the acid and two salts move into the symplast for subsequent translocation. When the results of the three environmental regimes were compared, the absorption of the monoethanolamine and potas sium salts were greatly reduced under low humi dity or water stress, whereas the acid and esters were not affected.     

Penetration of clopyralid and related weak acid herbicides into and through isolated cuticular membranes of Euonymus fortunei

A model system consisting of chemically isolated cuticular membranes placed on agar was used to study the penetration of various formulations of ¹⁴C-labelled clopyralid, fluroxypyr, triclopyr, picloram, and 2,4-D into and through cuticular membranes. Clopyralid, commercially formulated as the acid, or 1-decyl ester was rapidly absorbed after 12 h by isolated cuticles of Euonymus fortunei. There was less absorption of the monoethanolamine and potassium salt formulations when compared to the acid and 1-decyl ester. However, in terms of the absorbed ¹⁴C-activity that partitioned into the agar, there was no difference between the acid and salt formulations with approximately 90% being partitioned after 48 h. Conversely, the 1-decyl ester formulation of clopyralid was retained in the cuticle; less than 5% of the absorbed fraction was recovered in the agar after 48 h. When the acid forms of clopyralid, fluroxypyr, triclopyr, picloram, and 2,4-D were compared, there was little or no difference in absorption among the herbicides. However, the ¹⁴C-activity from clopyralid partitioned the most (90%) and triclopyr the least (50%) into the agar. When ester formulations of clopyralid, fluroxypyr, and triclopyr were compared, at least 95% of the ¹⁴C-activity was absorbed 24 h after application. However, of the amount absorbed, significantly more of the butoxyethyl ester of triclopyr (36%) partitioned into the agar than did the 1-decyl ester of clopyralid (6%) or the 1-methylheptyl ester of fluroxypyr (5%). Differential retention of various herbicide formulations in this model system may explain, in part, the differences in absorption and translocation among radiolabelled clopyralid formulations observed in previous research (Kloppenburg & Hall, 1990).     

Basis for the selective action of fluroxypyr

The dose-response, foliar uptake, translocation and metabolism of the methylheptyl ester (MHE) of fluroxypyr were examined in lambs-quarters (Chenopodium album L.), wild buckwheat (Polygonum convolvulus L.), Canada thistle (Cirsium arvense L. Scop.) and field bindweed (Convolvulus arvensis L.). Under controlled environment growth room conditions, E₅₀ values, determined from shoot dry weights of the susceptible species, wild buckwheat (16 g ha^?1) and field bindweed (40 g ha^?1), were markedly different than those of the tolerant species, lambsquarters (331 g ha^?1) and Canada thistle (800 g ha^?1). Regardless of species, more than 80% of applied [¹⁴C]fluroxypyr-MHE was absorbed by foliar surfaces 120 h after treatment. Translocation of radioactivity out of the treated leaves of susceptible species was significantly greater than that of tolerant species. For example, 120 h after treatment with [¹⁴C]-fluroxypyr-MHE, the proportion of applied radioactivity translocated in tolerant Canada thistle and lambsquarters was 15 and 10%, respectively, whereas in susceptible wild buckwheat and field bindweed it was 41 and 40% of applied radioactivity, respectively. High-performance liquid chromatography (HPLC) of plant extracts indicated four distinct chroma-tographic peaks common to all four species. More fluroxypyr was recovered in the susceptible species (70%) than in the tolerant species (30%), 120 h after application. Selectivity differences between the tolerant and susceptible species may be the result of enhanced metabolic transformation of the herbicide to more polar, non-phytotoxic compounds with limited mobility within the tolerant species. Les bases de la sélectivité du fluroxypyr La courbe dose effet, la pénétration foliaire, la migration et le métabolisme de Tester méthyle-heptyle (MHE) du fluroxypyr ont étéétudiés chez le chénopode blanc (Chenopodium album L.), la renouée faux-liseron (Polygonum con-vulvulus L.), le chardon des champs (Cirsium arvense L. Scop.) et le liseron des champs (Convolvulus arvensis L.). En conditions de crois-sance contrôlées, les valeurs ED₅₀, déterminées à partir du poids de matière sèche des parties aériennes étaient nettement différentes chez les plantes sensibles et chez les plantes résistan-tes:renouée faux-liseron, 16 g ha^?1; liseron des champs, 40 g ha^?1; chénopode blanc, 331 g ha^?1; chardon des champs, 800 g ha^?1. Quelle que soit 1'espèce, plus de 80% du [¹⁴C]fluroxypyr-MHE pénétrait dans les feuilles en 120 h. La migration de la radioactivité hors des feuilles traitérs était significativement plus importante chez les plantes sensibles que chez les plantes tolérantes. Par exemple, 120 h après le traite-ment avec du [¹⁴C]fluroxypyr-MHE, la proportion de radioactivité appliquée qui avait migré dans le chardon des champs et le chénopode, tolérants, était respectivement 15 et 10%, alors que chez la renouée faux-liseron et le liseron des champs, sensibles, elle était respectivement 41 et 40%. Des analyses par HPLC des extraits de plantes montraient quatre pics chro-matographiques distincts dans chacune des quatre espèces. Davantage de fluroxypyr était retrouvé 120 h après 1'application chez les plantes sensibles que chez les plantes résistantes (70% contre 30%). Les différences de sensibilité entre espèces pourraient être dues chez les plantes tolérantes à un métabolisme plus important de l'herbicide en composés plus polaires, non phytotoxiques et peu mobiles. Grundlagen für die selektive Wirkung von Fluroxypyr Die Dosis/Wirkungs-Beziehung, Blattaufnahme, Translokation und Metabolismus des Methylheptyl-Esters (MHE) von Fluroxypyr wurden bei Weißem Gänsefuß (Chenopodium album L.), Gemeinem Windenknöterich (Polygonum convolvulus L.), Acker-Kratzdistel (Cirsium arvense (L.) Scop.) und Gemeiner Ackerwinde (Convolvulus arvensis L.) untersucht. Unter den kontrollierten Umweltbedingungen eines Phytotrons wurden anhand des Trockengewichts die ED₅₀-Werte bestimmt, die bei den empfindlichen Arten Polygonum convolvulus mit 16 g ha^?1 und Convolvulus arvensis mit 40 g ha^?1 sich deutlich von denen der toleranten Arten Chenopodium album mit 331 g ha^?1 und Cirsium arvense mit 800 g ha^?1 unterschieden. Unabhängig von der Art waren mehr als 80 % der Aufwandmenge von [¹⁴C]-Fluroxypyr-MHE durch die Blattoberflächen 120 h nach der Behandlung aufgenommen. Die Translokation der Radioaktivität aus den behandelten Blättern war bei den empfindlichen Arten signifikant größer als bei den toleranten. Z. B. waren 120 h nach der Behandlung bei den toleranten Arten Cirsium arvense und Chenopodium album 15 bzw. 10 % der Radioaktivität transloziert, während es bei den empfindlichen Arten Polygonum convolvulus und Convolvulus arvensis 41 bzw. 40 % waren. Bei allen 4 Arten ergab eine HPLC-Untersuchung der Pflanzenextrakte 4 distinkte Peaks. Bei den empfindlichen Arten wurde 120 h nach der Anwendung mit 70 % mehr Fluroxypyr wiedergefunden als bei den toleranten (30 %). Die Selektivitätsunterschiede zwischen den toleranten und empfindlichen Arten könnten auf einen beschleunigten Metabolismus des Herbizids zu stärker polaren, nichphytotoxischen Stoffen mit eingeschränkter Mobilität bei den toleranten Arten zurückgeführt werden.     

Herbicidal control of Cirsium arvense (L.) Scop,roots and shoots in no-till spring wheat (Triticum aestivum L.)*

Three herbicide treatments were applied each year over a period of 4 years to Cirsium arvense (L.) Scop, infestations in no-till spring wheat (Triticum aestivum L.) in North Dakota, USA. Both chlorsulfuron at 30 g ai ha^?1+a non-ionic surfactant and a mixture of clopyralid+2,4-D at 70+280 g ai ha^?1 gradually reduced Cirsium arvense shoot density, root biomass, and adventitious root buds over the 4-year treatment period in two trials. These two treatments did not merely induce adventitious root buds to become dormant. They virtually eliminated roots to a depth of 50 cm by year 4. Tribenuron methyl at 10 g ai ha^?1+ a non-ionic surfactant was less effective in reducing shoot density and root biomass. Lutte herbicide contre les racines et les tiges de Cirsium arvense (L.) Scop, dans du bli de printemps non laboure (Triticum aestivum L.) Trois traitements herbicides ont été appliqués chaque année pendant 4 ans, contre des infestations de Cirsium arvense (L.) Scop, dans du blé de printemps (Triticum aestivum L.) non labouré dans le Dakota Nord, USA. Tant le chlorsulfuron à 30 g m.a. ha^?+un surfactant nonionique qu'un mélange de clopyralide+2,4-D à 70+280 g m.a. h^? ont reduit progres-sivement la densité des pieds de Cirsium arvense, la biomasse racinaire, et les bourgeons racinaires adventices pendant les 4 années de traitements dans les 2 essais. Ces traitements ont à peu près éliminé les racines sur une profondeur de 50 cm en 4 ans. Ces deux traitements n'ont pas induit de dormance des bourgeons racinaires adventices. Le tribenuron methyl à 10 g m.a. ha^?+un surfactant non ionique a été moins efficace dans la réduction de la densité de plante et de la biomasse racinaire. Chemische Bekämpfung von Cirsium arvense (L.) Scop, in direktgesätem Sommerweizen (Triticum aestivum L.) In direktgesäter Sommerweizen (Triticum aestivum L.) wurdel in North Dakota. USA, Bestände von Cirsium arvense (L.) Scop, über 4 Jahre jährlich 3 Herbizidbehandlungen unterzogen. Sowohl Chlorsulfuron mit 30 g AS ha^?1 nichtionischem Netzmittel als auch eine Mischung von Clopyralid+2,4D mit 70+280 g AS ha^?1 verringerten die Sproßdichte der Acker-Kratzdistel, die Wurzelbiomasse und die Adventivknospen an den Wurzeln in 2 Ver-suchen graduell. Durch diese beiden Behand-lungen wurden nicht nur die Adventivknospen dormant, sondem auch die Wurzeln bis zu einer Tiefe von 50 cm bis zum 4. Jahr fast ganz elimi-niert. Tribenuron-methyl mit 10 g AS ha^?1 nichtionischem Netzmittel war hinsichtlich der Reduktion von Sproßdichte und Wurzelbiomasse weniger wirksam.     

Effects of dose and application timing on the seed production of three weed species treated with MCPA or tribenuron-methyl

The seed production of Fallopia convolvulus (L.) A. Love, Galium spurium L, and Thlaspi arvense L., treated with MCPA or tribenuron-methyl, was studied in a pot experiment. The herbicides were applied in doses from 1/16 to 1/l of a full dose at five different growth stages. The largest reduction of seed production was observed on plants treated when one true leaf had developed (F. convolvulus, both herbicides) or at the beginning of the generative phase (G. spurium treated with tribenuron-methyl and T. arvense treated with either herbicide). Tribenuron-methyl (0.375 g a.i. ha^?1) or MCPA (0.1875 kg a.i. ha^?1) applied at bolting stage was enough to reduce the seed production of T. arvense by 83% and 100%, respectively. The seed production of F. convolvulus, treated with 0.75 kg MCPA at the cotyledon stage, was reduced by 70%. Plants of G. spurium with 5–9 axillary shoots, treated with 3 g tribenuron-methyl, produced 45% fewer seeds than the control. Both herbicides (at least at the highest doses) reduced seed production of all three species more than shoot dry matter.     

Sublethal effects of chlorsulfuron on black bindweed (Polygonum convolvulus L.)

Effects of the herbicide chlorsulfuron on growth and reproduction of black bindweed (Polygonum convolvulus L.) plants were investigated in a controlled environment chamber and a greenhouse over a full life cycle. Biomass of P. convolvulus was stimulated at 0.4 g a.i. ha^?1, but at higher doses it was reduced compared with controls. Leaf production of plants treated with 1.6 g a.i. ha^?1 was initially totally inhibited, but these plants resumed leaf production 10 days after treatment. Chlorsulfuron treatment resulted in higher proportions of small and large leaves compared with controls. Because the life-span of the plants increased with increasing doses of chlorsulfuron, seed production was not affected at doses up to 1.6 g ha^?1, even though significant effects were found on both biomass and leaf production. At rates of 1.6–4 g a.i. ha^?1 seed production decreased. Plant mortality was low in this study, reaching 33% at the highest rate of chlorsulfuron. Effets sublétaux du chlorsulfuron sur la renouée faux-liseron (Polygonum convolvulus L.) Les effets du chlorsulfuron sur la croissance et la reproduction de la renouée faux-liseron (Polygonum convolvulus L.) ont étéétudiés en serre et en conditions controlées sur un cycle complet. La biomasse de P. convolvulusétait stimulée à 0,4 g m.a. ha^?1 mais à doses plus élevées elle était réduite par rapport à celle des témoins. La production de feuilles de plantes traitées à 1,6 g m.a. ha^?1était initialement totalement inhibée mais ces plantes reprenaient leur production de feuilles 10 jours après le traitement. Les plantes traitées au chlorsulfuron avaient une plus grande proportion de feuilles petites et grandes que les témoins. Comme la durée de vie des plantes s'accroissait avec la dose de chlorsulfuron, la production de graines n'était pas affectée jusqu'à la dose 1,6 g m.a. ha^?1, meme si des effets significatifs étaient détectés sur la biomasse et la production de feuilles. À des doses comprises entre 1,6 et 4 g m.a. ha^?1, la production de graines diminuait. La mortalité des plantes était faible dans cette étude, atteignant 33%à la plus haute dose de chlorsulfuron. Subletale Wirkungen von Chlorsulfuron auf den Gemeinen Windenknoterich (Polygonum convolvulus L.) In Ecophyt- und Gewachshausversuchen zur Wirkung von Chlorsulfuron auf Wachstum und Reproduktion des Gemeinen Windenknoterichs (Polygonum convolvulus L.) war die Biomassebildung bei 0,4 g AS ha^?1 verstarkt, bei hoheren Dosen jedoch verringert. Bei 1,6 g AS ha^?1 war die Blattentwicklung zunachast fur 10 Tage nach der Behandlung ganzlich unterdruckt. Der Anteil kleinerer und großerer Blatter war hoher. Mit zunehmendem Aufwand des Herbizids verlangerte sich der Entwicklungszyklus, so daß bis zu 1,6 g AS ha^?1 die Samenproduktion nicht zuruckging, trotz signifikanter Wirkung sowohl auf die Biomasse als auch auf die Blattbildung. Bei Dosen Uber 1,6 bis 4,0 g AS ha^?1 wurden weniger Samen gebildet. Die Absterberate war bei diesen Versuchen niedrig und betrug bei der hochsten Chlorsulfuron-Dosis 33%.     

Control of Avena fatua L. and Cirsium arvense (L.) Scop. with mixtures of 3,6-dichloropicolinic acid and four herbicides for control of A. fatua

Control of Avena fatua (L.) (wild oat) with diclofop methyl applied at 0·7 kg ha^?1 at the two-leaf stage and difenzoquat at 0·84 kg ha^?1 at the four-leaf stage in wheat (Triticum aestivum L.) under field conditions was good and not affected when either of these herbicides was mixed with 3,6-dichloropicolinic acid as the monoethanolamine salt at 0·14, 0·20 or 0·30 kg ha^?1. In the glasshouse, mixtures containing 3,6-dichloropicolinic acid at rates as high as 0·6 kg ha^?1 also did not affect control of A. fatua. When barban at 0·35 kg ha^?1, or flamprop methyl at 0·56 kg ha^?1 was mixed with similar rates of 3,6-dichloropicolinic acid and applied at the two-leaf and four-leaf stage of A. fatua respectively, a reduction in control of A. fatua (antagonism) occurred under both field and glasshouse conditions. The herbicides for control of A. fatua did not influence the fresh weight suppression of C. arvense shoots obtained in the glasshouse with 3,6-dichloropico-colinic acid at 0·3 kg ha^?1. Early tolerance of wheat (cv. Neepawa) was acceptable with all mixtures. Wheat yields with diclofop methyl or difenzoquat alone or in mixture with 3,6-dichloropicolinic acid were increased over the yields from the A. fatua-infested control.     

Absorption,translocation and metabolism of 14C-glyphosate in several weed species*

The pattern and extent of ¹⁴C-glyphosate [N-(phosphonomethyl)glycine] translocation from the treated leaf and metabolism of ¹⁴C-glyphosate were studied in field bindweed (Convolvulus arvensis L.), hedge bindweed (Convolvulus sepium L.). Canada thistle [Cirsium arvense (L.) Scop.] tall morning glory [lpomoea purpurea (L.) Roth.] and wild buckwheat (Polygonum convolvulus L.). ¹⁴C was translocated throughout the plants within 3 days with accumulation in the meristematic tips of the roots and shoots evident. Cross and longitudinal sections of stems and roots showed that the ¹⁴C was localized in the phloem. Field bindweed translocated 3–5% of the applied ¹⁴C from the treated leaf, hedge bindweed 21.6%, Canada thistle 7.8%, tall morningglory 6.5%, and wild buckwheat 5%. Field bindweed, Canada thistle, and tall morningglory metabolized the parent glyphosate to aminomethylphosphonic acid to a limited extent. This metabolite made up less than 15% of the total 14C. Of the total ¹⁴C applied to excised leaves, 50% had disappeared within 25 days.     

Chemical control of nodding thistle (Carduus nutans L.) in New Zealand pastures

Broadcast sprays of several herbicides were applied at different times of the year at several sites in Hawkes Bay, Canterbury and Otago. For good thistle control, date of application was more important than types of herbicide. In Hawkes Bay, applications made in April, May and June tended to be the most effective. Under slightly cooler Canterbury conditions, April, September and October were the best application dates. In the Otago trials, spring emergence of thistle seedlings meant that the most consistent results came from September or October applications. At all sites, applications made in July or August were relatively ineffective, probably because of low winter temperatures and slow thistle growth rates. MCPA (potassium salt) at 1·0 kg ha^?1 was the standard herbicide used in all experiments. MCPA at 0·5 kg ha^?1, MCPB (sodium salt) at 0·5 and 1·0 kg ha^?1 and 2,4-D at 0·5 kg ha^?1 did not kill as many thistles as MCPA at 1·0 kg ha^?1. MCPA at 1·5 kg ha^?1 and MCPB (butyl) ester + clopyralid at 0·5 + 0·015 or 1·0+0·03 kg ha^?1 gave consistently better control than MCPA at 1·0 kg ha^?1 2,4-D at 1·0 or 1·5 kg ha^?1, MCPB at 1·5 or 2·0 kg ha^?1, and MCPA + MCPB at 0·33 + 1·0 or 0·67 + 0·5 kg ha^?1 gave results very similar to MCPA at 1 kg ha^?1. Thistle control varied between sites and years. Some of the variation may have been due to different proportions of first and second year thistles present at spraying, and to variation in genetically determined herbicide susceptibility. Chemical control of thistles was short term only, because of dormant seeds in the soil.     

Use of mesotrione and tembotrione herbicides for post-emergence weed control in alkaloid poppy (Papaver somniferum)

Two field experiments were carried out a year apart on the alkaloid poppy (Papaver somniferum) in 2012 and 2013 in north-west Hungary, to assess the efficacy of mesotrione and tembotrione herbicides for post-emergence weed control. Our experiments tested (1) a single application of mesotrione at 144 g active ingredient (a.i.) ha^–1, (2) two separate applications of mesotrione at 144 g a.i. ha^–1, (3) a single application of tembotrione at 88 g a.i. ha^–1, (4) two separate applications of mesotrione at 88 g a.i. ha^–1, and (5) the combination of a single application of mesotrione at 144 g a.i. ha^–1 followed by a single application of tembotrione at 88 g a.i. ha^–1. Both non-treated and hand-weeded plots were used as controls. Among the most important weeds, Chenopodium album was most successfully controlled in the majority of the test treatments, but Fallopia convolvulus and Polygonum aviculare tolerated each herbicide application in 2012, likely due to the dry weather conditions. Because of the botanical similarity to the crop, none of the treatments proved to be significant against Papaver rhoeas. One dosage of tembotrione alone never reduced the dry weights of the target weed species or weed numbers significantly. The cuticular wax layer of the opium poppy can provide a natural defence against these herbicides, but some temporary phytotoxic yellowish discoloration occurred after tembotrione treatments. Our results show that mesotrione in combination with tembotrione is the most effective treatment and should be employed in poppy cultivation.     

A second survey of cereal weeds in central southern England

A survey of grass weeds of cereals in central southern England made in 1981 was repeated in 1982 between 28 June and 23 July. Dicotyledonous weeds were also assessed in 1982. A total of 1021 fields were surveyed, 702 in winter wheat. 198 in winter barley and 121 in spring barley. A total of twenty-four grass weeds were found and their levels of infestation were scored. The most frequently found grass weeds were the same as in 1981. In all cereals combined, these were Elymus (Agropyron) repens in 35% of fields, Avena fatua in 32%, Alopecurus myosuroides in 26% and Poa trivialis in 24%. Sixty-three species of dicotyledonous weeds were recorded and of these, eighteen species occurred in 2% or more of fields. The eight most frequent were Viola arvensis, Galium aparine, Stellaria media, Myosotis arvensis, Polygonum aviculare, Convolvulus arvensis, Bilderdykia (Polygonum) convolvulus and Lamium purpureum. Most species were fairly uniform in distribution, but Galium aparine, Convolvulus arvensis and Cirsium arvense were most frequent in the east while Viola arvensis was least frequent there. The cereals varied in weediness, 32% of winter barley, 23% of spring barley and only 7% of winter wheat fields had no weeds recorded.     

Influence of picloram on Cirsium arvense (L.) Scop, control with glyphosate

Low rates of picloram in mixture with glyphosate provided a rapid enhancement of the onset of injury to the shoots of Cirsium arvense (Canada thistle or creeping thistle) under field (0.07+1.0 and 0.07+1.5 kg ha^?1) and greenhouse (0.035+0.42 and 0.07+0.84 kg ha^?1) conditions. Picloram slightly reduced the amount of ¹⁴C-glyphosate absorbed at 24 and 48 but not 72 h after treatment. Movement of ¹⁴C-glyphosate from the treated leaves to the shoot apex, remainder of the shoot and roots was reduced in the presence of picloram. Necrosis of the treated leaves above the treated spots was evident, presumably indicating acropetal movement of either or both herbicides. With the picloram + glyphosate mixtures there was increased shoot regrowth over glyphosate alone at 1 year after treatment under field, and with certain mixtures at 18 days and 4 weeks after treatment under greenhouse conditions. Following application of the mixtures, accumulation of glyphosate in the shoots may be responsible for the enhanced onset of shoot injury while failure of enough glyphosate to translocate to, and cause death of, the roots may be responsible for the increased shoot regrowth over glyphosate alone.     

Effect of ammonium sulphate and related salts on the phytotoxicity of dichlorprop and other herbicides used for broadleaved weed control in cereals

In glasshouse experiments, additions of 10–100 g 1^?1 ammonium sulphate enhanced the phytotoxicity to broadleaved weeds and cereals of several water-soluble herbicides applied post-emergence in 75–300 1 ha^?1 with hydraulic nozzles. Studies with dichlorprop potassium salt and chickweed Stellaria media (L.) Vill. examined interactions between ammonium sulphate and environmental, application and formulation factors. Simulated rainfall immediately after spraying greatly reduced dichlorprop activity, whether or not ammonium sulphate was present. However, when there was an interval of 2–24 h between spraying and rainfall, the additive increased phytotoxicity. Surfactants tended to reduce dichlorprop phytotoxicity to Stellaria media, both in the presence and absence of ammonium sulphate. Certain other inorganic salts including sodium sulphate also enhanced phytotoxicity. Applications by rotary atomizer in very low spray volume (15 1 ha^?1, 250–280 μm drops) were less effective than conventional 150 1 ha^?1 applications. When very low volume application was used, addition of ammonium sulphate or nitrate tended to reduce activity further. In the field, ammonium sulphate significantly increased the effects against weeds of a commercial dichlorprop potassium salt formulation applied conventionally in 200 1 ha^?1 spray volume. Neutralized phosphoric acid had a similar effect but a mixture of this additive and ammonium sulphate reduced phytotoxicity. Both additives slightly increased dichlorprop injury to barley.     

The allelopathic activity of Californian thistle (Cirsium arvense (L.) Scop.) in Tasmania

The phytotoxicity of extracts from the roots and foliage of Cirsium arvense (L.) Scop, was studied using seven test species. Water and alcohol extracts of C. arvense inhibited the germination of its own and Trifolium subterraneum L. seed, and inhibited the growth of its own seedlings, three annual thistles, and Lolium perenne L., T. subterraneum and Hordeum distichon L. The results are related to phytosociological patterns observed in the field, and it is suggest that the presence of phytotoxins in the soil may make the establishment of some pasture and crop species difficult in areas infested with C. arvense. Activité allélopathique du chardon Cirsium arvense L. Scop, en Tasmanie La phytotoxicityé d'extraits obtenus à partir des racines et du feuillage de Cirsium arvense (L.) Scop, a étéétudiée en tulisant sept espèces servant de tests. Des extraits aqueux et alcooliques de C. arvense inhibèrent sa propre germination et celle des semences de Trifolium subterraneum L. Ils inhibèrent également la croissance de ses propres plantules, de trois chardons annuels, de Lolium perenne L. de T. subterraneum et de Hordeum distichon L. Les résultats sont rapprochés des évolutions phytosociologiques observées au champ, et il est suggéré que la présence de phytotoxines dans le sol puisse rendre difficile l'implantation de certaines espèces fourragères ou autres dans les endroits infestés par C. arvense. Die allelopathische Aktivität von Cirsium arvense (L.) Scop. in Tasmanien Wurzel- und Blattextrakte von Cirsium arvense (L.) Scop. wurden auf ihre phytotoxische Wirkung mit sieben Test-pflanzen geprüft. Wasser- und Alkoholauszüge von C. arvense hemmten die Keimung der eigcnen und der Samen von Trifolium subterraneum L. Das Wachstum der eigenen Keimlinge, sowie von drei annuellen Distelarten, von Lolium perenne L., T. subterraneum und von Hordeum distichon L, wurde gehemmt. Die Ergebnisse zeigen einen Zusammenhang mit pflanzensoziologischen Feldbeobachtungen und es ist denkbar, dass die Gegenwart von Phytotoxinen im Boden den Aufwuchs von Grünlandpflanzen und Feldfrüchten in Fiächen, die mit C. arcense verseucht sind, erschweren kann.     

Cirsium arvense (L.) Scop. competition with winter wheat (Triticum aestivum L.)

A series of field experiments was conducted to evaluate the competitive effect of Cirsium arvense (L.) Scop. on winter wheat (Triticum aestivum L. ‘Norstar’) yield. Grain yield at the centre of dense C. arvense patches ranged from 28–71% of the yield in adjacent weed-free plots, based on measurements made at 11 experimental sites over a 2-year period. The mean reduction in yield was 49%. Two models were used to describe grain yield reduction in terms of C. arvense shoot density: (a) linear regression of percentage yield reduction on the square root of shoot density, and (b) non-linear regression, based on a rectangular hyperbola. Both models give similar yield loss estimates at commonly occurring shoot densities of C. arvense, but the non-linear model accounted for more of the observed variation in grain yield. The major yield component affected by C. arvense competition was spikes per unit area, with kernel weight affected to a lesser extent.     

Characteristics of seeds and seedlings from weeds treated with sublethal herbicide doses

Size, germination and viability of seeds as well as growth of seedlings derived from three weed species were studied in a pot trial. Fallopin convolvulus (L.) A. Loeve, Galium. spurium L. and Thlaspi arvense L. were treated with MCPA or tribenuron-methyl at four doses and at five growth stages, from seedling stage to flowering, In G. spurium subnormal doses of tribenuron-methyl, applied at intermediate growth stages, greatly reduced seed weight, gennination, viability, seedling shoot biomass and root biomass. Germination and viability, as well as the shoot biomass and root biomass of seedlings, were highly correlated with seed weight. In addition, but to a smaller extent, seed weight was reduced in F. convolvidus and T. arvense by tribenuron-methyl and in G. spurium by MCPA. Germination was reduced in F. convolvulus by MCPA and in T. arvense by tribenuron-methyl. However, the effects varied greatly depending on the growth stage at application.     

Alternatives to hexazinone and terbuthylazine for chemical control of Cytisus scoparius in Pinus radiata plantations in New Zealand

Two herbicides used for post‐plant weed control in commercial forests in New Zealand, terbuthylazine and hexazinone, are not endorsed for use on land certified by the Forest Stewardship Council (FSC). These herbicides are effective for controlling competitive woody weeds, such as Cytisus scoparius (broom). To investigate the potential of non‐residual, alternative herbicides for the control of C. scoparius after planting, a range of treatments were implemented at two trials. The trials were established in newly planted Pinus radiata plantations where C. scoparius dominated. The objectives were to (i) optimise application rates of alternative herbicides and compare their efficacy to current practice and (ii) identify if treatment efficacy varied across sites. Treatments at each site included weedy and weed‐free controls, current practice using terbuthylazine and hexazinone, applied as both spot treatment and broadcast application, and a range of new treatments consisting of different dosage combinations of clopyralid, triclopyr and picloram. Broadcast application of the clopyralid, triclopyr and picloram mixture showed increasing weed‐control efficacy against C. scoparius with increasing dose rate, resulting in increased tree volume. Broadcast application of the clopyralid, triclopyr and picloram mixture at 75% or 100% of a typical industry use rate (100% industry rate includes clopyralid 1.5 kg a.i. ha^?1, triclopyr 0.15 kg a.i. ha^?1 and picloram 0.05 kg a.i. ha^?1) achieved greatest tree volume by year four with tree volumes exceeding that obtained using the operational spot treatment with terbuthylazine and hexazinone. Treatment rankings were similar between locations. The result supports the use of clopyralid, triclopyr and picloram to control C. scoparius during the first year of P. radiata establishment.     

Glyphosate effects on Canada thistle (Cirsium arvense) roots, root buds, and shoots

Glyphosate ? ? Mention of irademark or proprietary product does not constitute a gtiarantee or warranty oC the product by the U.S. Department of Agriculture and does nut imply its approval to the exclusion of other products thai may also be suitable.
was sprayed at 0009–1·12 kg a.i. ha^?1 on the foliage of large potted glasshouse-grown Canada thistle [Cirsium arvense (L.) Scop.], which had extensive, well-developed roots. Increasing the glyphosate rate progressively reduced the total number of visible adventitious root buds plus emerged secondary shoots per plant proportionately more than root biomass, 10 days after treatment. Cortical tissue of thickened propagative roots became soft, water-soaked, darkened, and some regions decomposed, exposing strands of vascular tissue. Lateral roots completely decomposed. When thickened roots were segmented to stimulate secondary shoot emergence from root buds 10 days after foliar treatment, Fewer secondary shoots emerged than expected from the number of visible adventitious root buds present on both control and herbicide-treated plants. Increasing the rate of glyphosate also reduced the regrowth potential of root buds proportionately more than root biomass. Regrowth potential was measured as the number of emerged secondary shoots 35 days after segmenting unearthed roots from plants that had been sprayed 10 days earlier. When foliar-applied at 0·28 kg ha^?1, glyphosate decreased the regrowth potential of root buds to zero in 2 and 3 days, as measured by secondary shoot dry weight and number, respectively, even though root fresh weight was unchanged 3 days after foliar treatment. These dose-response and time-course experiments demonstrate that glyphosate did not reduce root biomass as much as it decreased root bud numbers and secondary shoot regrowth potential from root buds.     

Effects of two pathogens on the performance of Cirsium arvense in a successional fallow

Biological control of weeds by natural antagonists is of increasing interest. To reduce densities of the weed Cirsium arvense (creeping thistle) in a successional fallow, we applied spores of two pathogens, the biotrophic rust Puccinia punctiformis and the perthotrophic Phoma destructiva, for three consecutive years individually at different dates and combined. The proportion of systemically Puccinia punctiformis-infected C. arvense was not influenced by the treatments, but local rust infection was a good predictor of systemic infection in the following season. Artificial inoculations with P. destructiva increased the incidence of this pathogen in the third year as a result of synergistic effects, when co-inoculated with P. punctiformis. Inoculations with either pathogen had little effect on C. arvense shoot density, although there were transient reductions after combined inoculations with both fungi compared with the fungicide treatment. Cirsium arvense decreased from 60% to 5% cover within 3 years, while the cover of the co-occurring fallow vegetation increased. Under field conditions, with an already high degree of natural P. punctiformis infection, the effects of inoculations of the single pathogens were minor, but reductions in shoot density after combined inoculations indicate that this inoculation may have the potential to cause a decline of this weed.     

Response of teff (Eragrostis tef(Zucc.) Trotter) to 2, 4-D and MCPA at various growth stages

Teff (Eragrostis tef (Zucc.) Trotter) cv.DZ-01- 354 was sprayed at one-, three-, four-, five- and six-leaf stages with 2.4-D (amine salt) and MCPA (potassium salt) each at 0.75 and 1.5 kg a.e. ha^?1. Teff was also grown in different temperature regimes to see the relation between apical and vegetative development. Photomicrographs were made to determine the stage of development of the growing point and dry matter measurements were made to assess the effects of the herbieide. Teff sprayed at the one leaf stage was killed by both herbieides. At the three- and four-leaf stages 2, 4-D at both rates and MCPA at 1.5 kg a.i. ha^?1 caused severe leaf deformities and reduced dry weights. Less severe effects were noted at the five-leaf stage indicating that teff was then more tolerant to these herbicides. This coincided with a fully elongated shoot apex. However, when sprayed at the six-leaf stage there was evidence of herbicide-induced panicle deformities. Teff was more susceptible to 2, 4-D than to MCPA and both affected the roots more than the shoots. A close correlation was found between leaf number and the development of shoot apex under all the different temperature and day length conditions.