Response of Sorghum halepense demographic processes to plant density and rimsulfuron dose in maize

In spatially heterogeneous weed infestations, variable dose technologies could be used to minimise herbicide use; high doses could be applied to reduce high‐density patches and low doses to maintain weed populations in low‐density portions of a field. To assess the potential short‐ and long‐term effects of variable herbicide dose and site‐specific management, the major weed demographic processes were described and parameterised in this study. Various doses of rimsulfuron (from 0 to 12.5 g a.i. ha^?1) were applied to different densities of Sorghum halepense (0–100 plants m^?2). Contrary to similar studies with other weed species, higher herbicide efficacy was not observed at low densities, suggesting that the same rimsulfuron dose should be applied regardless of the S. halepense density. The highest percentage of control was obtained with the full rimsulfuron dose. However, it did not guarantee a decrease of the infestation in the following season in the field areas where the initial S. halepense density was lower than 60 plants m^?2. Reduced doses of rimsulfuron to control S. halepense cannot be recommended based on our results.     

Influence of propaquizafop application rate and time on Sorghum halepense (L.) Pers. control and cotton (Gossypium hirsutum) yield

Field experiments were carried out from 1990 through 1992 to study the effect of propaquizafop application rate and application timing of fluazifop, haloxyfop, propaquizafop, quizalofop, and hoeing on Sorghum halepense (L.) Pers. control and seed cotton yield. Control of S. halepense with propaquizafop applied to plants 20–35 cm tall was not affected by rate of application and was similar to that obtained with fluazifop applied at the recommended rate. Cotton yield following all herbicide treatments was greater than that of the weedy control, but lower than that of the weedfree control. S. halepense control with fluazifop, haloxyfop, propaquizafop, and quizalofop applied to plants 20–35 or 35–80 cm tall was greater than that obtained with their application to plants 5–15 or 10–25 cm tall. Ho-eing, applied once at any S. halepense growth stage, provided less control than any herbicide treatment on the same date. Cotton yield was increased by all herbicide treatments and hoeing compared to that of the weedy control, but the highest yield was obtained after herbicide appli-cation to S. halepense plants 10–25 cm tall. However, none of the herbicide treatments or hoeing increased cotton yield to the level of the weedfree control.     

Foliar absorption and translocation of nicosulfuron and rimsulfuron in five annual weed species

Ambrosia artemisüfolia L. (common ragweed) and Digitaria ischaemum Schreb. (smooth crabgrass) are not controlled by nicosulfuron and rimsulfuron at the highest recommended application rates, whereas Panicum miliaceum L. (wild proso millet), Amaranthus retroflexus L. (redroot pigweed) and Avena fatua L. (wild oat) are susceptible. The foliar absorption and translocation of ¹⁴C-nicosulfuron and ¹⁴C-rimsulf uron were studied in these weed species up to 48 h after treatment (HAT). Differences in herbicide uptake and translocation were not correlated with the species susceptibility. By 48 HAT, more than 50% of both herbicides remained on the treated leaf surface. Foliar absorption of rimsulfuron was greater than that of nicosulfuron in A. retroflexus, P. miliaceum and A. artemisüfolia. Most of the absorbed herbicide remained in the treated leaf of each weed species. Export of ¹⁴C–nicosulfuron ranged from 28 to 54% of that absorbed, in contrast to 15 to 39% for ¹⁴C–rimsulfuron. The absorption and translocation rates of both herbicides were highest within the initial 6 HAT, and decreased thereafter. Both herbicides showed approximately the same distribution pattern within each weed species.     

Application timing of asulam for torpedograss (Panicum repens L.) control in sugarcane in Okinawa island

Field and glasshouse experiments were conducted from 1995 through 1996 to evaluate application timing of asulam (methyl sulfanilylcarbamate) for torpedograss (Panicum repens L.) control in relation to plant age in sugarcane. Above‐ground shoots of torpedograss were completely controlled with asulam at 2–4 kg active ingredient (a.i.) ha^?1 applied 60 or 80 days after planting (DAP) in artificially infested pots. But some newly developed rhizome buds survived after asulam application resulting in 1–25 and 76–100% or more regrowth in 60 and 80 DAP‐applied pots, respectively. Whereas the herbicide at 2–4 kg a.i. ha^?1 applied within 60 DAP completely controlled above‐ground shoots, applied 80 DAP at 2 kg a.i. ha^?1 it did not completely control the weed in the artificially infested field. Regrowth levels were 1–25 and 76–100% or more in 60 and 80 DAP‐applied plots, respectively. Asulam at 2–3 kg a.i. ha^?1 applied 20, 40, 60 or 80 DAP in a naturally infested field completely controlled above‐ground shoots and regrowth levels were 76–100 or more, 51–75, 1–25 and 26–50% in these same DAP applied plots, respectively. The herbicide applied at 4 kg a.i. ha^?1 caused chlorosis on younger sugarcane leaves (one‐leaf stage), but when applied at 2–3 kg a.i. ha^?1, no injury symptoms were shown. The herbicide at 2–4 kg a.i. ha^?1 applied within 60 DAP resulted in remarkably higher yield and shoot biomass of sugarcane than that applied 80 DAP. This study suggested that asulam at 2–3 kg a.i. ha^?1 should be applied 60 days after planting for the maximum control of torpedograss regrowth and better yield of sugarcane. This study also indicated that torpedograss cannot be completely controlled with a single application of asulam in a naturally infested field because of rhizome fragmentation by cross plowing and distribution of rhizomes into different soil layers that require different times to emerge. The shoots emerging after asulam application could not be controlled. Another study is required to determine the interval between sequential applications of asulam for better control of torpedograss in a naturally infested field.     

Weed control and selectivity in maize (Zea mays L.) with tembotrione mixtures

Field and pot trials were conducted in two sites of northern Greece (Thermi and Lepti) to study selectivity and weed control in maize (Zea mays L.) with herbicide mixtures based on tembotrione. Treatments included tembotrione (plus isoxadifen-ethyl safener) applied alone at 100 g ai/ha and three mixtures of tembotrione with: (i) rimsulfuron at 10 g ai/ha, (ii) nicosulfuron at 40 g ai/ha and (iii) foramsulfuron at 60 g ai/ha (label rates for weed control in maize). Herbicides were applied at the 7- to 8-leaf growth stage of maize in Thermi and at the 6- to 7-leaf growth stage in Lepti. Six weeks after treatment, control of rhizomatous Sorghum halepense with tembotrione alone was 63% in Thermi and 60% in Lepti, with plants showing the typical bleaching symptoms of the HPPD-inhibiting herbicides. Control of rhizomatous S. halepense with the mixtures was improved from 63% to 86% in Thermi and from 60% to 82% in Lepti compared with the single treatment of tembotrione, with plants showing only the symptoms of reddish/purplish color of the ALS-inhibiting herbicides. Control of common broadleaf weeds of maize, such as Xanthium strumarium, Amaranthus retroflexus, Datura stramonium, and Chenopodium album was excellent (92%–100%) either with tembotrione alone or with the mixtures, with plants showing the typical bleaching symptoms of the HPPD-inhibiting herbicides. None of the mixtures affected the ear length and grain yield of maize. All chemical treatments gave higher grain yield than that of the non-treated control and comparable yield to that of the weed-free control. Grass control (Echinochloa crus-galli, E. phyllopogon, and Setaria viridis) with tembotrione alone was above 90% in the pot experiments which was similar to that achieved with the mixtures. Overall, there was an adequate margin of safety in the use of tembotrione in mixture with ALS-inhibiting herbicides for improved weed control in maize, particularly where rhizomatous S. halepense is problematic.     

Modelling interactions between herbicide dose and multiple weed species interference in crop–weed competition

The effects of a range of herbicide doses on crop–multiple weed competition were investigated. Competitivity of Galium aparine was approximately six times greater than that of Matricaria perforata with no herbicide treatment. Competitivities of both weeds decreased with increasing herbicide dose, being well described by the standard dose–response curve with the competitivity of M. perforata being more sensitive than that of G. aparine to a herbicide mixture, metsulfuron‐methyl and fluroxypyr. A combined model was then developed by incorporating the standard dose–response curve into the multivariate rectangular hyperbola competition model to describe the effects of multiple infestation of G. aparine and M. perforata and the herbicide mixture on crop yield. The model developed in this study was used to predict crop yield and to estimate the herbicide dose required to restrict crop yield loss caused by weeds to an acceptable level. At the acceptable yield loss of 5% and the weed combination of 120 M. perforata plants m^?2 and 20 G. aparine plants m^?2, the model recommends a mixture of 1.2 g a.i. ha^?1 of metsulfuron‐methyl and 120 g a.i. ha^?1 of fluroxypyr.     

Diclofop-methyl antagonism by broadleaf weed herbicides: the importance of leaf expansion rate

Avena saliva cv. Amuri and A. fatua were sprayed with diclofop methyl (1.0 kg a.i. ha^?1) alone and in combination with 2,4-D (1.1 kg a.i. ha^?1), bentazone (1.0 kg a.i. ha^?1), chlorsulfuron (15 g a.i. ha^?1) or dicamba (0.3 kg a.i. ha^?1). Effects of the herbicides on leaf extension rate during the first 8 to 10 days after spraying and subsequent growth (dry weight) after 57–75 days were determined by comparison with unsprayed plants. Diclofop-methyl applied alone did not cause a decrease in leaf extension rate of A. saliva or A. fatua until at least 4 days after spraying. All broadleaf weed herbicides in combination with diclofop-methyl caused a decrease in leaf extension rate of both species within 2 days of spraying. Ten days after spraying, leaf extension rates for plants sprayed with a broadleaf weed herbicide plus diclofopmethyl (all combinations) were lower than for unsprayed plants but greater than for plants sprayed with diclofop-methyl alone. With the exception of A. fatua sprayed with bentazone, long-term growth of plants sprayed with a broadleaf weed herbicide plus diclofop-methyl (all combinations) was lower than for unsprayed plants but greater than for plants sprayed with diclofop-methyl alone. Bentazone applied with diclofop-methyl caused a substantial decrease in leaf extension rate of A. fatua within 24 h of spraying but at harvest, dry weight of plants from this treatment was similar to or less than that for plants sprayed with diclofop-methyl alone. Application of diclofop-methyl with bentazone at a rate of 0.3 kg a.i. ha^?1 also caused a reduction in leaf extension rate of A. fatua within one day of spraying. At this rate of bentazone, dry weight of plants at harvest was intermediate to that of unsprayed plants and those sprayed with diclofop-methyl alone. It is proposed that decreased leaf expansion rate during the first few days afte spraying is the cause of broadleaf weed herbicide antagonism of diclofop-methyl.     

Field persistence of chlorsulfuron and DPX-L5300 in relation to rotational crops

A pot bioassay procedure, based on root growth of pre-germinated maize was used to study residual phytotoxicity of chlorsulfuron and DPX-L5300 methyl-([4-methoxy-6-methyl-1,3,5-triazin-2-yl(methyl) carbamoyl]sulphamoyl)benzoate under field conditions. The results indicate that residual bioactivity of both herbicides, applied either pre-or post-emergence at 5, 10, 20 and 40 g a.i. ha^?1, was increased with increasing rate of application. Chlorsulfuron persisted longer than DPX-L5300, and both herbicides, when applied pre-emergence, persisted longer than when applied post-emergence. Pot bioassay did not detect any residues eight months after either application. Maize and sunflower, planted as rotational field crops eight months after pre-emergence application, were not injured by either herbicide. Also, these crops were not affected when planted four months after post-emergence application of any of the DPX-L5300 rates or 5 or 10 g a.i. ha^?1 of chlorsulfuron, but their fresh weight was significantly reduced where 20 or 40 g a.i. ha^?1 of chlorsulfuron were applied.     

Grass weed control with herbicide-treated crop seeds

Fluazifop-butyl applied in lung oil at rates of 4.4 to 0.5 g a.i. kg^?1 soybean seeds was evaluated in the glasshouse for control of Eleuisine indica. Soybean seeds pretreated with herbicide at 4.4 to 2.1 g a.i. kg^?1 gave 100% control of E. indica at the highest sowing rate of four seeds per pot and 90 to 80% control when sowed at one seed per pot. Soybeans were not injured by the seed treatment. Cotton seeds pre-treated with fluazifop at 2.2 g a.i. kg^?1 seeds and sown 4 cm apart in a row across a 20 ± 20cm tray of soil containing seeds of Echinochloa crus-galli produced a weed-free band 12 cm wide centred on the row of cotton, without injury to cotton. CGA-82725 (2-propynyl 2-(4-((3, 5-dichloro-2-pyridinyl)oxy)phenoxy) propanoate) at 2–3 g a.i. kg^?1 seeds was as effective as 4–4 g fluazifop-butyl in controlling E. indica. but growth of soybean was retarded. Sethoxydim gave less control than fluazifop butyl at comparable rates and did not injure soybeans.     

Orobanche ramosa L. (broomrape) control in tomato (Lycopersicon esculentum Mill.) with chlorsulfuron, glyphosate and imazaquin

Chlorsulfuron, giyphosate and imazaquin were evaluated in pot and field studies for their efficacy in controlling broomrape (Orobanche ramosa L.) in tomato (Lycopersicon esculentum Mill.) in Northern Greece. All herbicides were applied four to five weeks after tomato transplanting, when the crop was at early flowering stage and broomrape had started to develop underground attachments. The number of emerged broomrape shoots and underground attachments were less affected by herbicide treatments than the dry weight, suggesting that the herbicides suppress the growth of broomrape rather than kill its underground organs. In the pot experiments, chlorsulfuron applied at 5 g AI ha^?1 was the most effective treatment for broomrape control and the least toxic to the crop. Imazaquin and glyphosate applied at 37 and 180 g AI ha^?1, respectively, controlled broomrape but imazaquin reduced crop yield. In the field, similar rates of glyphosate and higher rates of imazaquin were not toxic to the crop but were less effective on broomrape. Chlorsulfuron applied at 10 g AI ha^?1 controlled broomrape emergence by 88%. When the herbicide was applied twice (5+10 g AI ha^?1), it gave complete control of broomrape but delayed crop maturity. The yield of tomato was not increased as a result of these treatments because of low broomrape infestation and a short competition period.     

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%.     

Field emergence and the long‐term efficacy of control of Heracleum sosnowskyi plants of different ages in southern Poland

Heracleum sosnowskyi is one of the three so‐called tall or giant hogweeds currently invading Asia, Europe and North America. These plants are dangerous invasive weeds, causing severe skin injuries in humans and animals. In the present study, based on four field experiments, we assessed seedling emergence in the field and evaluated methods for the long‐term mechanical and chemical control of H. sosnowskyi of various ages (1–5 years old). The field experiments were set up in the mountainous regions of southern Poland, on soil not previously infested with H. sosnowskyi seeds. The results showed that the successful eradication of this species from an invaded area is possible. The results revealed that when no new flush of seeds is delivered to the soil seedbank, the longevity of H. sosnowskyi seeds is approximately five years, with the majority of seedlings emerging in the spring of the first year following sowing. Long‐term shoot cutting, particularly the intensity of this technique, is ineffective for the control of H. sosnowskyi. Cutting three times a year for five years resulted in an H. sosnowskyi control outcome of 42–97%. Total control of this weed is obtained either by cutting the roots of plants up to 5 years old at a depth of 15 cm or by continuous (5 years long) herbicide spraying three times during the vegetative season, using a tank mixture of glyphosate and flazasulfuron (1260 g a.i. glyphosate ha^?1 + 50 g a.i. flazasulfuron ha^?1).     

Sorghum halepense (L.) Pers. control with foliar-applied herbicides in conventional and no-tillage soyabeans*

Separate field experiments were conducted to evaluate Sorghum halepense (L.) Pers. (johnson-grass) control with foliar-applied herbicides in soyabeans (Glycine max (L.) Merr. cv. Williams) grown in tilled (mould board plough) or no-tillage fields. Fluazifop-butyl, sethoxydim, CGA-82725 and mefluidide were applied post-emergence to 45-cm high S. halepense and glyphosate was applied with a wick bar to 90-cm high S. halepense in the conventional and no-tillage studies. HOE-00581 {ethyl 2-[4-[(6-chloro-2-benzoazolyl)oxyl]-phenoxy]propanoate} was applied to 45-cm high S. halepense only in the no-tillage studies. Fluazifop-butyl, sethoxydim, CGA-82725, HOE-00581 (no-tillage only) and glyphosate provided good control of S. halepense in conventional and no-tillage soyabeans and generally increased soyabean yields compared to weedy controls, when low precipitation was not limiting yields. Mefluidide at 0.3 kg ai ha^?1 provided the least S. halepense control in the conventional and no-tillage studies. The studies were not designed to compare S. halepense control in the two tillage systems; however, these data show that tillage to disrupt S. halepense rhizomes was not required to obtain good control of S. halepense with foliar applications of fluazifop-butyl, sethoxydim, CGA-82725, HOE-00581 and glyphosate. La lutte contre Sorghum halepense (L.) Pers. utilisant des herbicides foliaires dans le soja en culture classique et en non-culture Plusieurs essais ont été installés sur le terrain dans le but d'évaluer des herbicides foliaires pour la destruction de Sorghum halepense (L.) Pers. dans le soja (Glycine max (L.) Merr. var. Williams) cultivé en terre labourée et en non-culture. Le fluazifop-butyle, le séthoxydime, le CGA-82725 et le méfluidide ont été appliqués en postlevée sur S. halepense haut de 45 cm et le glyphosate a été appliqué sur S. halepense haut de 90 cm, utilisant un frotteur, dans les deux sytèmes de culture. HOE-00581 (éthyle 2-[4-[(6-chloro-2-benzoazolyl)oxyl]phénoxy]propanoate) a été appliqué sur S. halepense haut de 45 cm uniquement dans les systèmes de·non-culture. Le fluazifop-butyle, le séthoxydime, le CGA-82725, le HOE-00581 et le glyphosate ont bien maitriséS. halepense dans les deux systèmes de culture du soja, tout en augmentant les rendements de soja par rapport au témoin enherbé, là où une précipitation insuffisante n'est pas intervenue. Le méfluidide à 0,3 kg ai ha^?1 a donné la plus faible destruction de S. halepense en culture classique et en non-culture. Une comparaison de la destruction de S. halepense dans les deux systèmes de culture n'était pas le but principal de ces travaux; cependant ces données font voir qu'un labourage pour briser les rhizomes de S. halepense n'est pas de rigueur pour obtenir une bonne maîtrise de l'adventice par des applications foliaires de fluazifop-butyle, séthoxydime, CGA-82725, HOE-00581 et glyphosate. Sorghum halepense (L.) Pers. Bekämpfung mit blattwirksamen Herbiziden in Soyakulturen mit und ohne Bodenbearbeitung Es wurden separate Feldversuche zur Bekämpfung von Sorghum halepense (L.) Pers. mit blattwirksamen Herbiziden in Soyakulturen (Glycinemax (L.) Merr. cv. Williams), ohne und mit Bodenbearbeitung (Mouldboard Pflug), ausgeführt. Fluazifop-Butyl, Sethoxydim, CGA-82725 und Mefluidid wurden postemergent auf 45 cm hohe und Glyphosat mit einem Docht-Streichgerät (wick bar) auf 90 cm hohe S. halepense appliziert; diese Produkte kamen in den Feldern mit und ohne Bodenbearbeitung zur Anwendung. HOE-00581 {Aethyl 2-[4-[(6-chlor-2-benzoazolyl)oxyl]phenoxy]propanoat} wurde nur auf den Parzellen ohne Bodenbearbeitung auf 45 cm hohe S. halepense appliziert. Fluazifop-Butyl, Sethoxydim, CGA-82725, HOE-00581 (Ohne Bodenbearbeitung) und Glyphosat erzielten in bearbeiteten und unbearbeiteten Feldern eine gute Bekämpfung von S. halepense und bewirkten im allgemeinen eine Erhöhung der Ernteerträge, sofern nicht geringe Niederschläge als limitierender Faktor auftraten. Mefluidid (0,3 kg ai ha^?1) ergab die geringste Wirkung in bearbeiteten und unbearbeiteten Feldern. Diese Versuche waren nicht geplant um den Erfolg der S. halepense Bekämpfung unter den zwei Anbaubedingungen (mit resp. ohne Bodenbearbeitung) miteinander zu vergleichen; immerhin zeigen die Ergebnisse, dass eine Bodenbearbeitung zur Zerkleinerung der S. halepense-Rhizome nicht notwendig ist, um gute Effekte mit Fluazifop-Butyl, Sethoydim, CGA-82725, HOE-00581 und Glyphosat zuerzielen.     

Effects of Low Doses of Glyphosate on Agronomic Traits of Upland Rice

Research has shown the occurrence of the hormesis effect in some upland rice cultures resulting from low-dose application of glyphosate. Glyphosate herbicide is widely used in Brazilian agriculture for controlling the large quantity of weeds. The aim of this work was to verify the effects of low-dose application of glyphosate herbicide on agronomic characteristics in upland rice. The experimental design used was randomized blocks comprising five low-dose applications of glyphosate herbicide (10, 20, 40, 70, and 100?g acid equivalent [a.e.] ha^?1) and the control, in two stages of development of the rice culture (tillering [V4] and floral differentiation [R1]) with four repetitions. The agronomic traits of upland rice were evaluated. Data were subjected to variance analysis, polynomial regression analysis for the quantitative factor, and Tukey’s test for the qualitative factor at p?<?0.05. The grain yield and the number of spikelets per panicle increased with the application of 10?g a.e. ha^?1 of glyphosate at the floral differentiation stage. Until the low dose of 75?g a.e. ha^?1, there was an increase in the number of panicles. Low doses between 70 and 100?g a.e. ha^?1 applied in R1 provided less spikelets per panicle, lower 100-grain weight, and lower grain yield. The leaf flavonoid content increased due to the increase in the low doses of glyphosate herbicide.

     

Testing the performance of registered herbicides on the control of Campuloclinium macrocephalum (Asteraceae) in South African grasslands

We report on the performance of the registered herbicides picloram and metsulfuron‐methyl on the control of Campuloclinium macrocephalum (pompom weed) in grasslands. Herbicide trials in hydric and xeric grasslands were treated for three consecutive years in either summer (February) or autumn (April) and monitored for an additional 3 years after spraying ceased. Uncontrolled factors such as a host‐specific rust, fire and drought were observed from the second year of the study. Metsulfuron‐methyl and picloram did not differ in efficacy according to the timing of applications, but average mortality of marked plants was <80% expected of registered herbicides. Populations of C. macrocephalum in plots were reduced proportionately to the percentage mortality of marked plants. Picloram and metsulfuron‐methyl applied at 252 g a.i. ha^?1 and 45 g a.i. ha^?1, respectively, were not detectable by gas chromatography in the upper 25 cm of the soil profile during any of the sampling intervals from 0 to 56 days after treatment. Three annual applications of registered herbicide did not reduce C. macrocephalum successfully, and it is estimated that between five (summer) to seven (autumn) annual treatments are required to reduce weed density to <1 plant per plot (25 m²). Future research should focus on rust–herbicide interactions, the role of fire in seedbank management and fire as a treatment that could be integrated with chemical control.     

Tolerance of spring wheat (Triticum aestivum L.) to trifluralin deep-incorporated in the autumn or spring

Field experiments at Lacombe on a Ponoka loam soil (9·6% organic matter) during 1982 and 1983 investigated the tolerance of spring wheat (Triticum aestivum L.) cv. Neepawa in a weed free situation to trifluralin applied at 0·0–3·0 kg ai ha^?1 in the autumn or spring and incorporated to a depth of 10 cm. Rates of trifluralin above 1·0 kg ai ha^?1 applied in the autumn or spring reduced the percent stand of wheat compared to an untreated control. Two weeks after emergence the crop showed 37 or 47% injury indicated by delayed growth, following application at 1·0 kg ai ha^?1 in the autumn or spring, respectively. The wheat recovered throughout the course of the growing season. At harvest, trifluralin applied in the autumn or spring at rates below 1·0 kg ai ha^?1 caused a yield increase while higher rates caused a yield decrease compared to the untreated control. Spring application caused a greater yield loss than autumn application. The tolerance of spring wheat to trifluralin at rates required for weed control (1·1 kg ai ha^?1 or higher) on this soil type is marginal.     

Pre-emergence herbicides for the control of broomrape (Orobanche cernua Loefl.) in sunflower (Helianthus annus L.)

Field experiments were conducted from 1989 to 1992 to determine the effects of pre-emergence herbicides in sunflower (Helianthus armuus L.) on: (1) the control of Orobanche cemua Loefl. (broomrape) and (2) crop damage and crop yield. Herbicides tested belong to the imidazolinone, sulfonylurea and substituted amide families. Imazethapy r (20–40 g ha^?1), imazapy r (12.5–25 gha^?1) and chlorsulfuron (4–6 gha^?1) controlled broomrape efficiently without crop injury. With good O. cernua control and good crop tolerance, sunflower seed yield from these treatments were generally similar to the non-infested checks and higher than the infestedchecks. Imazaquin (20–40 gha^?1), triasulfuron(4gha^?1), pdmisulfuron(3g ha^?1), acetochlor (4–4 kg ha^?1) and metazachlor (2 kg ha^?1) were less effective. Imazamethabenz (200–600 g ha^?1) and metolachlor (3–3 kg ha^?1) were ineffective. Wetconditions aftercropsowing considerably decreased O. cemua control with pre-emergence herbicides probably caused by enhanced degrädation. Des herbicides de prelevee pour la lutte contre Vorobanche (Orobanche cemua Loefl.) dans le toumesol (Helianthus annuus L.) Des expérimentations au champ ont été conduites de 1989 á 1992 pour determiner les effets d'herbicides de pré1evée du toumesol sun (a) la destruction de l'orobanche (Orobanche cernua Loefl.) et (b) la phytotoxcité sur la culture. Les herbicides testés appartenaient aux imidazolinones, aux sulfonylurdes et aux amides substituées. L'imazethapyr (20 á 40 gha^?1), l'imazapyr (12,5 á25gha^?1)et le chlorsulfuron (4 á 6 gha^?1) détruisaient efficacement l'orobanche sans occasionner de phytotoxidt6 sur la culture. Dans ces conditions, les rendements étaient généralement semblables à ceux des témoins non infestés et supérieurs à ceux des témoins infestés. L'imazaquin (20 à 40 g ha^?1), le triasulfuron (4 gha^?1), le primisulfuron (3 g ha^?1), lacétolachlor (4,4 kg ha^?1) et le métazachlor (2 kg ha^?1) étaient moins efficaces. L'imazaméthabenz (200 á 600 g ha^?1) et le métolachlor (3,3 kg ha^?1) etaient inefficaces. Des conditions humides aprfes le semis diminuaient considérablement la destruction de O. cemua par les herbicides de prélevée, probablement à cause d'une dégradation plus élevée. Vorauflaufherbigide zur Bekdmpfung der Sommerwurz Orobanche cemua Loefl. in Sonnenblume (Helianthus annuus L.) Zwischen 1989 und 1992 wurden in Sonnenblume Feldversuche zur Wirkung von Vorauflaufherbiziden aus den Gruppen der Imidazolinone, Sulfonylharnstoffe und substitutierten Amide auf die Sommerwurz Orobanche cernua und auf Kulturpflanzenschaden sowie den Ertrag durchgefuhrt. Mit Imazethapyr (20 bis 40 g ha^?1), Imazapyr (12,5 bis 25 g ha^?1) und Chlorsulfuron (4 bis 6 g ha^?1) lieβ sich die Sommerwurz wirksam bekampfen, ohne daβ Schaden an der Sonnenblume auftraten, und die Ertrage waren allgemein ahnlich oder hoher als bei der nichtparasitierten Kontrolle. Imazaquin (20 bis 40 ha^?1), Triasulfuron (4 g ha^?1).Primisulfuron (3 g ha ^?1). Acetochlor (4,4 kg ha ^?1 und Metazachlor (2 kg ha ^?1) waren weniger wirksam. Imazamethabenz (200 bis 600 g ha^?1) und Metolachlor (3,3 kg ha^?1) hatten keine Wirkung. Bei Niederschlagen nach der Saat der Sonnenblume war die Bekampfung der Sommerwurz mit Vorauflaufherbiziden vermutlich wegen verstärkten Abbaus erheblich schwächer.     

The effect of the herbicide glyphosate on non‐target spiders: Part II. Indirect effects on Lepthyphantes tenuis in field margins

We have examined the indirect effect of the herbicide glyphosate on the spider Lepthyphantes tenuis in field margins. Glyphosate was applied to a randomised block design field experiment comprising 360, 720 and 1440 g glyphosate AE ha^?1 treatments and an unsprayed control. Spiders were sampled in each month from June to October 1998. Spider abundance was significantly lower in all the treatments than in the unsprayed control. Abundance was also significantly lower in the 720 and 1440 g treatments than in the 360 g treatment. No significant difference could be detected between the 720 and 1440 g treatments. Poisson regression models showed that patterns of decline in L tenuis were related to increasing dead vegetation and decreasing vegetation height. Glyphosate applications only had a within‐season indirect habitat effect on L tenuis as field margins sprayed 16 months after an application of 360 g glyphosate ha^?1 showed no detrimental effect. © 2001 Society of Chemical Industry     

Modelling the effects of sub-lethal doses of herbicide and nitrogen fertilizer on crop–weed competition

The effects of sub‐lethal dose of herbicide and nitrogen fertilizer on crop–weed competition were investigated. Biomass increases of winter wheat and a model weed, Brassica napus, at no‐herbicide treatment with increasing nitrogen were successfully described by the inverse quadratic model and the linear model respectively. Increases in weed competitivity (β₀) of the rectangular hyperbola and parameter B in the dose–response curve for weed biomass, with increasing nitrogen were also successfully described by the exponential model. New models were developed by incorporating inverse quadratic and exponential models into the combined rectangular hyperbola with the standard dose–response curve for winter wheat biomass yield and the combined standard dose—response model with the rectangular hyperbola for weed biomass, to describe the complex effects of herbicide and nitrogen on crop–weed competition. The models developed were used to predict crop yield and weed biomass and to estimate the herbicide doses required to restrict crop yield loss caused by weeds and weed biomass production to an acceptable level at a range of nitrogen levels. The model for crop yield was further modified to estimate the herbicide dose and nitrogen level to achieve a target crop biomass yield. For the target crop biomass yield of 1200 g m^?2 with an infestation of 100 B. napus plants m^?2, the model recommended various options for nitrogen and herbicide combinations: 140 and 2.9, 180 and 0.9 and 360 kg ha^?1 and 1.7 g a.i. ha^?1 of nitrogen and metsulfuron‐methyl respectively.     

Eleven years of integrated weed management: long‐term impacts of row spacing and harvest weed seed destruction on Lolium rigidum control

Long‐term research aimed to determine whether narrow row spacing and harvest weed seed destruction, in combination with herbicide use, would be sufficient to drive a Lolium rigidum population to extinction. A trial was run from 1987 to 2013, with treatments including crop row spacings of 9, 18, 27 or 36 cm and crop residue burning or retention. Herbicides were applied to reflect regional practices. The initial trial design was randomised, but treatments were maintained in each plot over the following years. Lolium rigidum seed production at harvest was assessed from 2003 to 2013. Average crop yield was higher in the unburnt plots (1638 kg ha^?1) than the burnt plots (1530 kg ha^?1) and greater at narrow row spacing, with an average yield of 1658, 1637, 1548 and 1492 kg ha^?1 in the 9‐, 18‐, 27‐ and 36‐cm spacings. Lolium rigidum seed at harvest was reduced in the burnt plots (57 seeds m^?2) compared with the unburnt plots (297 seeds m^?2) and was reduced at narrow row spacing, with an average of 58, 78, 223 and 333 seeds m^?2 in the 9‐, 18‐, 27‐ and 36‐cm row spacings. By 2013, L. rigidum seed production was reduced to an average of 0 seeds m^?2 in the narrow row spacing, burnt plots.