bluuebunny/crossref_metadata_2025 huggingface dataset:
Patchy distribution of weeds and some implications for modelling population dynamics: a short literature review
Authors: van GROENENDAEL J. M.
Published: July 2006

Until recently the modelling of crop‐weed interactions has largely ignored the complexities resulting from the patchy distribution of weeds and the multi‐species nature of weed communities. Some progress has now been made in dealing with these two sources of variation. A population dynamical approach has proven to be quite helpful in this respect. In this approach the whole life‐cycle of the species is considered, divided in a step by step fashion into separate stages, thereby offering a top‐down modelling approach. Such models can easily be extended over a period of years, helping in developing long‐term control strategies: complexity can be added as the need arises. Spatial heterogeneity can be taken into account by explicitly defining a spatial scale and the dispersal process. The multi‐species nature of competition can be dealt with by using neighbourhood models of plant interference. A few recent contributions from the literature, using weeds as an example, are reviewed here against a more general background of weed demography.
Prediction of herbicide activity
Authors: JENSEN P. K. , KUDSK P.
Published: July 2006

The performance of a herbicide is influenced by a number of factors, such as temperature, humidity, weed species and stage of development of the weed. Trials in glasshouses and climatic chambers have shown that the shape of the dose‐response curve of a herbicide is dependent only on the mode of action of the herbicide. Therefore, the performance of a herbicide under different climatic conditions can be described as a parallel displacement of the dose‐response curve. The same seems to be the case regarding the performance of a herbicide against different weed species or against one weed species at different growth stages. The trial programme is in an introductory phase, but the intention is, on the basis of trials where the influence of the above mentioned factors are quantified, to build up a simulation model that adjusts the dose to the conditions prevailing at the time of spraying. In this paper, the results from trials in climatic chambers to test the effect of a herbicide under different climatic conditions, and glasshouse trials with three weed species at three stages of development, are summarized.
Untersuchungen Zum Einfluss einer Pflanzenscutzmittelspritzfolge auf das Rückstandsverhalten von Terbutryn und die mikrobielle Aktivität im Boden. Teil I. Rückstandsverhalten von Terbutryn
Authors: AUSPURG B. , PESTEMER W. , HEITEFUSS R.
Published: July 2006

Laborversuche zum Abbauverhalten von Terbutryn ergaben in Abhängigkeit von den Inkubationsbedingungen (10 und 20°C; 30 und 60% WK max) Halbwertszeiten von 19–113 Tagen (einfache Dosierung) bzw. 62–258 Tagen (zehnfache Dosierung), wobei kaum Unterschiede in der Abbauleistung zwischen zwei verschieden sorptiven Böden zu verzeichnen waren. Die Untersuchung der wasserextrahierbaren Rückstände zeigte, daß Terbutryn in beiden Böden stark sorbiert wird, da nur 12 bzw. 18%‘pflanzen‐verfügbar’ waren. Im Freiland ließ sich die schnelle Konzentrationsabnahme von Terbutryn bestätigen und konnte mit Hilfe eines mathematischen Modells gut simuliert werden. Die im Labor bei gleichzeitiger Anwendung weiterer Pflanzenschutzmittel beobachtete Verzögerung (Dinosebacetat) bzw. Stimulation (Triadimefon, Parathion) des Terbutryn‐Abbaus konnte unter Praxisdingungen im Freiland nicht bestätigt werden.
Broomrape control in faba bean (Vicia faba L.) with glyphosate and imazaquin
Authors: SAUERBORN J. , SAXENA M. C. , MEYER A.
Published: July 2006

Field studies were carried out to evaluate the efficacy of imazaquin and glyphosate in controlling broomrape (Orobanche crenata Forsk. and O. aegyptiaca Pers.) in faba bean (Vicia faba L.) in Northern Syria. Several rates and times of application of the herbicides were tested. Nearly complete control of broomrape was achieved with both the herbicides when they were sprayed twice (when the broomrape attachments to the faba bean roots were at tubercle stage of develoment and 15 days later) at a rate of application of 80 g a.i. ha−1 for glyphosate and 10 g a.i. ha−1 for imazaquin.

However, the yield of faba bean did not increase with these treatments, suggesting that the herbicides at these rates were still causing some physiological disorder in the plant that counteracted the beneficial effect of broomrape control on the performance of faba bean plants.
Agronomic performance of a triazine resistant foxtail millet (Setaria italica (L.) Beauv.)
Authors: DARMENCY H. , PERNES J.
Published: July 2006

The agronomic performance of a foxtail millet line resistant to atrazine, obtained through interspecific hybridization between Setaria viridis and S. italica, was compared to that of the original susceptible cultivar of S. italica. In spite of lower grain yields when both were grown in identical conditions, the use of this resistant material is justified because its yield when weeded with atrazine was similar to that of the susceptible cultivar with handweeding. There were no differences in early season growth rates between these lines at cool temperatures.
Isozymic discrimination of tropical Australian populations of mesquite (Prosopis spp.): implications for biological control
Authors: PANETTA F. D. , CARSTAIRS S. A.
Published: July 2006

Isozymic variation was investigated in five Australian populations and six reference collections of mesquite (Prosopis section Algarobia). Within nine enzyme systems, a total of 18 loci were examined in detail. 17 of which were polymorphic. Classification and ordination techniques revealed that two of the Australian populations were referable to P. pallida (syn. P. limensis) and another to a polyploid form of P. juliflora. Although the remaining two Australian populations were closely related, only one showed direct evidence of introgression of genes from P. pallida, and the existence of an additional, undetermined parent species was suggested. Owing to the apparent widespread distribution of P. pallida in northern Australia, it may be expedient to seek potential biological control agents from extra‐Australian populations of either this or other species within series Pallidae. However, little is known regarding the general level of host specificity exhibited by the fauna which attacks species in section Algarobia. The overall degree of similarity of the taxa examined in this survey suggests that useful agents for Australian Prosopis might be obtained from the fauna associated with species from both series Pallidae and series Chilenses of section Algarobia.
Untersuchungen zur Wirtseignung verschiedener geographischer Herkünfte von Ackerunkräutern gegenüber dem Rübenzystenälchen Heterodera schachtii Schmidt
Authors: GLEIßL W. , BACHTHALER G. , HOFFMANN G. M.
Published: July 2006

Verschiedene geographische Herkiinftc innerhalb Bayerns von fiinf Ackcrunkraularlen wurden auf ihre Eignung als Wirtspflanzen des Rubenzysten‐alchens Heterodera schachtii Schmidt untersucht. Dabei forderten die Wurzeldit Tusaie siimtlicher geprufler Herkunlte von Capsella bursa‐pasforis und Stellaria media den Larvenschlupf aus Zys‐ten; Chenopodium album‐. Viola arvensis‐ und Galium aparinc‐Hcrkunflc wirkten neutral. Bei erstgenannten Artcn konnten ini Biotest regel‐maBig Zyslenneubildungen fcslgcstelll werden, wahrend an den Wurzein von Chenopodium album nur vcreinzell. an denen von Viola arrensis und Galium aparine in keinem Fall frische Zysten gebildel wurden. Auch hinsichllieh des Einflus.ses aufdie Populationsdichtc (Pf/Pi‐Wert = Quotient aus Endverseuehung und Ausgangsvcrseuchung) tralen keine Untersehiede auf. Die Wirtseignung einer Unkrautspezies gegeniiber Heterodera achachtli stellt somit, zumindesl innerhalb eines begrenzten geographischen Raumcs, eine artspe‐zifisehe Eigenschafl dar.
Dynamik des Samenspeichers in einigen mediterranen Kulturböden
Authors: BERNHARDT K.‐G. , HURKA H.
Published: July 2006

Die Zusammensetzung der Samenspeicher in Kulturfeldern im Mittelmeerraum hängt von unterschiedlichen Faktoren ab. Zum einen ist es die Bodenart, die aufgrund ihrer Struktur auf den Samenvorrat im Boden einwirkt. Weitaus grösser sind aber die Auswirkungen der anthropogenen Beeinflussung wie mechanische Bodenbearbeilung und chemische Behandlungen. Damit zeigen sich für mediterrane Kulturböden die gleichen Einflüsse auf den Samenspeicher wie im mittel‐europäischen Bereich.
Phenology and seed production of variegated thistle, Silybum marianum (L.) Gaertn., in Australia in relation to mechanical and biological control
Authors: DODD J.
Published: July 2006

Production of viable seeds occurred in immature capitula of Silybum marianum following simulated slashing and mowing. In the slashing treatment, capitula with 20 cm or less of stem attached produced viable seeds if cut off when at least half the florets were open, the proportion of viable seeds ranging from 0·3% in capitula at midanthesis to 12% in those at the end of anthesis. Following mowing, viable seeds were produced in full‐sized buds which were close to anthesis and in capitula at any stage of anthesis at the time of plant cutting, the proportion increasing from 0·1% in capitula at the start of anthesis to 30% in those at the end. Within a capitulum, anthesis usually lasted five days in irrigated plants. Ripe seeds were released about 17 days later. Seed production averaged 190 seeds for the primary capitulum and 114 in others. In a flowering season starting in early November and lasting about two months, individual plants had the potential to produce an average of 55 capitula, representing an output of 6350 seeds per plant, of which 94% were viable. In view of the prolonged flowering season and the large seed output of S. marianum, it is argued that the restricted period of oviposition by the weevil Rhinocyllus conicus and the low density of larvae per capitulum might limit its impact as a biological control agent for this weed in Australia.
Assessment of competition between crops and weeds
Authors: VLEESHOUWERS L. M. , STREIBIG J. C. , SKOVGAARD I.
Published: July 2006

A two‐species model was used to summarize results of four experiments with two component mixtures of barley (Hordeum vulgare L.), peas (Pisum sativum L.), Chenopodium album L. and Sinapis alba L. grown in pots in greenhouses. The results, covering a wide range of plant densities both in mixtures and pure stands, showed that the model was not always able to describe the relationship between the yield of a species and the densities of itself and its companion species. The deviations from the model were in all instances greatest for the least competitive species. The model that quantifies competition and niche differentiation appeared to be too general because competition between species was not independent of the wide plant density ranges used here. The results are discussed in relation to possible improvements of the model and an analogy between the principles of assessing crop weed competition and the assessment of the relative potency of herbicides in bioassay studies is put forward.
Pre‐treatment environmental effects on the uptake, translocation, metabolism and performance of fluazifop‐butyl in Elymus repens
Authors: COUPLAND D.
Published: July 2006

The performance of fluazifop‐butyl against Elymus repens (L.) Gould was significantly influenced by the environmental conditions in which the plants had grown prior to treatment as follows: soil moisture deficit (greatest reduction of herbicide performance) > cool temperatures > low light intensity. The level of control under conditions in which none of these factors was reduced (so‐called ‘standard’ conditions) was similar to that observed for‘low light’regime plants. Significant effects of environment on spray retention, foliar uptake and amounts of herbicide translocated to the roots and rhizomes were observed. The lowest rates of herbicide uptake were found with plants grown under cool conditions, the greatest amount of basipetal herbicide translocation being associated with low light intensities. Rates of herbicide de‐esterification were much lower in plants grown under low light intensities, cool temperatures, or soil moisture deficits than in those plants grown under the ‘standard’ conditions. This result was confirmed by studies of herbicide deesterification using cell‐free leaf homogenates.
Possible rôle of allelopathy in the competition between tomato, Senecio vulgaris L. and Chenopodium album L.
Authors: Qasem J. R. , HILL T. A.
Published: July 2006

Summary. The allelopathic effect of Chenopodium album L. (fat‐hen) and Senecio vulgaris L. (groundsel) on tomato (Lycopersicon esculentum Mill cv. Ailsa Craig) plants was investigated under glasshouse conditions. A new technology was used to separate competitive from allelopathic effects. These experiments suggested that C. album had an effect on tomato through allelopathy. C. album leach‐ates significantly reduced shoot fresh and dry weights and the accumulation of N, P, K, Ca and Mg of tomato shoots. No effect was found on the quantities of these elements in tomato roots. Leachate of five plants of C. album per pot was sufficient to reduce tomato growth. Addition of 10 or 20 g kg−1 of C. album dried shoots to the soil mixture significantly decreased the fresh and dry weights of tomato plants. S. vulgaris leachates did not show significant effects on the growth or nutrient accumulation of tomato plants.
How big is a bracken plant?
Authors: SHEFFIELD E. , WOLF P. G. , HAUFLER C. H.
Published: July 2006

Summary. Horizontal starch gel electrophoresis and isozyme analysis of pinnule extracts proved to be an effective non‐destructive method by which to determine the extent of individual plants of Pteridium aquilinum (bracken). Samples from all seven localities studied were found to contain several distinct genotypes, thereby confirming the heterogeneous nature of bracken stands. Individual plants were found to vary considerably in extent, both in Britain and the U.S.A. The maximum dimension measured for the most extensive individual sampled was 390 m. Individuals of this size must represent plants of considerable antiquity. The confident identification of very large plants of a single genotype has implications for control and management trials on bracken, where small plots have often been used.
Effets competiteurs d'Avena fatua L. sur le blé comme bases d'une lutte efficace contre les adventices
Authors: WIMSCHNEIDER W. , BACHTHALER G. , FISCHBECK G.
Published: July 2006

Die von 1975 bis 1979 durchgefuhrten Gefafiver‐suche zum Konkurrenzverhalten zwischen Avena fatua L. (Flug‐Hafer) und zwei Sommerweizen‐sorten ergaben folgende Wirkungen auf den Kornertrag: Im Wettbewerb um die Nahrstoffe nahm die Konkurrenz des FIug‐Hafers mil hoheren Dungungsgaben überproportional zu (Anstieg des Minderertrages von 13 auf 23%). Temporare Trockenheit steigerte die Konkur‐renzwirkung von Avena fatua. Die Besatzdichte von 4 Avena‐fatua‐ und 16 Weizenpflanzen/ Gefa'B bewirkte einen Ertragsrückgang bei Wei‐zen um 9% und 8 Avena‐fatua‐PRanzen/GefaB einen solchen von 14%. Der EiweiBgehalt im Weizenkorn wurde um durchschnittlich 5,5% gemindert. Lichtmessungen ergaben je nach Zeit‐raum eine Reduktion der fur den Weizen nutz‐baren Strahlung bei hoher Flug‐Hafer‐Dichte um 30 bis 35%. Der dadurch bedingte Ertragsverlust betrug im vierjahrigen Durchschnitt 19%. Sortenunterschiede traten nur bei Lichtkonkur‐renz auf. Die Wurzelkonkurrenz beeinfluBte vor‐rangig den Strohertrag, die Lichtkonkurrenz hingegen verstarkt den Kornertrag. Der Zeitfak‐tor wirkte sich vor allem bei hoher Düngung und bei hohem Besatz mil Avena fatua aus. Ein Entwicklungsvorsprung des Flug‐Hafers von 5 Wochen brachte einen Minderertrag des Weizens von 45% gegenüber gleichzeitiger Saat. Aus den Ergebnissen lassen sich pflanzenbauliche Konse‐quenzen bezüglich der Nahrstoffversorgung, der Saatzeit und des Bekampfungstermins ableiten.
Distribution of 14C‐glyphosate in legumes parasitised by Orobanche crenata. Répartition du glyphosate 14C dans des légumes parasités par Orobanche crenata
Authors: ARJONA‐BERRAL A. , MESA‐GARCIA J. , GARCIA‐TORRES L.
Published: July 2006

Absorption and translocation of 14C‐glyphosate was evaluated under controlled conditions in peas (Pisum sativum L.) and broad beans (Vicia faba L.) parasitised or not by crenate broomrape Orobanche crenata Forsk.). Absorption increased with time up to 12 days after treatment, and reached about 50% of the 14C‐glyphosate applied. Three days after treatment 70–85% of the total herbicide absorbed had been translocated out of the treated leaflet. There was no consistent differ ence in absorption and translocation between infected and non‐infected plants 12 days after treatment. The 14C‐glyphosate concentration in the root system increased with time in broad beans. In peas it remained more or less constant from 3 days after treatment. Generally, pods were stronger sinks for glyphosate than other parts of the plant. Herbicide accumulation in broomrape increased with its growth stage, and the parasite was a much stronger sink for glyphosate than the legume root system.
Wirksamkeit verschiedener Herbizidbehandlungen auf Equisetum arvense L. in Gerste und Mais in Quebec, Kanada
Authors: VEZINA L.
Published: July 2006

Des expériences ont été conduites sur terrain infesté par la prèle de champs, à Saint‐Simon, dans la province de Québec au Canada, du printemps 1985 à l'automne 1987. Elles ont été réalisées pour mesurer d'une part l'effet répressif de diverses successions d'interventions herbicides effectuées dans l'orge et le maïs‐grain cultivés en rotation et d'autre part l'influence de ces deux cultures sur l'évolution de trois peuplements de la prèle des champs. L'orge s'est avérée plus compétitive que le maïs‐grain à l'égard de la mauvaise herbe. L'orge a empêché les peuplements de prêle d'augmenter au fil des années alors que dans les parcelles de maïs‐grain les densités de tiges ont connu annuellement une hausse. Le MCPA amine utilisé tôt en post‐levée des cultures ne réprime la plante que temporairement et n'exerce après quelques années aucun effet significatif sur les densités de tiges. Dans le maïs, les applications d'une association de bromoxynil et de MCPA effectuées tardivement entre les rangs ont entraîné après deux années d'utilisation sur trois, une diminution de 8% de la densité des tiges dans le peuplement. Dans les parcelles témoins le nombre de tiges a augmenté en trois ans de 60%. L'application d'amitrole après la récolte de l'orge, sur une repousse de la plante et sur ses parties aériennes épargnées par le passage de la moissonneuse‐batteuse, a permis une répression efficace de longue durée. L'utilisation du MCPA aminé au cours des printemps suivants a retardé le rétablissement de l'adventice.
A mathematical model to predict Sorghum halepense (L.) Pers. seedling emergence in relation to soil temperature
Authors: ARNOLD R. L. BENECH , GHERSA C. M. , SANCHEZ R. A. , INSAUSTI P.
Published: July 2006

A mathematical model to predict Sorghum hale‐pense seedling recruitment dynamics in relation to soil temperature was derived from the experimen‐tal results obtained in a previous investigation. The model is based on the assumption that soil temperature controls seedling recruitment of S. halepense by controlling release from dormancy and germination rate once dormancy breakage has been produced. The previous analysis sup‐plied mathematical functions to describe both the release from dormancy as controlled by tempera‐ture fluctuations, and the response to ‘thermal time’ after dormancy breakage. These relation‐ships were used in the construction of the model. This was tested against experimental field data with two differently aged seedbanks, in two seasons: spring and autumn. In each case in situ germination was monitored in plots with bare soil or soil surface shaded to simulate cover by a canopy. Soil temperature was recorded hourly and was used as an input of the model.

A good description of seedling emergence dynamics in the field was obtained with the model, showing that seedling recruitment can be predicted using soil temperature data. The practi‐cal value of the developed model is discussed.
Glyphosate injury on Cyperus esculent us leaves and basal bulbs: histological study
Authors: CAÑAL M. J. , ALBUERNE M. , TAMÉS R. SANCHEZ , FERNANDEZ B.
Published: July 2006

The effect of glyphosate on leaves and basal bulbs of yellow nutsedge (Cyperus esculentus L.) plants was studied. Treatment with glyphosate did not affect leaf anatomy, although light necrotic spots were seen on the veins. In contrast, basal bulb organization was greatly affected with large necrotic zones and disorganization in the vascular cylinder due to herbicide accumulation. Depletion or disappearance of vacuolar phenols was observed in bulbs of plants treated with the highest doses of glyphosate. The most remarkable effect of glyphosate was the appearance of one layer of sclerenchymatic cells between root and rhizome primordia and the cortical tissues which could play an important role in the inhibition of rhizome and root emergence by the herbicide.
Adsorption of transformation products of atrazine by soil
Authors: BROUWER W. W. M. , BOESTEN J. J. T. I. , SIEGERS W. G.
Published: July 2006

The adsorption of atrazine and its transformation products, desisopropylatrazine (2‐chloro‐4‐ethylamino‐6‐amino‐l,3,5‐triazine), desethyl‐atrazine (2‐chloro‐4‐amino‐6‐isopropylamino‐l,3,5‐triazine) and hydroxyatrazine (2‐hydroxy‐4‐ethylamino‐6‐isopropylamino‐l,3,5‐triazine) to four top‐soils was measured. Adsorption coefficients decreased in the order hydroxy atrazine, atrazine, desisopropylatrazine, and desethyl‐atrazine: the distribution coefficient between organic matter and water (KOM) ranged from 40 to 100 dm3 kg−1 for atrazine, from 30 to 60 dm3 kg−1 for desisopropylatrazine, from 20 to 50 dm3 kg−1 for desethylatrazine and from 100 to 590 dm3 kg−1 for hydroxy atrazine. Data are discussed in the context of earlier literature.
Variations in the resistance of Stellaria media to mecoprop due to biotype, application method and 1‐aminobenzotriazole
Authors: LUTMAN P. J. W. , HEATH C. R.
Published: July 2006

An investigation was made into the resistance of some biotypes of Stellaria media to mecoprop. Comparison of the sensitivity of five biotypes to foliar applications of mecoprop salt confirmed the presence of resistant and sensitive types and one of intermediate sensitivity. Applications of mecoprop through the roots of plants growing in nutrient culture were also more active on biotypes sensitive to foliar mecoprop, although the differences were less marked than they were with foliar treatments. Thus, possible differ ences in retention, uptake and translocation do not seem to be important causes of resistance. Consequently, it appears that resistance is associated with detoxification of mecoprop at the site of action. In two further experiments the cytochrome P450 mixed function oxidase inhibitor, 1‐aminobenzotdazole, had only a small effect on the susceptibility of resistant S. media plants to mecoprop. The importance of these data in the elucidation of the mechanism of resistance is discussed.
Effect of different levels of mannitol‐induced water stress on the tolerance of cultivated oat (Avena sativaL.) to didofop‐methyl
Authors: DASTGHEIB F. , ANDREWS M. , FIELD R. J. , FOREMAN M. H.
Published: July 2006

The effect of degree of water stress inAvena sativaon diclofop‐methyl efficacy was assessed. Within 24 h of applying stress by adding mannitol to the root medium (0 to 12.5%), the rate of leaf extension of the youngest leaves (leaves 3 and 4) decreased with increasing mannitol concentration. Without water stress, application of diclofop‐methyl had little effect on extension rate of leaves 3 and 4 during the first 4 days after spraying. Subsequently, it caused a significant decrease in the extension rate of leaf 4 with more pronounced effects on later leaves. Diclofop‐methyl had little effect on leaf extension rate of plants given mannitol. Shoot dry weight at harvest for unsprayed plants decreased with increased mannitol concentration and for sprayed plants it was greater without mannitol than with mannitol (all levels). However, at mannitol concentrations greater than 4%, shoot dry weight for sprayed and unsprayed plants was not significantly different. Sprayed plants exposed to 2–8.5% mannitol produced seed heads but those at zero mannitol did not. When the root medium of all treatments was flushed of mannitol one week after spraying, then main‐tained without mannitol, shoot dry weight at harvest for unsprayed plants decreased slightly with increased mannitol concentration applied initially. However, shoot dry weight for sprayed plants increased with increased mannitol concentration. Without mannitol two weeks after spraying, chlorophyll concentrations of leaves 3 and 4 were greater and water saturation deficit (WSD) values were lower for unsprayed plants than sprayed plants but there were no differences at 6.2% mannitol. It is proposed that tolerance to diclofop‐methyl byA. sativaas a result of water stress, is primarily due to a decreased rate of leaf expansion resulting in lower demand for membrane synthesis and less strain on membranes damaged by the herbicide.
Predicting the growth and competitive effects of annual weeds in wheat
Authors: WILSON B. J. , WRIGHT KATHRYN J.
Published: July 2006

The growth and competitiveness of 12 annual weed species were studied in crops of winter wheat, in which weeds were sown to give a wide range of plant densities. Weed growth patterns were identified; early species which senesced in mid‐summer were less competitive than those with a growth pattern similar to that of the crop. Most species had little effect on crop yield in 1987, and this was attributed to a high crop den sity. Crop yield‐weed density relationships for all species in 1988 and for Galium aparine in 1987 were well described by a rectangular hyperbola. Species were listed in the following competitive order based on the percentage yield loss per weed m−2: Avena fatua > Matricaria perforata > Galium aparine > Myosotis arvenis > Poa trivialis > Alopecurus myosuroides > Stellaria media > Papaver rhoeas > Lamiumpur‐pureum > Veronica persica > Veronica hederi‐folia > Viola arvensis. Prediction of yield loss is discussed. The assumptions inherent in using Crop Equivalents (based on relative weights of weed and crop plants), are challenged; with intense competition, weed biomass at harvest failed to replace lost crop biomass, and harvest index was reduced. It is concluded that a competi tive index, derived from yield density relation ships, and expressed as the percentage yield loss per weed m−2, is more likely to reflect the com petitive ability of a species than an index obtained from plant weights in the growing crop.
Differential toxicity of simazine and diuron to Torilis arvensis and Lolium rigidum
Authors: DE PRADO R. , SCALLA R. , GAILLARDON P.
Published: July 2006

In a soil application, Torilis arvensis was nearly as susceptible as Lolium rigidum to simazine but was 18‐fold more tolerant to diuron. Treat ment with diuron inhibited photosynthesis in L. rigidum but had only a limited effect in T. arvensis although chloroplasts isolated from both species displayed similar susceptibility. 14C‐diuron degradation in plants was limited, with the formation of conjugates of mono‐methyl‐diuron in T. arvensis and N‐dealkylated derivatives of diuron in L. rigidum. 14C‐diuron entered the roots and was translocated throughout the leaves of L. rigidum but was restricted to stems, leaf petioles and leaf veins of T. arvensis. This difference in transport pattern is proposed to explain the tolerance of T. arvensis to diuron.
Fate of fluroxypyr in soil
Authors: LEHMANN R. G. , MILLER J. R. , OLBERDING E. L. , TILLOTSON P. M. , LASKOWSKI D. A.
Published: July 2006

Fluroxypyr‐MHE (methylheptyl ester) was added to four soils and incubated at 26 ± 1°C and approximately 0.1 MPa moisture. After initial rapid hydrolysis of the ester to fluroxypyr, fluroxypyr degraded with half‐lives of 12, 12, 23, and 7 days in Barnes loam, Catlin silt loam, Hanford sandy loam, and Mhoon clay soils, respectively. Two metabolites (4‐amino‐3,5‐dichloro‐6‐fluoro‐pyridin‐2‐ol and 4‐amino‐3, 5‐dichloro ‐ 6 ‐ fluoro ‐ 2 ‐methoxypyridine) were identified, with the pyridinol at its maximum concentration after 2 to 4 weeks of incubation, and the methoxypyridine after 8 weeks. Degradation rates of fluroxypyr and its pyridinol were not significantly altered by diurnally varying soil temperature (21°C to 32°C) or moisture, nor by the presence of growing grass. Methoxypyridine dissipation was more rapid under greenhouse conditions, suggesting that laboratory studies underestimated the dissipation rate of this metabolite.
Antagonistic effects of 2,4‐D amine and bentazone on control of Avena fatua with tralkoxydim
Authors: JENSEN K. I. N. , CASELEY J. C.
Published: July 2006

Control of Avena fatua with tralkoxydim was significantly reduced in glasshouse experiments when the herbicide was tank‐mixed with either 2,4‐D amine or bentazone. Antagonism increased with increasing rates of these broadleaf herbicides in the tank‐mixture and it could, in turn, be decreased by increasing rates of tralkoxydim. When herbicide solutions were applied to single leaves with a micropipette applicator, bentazone was antagonistic only when mixed in the same droplet with tralkoxydim and not when the two herbicides were applied adjacently in separate droplets. In contrast, both separate and combined applications of 2,4‐D amine and tralkoxydim were antagonistic. There was no antagonism when mixtures with either 2,4‐D amine or bentazone were applied between the leaf sheath and culm. Antagonism could be circumvented by sequential applications of the herbicides. When tral‐oxydim was applied first, there was no loss of A. fatua control if bentazone application was delayed 0.5 h or if 2,4‐D amine was delayed 24 h. Results suggest that bentazone affects only cuticular penetration of tralkoxydim, whereas 2,4‐D amine also influences subsequent translocation.
Competition for light between velvetleaf (Abutilon theophrasti) and soybean (Glycine max)
Authors: AKEY W. C. , JURIK T. W. , DEKKER J.
Published: July 2006

We examined factors affecting conversion of light into dry matter of velvetleaf (Abutilon theophrasti) and soybean (Glycine max) grown in a replacement series near Ames, Iowa, U.S.A. in 1986 and 1987. Velvetleaf was taller than soybean over most of the growing season and had more branches, especially at the top of the canopy. Velvetleaf had greater light interception than soybean in the upper part of the canopy, particularly early and late in the day, although total light interception by canopies of the two species was similar on most sample dates. Velvetleaf had higher light utilization efficiency, or conversion of intercepted light into dry matter, in the middle and later part of the growing season. This combination of traits appears to give velvetleaf an advantage over soybean in competition for light.
Penetration of clopyralid and related weak acid herbicides into and through isolated cuticular membranes of Euonymus fortunei
Authors: KLOPPENBURG D. J. , HALL J. C.
Published: July 2006

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).
Dynamics and control of Sorghum halepense (L.) Pers. shoot populations: a test of a thermal calendar model
Authors: VITTA J. I. , LEGUIZAMÓN E. S.
Published: July 2006

The dynamics of Sorghum halepense tiller emergence and rhizome biomass were studied in field experiments. The effect of different application dates of a post‐emergence herbicide on crop yield was measured. The relationship between accumulated thermal units (A.T.U.) and the percentage of emerged tillers in soybean was described by a single non‐linear regression model, independent of initial bud density. The estimates of population density were generally higher than those predicted by the original model developed by Satorre, Ghersa & Pataro (1985). In the absence of a crop, the higher the density of the weed the more concentrated the tiller emergence in the early part of the tillering period. The rhizome biomass reached a minimum value at about 230°C days, and was independent of the initial weed density. The maximum herbicide efficiency was achieved when the application was performed closest to the period of minimum rhizome biomass. The results show the feasibility of optimizing S. halepense control by calculating the period f minimum rhizome biomass. Such a criterion ls consistent with the maximization of crop yields.
Effect of low temperatures on 2,4‐D behaviour in maize plants
Authors: GAUVRIT C. , GAILLARDON P.
Published: July 2006

The foliar surface of 4‐leaf maize plants was found to be poorly wettable and retained 106 μl g−1 dry matter when sprayed with a U46D (2,4‐D formulation) blank. The third leaf retained 141 μl g−1. A 7‐day cold spell (17/9°C) increased retention per unit dry matter by 53% (135% on the third leaf). Cold stress lowered epicuticular wax quantity by 29% on the third leaf. Contact angles of formulated 2,4‐D lay between 115 and 125° and were not significantly affected by cold stress. 2,4‐D rapidly entered into maize third leaf (66% in 24 h) but migration from it was less than 1.5%. 2,4‐D was readily degraded in maize (80% in 72 h). The most abundant metabolite was probably an ester conjugate; little of the hydroxy derivatives were found. Cold stress reduced 2,4‐D degradation, and 72 h after treatment the amount of undegraded 2,4‐D was 78% higher in cold‐stressed maize plants. It was concluded that 2,4‐D selectivity in maize results from low spray retention per unit dry matter and active degradation of penetrated herbicide. Cold stress affects both factors.
Survey of herbicide residues in soil and wells in three citrus orchards in Valencia, Spain
Authors: de BARREDA D. Gómez , LORENZO E. , GAMÓN M. , MONTEAGUDO E. , SAEZ A. , de la CUADRA J. D. , del BUSTO A. , RAMOS C. , CARBONELL E.A.
Published: July 2006

Soil samples taken in summer 1989 and winter 1990 at different depths from three citrus orchards of the Valencia region (Spain) with a long history of residual herbicide treatments were analysed with bioassays and chromatographic procedures. The herbicides involved were atrazine, bromacil, diuron, simazine, terbuthylazine, terbumetone, terbutryn and trifluralin. Water samples from wells in the orchards were also analysed. The concentrations of the herbicides were very low, often below the limit of determination, and were always highest in the upper layers of soil. After a very unusual period of heavy rain, small quantities of some chemicals were found in the well water. The conclusion was that in these orchards the herbicides applied at currently used rates are unlikely to accumulate in any layers of the soil.
Soil properties affecting the distribution of 37 weed species in Danish fields
Authors: ANDREASEN C. , STREIBIG J. C. , HAAS H.
Published: July 2006

The distribution of 37 common weed species in eight common Danish crops in response to seven edaphic factors was evaluated using linear logistic regression with adjustment for over‐dispersion. The main effects of soil properties on weed distribution were adjusted for crop type and sample year by the regression. Crop type and soil clay content were generally those explanatory variables that had the greatest influence on occurrence of the weed species, but all other factors examined (sample year, loss on ignition, pH, P, K, Mg and Mn) also had an effect on the occurrence of some weed species.
Selection of sorghum (Sorghum bicolor (L.) Moench) varieties resistant to the parasitic weed Striga hermonthica (Del.) Benth
Authors: OLIVIER A. , RAMAIAH K. V. , LEROUX G. D.
Published: July 2006

Pot and field experiments were performed in Burkina Faso in 1987 and 1988 to evaluate the resistance of selected ‘low‐stimulant’ sorghum (Sorghum bicolor (L.) Moench) varieties to the parasitic weed (Striga hermonthica (Del.) Benth. In a pot experiment, the variety IS‐7777 supported the lowest number and had the latest emergence of Striga, compared with the other varieties tested. The varieties IS‐14825, IS‐6961, IS‐7739, IS‐14928 and IS‐14975 also had signifi cantly lower numbers of emerged Striga per pot than the resistant control Framida. The resist ance of IS‐7777 was confirmed in field experi ments, as was that of IS‐7739, IS‐6961 and IS‐14928. However, the yield potential of these poorly adapted varieties was low in Striga‐infested fields. The varieties IS‐14975, IS–14825 and Seguetana Niarabougou exhibited a low susceptibility associated with a grain yield equivalent to that of the other varieties in farm fields infested by Striga. As Seguetana is already grown by Sahelian farmers, its use could be recommended in the absence of resistant varieties adapted to Sahelian agroclimatic conditions. The exceptionally high level of restance exhibited by IS‐7777 could be exploited in studies on the genetics and mechanisms of resistance of the host plant to the parasite, as well as in sorghum improvement programmes.
MALHERB: ein Computerprogramm zur Bestimmung von Ackerunkräutern
Authors: LONCHAMP J.‐P. , BARRALIS G. , GASOUEZ J. , JAUZEIN P. , KERGUELEN M. , LE CLERCH J. , MAILLET J.
Published: July 2006

MALHERB est un logiciel de reconnaissance des mauvaises herbes des cultures. Ce logiciel permet la détermination, au stade adulte, de 490 espèces dont 82 graminées. Il utilise différentes descriptions d'une même espèce tenant compte de la variabilité intra‐spécifique et des difficultés de reconnaissance de certains organes. Les notions botaniques ne sont pas indispensables pour l'utilisation du logiciel. MALHERB gère une base de connaissances constituée essentiellement de 2 fichiers distincts contenant des ‘Plantes feuillées à port de graminées’ et des ‘Plantes feuillées à port different’. Les fichiers comportent, d'une part la description d'espèces à partir de caractères morphologiques et, d'autre part, des données ecologiques concernant leur répartition géographique, les cultures, le pH, la texture du sol auxquels elles sont associées. Le logiciel détermine d'abord des groupes d'espèces ayant en commun certains caractères, puis propose a l'utilisateur une clé spécifique à chaque groupe. Dans le cas où l'échantillon ne comporte pas certains organes necessaires à la détermination, MALHERB propose alors une reconnaissance fondée sur la comparaison de profils de caractères écologiques stationnels conduisant à un classement de vraisemblance (théorie de comparaison d'ensembles flous).
Sugarbeet tolerance and weed control efficacy with split applications of phenmedipham plus desmedipham
Authors: NORRIS R. F.
Published: July 2006

Sugarbeet and weeds were treated with phenmedipham plus desmedipham either as single applications or as split applications in which 50% of the equivalent single application rate was applied at each application. Split application did not alter the phytotoxicity to the crop when environmental conditions did not predispose the Sugarbeet to injury by the herbicide. Split applications at 1‐1 or 1‐4 kg ha−1 spaced from 0‐5 to c. 5 days apart caused more injury to the crop than the respective single applications when environmental conditions were such that injury to the crop resulted from the single applications. Injury to Sugarbeet following application of 0‐72 kg ha−1 of phenmedipham plus desmedipham was always low, regardless of the type of application. Susceptible weeds were controlled by single applications of 1 1‐1 −4 kg ha−1, but 0‐72 kg ha−1 did not reliably provide adequate control. Split applications c. 3‐8 days apart gave improved control. Control achieved by 0‐72 kg ha−1 of the herbicide applied as split treatments equalled or exceeded that produced by single applications of 1‐4 kg ha−1. Improvement in the control of tolerant weed species by split applications of phenmedipham plus desmedipham was species dependent. Use of low‐rate split applications of phenmedipham plus desmedipham thus resulted in reduced injury to the Sugarbeet, and the introduction of less herbicide into the ecosystem, while maintaining or improving the control of susceptible weeds.
Long‐term stability of distribution of Alopecurus myosuroides Huds. within cereal fields
Authors: WILSON B.J. , BRAIN P.
Published: July 2006

The incidence of Alopecurus myosuroides seedheads was monitored annually for 10 years in the cereal fields of a 173‐ha arable and dairy farm. A. myosuroides persisted at low population densities, despite the use of herbicides and grass breaks in the rotation. The distribution of the weed was irregular, with none occurring on at least 60% of the positions surveyed in the cereal fields. Spatial distributions were compared between years, and some significant correlations were found from year to year in continuous cereals, and in cereal crops separated by a 3‐year grass ley.
Frequency distribution of weed counts and applicability of a sequential sampling method to integrated weed management
Authors: BERTI A. , ZANIN G. , BALDONI G. , GRIGNANI C. , MAZZONCINI M. , MONTEMURRO P. , TEI F. , VAZZANA C. , VIGGIANI P.
Published: July 2006

Summary: Résumé: Zusammenfassung

Weed density was sampled in a number of quadrats in five crops and at eight locations in Italy. For every location and species of crop and weed, a mean/variance pair was calculated. The relationship between these two parameters was significantly influenced by crop and, to a lesser extent, by site, but not by species of weed. The goodness of fit of the negative binomial distribution to the samples was assessed. Its k exponent was estimated on the basis of the observed variance/mean regression. A good fit was found for weed populations with fewer than 10 plants m−2. The applicability of a sequential sampling procedure based on the negative binomial distribution to a weed control strategy that uses a threshold density is discussed.

Denombrement de la fréquence des adventices et applicabilité a une méthode d'échantillonnage séquentiel pour un desherbage integré

La densité en adventices a étééchantillonnée dans plusieurs cadres dans 5 cultures et à 8 endroits en Italic. Pour chaque lieu et espèce de culture et de mauvaise herbe un couple moyenne/variance a été calculé. La relation entre ces deux paramètres était très dépendante de la culture et à un degré moindre du lieu, mais n'était pas influencé par l'espèce d'adventice. La validité de l'application de la distribution binomiale négative aux échantillons a été estimée. Son coefficient k était estimé sur la base de la regression observée sur variance/ moyenne. Une bonne adéquation a été mise en évidence pour des populations inférieures à 10 plantes m−2 L'applicabilité d'un protocole d'échantillonnage séquentiel basé sur la distribution binomiale négative, à une stratégic de désherbage utilisant un seuil de densité est discutée.

Frequenzverteilung in Unkraut‐Vegetationsaufnahmen und Aufnahmemethode im Rahmen der integrierten Unkrautbekämpfung

Auf der Basis der Dichte von Unkräutern in 5 Kulturen an 8 Orten in Italien wurden Mittelwert und Varianz berechnet. Das Verhältnis dieser beiden Parameter wurde durch die Kulturpflanzenart signifikant, weniger durch den Ort und gar nicht durch die Unkrautart beeinflußt. Die Güte der Anpassung an dienegative Binomialverteilung der Erhebungsdaten wurde bestimmt. Ihr k‐Exponent wurde nach der beobachteten Varianz/Mittelwerts‐Regression bestimmt. Für Populationsdichten von < 10 Pflanzen m−2 ergab sich eine gute Anpassung. Die sich aus der negativen Binomialverteilung ergebende Bekämpfungsstrategie aufgrund von Schadensschwellen wird diskutiert.
Potential use of activated carbon as a protectant against pre‐emergence herbicides in direct‐seeded processing tomatoes
Authors: MORGAN W. C. , MORGANS A. S.
Published: July 2006

Summary: Résumé: Zusammenfassung

Activated carbon protected direct‐seeded tomato (Lycopersicon esculentum Mill., cv. UC 82B) against pre‐emergence applications of metribuzin and metolachlor, but not of oxyfluorfen or oxadiazon. Accurate placement of activated carbon on the soil surface directly above the seed was necessary for protection of tomato seedlings. Displacement of the carbon by overhead watering reduced its protective properties. A major disadvantage of the technique is that weed seeds under the activated carbon are also protected. Also, of the chemicals examined here, those against which it did provide protection did not control Solanum nigrum L.

Utilisation potentielle du charbon actif comme phytoprotecteur des tomates conduites en semis direct contre les herbicides de prelevee

Le carbone actif a protege des tomates en semis direct (Lycopersicon esculentum Mill., cv UC 82 B) contre des applications de prelevee de metribuzine et de metolachlor mais pas d'oxy‐fluorfen ou oxadiazon. Une locahsation précise du charbon actif sur la surface du sol directe‐ment au dessus de la graine est necessaire pour la protection des plantules de tomate. Le déplacement du charbon par arrosage réduit ses propriétés de protection. Un inconvénient important de la technique est que les graines d'adventices sous le charbon actif sont égale‐ment protégées. En outre, les produits chimiques examinés ici qui assurent une protection, ne sont pas actifs contre Solanum nigrum L.

Aktivkohle als Schutzmittel gegen Vorauflauf‐Herbizide in gesdten Tomaten

Mit Aktivkohle konnten gesate Tomaten (Lycopersicon esculentum Mill., ‘UC 82B’) gegen die Vorauflauf‐Anwendungen von Metribuzin und Metolachlor geschutzt werden, jedoch nicht gegen Oxyfluorfen oder Oxadiazon. Fur den Schutz der Tomaten‐Keimpflanzen mußte die Aktivkohle ganz genau uber den Samen auf die Bodenoberflache ausgebracht werden. Ver‐schwammen der Kohle durch Beregnung reduzierte ihre Schutzwirkung. Ein großer Nachteil dieser Methode liegt darin, daß keimende Unkrauter unter der Aktivkohle ebenso geschutzt werden. Auch konnte mit den hier untersuchten Herbiziden Solanum nigrum L. nicht bekampft werden.