Weed size hierarchies in Denmark     

P. K. JENSEN 《Weed Research》1991,31(1):1-7

In 962 field trials in different crops, the size of a number of weed species was investigated. The weeds were ranked according to their size on a single occasion. The ranks of the species were examined relative to two weed species, Viola arvensis and Matricaria inodora. The ranking was, however, independent of which of the two species were used as standard. The correlation between the rankings with Viola arvensis as standard, and the rankings with Matricaria inodora as standard were r= 0-93 for spring sown crops, and r= 0.84 for autumn sown crops. Sinapis arvensis was the largest weed species in spring sown crops, with a weight of 14.5 times that of Viola arvensis, followed by Brassica napus, Galeopsis spp., Thlaspi arvense and Amsinckia spp. Viola arvensis. Veronica spp. and Lamium spp. were the smallest weed species in spring sown crops. Galium aparine was the largest species in autumn sown crops, whereas spring germinating species such as Polygonum spp. were among the smallest. The ranks of Viola arvensis, Myosotis arvensis, Lapsana communis, Matricaria inodora and Lamium spp. were almost identical in spring sown crops and in autumn sown crops.  相似文献   

Split application of herbicides in peas   总被引：1，自引：0，他引：1  

P. K. JENSEN 《Weed Research》1992,32(4):295-302

The efficacy of split application of herbicides in peas compared to a single treatment with the same total dosage was investigated in field trials. The results of four efficacy trials and two tolerance trials, employing some of the commonly used tank mixtures of herbicides, are described. The tank mixtures consisted of cyanazine or pendimethalin in mixture with bentazone, bentazone/MCPA, MCPB or MCPA. Split application enhanced the weed control compared to the efficacy of a single application at the same total dosage. The improved weed control was considered to be mainly due to the fact that sequential use makes it possible to target a larger proportion of the weeds at the sensitive cotyledon stage than is possible with a single application, which must be delayed until the majority of the weeds have emerged. The use of split application increased the reliability of the weed control, as the efficacy remained high if just one of the treatments was carried out at a favourable time for the efficacy of the tank mixture. The tolerance trials showed that, when a single application treatment at the optimal time for efficacy was compared to split application, then there was a tendency for there to be a higher yield after the split application treatment, caused by greater crop damage after the single-dose application. Applications fractionnees d'herbicides en cultures de pois L'efficacité d'une application fractionnée d'herbicides en cultures de pois a étéétudiée en essais de plein champ, en comparaison d'une application simple apportant la même dose totale. Les résultats obtenus dans 4 essais d'efficacité et 2 de sélectivité, avec quelques uns des mélanges d'herbicides communément pratiqués sont décrits. Les mélanges étaient à base de cyanazine ou de pendimethaline avec de la bentazone, de la bentazone/MCPA, du MCPB ou du MCPA. Les applications fractionnées ont augmenté l'efficacité herbicide en comparaison d'une simple application à la même dose globale. L'amélioration de l'activité herbicide est supposée être due par le fait qu'une utilisation séquentielle fait qu'il est possible d'atteindre une plus grande proportion de mauvaises herbes au stade cotylédonnaire sensible, que celle qu'il est possible d'atteindre avec une application unique qui doit attendre que la majorité des adventices soit levée. L'utilisation des applications fractionnées a augmenté la régularité du desherbage attendu que l'efficacité est demeurée élevée quand seulement un des traitements avait été appliqué au moment favorable pour l'efficacité du mélange. Les essais de sélectivité ont montré que pour une simple application appliquée au moment optimal pour l'efficacité comparée à une application fractionnée on avait tendance à avoir un rendement moins élevé, ceci étant liéà une phytotoxicité plus grande liée aux simples applications. Geteilte Anwendungen von Herbiziden in Erbsen Die Wirkung geteilter Anwendungen von Herbiziden in Erbsen wurden im Freiland im Vergleich zu Einzel-Behandlungen mit derselben Gesamtdosis untersucht. Die Ergebnisse von 4 Wirkungs- und 2 Toleranzversuchen mit einigen häufig vorgenommenen Tankmischungen werden beschrieben. Die Tankmischungen bestanden aus Cyanazin und Pendimethalin in Mischung mit Bentazon, Bentazon/MCPA, MCPB oder MCPA. Die geteilte Anwendung verstärkte die Unkrautbekämpfung. Diese Verbesserung war vermutlich vorrangig darauf zurückzuführen, daß man mit den aufeinander folgenden Teilanwendungen einen größeren Teil der Unkräuter im empfindlichen Keimblattstadium trifft, im Gegensatz zur Einzel-Behandlung, bei der man die Hauptkeimwelle der Unkräuter abwarten muß. Durch geteilte Anwendungen wurde die Unkrautbekämpfung verläßlicher, weil die Wirkung auch dann groß blieb, wenn nur eine der Behandlungen zu einem günstigen Zeitpunkt stattfand. Im Toleranzversuch erwies sich das Verfahren der Teilanwendungen verträglicher und tendierte zu höheren Erträgen, denn bei den Einzel-Behandlungen zum Zeitpunkt optimaler Wirkung traten größere Schäden an den Kulturpflanzen auf.  相似文献   

A Japanese powdery mildew isolate with exceptionally large infection efficiency on Mlo-resistant barley   总被引：1，自引：2，他引：1  

M. F LYNGKJÆR  H. P JENSEN  H. ØSTERGÅRD 《Plant pathology》1995,44(5):786-790

A Japanese field isolate (Race I) of Erysiphe graminis f.sp, hordei was tested on 17 barley lines carrying the mlo powdery mildew resistance gene. Race I produced many successful infections with infection type larger than or equal to 2 on six lines (M66, MC20, SRI, SR7, A tem and Totem), On the remaining 11 lines it reacted with infection type 0. Colony numbers on the Mlo-lines were between 26% and 12 9% of the numbers on a susceptible cultivar Manchuria, These numbers were larger than, or similar to those produced by isolate HL3/5, which has the highest recorded infection efficiency on Mlo-resistant cultivars. The interaction between isolates and lines was highly significant. The isolate GE3, from which HL3/5 was derived by selection, gave rise to occasional colonies corresponding to less than 03° o of the number produced on cv. Manchuria.  相似文献   

Longevity of seeds of four annual grass and two dicotyledon weed species as related to placement in the soil and straw disposal technique     

P K JENSEN 《Weed Research》2009,49(6):592-601

Persistence of seeds of the four winter annual grass species, Alopecurus myosuroides , Bromus sterilis , Bromus hordeaceus and Vulpia myuros , were studied under field conditions. The studies also included the two dicotyledon species, Tripleurospermum inodorum and Galium aparine . Seed samples were stored in the field at different depths in the plough layer for a year. Following germination, seedling emergence was taken as an indicator of field persistence. In a supplementary investigation, seed samples were placed on the soil surface or buried at 2 cm for a month and then tested for viability. Persistence of the two Bromus species was very short, irrespective of depth and duration of burial. Persistence of the other species was positively correlated with incorporation of seeds to a few centimetres depth. Increasing the depth of incorporation below 2 cm had a variable influence on persistence. Persistence of seeds placed directly on the soil surface was short, whether they were left there for a year or a month. Whether seeds at the soil surface were left uncovered or covered with chopped straw had limited influence on seed persistence. However, straw cover significantly increased persistence of A. myosuroides seeds and there was the same tendency with T. inodorum .  相似文献   

More on learning in Paramecia     

JENSEN DD 《Science (New York, N.Y.)》1957,126(3287):1341-1342

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Experimental hepatic necrobacillosis in beef cattle     

JENSEN R  FLINT JC  GRINER LA 《American journal of veterinary research》1954,15(54):5-14

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Parakeratosis of the rumens of lambs fattened on pelleted feed     

JENSEN R  FLINT JC  UDALL RH  DEEM AW  SEGER CL 《American journal of veterinary research》1958,19(71):277-282

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Rumenitis and its relation to rate of change of ration and the proportion of concentrate in the ration of cattle     

JENSEN R  CONNEL WE  DEEM AW 《American journal of veterinary research》1954,15(56):425-428

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Veterinary medicine in Russia     

JENSEN R 《Journal of the American Veterinary Medical Association》1959,134(6):249-260

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Antagonistic effects of 2,4-D amine and bentazone on control of Avena fatua with tralkoxydim     

K. I. N. JENSEN  J. C. CASELEY 《Weed Research》1990,30(6):389-395

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.  相似文献