摘要:

SummaryThe effects of tropical weeds on the yield of while yam were studied outdoors in wooden boxes. When the foliage and roots of weeds were in physical contact with the crop until harvest (full interference), tuber yield of yam was reduced by 76–79% of that obtained under weed‐free conditions over 3 years of study. When there was no physical contact between roots of crop and weeds, the leachate from the weed zone caused tuber yield reductions of 42, 40 and 38% in 1978, 1979 and 1980, respectively, when it was applied to the yam zone. This leachate also reduced leaf area index (LAI) in the yam crop but the adverse effects on yam root and shoot biomass were less pronounced. This technique made it possible to separate competitive interference from allelopathic interference of tropical weeds with the yam c

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1989.tb00833.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SummaryThe survival and growth of seedlings ofRumex obtusifoliusL. andRumex crispusL. were investigated from 1982 to 1984. A sward was established by the sowing of seeds ofDactylis glomerataandTrifolium repensand managed under two cutting frequencies. Five hundred seeds of eachRumexspecies were sown m−2. The total number of emergent seedlings of eachRumexspecies over two seasons was 230–360 m−2. About 85% of them emerged within 3 months of sowing. BothRumexspecies showed the same pattern of survivorship. Survival was clearly enhanced by frequent cutting during the second season. About 20% of the emerged plants survived through to the third season. Plants that emerged during the first season only flowered during the second season. The flowering percentage of total surviving plants was significantly higher inR. obtusifoliusthan inR. crispus. Rumex obtusifoliuswas higher in dry matter of aerial parts defoliated during the second season and more individual plants survived through to the third season than forR. crispus.Moreover, dry matter production of grass and clover was depressed by 25–30% in mixtures withR. obtusifolius.compared with production in mixtures withR.

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1989.tb00834.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SummaryA transplant experiment was performed to compare the survivorship ofRumex obtusifoliusL. andRumex crispusL., and also to determine the environmental characteristics of grasslands seriously colonized withR. obtusifolius.One‐month‐old seedlings of eachRumexspecies were transplanted into three old reseeded swards with different infestation levels ofR. obtusifoliusplants.Rumex crispuswas absent from all swards. Their survival was monitored at monthly intervals for 4 years (May 1982 to May 1986). The mortality ofR. obtusifoliuswas greater in the third and fourth years in all swards, less than 2% of the phytometers being alive in the fifth spring. The number ofR. crispustransplants declined more gradually in the course of the experiment and 4–24% of the phytometers still survived by the end of the experiment. This suggests thatR. obtusifoliusplants colonized in sown grasslands in the cool‐climate region have a comparatively short life expectation of 3–4 years. Mortality rate, growth in size and flowering percentage tended to vary significantly between sites: higher in more productive swards. In years 2 and 3 there were seven‐fold differences in mean dry matter weights of plants that produced an inflorescence and those that remained in a vegetative phase. The mortality of transplants was not size dependent in eitherRumexspecies. Phytometers died at random irrespective of the indiv

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1989.tb00835.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SummaryBroadcast sprays of several herbicides were applied at different times of the year at several sites in Hawkes Bay, Canterbury and Otago. For good thistle control, date of application was more important than types of herbicide. In Hawkes Bay, applications made in April, May and June tended to be the most effective. Under slightly cooler Canterbury conditions, April, September and October were the best application dates. In the Otago trials, spring emergence of thistle seedlings meant that the most consistent results came from September or October applications. At all sites, applications made in July or August were relatively ineffective, probably because of low winter temperatures and slow thistle growth rates. MCPA (potassium salt) at 1·0 kg ha−1was the standard herbicide used in all experiments. MCPA at 0·5 kg ha−1, MCPB (sodium salt) at 0·5 and 1·0 kg ha−1and 2,4‐D at 0·5 kg ha−1did not kill as many thistles as MCPA at 1·0 kg ha−1. MCPA at 1·5 kg ha−1and MCPB (butyl) ester + clopyralid at 0·5 + 0·015 or 1·0+0·03 kg ha−1gave consistently better control than MCPA at 1·0 kg ha−12,4‐D at 1·0 or 1·5 kg ha−1, MCPB at 1·5 or 2·0 kg ha−1, and MCPA + MCPB at 0·33 + 1·0 or 0·67 + 0·5 kg ha−1gave results very similar to MCPA at 1 kg ha−1. Thistle control varied between sites and years. Some of the variation may have been due to different proportions of first and second year thistles present at spraying, and to variation in genetically determined herbicide susceptibility. Chemical control of thistles was short

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1989.tb00836.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SummaryThe rate of photosynthesis in intact leaves attached to plants of an atrazine‐resistant cultivar ofBrassica napusL. was compared with that in leaves of an atrazine‐susceptible, rather isogenic cultivar, in a number of irradiance series. The resistant cultivar had been obtained from the susceptible cultivar by crossing the resistant biotype ofBrassica campestrisL. with the susceptible cultivar ofB. napus, and using the fourth back‐cross for comparison. At a natural CO2concentration (360 cm3m−3) the rate of photosynthesis of leaves of the atrazine‐resistant cultivar was significantly (17–21%) less than that of leaves of the susceptible cultivar, over the whole range of irradiances up to 250 W m−2At the enriched CO2concentration of 1500 cm−3m−3this reduction in rate

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1989.tb00837.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SummaryThe effects of weed removal at five dates after planting the crop were examined and compared with weed‐free and unweeded controls. The results revealed that the total weed population increased up to 6 weeks after planting and then decreased drastically in both the years. Total dry weight of weeds (at weeding and at haulm‐cutting) was greatest in the unweeded control, followed by weeding at 10 weeks after planting. In both years, maximum yield was obtained where plots were kept weed‐free, followed by weeding at 4 and 6 weeks after planting. The remaining treatments, including weeding at 2 weeks after planting, resulted in significant reductions in tuber yield. In unweeded control plots the tuber yield of potato was reduced by 4

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1989.tb00838.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SummaryA survey of dicotyledonous weeds of spring cereals was conducted prior to herbicide application in 1985 in six districts of north‐east Scotland, which involved a total of 113 fields. Results were similar to those from an earlier survey in 1973. The main species remained the same but in four of the six districts, total weed densities were lower.Stellaria mediawas the most common species except in Upper Banffshire and Morayshire whereGaleopsisspp. andPolygonum aviculare, respectively, were predominant. The main changes apparent were a declineof Spergula arvensisandPolygonum persicaria, and an increase inMatricaria perforataandViola arvensisin several district

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1989.tb00839.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SummaryAbsorption, translocation and metabolism of14C‐pyridate were compared in tolerant maize. moderately susceptiblePolygonum lapathifoliumand susceptibleChenopodium album.Foliar absorption was limited in all species, but comparatively higher penetration levels were observed in younger leaves of dicotyledonous species. The absorbed radioactivity was not very mobile and translocation appeared mainly sym‐plastic. Herbicide selectivity could not be explained on the basis of absorption and transport.ChenopodiumandP. lapathifoliumdegraded pyridate and formed unstable water‐soluble conjugates that easily released a phytotoxic metabolite. By contrast, more stable unidentified water‐soluble metabolites were found in maize. That metabolic difference could explain the selectivity of p

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1989.tb00840.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

RésuméUne sensibilisation des agriculteurs au problème des bromes envahissant des céréales nous a incitéà rechercher si les caractéristiques germinatives de ces espèces pouvaient expliquer leur comportement au champ. Cet article étudie plus particulièrement la réponse des bromes à la lunnère. Douze espèces annuelles ont été testées: 6 pour le sous‐genreBromus, 6 pour le sous‐genreAnisanthaKoch;Bromus catharticusVahl a été rajouté car il peut se comporter comme annuel. La photosensibilité est très marquée surtout à basse température où elle est négative. Les différentes espèces ont été comparées entre elles en tenant compte de leur origine géographique. La photosensibilité négative est beaucoup plus importante pour le sous‐genreAnisanthaKoch et pour les lots d'origine méditerranéenne. L'intensité et la persistance de ce phénoméne lui permettent certainement de jouer un rôle non négligeable dans le

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1989.tb00841.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SummaryTri‐allate degraded faster in soil from a site (T1) that had received 1·7 kg ha−1of tri‐allate annually for 23 years than in soil from an adjacent site (TO) that had received no pesticide application. Soil from the untreated site, which had been removed to a glasshouse and treated three times per annum with tri‐allate at 1·7 kg ha−1for 7 years (T2), also showed faster degradation. Soil previously treated with tri‐allate showed an increased degradation rate for carbofuran and EPTC but not for aldicarb. A further experiment, 2 years after the last treatment with tri‐allate, showed that the enhanced degradation effect was still present. Degradation rates were always in the order T1>T2>T0 for tri‐allate, EPTC and carbofuran. Half‐life for degradation was reduced for tri‐allate and carbofuran by approximately 40% in the previously treated soils and for EPTC by approximately 80% when compared with the prev

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1989.tb00842.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY