摘要:

SummaryAspects of the population: dynamics ofStriga hermonthica(Del.) Benth. on pearl millet (Pennisetum americanum(L.) K. Schum.) were studied in Sahelian Mali. Seasonal development was recorded and density‐dependent mortality and fecundity in post‐emergent populations investigated. An attempt was also made to assess yield loss due toS. hermonthicaattack using a regression approach. The firstS. hermonthicaplants emerged 42 days after crop germination, and the minimum time to complete the life cycle from emergence was 56 days. Results indicated a premature mortality of 66% in emerged populations. The growth stage reached by the time of host plant death appeared to be important in determining survival to maturity, premature mortality being greatest in plants that had not reached flowering by this time. The potential seed output per plant was estimated at 10 985. There was no evidence that the fecundity ofS. hermonthicawas affected by the density of emerged populations. Regression models showed a significant relationship between millet yield and emergedS. hermonthicadensity. The results suggest that lower densities give a relatively larger decrease in yield perS. hermonthicaplant. The results of the study are discussed in relation to their implications for cont

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1996.tb01650.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

SummaryPennisetum clandestinumHochst ex Chiov. (kikuyugrass) is a C4grass that has become an invasive weed in temperate climates. We examined ecophysiological mechanisms that have allowed it to become a successful weed in these locations by comparingP. clandestinumand two other common turigrass species,Festuca arundinaceaSchreb. (tall fescue cv. Mojave), a C3cool‐season grass, andStenotaphrum secundatum(Walt.) Kuntze (St. Augustinegrass), a C4warm‐season grass, grown in a warm or cool growth regime. We measured rates of photosynthesis over a range of leaf temperatures and also measured growth rate parameters of these species. At leaf temperatures between 25^C and 40^CP. clandestinummaintained the highest rates of photosynthesis in both temperature regimes. Under warm temperatures, this species rapidly increased biomass and leaf area to a greater extent than either of the other two grasses. Theoretical whole plant photosynthesis (mean leaf area × mean photosynthetic rate) was higher forP. clandestinumthan for the other two species in both growth regimes and over most leaf temperatures. Our results suggest thatP. clandestinumis a successful weed in Mediterranean climates as a result of its capacity to photosynthesize over the full range of temperatures found in those climates, its rapid growth during warm weather and its apparent tolerance to moderately cool temperat

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1996.tb01651.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

SummaryThe effect of non‐ionic nonylphenol (NP) surfactants containing 4–14 ethylene oxide (EO) molecules on the distribution of asulam and diflufenican was investigated inPteridium aquilinumL. Kuhn andAvena fatuaL. The distribution of the herbicides was dependent on the EO content and concentration of surfactant and differed between plant species and herbicide. The surface properties of contact angle, droplet diameter and surface tension were examined. For solutions of asulam, the greatest reductions in contact angle, surface tension and greatest droplet diameter were obtained with surfactants of EO 6.5–10 (at 0.001–0.1%). For solutions of diflufenican, these responses were greatest when applied with surfactant of EO 4. Surfactants of EO 6.5–10 increased the uptake and translocation of [14C]asulam inP. aquilinum,particularly at surfactant concentrations of 0.01 % and 0.1 %. All surfactants increased uptake of [14C]asulam inA. fatuawith no significant effects of surfactant EO number or concentration. For both species, there was a positive correlation between the optimum surface characteristics of the herbicide droplets and the uptake of asulam. With diflufenican, greatest uptake and translocation by mature frond tissue ofP. aquilinumoccurred at the highest concentration of surfactant EO 4; inA. fatua,however, uptake and translocation were not significantly affected by any of the su

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1996.tb01652.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

SummaryThe influence of nonylphenoxy surfactants and glyphosate salt formulation on spray retention, phytotoxicity and [14C]glyphosate uptake was investigated in wheat (Triticum aestivumL). andKochia scopariaL. The amount of spray retained, and uptake of [14C]glyphosate increased with increasing hydrophilic‐lipophilic balance (HLB) value of surfactants. The volume of spray delivered to the plant treatment area and retained by wheat andK. scopariaplants increased with increasing surfactant HLB values, but this only partly accounted for the higher spray retention. Spray retention by leaves of plants was not affected by calcium chloride, either alone or with ammonium sulphate in the glyphosate spray solution. [14C]Glyphosate absorption by wheat andK. scopariawas reduced by calcium chloride alone, but not in mixtures with ammonium sulphate, regardless of surfactant. Phytotoxicity and uptake of glyphosate salt formulations for wheat was: isopropylamine>ammonium>sodium>calcium; these results indicate that the surfactant selected is important to maintain glyphosate efficacy and that sodium and calcium cations antagonize glyphosate by forming salts that are absorbed less than commercial isopropylamine formulation

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1996.tb01653.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

SummaryThe importance of the position of weeds with respect to crop rows in the determination of crop yield‐weed density relationships and the usefulness of relative cover (RC) of the weeds as an explanatory variable were studied in soyabean [Glycine max(L.) Merrill] competing with two summer weeds with contrasting canopy structure (Xanthium strumariumL. ssp.italicumandEchinochloa crus‐galliL.). The position of the weeds was of little importance in the relationship between yield loss and weed density. This information is important because published experiments have used different types of weed distribution (e.g. evenly distributed or sown in rows). For both weed species it was possible to obtain a single relationship between yield loss and RC for measurements made from 30 days after crop emergence to soyabean canopy closure. The competitive effect of the weeds appeared to be strictly related to RC, indicating that for weeds growing taller than the crop the main competitive factor may be the shading caused by the leaves of the weeds situated above the crop can

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1996.tb01654.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

SummaryWeed removal experiments were conducted in growers' fields in northern Colorado to assess the effect of duration of competition, weed density, weed competitiveness and crop density on irrigated seeded onion (Allium cepaL.). Duration of competition, expressed in thermal time units (TTUs) with a base of 7.2^C, explained 65% of the variation in the reduction of onion relative yield. The first significant reduction in onion relative yield was at 90 TTUs, averaged over weed load (weed density adjusted by competitiveness) and onion density. A polynomial multiple regression model, accounting for duration of competition and weed load, explained 75% of the variation in onion relative yield. A non‐linear multiple regression model, combining a gamma function response of relative yield to duration of competition plus a hyperbolic response of relative yield to weed load, was as good a predictor and a better description of the system. Onion relative yield was more sensitive to the duration of weed competition than to weed load. Bulb size class distribution and the resulting average onion price were affected by weed competition. Polynomial models were used to describe changes in bulb size class proportions as a function of duration of competition, weed load and onion densit

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1996.tb01655.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

SummaryA bioassay method using the radicles of pea (Pisum sativumL.) and lupin (Lupinus angustifoliusL.) was developed for the assessment of trials on herbicides of common use in the sulfonylurea class (chlorsulfuron, triasulfuron and metsulfuron‐methyl) and in the sulfonanylide class (flumetsulam and metosulam). Soils within a range of pH 5.8–8.4 with textures from sand to clay were used in these experiments. The sensitivities of the species were similar in chlorsulfuron and flumetsulam trials and their response range varied with soil type and herbicide, e.g. between 0.75 and 6.0 ng triasulfuron g−1in the Wimmera grey clay and between 0.125 and 8.0 ng chlorsulfuron g−1soil in the Mallee sand. The method was demonstrated in a wide range of uses, encompassing tests of the initial bioactivity of formulations of chlorsulfuron and flumetsulam, monitoring the field leaching and persistence of triasulfuron and measuring relative potencies between the classes, using metsulfuron‐methyl and metosulam. The bioassay response provided a high level of reproducibility and precision, which was measurable by the logistic curve‐fitting procedure. In each case,R2values were>0.90 and lack‐of‐fit tests were clearly non‐significant at the 0.05 level. Chi‐square tests were used to measure differences between ED50's. The method does not require the pre‐germination and selection of seedlings, daily watering or root‐washing and results are obtained 7 days from sowing, providing favourable use for routine analyses

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1996.tb01656.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

GoldwasserY, KleifeldY, GolanS, BarguttiA&RubinB (1995) Dissipation of metham‐sodium from soil and its effect on the control of Orobanche aegyptiac

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1996.tb01657.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY