摘要:

SummaryLaboratory studies have shown that the amounts of glutathione (GSH) and cysteine are higher in grass species that are moderately tolerant, such as wheat (Triticum aestivumL., cv. Fredrick), and moderately susceptible, such as barley (Hor deum vitlgareL., cv. Legér) and triticale (cv. OAC Trillium), to fenoxaprop‐ethyl (FE) than in species that are very susceptible to the her bicide, such as oat (Avena salivaL., cv. OAC Woodstock), wild oat (Avena fatuaL.), yellow foxtail (Setaria glanca(L.) Bcauv.), large crab grass (Digitaria sanguinalis(L.) Scop.) and bar nyard grass (Echinochloa crus‐galli(L.) P.B.). The safener, fenchlorazole‐ethyl (FCE) was found to increase and decrease, respectively, the amounts of GSH and cysteine in the moderately tolerant and moderately susceptible species but had no effect on the susceptible species. It is sug gested that in the moderately tolerant and moderately susceptible species, especially following FCE treatment, more GSH is available to detoxify the herbicide. Glutathione‐S‐tranferase activity (GST) for FE was found to be very low in all of the species tested.In vitroexperiments at physio‐logical pH. demonstrated that FE may conjugate with GSH nonenzymatically. Therefore, it is suggested that nonenzymatic conjugation of fenoxaprop‐ethyl with glutathione may be an important mechanism for tolerance of some grasses to

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1995.tb02026.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummaryClonal growth and fragment regeneration ofRumex obtusifoliusL. were analysed in two dif ferent studies. Clonal growth system was des cribed by a morphological study of underground structure of different‐aged individuals, using maximal branching order in the stem system as an age estimator. Glasshouse experiments were conducted, testing the regenerative capacity of different below‐ground parts and the estab lishment of above root‐collar fragments planted at different depths under contrasting water regimes. Results showed the presence of a ‘phalanx’ type clonal growth system in grassland populations ofRumex. The main structure in volved in clonal growth proved to be the stem system; the region above the root collar was also the only part able to regrow after damage. Stem fragment regeneration occurred to depths of 15 cm, but was prevented in soils maintained at waterlogging and field capacity. The significance of these results in relation to nonchemical con trol ofRumexpopulations in grasslands is

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1995.tb02027.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummaryA biotype ofSonchus oleraceusL. and two bio types ofSisymbrium orientateTorn., SSO 3 and NSO 1, are the first dicot weeds in Australia to develop resistance to ALS‐inhibiting herbicides. The resistant biotypes had been exposed to va rying periods of selection with sulfonylurea her bicides. All three biotypes are resistant to a range of sulfonylurea and imidazolinone herbicides. TheS. orientalebiotypes are also resistant to the triazolopyrimidine herbicide, flumetsulam. LD50ratios of resistantSonchus oleraceusfor sulfony lurea and imidazolinone herbicides are greater than 64‐fold and 4.5‐fold, respectively. GR50ratios are greater than 9 for sulfonylureas and 7.4 for imazapyr. The LD50ratios for bothS. orien talebiotypes for chlorsulfuron, sulfometuron methyl, metsulfuron‐methyl, flumetsulam and imazethapyr are greater than 110‐, 15‐, 7‐, 24‐ and 29‐fold, respectively. All resistant biotypes are susceptible to MCPA, diuron and diflufenican, herbicides which d

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1995.tb02028.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummaryThe impact of drilling date onApera spica‐ventiandAlopecurus myosuroidesin winter cereals was investigated in field trials in 1991 and 1992. Two drilling dates were considered with an inter val of 14 to 16 days between dates. Generally, drilling date had an inconsistent effect on weed plant populations in spring, but seedling emerg ence of both species appeared to be delayed at the later drilling compared with the earlier date. This delay may partly explain the reduced com petitive ability ofA. myosuroidesin wheat in 1991 and 1992 and ofA. spica‐ventiin wheat in 1991 at the later drilling date. The seed popula tion per plant of both species was lower at the later date in some instances, whereas in others drilling date had no effect. Reduced seed produc tion was mainly caused by a reduction of the number of inflorescences per plant. The poten tial of utilizing drilling dates as a cultural control measure against grass weeds is discus

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1995.tb02029.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummaryThe dynamics of weed populations were ana lysed in intensified cereal‐based cropping sys tems of the northern Guinea savanna in Nigeria, A total of four common weed associations were identified through cluster analysis. Five factors describing soil fertility conditions and field his tory best differentiated the weed communities according to a discriminant model. The analysis shows that maize‐based cropping systems with a high frequency of cereal cropping and a low fre quency of noncereal cropping tended to be domi nated by weeds such asCommelinaspp. andKyllinga squamulata. As soil fertility declined,Vernoniaspp. andEclipta prostratabecame more important. Increased frequency of noncereal crops in mixed cropping with cereals was associ ated with reduced incidence of weeds such asLeucas martinicensis, Oldenlandia corymbosa, Spermacoce verticillata, Litdwigia hyssopifolia, Celosia laxa, and,Ipomoeaspp. Further diversifi cation of cereal‐based systems to obtain a re duced frequency of cereals is likely to increase the incidence ofDactvloctenium aegyptiumin crop fields. The information provides guidance for technology development and transfer on weed control for intensifying systems in the northern Guinea savanna of A

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1995.tb02030.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummaryThe effects of soil temperature and soil moisture content on the rates of degradation of atrazine, were measured in the laboratory in soils from different sites in Portugal. Persistence of atrazine was measured in the same soils in the field during the spring and summer of 1984, 1985, 1986 and 1987. Weather records from the different sites, measured during the periods of the field experi ments, were used in conjunction with appropriate constants derived from the laboratory data in a computer program to simulate persistence in the field. The model generally overestimated the ob served soil residues, particularly during the first 7–14 days after application. The fit from the model was good from day 14 to the end of the experiment

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1995.tb02031.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummaryGrowth, development and nutrient accumula tion inChenopodium albumandSenecio vulgarisgrown in pure and mixed stands were investi gated through several experiments conducted under glasshouse conditions. Results showed that the two weeds were different in their growth, development and tissue concentration and accu mulation of mineral elements. The mean concen trations of nitrogen, phosphorus, potassium, calcium and magnesium in shoots ofC. albumwere higher than those ofS. vulgaris, while root concentrations of nitrogen, potassium and mag nesium were lower forC. album. Marked dif ferences between the two weed species in their responses to different potassium levels were found.C. albumhad a high specific requirement for potassium while the reverse was true forS. vulgaris. The competitive ability and accumula tion of nutrients byC. albumappeared to be greatly dependent on the availability of high potassium levels in the media.

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1995.tb02032.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

SummaryIntensive field surveys were conducted to deter mine the spatial distribution of composite broad leaf and grass weed seedlings in seven maize and five soybean fields in eastern Nebraska in 1992. Farmer fields where herbicides were applied in a 38‐cm band over 76‐cm spaced rows were chosen for this study. Weed populations were measured in the interrow and in the band‐treated intrarow. Spatial maps constructed for grass or broadleaf weeds revealed that individual species as well as species assemblages are highly aggregated. On average, 30% of the sample area in the 12 fields surveyed was free of broadleaf weeds and 70% free of grass weeds in the interrow area (no her bicide). Where a pre‐emergence herbicide was applied (intrarow), 71% of the sample area was free of broadleaf weeds and 94% free of grass weeds. Increasing the threshold to some value other than zero resulted in a larger field area not requiring a herbicide application. The results of these distribution studies indicate that herbicide use could be substantially reduced if weed dis tribution maps or real‐time plant sensing were available to provide information for intermittent herbicide application systems or refinement of economic t

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1995.tb02033.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY