摘要:

SummaryLosses in grain yield prevented by controlling weeds were measured in 59 fields of (southern hemisphere) spring‐sown wheat (Triticum aestivumL.) (cv, Otane) and 45 fields of spring‐sown barley (Hordeum vulgareL.) (cv. Corniche) in five consecutive growing seasons from 1988/89 until 1992/93 in the Canterbury region of New Zealand. The losses were measured as the differences in yield between weeded and non‐weeded plots located in randomly positioned pairs in the fields. In the first 2 years, the weeding was by push hoe in‘organically grown crops. For the last 3 years, the fields were under prophylactic herbicide regimens with nonweeded plots created by excluding commercial herbicide applications (made mostly in October for wheat and November for barley) with polyethylene sheets placed temporarily over the plots. For each season the distributions of yield losses were modelled using the normal distribution and probabilities of ‘breaking even’ on herbicide use derived by substituting cumulative probability density functions into a simple break‐even model for herbicide use. The model assumed that herbicide application in the current crop has no flow‐on economic effect for succeeding crops. The mean annual yield losses prevented by herbicide application were positively correlated with September and October rainfall for wheat and bailey respectively. As a consequence, the probabilities of breaking even on herbicide use increased with increasing spring rainfall. Using historical rainfall records, probabilities of breaking even were estimated for each of the 48 years from 1947 to 1994. Averaging over these years, the analysis revealed that at current grain prices prophylactic use of the commonly applied herbicides is likely to be uneconomic in 24% (95% confidence limits 6% and 50%) of fields of average‐yielding Otane wheat and in 26% (95% confidence limits 1% and 91 %) of fields of average‐yielding Corniche barley in Canterbury. It was concluded that there is potential for withholding herbicide treatments without jeopardizing profitability in these crops, particularly in seasons with

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1996.tb01674.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

SummaryThe effects of nitrogen fertilizer on the growth and density of natural weed populations in spring barley (Hordeum vulgareL.) and winter wheat (Triticum aestivumL.) were investigated in the absence of herbicide. An increased level of applied nitrogen did not enhance: weed germination, tended to decrease the total weed biomass and had a differential effect upon the biomass of individual weed species in both wheat and barky. In competition with barley,Chenopodium albumL. andLamiumspp. had lower nitrogen optima than the crop, whileUrtica urensL. had a higher nitrogen optimum. In competition with wheat,Stellaria media(L.) Vill.,Lamiumspp. andVeronicaspp. had lower nitrogen optima than the crop. The systematic changes in nitrogen effect with time were analysed by fitting orthogonal polynomials to the growth and density curves. The methodology could be recommended for other studies in which time or other systematic factors are included, as it supplies information which a traditional analysis of variance cannot provide. Since seed production is positively correlated with biomass, so nitrogen level affects seed production and, hence, the seed pool and future weed population, suggesting that fertilizer usage can be exploited in an integrated programme of crop: weed management. A trend towards lower N fertilizer application owing to concerns about the environment willfavour most of the weed species investigated in these experiments and change the composition of weed populations.

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1996.tb01675.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

SummarySeeds ofAbutilon theophrastiMedic., collected from plants growing in a continuous maize or soyabean field subjected to herbicide application, cultivation or no weed management for 10 years, differed significantly in their weight and germinability. The differences in mean weight and germinability of the progeny seeds were maintained when the parent plants were grown in a greenhouse under controlled conditions. The offspring of plants with or without previous exposure to atrazine responded similarly to the herbicide in all the measurements of the growth and development of the plants, except blooms. Significant differences between the two groups of plants were mainly observed in the weight and germinability of their seeds. Although plants with or without previous exposure to atrazine usually did not differ significantly in their response to the herbicide in terms of individual traits, they differed both in the amount and pattern of overall response across all traits. The difference in overall response between plants increased with increasing rate of atrazine. It is possible that previous exposure to the herbicide had caused minor variation in a group of inter‐correlated traits or in the strength or pattern of correlation among trait

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1996.tb01676.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

SummaryA ‘system management’ approach of biological weed control in crops is proposed and compared with other method's of biological weed control. It is based on the management of a weed pathosystem in order to maximize the natural spread and disease severity of a native or naturalized pathogen. This approach may be well‐suited to situations where it is necessary to control single weed species in crops, and where no immediate and complete control is required, the production of large amounts of the agent is rather limiting (e.g. when using biotrophic fungi), and/or the importation of an exotic agent is not possible. This strategy provides fundamental knowledge of underlying mechanisms of crop production systems and is aligned with the view of modern agro‐ecology, in which complete eradication of weeds is not desirable. The fundamental research required for a successful application of the ‘system management’ approach will be illustrated with the biological control project ofSenecio vulgarisL. using the naturalized rust fungusPuccinia lagenophoraeCooke. A five‐step procedure, together with selected results, will be presented. Main emphasis is given to the infection window, the study of the genetic structure of the plant and pathogen population, and the management of the infection conditions (a) to maximize the spread of the disease and the impact on the plants, and (b) to minimize the development of resistant plant populations. Joint application of herbicides at low doses, additional necrotrophic pathogens, and of biochemicals interfering with the weed's defence also will be envisaged, as well as their integration into general pest control practices. In this regard, biological weed control agents have to be seen as stress factors, not as weedkillers, and biological weed control as an integral part of a well‐designed pest management strategy, not

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1996.tb01677.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

SummaryIn this review the available information on the sexual reproduction ofCirsium arvenseL. (Scop.) is summarized and discussed in an ecological context. Certain aspects of its sexual reproduction system have givenC. arvensea reputation for low efficiency: the dioecious mating system and dependence on insects for pollination and non‐adaptive features for wind dispersal. The seeds are moderately persistent in soil and, for a temperate weed, have a high temperature requirement for germination. It is concluded that the contribution that sexual reproduction makes to the survival and spread of this species has been underestimated, partly owing to an inadequate number of studies. Seedling recruitment via sexual reproduction may be an important mechanism for initiating continued genetic diversity at intra‐ and inter‐population l

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1996.tb01678.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

SummaryThe competitive abilities of a wide range of genotypes of wheat (Trilicvm aestivumL.) and durum wheat (Triticum durumDesf.) againstLolium rigidumGaud, (annual ryegrass) were examined 1o determine the potential for breeders to select strongly competitive varieties, Considerable potential within the wheat genome to breed varieties with greater competitive ability was demonstrated. In 1993, 250 genotypes from around the world were screened and in 1994 a subset of 45 (mainly Australian) genotypes were further examined. A uniform density ofL. rigidumreduced grain yield of wheat by up to about 80% in 1993 and to 50% in 1994, depending on wheat genotype. Reduction in grain yield was correlated withL. rigidumdry matter. Wheats varied in competitive ability with source, and durum wheats were less competitive thanT. aestivum.The ‘old’ standard wheat varieties (released between 1880 and 1950) suppressed the weed more than all the current varieties, with the exception of eight F1hybrids. A doubling of the crop seeding rate of 10 of the genotypes in 1994 reduced the biomass ofL. rigidumby an average of 25% compared with the standard seeding rate. Ranking of competitive ability of varieties at high density was consistent at both seeding rates. The strongly competitive genotypes had high early biomass accumulation, large numbers of tillers, and were tall with extensive leaf display. The potential for breeding enhanced competitive ability in wheat is discus

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1996.tb01679.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

SummaryThirteen fungal species were isolated from diseased plants ofStriga hermonthica(Del.) Benth in northern Ghana. The pathogenicity of 12 isolates of the fungal species includingCurvularia fallaxBoed,Fusarium equiseti(Corda) Sacc.,Fusarium equisetivar.bullatum(Sherb.) Wollenw.,F. oxysporumSchlecht,F. solani(Mart) Sacc.,Macrophonuina phasealina(Tassi) Goidan, andSclerotium rolfsii(Sacc.) were evaluated against S.hermonthicaunder controlled environmental conditions. All isolates were pathogenic toS. hermonthicawhen propagated on wheat (Triticum aestivumL.) grains and incorporated pre‐planting into the soil. However, their virulence differed. Two isolates ofF. oxysporumand one isolate ofF. solanireduced the emergence ofS. hermonthicaby 88%, 98%, and 76%, respectively. Sorghum (Sorghum bicolor(L.) Moench) yield was increased by 26% whenS. hermonthicawas controlled. In contrast, in the control treatment withS. hermonthicano yield could be obtained. TheF. oxysporumisolates were not pathogenic on sorghum. Germination tests indicated that theF. oxysporumisolates were highly pathogenic toS. hermonthicaseeds. Although theF. solaniisolate reduced the emergence ofS. hermonthicain the pot experiments, it did not influence germination. This indicates that pathogens may attack different stages in the life cycle ofS. hermonthic

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1996.tb01680.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY