摘要:

SummaryThe spatial distribution ofElymus repensL. was mapped in five cereal fields during the 1994 season. Weed maps were created using a semi‐automated system mounted on a vehicle that travelled up the tramlines, centred on a 12‐m‐wide spray boom. Two operators detected weeds visually and recorded their presence and density by means of a simple push‐button system that recorded data from (2 × 1) m2areas, or cells, across the boom section on a portable computer. The position of the vehicle along the tramline was monitored by integrating output from a wheel sensor. Eight tramlines of one field were mapped three times consecutively, to assess detection and navigational error. Pair‐wise comparisons of the three runs gave approximately 85% repeatability on presence/ absence data, 80% on zero/low‐ or high‐density data and 85% on low/high‐density data when weeds were definitely present. Simultaneous comparisons of all three runs gave 78%, 69% and 75% respectively. Repeated runs of tramlines up to 550 m long recorded mean differences of approximately 2 m with a maximum error of 14 m (2.5%). The spatial distribution ofE. repenswithin the five fields was visibly patchy, but the size and morphology of patches varied both within and between fields. Thus, the potential reduction in herbicide usage as a result of patch spraying varied with patch morphology and infestation level. The effect of lowering the resolution from six (2 × 1) m2cells to three (4 × 1) m2cells across the 12‐m boom width showed little change in potential reductio

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1996.tb01658.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

SummaryThe comparative effects of lime, sulphuric acid, wood ash, glyphosate and ammonium nitrate onPteridium aquilinum(L.) Kuhn growth and development were evaluated in a Scots pine (Pinus sylvestrisL.) clear‐cut stand in south‐east Sweden over a 4‐year period.P. aquilinumgrowth was effectively controlled following the application of glyphosate, but the other treatments generally had little effect on growth in terms of shoot density and length. Shoot length was positively related to the number of shoots on plots treated with ammonium nitrate but negatively correlated with the number ofP. aquilinumshoots found on wood ash‐treated and control plots. In a bioassay aspen (Populus tremulaL.) seedling emergence and pH were significantly lower in humus treated with sulphuric acid, glyphosate, ammonium nitrate and in untreated humus as compared with the humus treated with lime and wood ash. The negative effect of humus on emergence of aspen seedlings may be caused by phytotoxic compounds at a lower pH level. Forest regeneration might be performed with shade‐tolerant species such as Norway spruce (Picea abies(L.) Karst.) planted beneath a thin canopy of trees to prevent the rapid increase ofP.

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1996.tb01659.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

SummaryResponse to paraquat was investigated in twoHordeum glaucumSteud. (wall barley) biotypes grown at warm (30^C) and cool (15^C) temperatures. Paraquat‐resistant (R) plants were nearly seven‐fold more tolerant when grown at 15^C than when grown at 3CPC. In contrast, there was a tendency for susceptible (S) plants to be more tolerant when grown at the higher temperature. The difference in response between the two biotypes grown at 30^ and 15^C increased from 3‐ to>40‐fold. Forty‐eight hours after foliar application, 62% less radiolabelled paraquat had translocated basipetally in the R compared with the S biotype. In addition, 26% more herbicide was retained within the treated zone of R compared with S plants. Thus, paraquat movement was restricted in the R biotype. It has been postulated that reduced mobility of the herbicide in the R plants is due to enhanced apoplasmic binding. In this study, paraquat binding to the cell walls and its release into the external solution was investigated in roots of R and S biotypes ofH. glaucumgrown under warm or cool conditions. No significant differences between the two biotypes were measured at either growth temperature. We propose that the mechanism of resistance to paraquat may involve a temperature‐dependent alteration in symplasmic transport of th

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1996.tb01660.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

SummaryGrowth, competitiveness and seed characteristics were compared in paraquat‐resistant and ‐susceptible biotypes ofHordeum leporinumLink collected from neighbouring fields. Dry weight and tiller production were greater in the susceptible biotype as compared with the resistant biotype in the absence of competition, however, the reproductive output was the same. Competitiveness in the field was estimated using a replacement series design that showed only slight differences between the two biotypes. There were no differences in seed weight, number of seeds per head, seed viability or seedling establishment between the two biotypes. When grown in pots in monoculture, the production of tillers was the same throughout the growing season, but inflorescences appeared on the resistant biotype earlier and matured earlier than did those of the susceptible biotype. We conclude that under field conditions the resistant biotype does not show a reduction in fitness as compared with the susceptible biot

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1996.tb01661.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

SummarySeeds ofSetaria glauca(L.) Beauv. buried in soil and exposed to natural temperature cycles exhibited seasonal changes in temperature, but generally not light; dark requirements for germination. Seeds were dormant at maturity in late September and October (autumn), and during burial from October to January they entered conditional dormancy, germinating up to ≥60% in light and darkness at daily thermoperiods of 25/15,30/15 and 35/20^C by January. During burial from February to May or June, seeds became non‐dormant and germinated up to 68–100% in light and darkness at 15/6,20/10,25/15,30/15 and 35/20^C in May or June. At maximum yearly temperatures in June or July–August, 65–89% of the seeds entered conditional dormancy (germinating at 30/15 and 35/20, but not at 15/6,20/10 and 25/15^C), and the others entered dormancy (not germinating at any thermoperiod). Thus, most buried seeds had an annual conditional dormancy/non‐dormancy cycle, but some had an annual dormancy/non‐dormancy cycle. Except for seeds buried in 1990 that lost the ability to germinate in darkness at all thermoperiods the first summer of burial, seeds incubated in light and in darkness exhibited the same patterns of seasonal changes in germination responses. Although conditionally dormant and non‐dormant seeds germinated to high percentages in darkness in Petri dishes, seedlings were found only in bags of seeds exhumed in April and May 1983, indicating that some factor(s) associated with the burial environment other than darkness prevented germination

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1996.tb01662.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

SummaryThe authenticity of weed distribution maps prepared by the geostatistical estimation method, kriging, was investigated. We concentrated on the total number of weed plants and the dominant weed genusVeronicaspp. in a 2.1‐ha field of winter wheat. Different sampling distances were evaluated. Our analyses showed that kriging weed densities based on seedling counts collected in, 0.25.m2circles in a sampling grid of approximately 10 m × 10 m gave good agreement with actual observations. Reducing the sampling grid to 20 m × 30 m gave poor agreement. New sampling methods combined with positioning devices and injection sprayers are discussed with reference to site‐specific weed manag

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1996.tb01663.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

SummaryA study in growth chambers with three irradiance levels was carried out over a four‐week period on individual seedlings of spring barley (Hordeum vulgareL.) and five weed species (Brassica rapaL. ssp.oleifera(DC.) Metzger,Chenopodium albumL.,Galeopsis tetrahitL.,Stellaria media(L.) Vill., andViola arvensisMurray). Increased irradiance resulted in larger dry weight, net photosynthetic rate, relative growth rate (RGR), net assimilation rate (NAR), and lower leaf area ratio (LAR). The number of leaves per plant, plant length, leaf area, and shoot/root ratio were unaffected by irradiance levels, During the experimental period the net photosynthetic rate increased, while NAR remained the same, and RGR, LAR, and shoot/ root ratio decreased. On the basis of leaf area and dry weight, especially at the high irradiance level during the last part of the experimental period, barley,B. rapa, andC. tetrahithad the largest values, followed byC. albumandS. mediawith medium values, andV. arvensiswith the smallest values. As for leaf area and dry weight,S. mediatook more advantage of the low than the high irradiance level compared withC. album.Species differences are discussed with regard to competitive abilit

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1996.tb01664.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

SummaryAs a part of a broader study, two experiments were carried out in growth chambers with three day/night temperature regimes (10/7, 20/14 and 30/21^C) studying growth characteristics of individual seedlings over a four‐week period. Experiment 1 was performed with spring barley (Hordeum vulgareL.),Galeopsis tetrahitL., andViola ArvensisMurray. Experiment 2, with three irradiance levels at 20/14^C, and one irradiance level at the other temperatures, was performed with spring barley,V. arvensis, Chenopodium albumL.,Brassica rapaL. sspoleifera(DC.) Metzger, andStellaria media(L.) Vill. Leaf area, dry weight, relative growth rate, net assimilation rate, and net photosynthetic rate generally showed an optimum at 20/14^C. Increasing irradiance resulted in a decreased specific leaf area. Expressed as fraction of shoot dry weight, green leaves decreased and stems, flowers, and yellow leaves increased with increased time, irradiance, and temperature. At all temperatures, barley,B. rapaandG. tetrahithad the largest dry weights, but at 20/14^C.C albumandS. mediaand at 30/21^CC. albumalso had large values. Differences in dry weight between species correlated more to morphological features than to assimilation rat

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1996.tb01665.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

SummaryMCPA is antagonistic to a range of herbicides but there is limited research on its compatibility with other broad‐leaved weed herbicides. In this study we assessed the joint action of MCPA ester and metsulfuron‐methyl onBrassica napusL. using the additive dose model (ADM). The fresh weight responses for selected ratios of the mixture were plotted on the ADM and compared to the predicted mixture response at three assessment levels ‐ 50, 75 and 90% control. The mixture demonstrated increasing synergism as the response level increased from 50 to 90%. This result for MCPA ester is in marked contrast to that of the MCPA amine formulation, which was shown in previous studies to be antagonistic towards sulfonylurea herbicides. Formulation is the major deciding factor in determining the compatability of phenoxy herbicides with other herbi

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1996.tb01666.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY