摘要:

Summary:Sugarbeet and weeds were treated with phenmedipham plus desmedipham either as single applications or as split applications in which 50% of the equivalent single application rate was applied at each application. Split application did not alter the phytotoxicity to the crop when environmental conditions did not predispose the Sugarbeet to injury by the herbicide. Split applications at 1‐1 or 1‐4 kg ha−1spaced from 0‐5 to c. 5 days apart caused more injury to the crop than the respective single applications when environmental conditions were such that injury to the crop resulted from the single applications. Injury to Sugarbeet following application of 0‐72 kg ha−1of phenmedipham plus desmedipham was always low, regardless of the type of application. Susceptible weeds were controlled by single applications of 1 1‐1 −4 kg ha−1, but 0‐72 kg ha−1did not reliably provide adequate control. Split applications c. 3‐8 days apart gave improved control. Control achieved by 0‐72 kg ha−1of the herbicide applied as split treatments equalled or exceeded that produced by single applications of 1‐4 kg ha−1. Improvement in the control of tolerant weed species by split applications of phenmedipham plus desmedipham was species dependent. Use of low‐rate split applications of phenmedipham plus desmedipham thus resulted in reduced injury to the Sugarbeet, and the introduction of less herbicide into the ecosystem, while maintaining or improving

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1991.tb01772.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Summary:Metribuzin efficacy and dissipation were determined in two silty clay loam soils following preplant (PP), pre‐emergence (PRE) and split (PP+PRE) application to tilled and no‐till soybeans in rotation with corn at Clay Center and Lincoln, Nebraska. A similar experiment was conducted in tilled and no‐till soybeans in rotation with wheat at Lincoln. Corn and wheat residue in no‐till plots reduced the amount of metribuzin that reached the soil by approximately 54 and 89%, respectively. No differences in weed control or soybean yield were observed between tillage treatments or time of metribuzin application in the corn‐soybean rotation. However, both weed control and yield were reduced in the wheat‐soybean rotation. Most of the metribuzin remained at the 0–5 cm depth, and dissipation was exponential. The mean metribuzin half‐life at the 0–5 cm depth across locations, tillage treatments, application time and rates was 11 days. The metribuzin half‐life was 4–19 days following PP application and 3–17 days following PRE application. The metribuzin concentration did not exceed 65 μg kg−1at the 5–10 cm or 10–20 cm depths in any treatment, indicating that little metribuzin had leached from the surface soil after PP or PRE application. The finding of a higher metribuzin concentration at 5‐20 cm depth in tilled plots than in no‐till could be attributed to higher initial soil concentrati

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1991.tb01773.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Summary:Fluroxypyr‐MHE (methylheptyl ester) was applied to small field plots containing Londo sandy loam soil. After 30 days, fluroxypyr had degraded to about 60% of the initial concentration, but was still the main component, while after 120 and 366 days the methoxypyridine metabolite was the main component in the soil. At 30, 120, and 366 days, lettuce, turnips, green beans, soybeans, and wheat were planted and grown with no observed injury. Residues of14C in the edible crop fractions were indistinguishable from14C in control plants exposed to14CO2, while residues in plant greens and chaff were low (0.1–0.2 mg kg−1), with little evidence of fluroxypyr and no evidence of metabolite uptake. These results indicate that the methoxypyridine metabolite, if present in the soil, does not harm and is not taken up into the p

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1991.tb01774.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Summary:Retention by a glass fibre filter of the liquid phase of a clay loam soil treated with14C‐diuron provides a novel method for analysis of the herbicide in soil solution. At 26.3% (w/w) soil moisture content, less than 10% of the applied diuron was found in solution, and this percentage decreased slightly with diuron dose. The herbicide was rapidly adsorbed on soil during the first day, but adsorption continued and the concentration of diuron in solution could be further reduced by 36–50% during the following 6 days. Drying the soil after treatment, with possible crystallization of herbicide applied at high doses, tended to fix the solution concentrations. Ethanol (3% v/v) in soil water favoured herbicide dissolution. Increasing soil moisture to 36.3% (w/w) slightly decreased the concentration of the herbicide in solution, but increased the percentage held in solution. Frost and a drying‐rewetting cycle had little or no subsequent effect on diuron concentration in soil sol

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1991.tb01775.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Summary:The incidence ofAlopecurus myosuroidesseedheads was monitored annually for 10 years in the cereal fields of a 173‐ha arable and dairy farm.A. myosuroidespersisted at low population densities, despite the use of herbicides and grass breaks in the rotation. The distribution of the weed was irregular, with none occurring on at least 60% of the positions surveyed in the cereal fields. Spatial distributions were compared between years, and some significant correlations were found from year to year in continuous cereals, and in cereal crops separated by a 3‐year grass

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1991.tb01776.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Summary:The effect of trifluralin on the growth and development of cotton plants in low‐organic‐matter soils from the northern Negev of Israel was studied. Trifluralin exhibited linear sorp tion isotherms on these soils, Trifluralin and dinitramine losses from soils under varying moisture regimes and application practices were determined in open systems. The data were fitted to both first‐order and biexponential kinetic equations. In about 50% of cases the biexponential kinetic model provided a better fit to the data, but no relationship could be found between the model parameters and environmental or soil properties. Losses were generally greater at field capacity than at 50% field capacity, and at 27°C than at 15°C, and in soils with a lower organic matter content. The trifluralin application rate was negatively correlated with vegetative growth parameters of cotton, but the correlation became weaker with increasing soil organic carbon content. Trifluralin delayed boll production in coarse textured soils, the longest delay occurring at higher application rates. It is concluded that in light soils that contain very little organic matter, trifluralin rates must be maintained at the minimum level required for adequate weed control to prevent damage t

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1991.tb01777.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Summary:The presence of the leaf blade for 5 days or longer on isolated single‐node stem segments ofPaspalum distichumwith an adequate supply of nutrients, water and light, produced better axillary bud growth than was observed on those segments without the leaf blade. Presence or absence of the leaf blade had no effect on segments in distilled water. Segments in Hoagland's solution of any strength exhibited significantly more growth than those in distilled water. In one‐half or full‐strength Hoagland's solution, segments generally showed signifi cantly more growth than segments in lower strength solutions. Segments subjected to flooding, daily watering, submergence or hydro‐ponic treatments exhibited significantly more growth than the segments that were watered every 3 days. Segments with the leaf blade retained, and those exposed to constant light, showed significantly better growth than segments without an attached leaf blade, or without light. It is concluded that the interactions between leaf blade, water, nutrients and light, which favoured photosynthesis and reduced transpiration, increased axillary bud growth. This interaction may provide a survival mechanism for isolated stems ofP. distichum, assisting its rapid spread in w

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1991.tb01778.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Summary:A paraquat‐resistant biotype of barley grass (Hordeum glaucumSteud.) was hybridized with barley and wheat in an attempt to transfer paraquat resistance to these crops. Although hybridizations with barley did not result in the production of a plant, cytological evidence of chromosome elimination of one parent, presumably ofH. glaucum, was obtained from squash preparations of young F1embryos. Hybridizations of wheat with both diploid and tetraploidH. glaucumresulted in the production of wheat haploids. These results indicate that it may not be possible to transfer paraquat resistance to barley and wheat using conventional hybridization technique

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1991.tb01779.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Summary:A model is presented to describe crop yield response in weed harrowing. The selectivity of harrowing, crop yield response to soil covering, and the competitive strength of the weeds are all variables in the model, which is derived from the hyperbolic yield‐density relationship, and therefore accounts for the effects of weed density. An advantage of the modelling approach is that the yield response can be separated into two parts, one derived from the positive weed‐killing effect of harrowing, and the other derived from the negative crop‐covering effect. Simulation runs based on experimental data showed that crop damage, when it occurs, cannot be ignored, and may sometimes even dominate the positive weed‐killing effect. Possible scientific and practical applications of the model are di

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1991.tb01780.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Summary:A series of field experiments was conducted to evaluate the competitive effect ofCirsium arvense(L.) Scop. on winter wheat (Triticum aestivumL. ‘Norstar’) yield. Grain yield at the centre of denseC. arvensepatches ranged from 28–71% of the yield in adjacent weed‐free plots, based on measurements made at 11 experimental sites over a 2‐year period. The mean reduction in yield was 49%. Two models were used to describe grain yield reduction in terms ofC. arvenseshoot density: (a) linear regression of percentage yield reduction on the square root of shoot density, and (b) non‐linear regression, based on a rectangular hyperbola. Both models give similar yield loss estimates at commonly occurring shoot densities ofC. arvense, but the non‐linear model accounted for more of the observed variation in grain yield. The major yield component affected byC. arvensecompetition was spikes per unit area, with kernel weight affected to a

ISSN:0043-1737    

DOI:10.1111/j.1365-3180.1991.tb01781.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY