Survey of yield losses due to weeds in central Alberta

2001 ◽  
Vol 81 (2) ◽  
pp. 339-342 ◽  
Author(s):  
K. Neil Harker
Keyword(s):  
Key Words ◽  
Weed Competition ◽  
Yield Losses ◽  
Key Words Competition

Weedy and weed-free yields were determined in fields of barley, canola, and peas in Lacombe County, Alberta, Canada from 1995 to 1997. Yield losses were most frequent and severe in peas, and least frequent and less severe in barley. Yield losses due to weed competition were not detectable at 33, 60, and 73% of the pea, canola, and barley sites, respectively. Key words: Competition, interference, barley, canola, peas

scholarly journals Light dynamics and free-to-grow standards in aspen-dominated mixedwood forests

2002 ◽  
Vol 78 (1) ◽  
pp. 137-145 ◽  
Author(s):  
Victor J Lieffers ◽  
Bradley D Pinno ◽  
Kenneth J Stadt
Keyword(s):  
Leaf Area Index ◽  
Key Words ◽  
Leaf Area ◽  
Light Transmission ◽  
Stand Density ◽  
Canopy Gaps ◽  
Light Competition ◽  
Area Index ◽  
Mixedwood Forests ◽  
Key Words Competition

This study examines light competition between aspen and spruce during the sequence of aspen development. Leaf area index and light transmission were measured or estimated for aspen stands from 2 to 125 years old. Light transmission was lowest at 15-25 years, and in some stands, transmission was less than 5% of above-canopy light. Hypothetical aspen stands with various stem configurations and heights were developed, and positions were identified that would meet or fail Alberta free-to-grow (FTG) standards. Light transmission was estimated at each position with the MIXLIGHT forest light simulator. Positions in canopy gaps or at the northern sides of canopy gaps had higher light. In general, however, there was little difference in available light between positions that met or failed FTG criteria. Stand density and size of aspen trees appears to be a better index to predict light transmission and spruce success in juvenile aspen stands than current FTG criteria. Key words: competition, free to grow, hardwood, spruce, light

Simulation of Competition for Photosynthetically Active Radiation Between Common Ragweed (Ambrosia artemisiifolia) and Dry Bean (Phaseolus vulgaris)

Weed Science ◽  
1996 ◽  
Vol 44 (3) ◽  
pp. 545-554 ◽  
Author(s):  
David Chikoye ◽  
Leslie A. Hunt ◽  
Clarence J. Swanton
Keyword(s):  
Leaf Area ◽  
Crop Yield ◽  
Photosynthetically Active Radiation ◽  
Growth And Development ◽  
Field Studies ◽  
Weed Competition ◽  
Yield Losses ◽  
Dry Bean ◽  
Common Ragweed ◽  
Active Radiation

The influence of weeds on crop yield is not only dependent on weed-related factors such as density and time of emergence, but also on environmental and management factors that affect both the weed and crop through time. This study was undertaken to develop the first physiologically based dry bean model that would account for the influence of weed competition. The specific objective was to develop a model that would account for the influence of weed competition on crop yield, and to use this model to test the hypothesis that crop yield losses resulted from competition for photosynthetically active radiation (PAR). To this end, a model that simulated the growth and development of dry bean was developed. The model performed daily calculations and simulated the phenology, leaf area expansion, dry matter production and distribution, and grain yield of dry bean based on weather and management information, but assumed adequate water and nutrients. The model was calibrated without weed competition at two locations and yr, and for these situations, adequately described the growth and development of the crop. Simulations were then run for five common ragweed densities and two times of emergence. Common ragweed leaf area was read into the model from input files and used to simulate weed shading. Shading of the dry bean canopy by common ragweed accounted for about 50 to 70% of the yield losses observed in field studies when weeds emerged with the crop. Weed shading did not account for the yield reduction measured from weeds that emerged at the second trifoliate stage of crop growth. The agreement between model predictions and field studies was consistent with the hypothesis that competition for PAR was a principal factor in weed-crop interaction. The ability to account for differences in weed densities, management, and environmental conditions suggested that modeling was a useful tool for evaluating the interaction among weeds and crops.

Herbicide Performance in Rice (Oryza sativa) under Three Flooding Conditions

Weed Science ◽  
1984 ◽  
Vol 32 (2) ◽  
pp. 157-162 ◽  
Author(s):  
Edward P. Richard ◽  
Joe E. Street
Keyword(s):  
Oryza Sativa ◽  
Drought Stress ◽  
Weed Control ◽  
Weed Competition ◽  
Yield Losses ◽  
Early Season ◽  
Rice Yields ◽  
Weed Emergence ◽  
Principal Advantage

A 3-yr study was conducted to compare the performance of several herbicides applied alone and in mixtures under three flooding conditions in dry-seeded rice (Oryza sativaL. ‘Labelle’). When the soil remained moist during the 2-week unflooded periods (1979 and 1981), weed emergence was slowed and no advantage with respect to enhanced weed control and increased rice yields could be demonstrated over that of the standard sequential propanil (3′,4′-dichloropropionanilide) application. However, in 1980 when drought stress may have reduced initial postemergence activity and weeds emerged during the 14-day unflooded periods, differences in weed control between herbicides were obtained. Results of this study also indicate that yield losses from weed competition resulted primarily from early season competition, and that the principal advantage of the residual herbicides in dry-seeded rice may be to eliminate the need for retreatment with propanil when flooding is delayed or fields are drained.

Maize/Weed Competition Experiments: Implications for Tropical Small-Farm Weed Control Research

1983 ◽  
Vol 19 (4) ◽  
pp. 341-347 ◽  
Author(s):  
R. Vernon ◽  
J. M. H. Parker
Keyword(s):  
Weed Control ◽  
Critical Period ◽  
Maize Yield ◽  
Weed Competition ◽  
Labour Demand ◽  
Small Farms ◽  
Yield Losses ◽  
Small Farm ◽  
Control Research ◽  
Maize Yields

SUMMARYTwo sets of experiments examined the effects of weeds on maize yields using weeding methods typical of small farms in Zambia where oxen are used for cultivation. Maize yield losses of 30% due to weeds were evident with common weeding practices. A critical period of competition, during which the crop should be kept clean, was demonstrated from 10 to 30 days after emergence. This is a period of peak labour demand and the prospect of using chemical weed control to ease the situation is considered. The value of weed competition data, given its variability between sites, is discussed.

Yield responses of oats and alfalfa to common hemp-nettle (Galeopsis tetrahit) interference

1991 ◽  
Vol 71 (1) ◽  
pp. 141-147 ◽  
Author(s):  
Anne Légère ◽  
Jean-Marc Deschênes
Keyword(s):  
Field Experiments ◽  
First Year ◽  
Weed Competition ◽  
Yield Losses ◽  
Weed Interference ◽  
Medicago Sativa L ◽  
Lower Height ◽  
Carry Over ◽  
Yield Responses ◽  
Early Harvest

Effects of various densities of hemp-nettle (Galeopsis tetrahit L.) on yields of oats (Avena sativa L.) and first year alfalfa (Medicago sativa L.) were investigated in field experiments. In both crops, emergence of hemp-nettle seedlings occurred after plot establishment such that final densities were generally greater than initial densities. Hemp-nettle plants within a stand were distributed normally over no more than seven 15-cm height classes. Very few plants were found in the lower height classes. Weight distribution according to the same height classes showed that average to tall individuals produced a large proportion of the weed biomass. Oat yields decreased as hemp-nettle density increased. In the density range of 28–248 hemp-nettle plants m−2, oat grain yield losses varied between 12 and 50%. Alfalfa was cut according to either a two-cut regime, or a three-cut regime which included an early harvest. Alfalfa yields decreased with increase in hemp-nettle density regardless of cutting regime, whereas effects of cutting regime on alfalfa yield varied with year of experiment. In each regime, timing of first harvest determined the duration of hemp-nettle interference and may have affected the degree of carry-over effects to later harvests. Key words: Hemp-nettle, Galeopsis tetrahit, weed competition, weed interference, crop losses

Shade Avoidance in Soybean Reduces Branching and Increases Plant-to-Plant Variability in Biomass and Yield Per Plant

Weed Science ◽  
2011 ◽  
Vol 59 (1) ◽  
pp. 43-49 ◽  
Author(s):  
Emily Green-Tracewicz ◽  
Eric R. Page ◽  
Clarence J. Swanton
Keyword(s):  
Light Quality ◽  
Biomass Accumulation ◽  
Field Trials ◽  
Weed Competition ◽  
Shade Avoidance ◽  
Internode Elongation ◽  
Yield Losses ◽  
Plant Yield ◽  
Reflected Light ◽  
Crop Weed Competition

Recent studies have suggested that soybeans express shade avoidance in response to low red : far-red (R : FR) light reflected from neighboring plants and that this response may determine the onset and outcome of crop–weed competition. We tested the hypothesis that the low R : FR ratio would trigger characteristic shade avoidance responses in soybean and that the subsequent phenotype would experience reproductive costs under non–resource-limiting conditions. Soybeans were grown in a fertigation system in field trials conducted in 2007 and 2008 under two light quality treatments: (1) high R : FR ratio (i.e., weed-free) i.e., upward reflected light from a baked clay medium (Turface MVP®), or (2) low R : FR ratio (i.e., weedy) of upward reflected light, from commercial turfgrass. Results of this study indicated that a reduction in the R : FR ratio of light reflected from the surface of turfgrass increased soybean internode elongation, reduced branching, and decreased yield per plant. Shade avoidance also increased the plant-to-plant variability in biomass and yield per plant. Per plant yield losses were, however, more closely associated with reductions in biomass accumulation than population variability as the expression of a shade avoidance response did not influence harvest index. While these results suggest that weed induced shade avoidance decreases soybean per plant yield by reducing branching, it is possible the productivity of a soybean stand as a whole may be buffered against these reduction by a similar, but opposite, expression of plasticity in branching.

Yield Losses Due to Weeds, Critical Period for Weed-crop Competition in Fenugreek (Trigonella foenum-graecum L.) 

2021 ◽  
Author(s):  
Ravindra Singh ◽  
Sharda Choudhary ◽  
R.S. Mehta ◽  
O.P. Aishwath ◽  
G. Lal
Keyword(s):  
Seed Yield ◽  
Critical Period ◽  
Growth Period ◽  
Weed Competition ◽  
Yield Losses ◽  
Trigonella Foenum Graecum ◽  
Weed Infestation ◽  
Competition Period ◽  
Trigonella Foenum Graecum L ◽  
Period Model

Background: Weed populations reduce crop yields by influencing the pattern of crop growth and development throughout the season and by directly competing with the crop for limiting precious resources, like light, water or nutrients. A number of the factors that influence magnitude of crop yield losses from weed interference include the timing of weed emergence relative to the crop, weed density, pattern of weed growth and development. Weed management is one among the foremost critical factors influencing crop yield. By providing a window of weed-free growth early within the season, the size advantage that crop seedlings have over weeds can be utilized to reduce the intensity of direct competition for resources at the stages of crop development when yield is being determined. Weeds are identified as a significance drawback since they create biotic stress in realizing the genetic yield potential of this valuable crop.Methods: A field experiment was carried out during the rabi season of 2010-11 to 2014-15 at ICAR- National Research Centre on Seed Spices, Ajmer, Rajasthan to estimate the yield losses because of weed infestation and to work out the critical period for weed control (CPWC) in fenugreek (Trigonella foenum-graecum L.). There were 14 treatments comprising of initial weedy periods of 15, 30, 45, 60, 75, 90 days after sowing (DAS) and weed free period upto 15, 30, 45, 60, 75, 90 DAS along with weedy till harvest (un-weeded check) and weed free till harvest (weed free check). The treatments were replicated three times in a randomized block design.Result: Maximum pod length (cm), number of pods/plant, number of seed/pod, test weight (g), seed yield (kg/ha), straw yield (kg/ha) and harvesting index (%) to the tune of 9.47, 41.2, 16.67, 12.60, 2297, 4954 and 31.73 were recorded at weed free throughout growth period. Weed infestation up to 30, 45, 60, 75, 90 DAS and weedy throughout growth period reduced the seed yield significantly to the magnitude of 567.3, 801.7, 913.3, 1253.3, 1393.7 and 1736.3 kg/ha. Yield losses in fenugreek increase from 2.95 kg/ha/day at 15 days weed infestation to 12.31 kg/ha/day at 135 days weed infestation. Maximum gross return (`104248/ha), net return (`67018/ha) were obtained at weed free throughout growth period with the B:C ratio 2.80 among the weed free treatments. The employment of response curves with weed free or weed competition period showed that seed yield of fenugreek were the highest with the field free from weeds throughout the growth period and the critical period of weed/fenugreek competition was 32 days after sowing and lies between 30-45 days after sowing. In regression approach for fenugreek seed yield and weed free or weed competition period the quadratic function was fitted to estimate the expected yields which had the high significant with the data recorded and have the highest values of R2. If we predict the seed yield losses based on the quadratic model for weed free period model, it declined from 42.04 at 0 DAS to 0.0% at 135 days. Similarly, weed infestation period model predicted the seed yield losses increased from 0.00 at 0 days weed infestation to 73.42% at 135 days. Critical period for weed competition in fenugreek was found to be 32 days after sowing. The CPWC is helpful for making decisions on the necessity for and timing of weed control.

Control of herbicide-resistant common waterhemp (Amaranthus tuberculatus var. rudis) with pre- and post-emergence herbicides in soybean

2007 ◽  
Vol 87 (1) ◽  
pp. 175-182 ◽  
Author(s):  
J. D. Vyn ◽  
C. J. Swanton ◽  
S. E. Weaver ◽  
P. H. Sikkema
Keyword(s):  
Glycine Max ◽  
Photosystem Ii ◽  
Key Words ◽  
Yield Losses ◽  
Common Waterhemp ◽  
Herbicide Resistant ◽  
Glycine Max L ◽  
Amaranthus Tuberculatus ◽  
Postemergence Herbicides ◽  
Weed Emergence

Common waterhemp was first identified in Ontario in 2002. Eight trials were conducted ove r a 3-yr period (2003-2005) at Cottam and Petrolia, Ontario to determine the efficacy of various preemergence and postemergence herbicides for the control of herbicideresistant waterhemp in soybean [ Glycine max (L.) Merr.]. Waterhemp was resistant to the a cetolactate synthase-inhibiting herbicides at both locations and to the photosystem II-inhibiting herbicides at Petrolia; therefore, results varied by location. Results at Petrolia also varied across years. Waterhemp interference resulted in soybean yield losses of up to 73% in weedy versus weed-free checks. Preemergence-applied metolachlor, dimethenamid, and linuron provided greater than 80% control and metolachlor plus metribuzin 94% or greater control of waterhemp 70 d after emergence at both locations. Acifluorfen, fomesafen, imazamox plus fomesafen, and glyphosate applied postemergence resulted in 87% or greater waterhemp control 70 d after application at Cottam in 2003 and 2004 and at Petrolia in 2004; however, waterhemp control with these herbicides was only 60 to 66% at Petrolia in 2005 due to prolonged weed emergence. Multiple herbicide applications per season may be required for effective waterhemp control in soybean. Key words:

scholarly journals Modelling weed competition and yield losses to study the effect of omission of herbicides in winter wheat.

1990 ◽  
Vol 38 (4) ◽  
pp. 711-718
Author(s):  
L.A.P. Lotz ◽  
M.J. Kropff ◽  
M.W. Groeneveld
Keyword(s):  
Winter Wheat ◽  
Crop Yield ◽  
Sandy Soil ◽  
Morphological Characteristics ◽  
Weed Competition ◽  
Yield Losses ◽  
Emergence Time ◽  
Weed Species ◽  
Competition For Light ◽  
Tuber Crops

Omission of application of various herbicides to winter wheat cv. Arminda, cv. Citadel, cv. Okapi, cv. Granada, cv. Sarino and cv. Tombola on clay and sandy soil in 1982-86 caused a significantly lower crop yield only when the densities of certain weed species were extremely high in spring. A dynamic model simulating the competition for light and water between broadleaved weeds and winter wheat was used to assess the observed small effects of weeds on yield in terms of the relative emergence time, physiological and morphological characteristics of weeds. Like the experiments, the simulations indicated that in the Netherlands weeds emerging in spring hardly affect crop yield. Weeds emerging in autumn, however, reduced crop yield considerably if they grew as tall as winter wheat (20% loss at a density of 100 plants/msuperscript 2). The results are discussed in relation to characteristics of crop rotation systems that include root and tuber crops. (Abstract retrieved from CAB Abstracts by CABI’s permission)

Lentil (Lens culinaris) and fababean (Vicia faba) tolerance to post-emergence applications of imazethapyr

1996 ◽  
Vol 76 (3) ◽  
pp. 525-529 ◽  
Author(s):  
D. A. Wall
Keyword(s):  
Leaf Area Index ◽  
Key Words ◽  
Leaf Area ◽  
Dose Response ◽  
Lens Culinaris ◽  
Western Canada ◽  
Yield Losses ◽  
Area Index ◽  
Pyridinecarboxylic Acid ◽  
Crop Tolerance

Dose response studies were conducted under field conditions from 1993 to 1995 to investigate the tolerance of lentil and fababean to post-emergence applications of imazethapyr (2-[4,5-dihydro-4-methyl-4(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-5-ethyl-3-pyridinecarboxylic acid). Imazethapyr was foliar applied at dosages of 5 to 100 g a.i. ha−1. Lentils were injured by imazethapyr in all 3 yr. The minimum imazethapyr dosages that reduced lentil yields were 20, 10, and 50 g a i ha−1 in 1993 1994 and 1995, respectively; at these dosages yield losses were 31, 21 and 29% in the 3 yr, respectively. This study shows that imazethapyr should not be applied to lentil crops since yields are severely reduced at or below current dosages recommended (50 g a.i. ha−1) for use in western Canada. Fababean tolerance to imazethapyr was examined in 2 yr only. In both years, crop tolerance was excellent and fababean yield was unaffected by imazethapyr at dosages up to 100 g a.i. ha−1. Key words: Crop injury, leaf area index, yield

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