Time Of Weed Removal Research Articles

Determination of the critical period of weed control in corn using a thermal basis

Field studies were conducted over 3 years in southeast Buenos Aires, Argentina, to determine the critical period of weed control in maize (Zea mays L.). The treatments consisted of two different periods of weed interference, a critical weed-free period, and a critical time of weed removal. The Gompertz and logistic equations were fitted to relative yields representing the critical weed-free and the critical time of weed removal, respectively. Accumulated thermal units were used to describe each period of weed-free or weed removal. The critical weed-free period and the critical time of weed removal ranged from 222 to 416 and 128 to 261 accumulated thermal units respectively, to prevent yield losses of 2.5%. Weed biomass proved to be inverse to the crop yield for all the years studied. When weeds competed with the crop from emergence, a large increase in weed biomass was achieved 10 days after crop emergence. However, few weed seedlings emerged and prospered after the 5-6 leaf maize stage (10-20 days after emergence).

A Plant Process Economic Model for Weed Management Decisions in Irrigated Onion

A simulation model was built as a decision aid for management of five weed species in direct seeded irrigated onion (Allium cepa L.). The model uses the state variable approach and simulations are driven by temperature and sunlight as photosynthetically active radiation (PAR). It predicts yield reduction caused by competition for PAR according to the ratio of crop leaf area index (LAI) to weed LAI and respective light extinction coefficients (k). Input variables are plant density by species and average number of leaves by species. Number of leaves per plant is used by the model to provide an estimate of initial leaf area per plant. The model calculates initial species LAIs by multiplying species density times average leaf area per plant. The model accurately describes competitive interactions, taking into account respective plant densities, time of emergence, and time of weed removal. It permits economic evaluation of management factors such as handweeding, chemical weed control, herbicide phytotoxicity due to early application, and control of weed flushes during the season. The model is also used to evaluate mechanisms of plant competition for sunlight. In a sensitivity analysis, onion yield loss was more sensitive to weed PAR interception than to PAR use efficiency, the latter a species-dependent constant in the model.

Effects of Weed Removal in Clusterbean (Cyamopsis tetragonoloba) under Different Rainfall Situations in an Arid Region

AbstractIn dry land agriculture, intensity and type of weed pressure depend upon the rainfall pattern during the crop season. A two year field study was conducted to determine the effect of time of weed removal in clusterbean (Cyamopsis tetragonoloba (L.) Taub.). Treatments consisting of weed removal at 10, 20, 30,40 and 50 days after sowing were compared with clean weeded and unweeded controls. The xerophytic weeds Gisekia pharnacioides (L.) M., Mollugo cerviana (L.) Ser. and Tribulus terrestris L. dominated in the low and erratic 1993 rainfall season while grassy weeds such as Eragrostis pilosa (Beauv) were predominant in the 1994 season with well‐distributed rainfall. The number of weeds was maximum at 30 days after sowing (DAS) in 1993 and at 40 DAS in 1994. The dry weight of weeds increased up to 50 DAS in 1993 and up to harvest in 1994. Removing weeds at 20 or 30 DAS increased the number of pods per plant, water use efficiency and seed yield of clusterbean. Water consumption was higher in unweeded plots. Water use efficiency decreased with the increase in time of weed removal beyond 20 days after crop sowing.

Optimum Weed Removal Timing in Drilled Salad Onions and Transplanted Bulb Onions Grown in Organic and Conventional Systems

ABSTRACT In field experiments with drilled salad onions, a single weeding made at 4 weeks after 50% crop emergence was sufficient to prevent significant yield loss due to weeds. Weed removal 5 or 6 weeks after 50% crop emergence was generally unsuccessful in averting crop losses. It is well known that the relative timing of crop and weed emergence is important in determining the balance of crop-weed interactions. In the present experiments, the pattern of crop and weed emergence varied between sites and years but the removal of early emerging weeds, at 4 weeks after 50% crop emergence, avoided weed interference consistently. In the transplanted bulb onion experiments, the crop began with an advantage over the weeds, and a single weeding made at 5, 6 or 7 weeks after planting was effective in preventing a reduction in yield. There was no difference in response between crops grown organically and those grown conventionally. Yield loss was due mainly to weed competition occurring prior to handweeding or mechanical injury to the crop following late or repeated weed removal. In the conventional crop, a single weeding that removed inter-row weeds but left within-row weeds in place gave yields little better than those of the unweeded crop.

EFEITOS DOS PERÍODOS DE COMPETIÇÃO DO MATO NA CULTURA DO AMENDOIM: I. SAFRA DA SECA DE 1988

O presente trabalho foi realizado em 1988, na Estação Experimental de Agronomia da Alta Paulista, em Adamantina, na safra da seca, para estudar o efeito de diferentes períodos de competição do mato no amendoim. Os tratamentos foram vinte, a saber: com e sem presença do mato em todo o ciclo da cultura e, os resultantes da combinação fatorial entre a presença e a ausência de mato no início da cultura e as épocas de remoção da flora infestante - 20, 30, 40, 50, 60, 70, 80, 90 e 100 dias após a semeadura. Cada parcela foi constituída de quatro linhas, com bordadura comum entre as unidades experimentais, perfazendo, com a área útil, 6,0 m2. As espécies da flora infestante que ocorreram com maior freqüência foram Cyperus lanceolatus Poir., Digitaria horizontallis Willd., Brachiaria decumbens Stapf. e Portulaca oleracea L. A convivência do mato com o amendoim diminuiu a produção de vagens e de grãos e a biomassa seca da planta. Não se observou efeito do mato sobre o índice de colheita e o rendimento de grãos em nenhum dos períodos estudados. Uma capina aplicada oito dias ou aos 73 dias após a semeadura, respectivamente, para os tratamentos sem e com mato no início, foi suficiente para a produção de vagens de amendoim estatisticamente igual à obtida quando a cultura foi mantida sem competição durante todo o ciclo.

RELATIVE CONTRIBUTION OF NON-MONETARY INPUTS IN RAINFED URDBEAN

Studies on the relative contribution of non-monetary inputs viz., variety, method of sowing, time of sowing, time of weed removal, in urdbean were conducted during kharif seasons of 1992 to 1994 to identify the priority component. Pooled data of three years revealed that improved weed management practice (weeding on 3rd week after sowing) was the important non-monetary input which resulted in increased yield. Next in the order was variety, method of sowing and time of sowing.

Timing the removal of weeds from drilled salad onions to prevent crop losses

Hand-weeding experiments were made over a 5 year period to determine the optimum time for weed removal in salad onions sown at different times of the year. Weed that remained from sowing until harvest, reduced onion fresh weight by up to 96% compared with the weed-free controls. In experiments made in the first 2 years, yield data from onion plots left weedy or kept weed-free for different periods indicated that a single, carefully timed weeding could be sufficient to prevent crop losses. However, the optimum weeding time varied from 21 to 56 days after 50% crop emergence. In subsequent experiments with salad onions sown on four different dates in each of 3 years, single and multiple weedings made within the defined optimum period did not consistently prevent crop losses.

The Concept and Application of Early Economic Period Threshold: The Case of DCPA in Onions (Allium Cepa)

The question of when to control weeds traditionally has been approached with the calculation of critical periods (CP) based on crop yields. The concept of economic critical period (ECP) and early (EEPT) and late (LEFT) economic period thresholds are presented as a comprehensive approach to answer the same question based on economic losses and costs of control. ECP is defined as the period when the benefit of controlling weeds is greater than its cost. EEPT and LEFT are the limits of the ECP and can be used to determine when first and last weed control measures should be performed. Calculation of EEPT accounts for the economic losses due to weed competition that occur between planting and postemergence weed control. In this way it is possible to better evaluate the economic feasibility of using preplant or preemergence control tactics. The EEPT for DCPA application is analyzed in the context of onion production in Colorado. The EEPT for DCPA application was calculated from an empirical regression model that assessed the impact of weed load and time of weed removal on onion yields. The EEPT was affected by control efficacy, weed-free yield, DCPA cost, and onion price. DCPA application was economically advisable in only one of 20 fields analyzed because of the tow DCPA efficacy (60%).

The Critical Period of Weed Control in Soybean [Glycine max(L.) Merr.

Field studies were conducted at three locations over 2 yr in southern Ontario to determine the critical period of weed control in soybean. This period generally consisted of two discrete periods, a critical weed-free period and a critical time of weed removal. The critical weed-free period was relatively short in duration and consistent across locations and years. A period of weed control lasting up to the fourth node growth stage (V4), approximately 30 days after emergence (DAE), was adequate to prevent a yield loss of more than 2.5%. The critical time of weed removal was variable across locations and years and ranged, for example, from the second node growth stage (V2) to the beginning pod growth stage (R3), approximately 9 to 38 DAE, at a 2.5% yield loss level. A phenologically based period of most rapid yield loss due to weed interference occurred from beginning bloom stage (R1) to beginning seed stage (R5). The short and consistent critical weed-free period indicates the duration of residual herbicide control necessary in soybean and supports use of nonresidual, postemergence herbicides and mechanical weed control.

Effect of time of weed removal on growth and yield of potato

SummaryThe effects of weed removal at five dates after planting the crop were examined and compared with weed‐free and unweeded controls. The results revealed that the total weed population increased up to 6 weeks after planting and then decreased drastically in both the years. Total dry weight of weeds (at weeding and at haulm‐cutting) was greatest in the unweeded control, followed by weeding at 10 weeks after planting. In both years, maximum yield was obtained where plots were kept weed‐free, followed by weeding at 4 and 6 weeks after planting. The remaining treatments, including weeding at 2 weeks after planting, resulted in significant reductions in tuber yield. In unweeded control plots the tuber yield of potato was reduced by 40–43%.

Effect of Duration and Type of Natural Weed Infestations on Soybean Yield1

AbstractThe time of weed removal from a crop may be as important as the extent of removal. A 4‐yr field study was conducted at two locations each year to define the extent of soybean [Glycine max(L.) Merr.] yield and population reduction occurring from the presence of natural weed populations. Soil types were Typic Ochraqualfs and Typic Albaqualfs. ‘Williams 79’ soybeans were planted at approximately 30 seeds m− 1of row using 76‐cm spacing between rows. Grass, broadleaf, or grass plus broadleaf weeds were allowed to interfere 0, 1, 2, 3, or 4 weeks, or all season (control), prior to their removal. Weed populations in the control plots ranged from 16 to 148 plants m−2in 1981 and increased to 104 to 1172 plants m−2in 1984. Allowing grass, broadleaf, or grass plus broadleaf weeds to interfere with soybeans for up to 4 weeks did not reduce soybean yields under ample soil moisture conditions. However, under drought conditions or extremely high weed infestations, yield losses with 4 weeks of interference were observed. No differences were found between the competitive effects of grasses or broadleaves on soybean yield with 4 weeks or less of interference. Significant yield reduction occurred every year at both locations when grass plus broadleaf weeds interfered all season. Yield reductions from all‐season grass‐only or broadleaf‐only weed interference occurred most years, but were dependent on location, weed density, and environmental conditions. Soybean populations were reduced where weeds were most dense and were associated with yield decreases.

Crop–weed competition studies in groundnut (Arachis hypogaea L.)

SUMMARYField experiments were made during the rainy seasons of 1979 and 1980 at Hissar, India, to study the effect of time of weed removal on the yield of groundnut. Removing weeds from 2 to 8 weeks after sowing led to significantly larger yields than that of plots which were not weeded. Maximum pod yield in both years was obtained when weeds were removed 4 weeks after crop sowing.

Crop-Weed Competition Studies in Mung Beans (Vigna radiata)

SUMMARYField experiments were done during the rainy seasons of 1980 and 1981 at Hissar, India; they studied the effects of time of weed removal on the yield of mung beans. Removing weeds at 10, 20 or 30 days after sowing led to significantly larger yields than that of the weedy check. Maximum seed yields in booth years were obtained when weeds were removed 20 days after sowing

The effects of time of weed removal on growth and yield of sugar beet

SUMMARYField experiments at Sutton Bonington between 1970 and 1974 tested how crop yields were affected by hand weeding at different stages in the life of early- and latesown crops. Losses where weeds were never controlled ranged from 95% where tallgrowingChenopodium albumL. predominated to 50% whenStellaria media(L.) Vill. andTripleurospermum maritimumL.) Koch ssp.inodorumHyl ex. Vaarama (T.inodorum) were most involved.In five of the seven crops examined the latest date (X) at which weeding had to commence to prevent irreversible effects on growth and yield and the earliest date at which weeding could cease without yield loss (Y) coincided. For late March/early April sowings this occurred 6 weeks after crop emergence, while for late April/early May sowings in which events were more rapid the same stage was reached 4 weeks after emergence. For an early-sown crop in 1973, when rainfall was frequent and heavy andC. albumprolific, X preceded Y with an interval of 4 weeks between the two dates (4–8 weeks after crop emergence, mid-May to mid-June). In complete contrast for a late-sown crop in 1974, when the weather was exceptionally dry andC. albumvirtually absent, Y preceded X and a single weeding at any time between 2 and 8 weeks after emergence would have prevented yield loss.Sugar beet had generally reached the late singling stage (4–6 true leaves) by the time weeding must have commenced. During the next 6 weeks, final yield was depressed by 120–150kg/ha (1·;5%) with each day that weeds were allowed to remain. However, leaf production continued throughout the season and the crop was capable of recovering from early checks caused by weed competition. It proved possible for crops whose weights were depressed by 25–30% when first weeded to recover completely by harvest.

The effects of herbicides, applied atone and in sequence, on the control of wild‐oats (Avena fatua) and broad‐leaved weeds, and on yield of winter wheat

SUMMARYExperiments were done to examine the effects of controlling wild‐oats and autumn‐germinating broad‐leaved weeds in winter wheat, early in winter or late in spring. The herbicides used were barban (winter), chlortoluron or isoproturon (winter), and benzoylprop‐ethyl, at the recommended doses and at half doses. Sequential treatments of two herbicides at half doses were also examined. All treatments were given a routine broad‐leaved herbicide treatment in spring.Yields of wheat were influenced more by the time of weed removal than by the degree of control achieved. Grain yields at three sites with dense autumn broad‐leaved weed populations were greatest following the use of chlortoluron or isoproturon. At three other sites with moderate to dense wild‐oat populations (60 to 240 plants/m1), the use of barban at the crop three‐leaf stage gave larger yields than benzoylprop‐ethyl in late spring at the early stem elongation stage of the crop. Seed formation from surviving A. fatua was similar with both wild‐oat herbicides. The treatment which reduced seed production of A. fatua and maintained crop yield most consistently was barban followed by benzoylprop‐ethyl, each at half the normal recommended dose.

Competition between Cyperus difformis and rice: the effect of time of weed removal

Summary: Résumé: ZusammenfassungExperiments in which Cyperus difformis L. was removed from rice (Oryza sativa L.) by hand al various stages of crop growth demonstrated severe competition between the weed and the crop. Where high populations of C. difformis competed with the rice for the whole of the growing season rice yields were reduced by 22% to 43%. Yield reduction caused by competition was greater under conditions of higher soil fertility.Competition entre Cyperus difformis et le riz; effet de l’épogue du sarclageDes expériences dans lesquelles Cyperus difformis L. a été enlevéà la main d'une culture de riz (Oryza sativa L.), à divers stades de la croissance de celui‐ci, ont révélé une compétition importante entre la mauvaise herbe et la culture. Là où des populations denses de C. difformis ont exercé leur compétition envers le riz pendant toute la durée la saison de croissance, les rendements du riz oni été réduits de 22%à 43%. La réduction de rendement provoquée par la compétition a été plus forte dans des conditions de fertilité du sol plus élevée.Konkurrenz zwischen Cyperus difformis und Reis: Einfiuss des Zeitpunktes der UnkrautentfernungIn Versuchen in denen Cyperus difformis L. von Hand aus Reis (Oryza sativa L.) zu verschiedenen Entwicklungsstadien der Kulturpflanze entferenl wurde, verdeuiIk hten die starke Konkurrenz zwischen Unkraut und Kulturpflanze.Wo viele C. difformis‐Pflanzen mil Reis über die ganze Vegetalionsperiode konkurrierten, gingen die Reiserträge um 22% bis 43% zurück. Die Ertragsernicdrigung war durch die Unkrautkonkurrenz unter Bedingungen hoher Boden‐fruchtbarkeit stärker.