Critical Time Of Weed Removal Research Articles

Periods of weed interference in maize crops cultivated in the first and second cycles

The interference of weeds in maize production may be reflected in grain yield losses that vary as a function of the density, stage and degree of aggressiveness of the species present. In the agricultural ecosystem, crops and weeds demand light, water, nutrients and space, which are frequently not available in sufficient quantities, leading to competition. The aim of this work was to determine the period of interference of weed plants, in particular of naked crabgrass (Digitaria nuda) on maize crop in the first and second harvest. The treatments were defined as increasing periods of coexistence and increasing control of weed community (7, 14, 21, 28, 35, 42, 49, and 56 days), two more controls, a control including one with weed control until the end of the culture cycle and another with coexistence until the harvest. For each period, were evaluated the stand of maize plants, length of ear, number of grains per row, number of rows per ear, cob, 100-grain weight, and grain productivity. The data obtained were subjected to analysis of variance using the F test, with average treatments compared using Tukey’s test at 5% probability. Crop productivity was evaluated by means of regressions, the critical periods of interference were estimated. The critical timing of weed removal was 25 days for both harvests. The critical weed free period was 54 and 27 days for the first and second harvest respectively. For the conditions of the first and second harvest, the critical period of weed control was of 29 and 2 days respectively.

Managing weeds using crop competition in soybean [Glycine max (L.) Merr.

Soybean (Glycine max (L.) Merr.) is an important crop worldwide for both protein meal and vegetable oil. Soybean accounts for more than 50% of the global oilseed production. Weed infestation is a complex and regular threat to soybean production all over the world. To combat this threat, chemical, mechanical, and cultural methods are generally used. There has been a revived interest in weed suppression through improved crop competitiveness as an alternative aid in weed management. Different approaches could be utilized to increase crop competitiveness such as adjustment of row spacing, optimum seeding rate, and use of genotypes with high weed-competitive ability. During the past several decades, adoption of narrow row spacing has become increasingly popular among soybean growers primarily because of yield advantage and early canopy closure, which directly provides greater weed suppression. Adoption of narrow rows significantly reduces the density and biomass of late-season emerging weeds and delays the critical time for weed removal compared with wide rows. An increase in seeding density/plant population also suppresses weeds by earlier canopy closure, especially when combined with narrow row spacing. Competitive abilities of different soybean cultivars against different weed species are not consistent. Interseeding cover crops after establishment of soybean also can be a viable option for weed suppression as long as cover crops do not compete with soybean, or act as weeds themselves. Integrated weed management is considered to be the most effective approach for long-term and sustainable management of weeds in soybean. The objective of this article is to provide an overview of currently known cropping practices for improving soybean competitiveness against weeds.

Critical Period for Weed Control of Chickpea in a Semi-Arid Region

Field studies were conducted to determine the critical period of weed control in chickpea (Cicer arietinum L.) cv. ‘Jam’. The treatments consisted of two different periods of weed interference and weed control. Weed interference and weed-free treatments were set up after the crop emergence. Beginning of CPWC was determined by allowing weeds to compete or were kept weed-free at 2 weekly intervals for 2 (weed-free control) to 12 weeks after emergence (WAE). The Gompertz and logistic equations were fitted to relative yield and total dry matter representing the critical weed-free and the critical time of weed removal, respectively. Results indicated that Crop yield, total dry matter, 100 seed weight, number of pod in plant and number of seed in plant declined steadily as the duration of weed competition increased, indicating weed infested conditions for the entire growing season led to 76.4-85.8% and 78.5-85.7% reduction in chickpea dry matter and seed yield compared with full-season weed-free treatments. Also, the major weeds in experiment were Stachys byzantine, Tragopogon dubius, Gypsophila pilosa and Euphorbia helioscpia. To prevent >10% yield and total dry matter loss, the maximum time weeds could be allowed to grow after crop emergence were 43 and 36 DAE respectively and Also, critical period for weed control at 5 % yield and total dry matter loss was 36-60 DAE and 26-71 DAE. But critical period at 2.5 % yield and total dry matter loss was widespreader than other loss level. These results suggested that weed control upgraded all of agronomical traits of chickpea especially seed yield and to minimizing loss level of yield removal weeds must be done at 19-80 DAE.

Delay in the critical time for weed removal in imidazolinone-resistant sunflower (Helianthus annuus) caused by application of pre-emergence herbicide

The critical time for weed removal (CTWR) is a period in the crop growth cycle when weed control must be initiated to prevent yield losses. Knowing the CTWR is useful for making decisions about the timing of weed control and in achieving efficient herbicide use from both biological and economic perspectives. Field studies were conducted in 2008 and 2009 at three locations in Serbia and one location in the USA to determine the CTWR in imidazolinone (IMI)-resistant sunflower grown with and without application of pre-emergence (PRE) herbicide. A four-parameter log-logistic model was fitted to data relating relative crop yield to increasing duration of weed presence. The CTWR without PRE herbicide treatment ranged from 14 to 26 d after emergence (DAE) corresponding to the V3 (three leaves) to V4 stages compared to 25 to 37 DAE, which corresponded to the V6 to V8 stages with PRE herbicide. The CTWR in IMI-resistant sunflower grown with PRE herbicide can be delayed by an additional 6 to 12 d compared to the crop grown without PRE herbicide under the present experimental conditions. The practical implication of this study is that the use of PRE herbicide could extend post-herbicide treatments by another 6 to 12 d with respect to the critical time required for weed removal without PRE herbicide in IMI-resistant sunflower.

The critical period of weed control in corn in Birjand region, Iran

The critical period for weed control (CPWC) is the period in the crop growth cycle during which weeds must be controlled to prevent unacceptable yield losses. Field studies were conducted in 2005 and 2006 in the University of Birjand at the south east of Iran to determine CPWC of corn using a randomized complete block design with 14 treatments and three replications. The treatments consisted of two different periods of weed interference, a critical weed-free period and a critical time of weed removal, were imposed at V3, V6, V9, V12, V15, and R1 (based on phonological stages of corn development) with a weedy check and a weed-free check. The CPWC was determined with the use of 2.5, 5, 10, 15 and 20% acceptable yield loss levels by non-linear regression method and fitting Logistic and Gompertz nonlinear equations to relative yield data. The CPWC of corn was from 5- to 15-leaf stage (19-55 DAE) to prevent yield losses of 5%. This period to prevent yield losses of 2.5, 10 and 20% was 4- to 17-leaf stage (14-59 DAE), 6- to 12-leaf stage (25-47 DAE) and 8- to 9-leaf stage (31-36 DAE) respectively.

Lanceleaf Sage (Salvia reflexa) Interference in Sugarbeet

Field studies were conducted in Powell, WY, in 2006 and 2007 to determine the influence of season-long interference of various lanceleaf sage densities and durations of interference on sugarbeet. The rectangular hyperbola model with the asymptote (A) constrained to 100% maximum yield loss characterized the relationship between lanceleaf sage density and sugarbeet yield loss. The estimated parameterI(yield loss per unit weed density as density approaches zero) was 3% for both root and sucrose yield loss. Increasing duration of lanceleaf sage interference had a negative effect on sugarbeet root yield. The critical timing of weed removal to avoid 5 and 10% root yield loss was 37 and 52 d after sugarbeet emergence, respectively. Lanceleaf sage interference did not affect percentage of sucrose content. These results indicate that lanceleaf sage is not as competitive as other weeds but that appropriate control measures should be undertaken to minimize sugarbeet yield loss from interference.

Wild Buckwheat (Polygonum convolvulus) Interference in Sugarbeet

Field studies were conducted in Powell, WY in 2006 and 2007 to determine the influence of season-long interference of various wild buckwheat densities and duration of interference on sugarbeet. Percent sucrose content was not affected by wild buckwheat interference. Root and sucrose yield loss per hectare increased as wild buckwheat density increased. The estimated percent yield loss as wild buckwheat density approaches infinity was 64 and 61% for root and sucrose yield loss, respectively. The estimated percent yield loss per unit weed density at low weed densities was 6% for both root and sucrose yield loss. Greater durations of wild buckwheat interference had a negative effect on sugarbeet root yield. The critical timing of weed removal (CTWR) to avoid 5 and 10% root yield loss was 32 and 48 d after sugarbeet emergence (DAE), respectively. These results show that wild buckwheat is competitive with sugarbeet and should be managed appropriately to forestall any negative effects on sugarbeet root and sucrose yield.

Venice Mallow (Hibiscus trionum) Interference in Sugarbeet

Field studies were conducted in Powell, WY, in 2006 and 2007 to determine the influence of season-long interference of various Venice mallow densities and duration of interference on sugarbeet. Sucrose concentration was not affected by Venice mallow interference. The effect of Venice mallow density on sugarbeet root and sucrose yield loss was described by the rectangular hyperbola model. Root and sucrose yield loss increased as Venice mallow density increased. The estimated asymptote,A(percent yield loss as density approaches infinity) was 61% for both root and sucrose yield loss, and the estimated parameter,I(percent yield loss per unit weed density as density approaches zero) was 6% for both root and sucrose yield loss. Sugarbeet root yield decreased as the duration of Venice mallow interference increased. The critical timing of weed removal to avoid 5 and 10% root yield loss was 30 and 43 d after sugarbeet emergence, respectively. Results show that Venice mallow is competitive with sugarbeet implying that it should be managed appropriately to reduce negative effects on yield and prevent seed bank replenishment and re-infestation in subsequent years.

Does the shade avoidance response contribute to the critical period for weed control in maize (Zea mays)?

SummaryThe effect of early weed emergence on crop seedling development has not been analysed within the context of a critical period study. Experiments were conducted to quantify the influence of a low light quality environment (i.e., low ratio of reflected red to far‐red light (R/FR)) on maize seedling growth and development under non‐limiting resource conditions. Weed‐addition and ‐removal series were constructed, such that the effects of R/FR on seedling growth and development were isolated from those of direct competition. Maize seedlings responded to the presence of weeds within 24 h of addition by increasing plant height, which was followed by a subsequent reduction in the rate of leaf appearance. Seedling biomass and leaf area decreased linearly in the weed removal series with increasing duration of weed presence. Conversely, seedlings in the weed‐addition series were unaffected. These results demonstrate that early exposure to weeds reduced the rate of seedling growth and development and that this effect was most pronounced if it was initiated upon emergence. This suggests that the existence of a period of developmental sensitivity to R/FR precedes the defined critical period for weed control in maize. These early physiological changes triggered by the R/FR ratio may contribute to the onset of the critical time of weed removal.

Critical Period for Weed Removal in Garden Egg (Solanum Incanum)

Field experiments were conducted at the Teaching and Research Farm, Adeyemi College of Education, Ondo during the 2004 and 2005 cropping seasons to determine the extent of yield loss due to weed infestation and the critical time for weed removal in garden egg (Solanum incanum). The experiment which was arranged in randomized complete block design and replicated three times consisted of two series of weed removal treatments. In the first series, plots were kept weed free of weeds by hand weeding for, 3, 6, 9 and 12 weeks after transplanting, thereafter left weedy till harvest while in the second series weeds were allowed to infest the plots for 3, 6 , 9 and 12 weeks after transplanting, then kept weedy till harvest, control plots were either kept weed free or left weedy till harvest. Uncontrolled weed infestation resulted to an average yield loss of 87.13% in two years . Keeping the crop weed infested beyond the first 6-12 weeks after transplanting was not significantly different from not weeding at all till harvest. On the other hand, keeping the crop weed free by hand weeding for the first 12 weeks after transplanting was similar to keeping it weed free for any length of time beyond this period. The critical period of weed removal was observed to be 3-6 weeks from transplanting.

Weed Management in Glyphosate- and Glufosinate-Resistant Sugar Beet

Field experiments were conducted to determine the critical period of weed interference in glyphosate- and glufosinate-resistant sugar beet, and to determine if PRE herbicides increased weed control or sugar beet root yield when glufosinate, glyphosate, or conventional POST herbicides were applied. Glyphosate- and glufosinate-resistant sugar beet root yields were reduced by up to 66 and 67%, respectively, when weeds remained all season in the weedy control treatment compared with yields when weed removal occurred as soon as the weeds were 2.5 cm tall, approximately 2 to 3 wk after planting (WAP). A critical period of weed interference did not occur in this research. The critical time of weed removal was approximately 8 WAP in 1998 and beyond 11 WAP in 1999. Weeds averaged 20 cm in height at 8 WAP and weed densities were greater in 1998 compared with 1999. The critical weed-free period for glyphosate- and glufosinate-resistant sugar beet was 4.5 to 5 WAP in 1998. In 1999, the critical weed-free period at the Michigan Sugar location was 1.5 WAP in glyphosate-resistant sugar beet, and 6.5 WAP in glufosinate-resistant sugar beet for the Michigan Sugar site. Glyphosate or glufosinate POST provided better weed control and resulted in greater sugar beet root yield compared with conventional POST herbicides when data were combined over PRE herbicide treatments. PRE herbicides improved the control of common lambsquarters andAmaranthusspecies in some of the site-years when data were combined over POST treatments, but sugar beet yield did not increase. Our research suggests that PRE herbicides will not be necessary in glyphosate- or glufosinate-resistant sugar beet. To avoid sugar beet yield loss, multiple POST applications of glyphosate or glufosinate will be needed until 6 to 9 WAP to prohibit yield loss from weeds emerging after the last POST application.

Critical Period of Weed Interference in Peanut

Field studies were conducted near Lewiston–Woodville and Rocky Mount, NC to evaluate the effects of mixed weed species on peanut yield. A combination of broadleaf and grass weeds were allowed to interfere with peanut for various intervals to determine both the critical timing of weed removal and the critical weed-free period. These periods were then combined to determine the critical period of weed control in peanut. The effects of various weedy intervals on peanut yield were also investigated. The predicted critical period of weed control, in the presence of a mixed population of weeds, was found to be from 3 to 8 wk after planting (WAP). Peanut yield decreased as weed interference intervals increased, demonstrating the need for weed control throughout much of the growing season in the presence of mixed weed populations.Nomenclature: Peanut, Arachis hypogaea L

Critical Period of Grass VS. Broadleaf Weed Interference in Peanut

Studies were conducted to evaluate the effects of grass and broadleaf weeds on peanut growth and peanut yield. In separate studies, grass or broadleaf weeds were allowed to compete with peanut for various intervals to determine both the critical timing of weed removal and the critical weed-free period. Hand-weeding and selective herbicides were used at appropriate times to remove and terminate weed growth. These periods were then used to determine the critical period of weed control. The effects of various weedy intervals on peanut yield were also investigated. The critical period of grass weed control was found to be from 4.3 to 9 wk after planting (WAP), whereas the critical period of broadleaf weed control was from 2.6 to 8 WAP. Peanut yields decreased as weed interference intervals for both grass and broadleaf weeds increased, demonstrating the need for control of both grass and broadleaf weeds throughout much of the growing season.Nomenclature: Peanut, Arachis hypogaea L

Planting Date and Glyphosate Timing on Soybean

Planting date of soybean may be one factor that affects the crop's ability to compete with weeds. Field experiments were conducted over 3 yr at two locations in Illinois to determine whether planting date affects optimal weed management strategies and the critical time of weed removal (CTWR) in glyphosate-resistant soybean. Across planting dates, a PRE application of metolachlor plus metribuzin followed by a single glyphosate application at a 10- or 20-cm weed height at Monmouth or at a 20-cm weed height at Urbana was effective at protecting yield. At Monmouth, higher yields occurred with sequential glyphosate applications than with a single application in the early planting in 2 yr when weeds were removed at a height of 10 cm. Across planting dates, highest yields at Monmouth occurred with a single glyphosate application when weeds were 20 to 30 cm tall. At Urbana, the CTWR was not affected by planting date and occurred between 176 and 290 growing-degree days (GDD) after planting, corresponding to the V1...

Volunteer Potato Density Influences Critical Time of Weed Removal in Bulb Onion

Volunteer potato is highly competitive with onion and few control tactics are effective for removing this weed from an onion crop. Both volunteer potato density and duration of interference reduce onion yield, but the interaction of these factors is unknown. Field trials were conducted in 2003 in Idaho, Oregon, and Washington to determine the influence of volunteer potato density on the critical time of weed removal (CTWR) in onion. Yield losses of 2.5, 5.0, and 10% were estimated to occur at 534, 654, and 830 growing degree days (GDD) after onion emergence, respectively, with a volunteer potato density of 0.5 plants/m2. At 2.0 volunteer potato plants/m2, yield losses of 2.5, 5.0, and 10% were estimated to occur at 388, 481, and 598 GDD after onion emergence, respectively. Volunteer potato at 2.0 plants/m2had to be removed at least one onion leaf stage sooner, compared to a weed density of 0.5 plants/m2, to avoid yield loss. Yield loss due to volunteer potato density or duration of interference was greatest among jumbo, colossal, and supercolossal market grades (P ≤ 0.1). Lowering potato tuber density in crops preceding onion will extend the critical time for weed removal and reduce the risk of crop loss.

Early-season insect defoliation influences the critical time for weed removal in soybean

To develop more effective pest-management strategies, it is essential to understand how different pests interact with each other and the crop. Field studies were conducted in 2003 and 2004 at two Nebraska locations to determine the effects of early-season crop defoliation on the critical time for weed removal (CTWR) in narrow-row soybean. Three soybean defoliation levels were selected to simulate 0, 30, and 60% leaf tissue removal by the bean leaf beetle. Weeds were allowed to compete with the crop until V2, V4, V6, R3, and R5 growth stages. There were also season-long weedy and weed-free treatments. Results indicated that the CTWR in soybean occurred earlier as defoliation levels increased from 0 to 60%. The CTWR occurred at V3, V2, and V1 growth stage for 0, 30, and 60% defoliation levels, respectively. Overall, 60% defoliation resulted in earlier CTWR by at least 14 d. Yield losses from defoliation and weed interference were primarily associated with a reduction in number of pods per plant−1.

The critical period of weed control in double-cropped soybean

Double-cropped soybean after winter cereals is the most common soybean production system in the eastern Mediterranean region of Turkey. Weeds are among the main obstacles to double-cropped soybean. A study was conducted in 2002 and 2003 to determine the critical period of weed control (CPWC) for double-cropped soybean. The treatments consisted of either allowing weeds to infest the crop for increasing durations after sowing, or maintaining plots weed-free for increasing durations after sowing. The Gompertz and logistic equations were fitted to relative yields representing the critical weed-free period and the critical time of weed removal, respectively. Johnsongrass (Sorghum halepense), common cocklebur (Xanthium strumarium) and field bindweed (Convolvulus arvensis) were the dominant weeds. For 5% crop loss level, the CPWC was almost all season long, whereas it was from V1 to R6-R7 growth stages for 10% yield loss level. These findings indicate that pre-sowing or pre-emergence control methods should be applied in the region to avoid greater crop losses.

A Review of the Effects of Row Spacing on Weed Management in Corn and Soybean

The adoption of narrow row spacings (rows less than 30 inches in width) in soybeans and corn has primarily been driven by the potential for higher yields in narrow- compared to wide-row production systems. In addition to the potential yield advantages, these systems can have a significant impact on the incidence of weeds within a given agroecosystem and on the approach that producers might take for weed management. A review of row spacing experiments included in this review revealed that narrow row spacings have provided significant reductions in the late-season density of weeds in the majority of soybean experiments but only rarely in corn. This research also indicates that narrow row soybeans are more likely to impact the critical time of weed removal in soybean than in corn. The objective of this article is to provide a brief review of the literature related to the effects of row spacing on late-season weed prevalence and management in corn and soybean and to discuss the implications of these results to current production systems.

WeedTurf: a predictive model to aid control of annual summer weeds in turf

Predicting weed emergence is useful for planning weed management programs. Unfortunately, our ability to anticipate initial emergence and subsequent levels of emergence from simple field observations or weather reports is often inadequate to achieve optimal control. Weed emergence models may provide predictive tools that help managers anticipate best management options and times and, thereby, improve weed control. In this study, the germination characteristics of four annual grass weeds (large crabgrass, goosegrass, green foxtail, and yellow foxtail) were investigated under different temperatures and water stresses to calculate base temperatures and base water potentials. These parameters were used to develop a mathematical model describing seedling emergence processes in terms of hydrothermal time. Hydrothermal time describes seed germination in a single equation by considering the interaction of soil water potential and soil temperature. The model, called WeedTurf, predicted emergence with some accuracy, especially for large crabgrass (lowest efficiency index [EF] value 0.95) and green foxtail (lowest EF value 0.91). These results suggest the possibility of developing interactive computer software to determine the critical timing of weed removal and provide improved recommendations for herbicide application timing.

Duration of volunteer potato (Solanum tuberosum) interference in bulb onion

Previous research with annual weed species indicates that critical timing of weed removal begins primarily after the two-leaf stage of onion, a time when postemergence (POST) herbicides can first be applied. Volunteer potato is difficult to manage and persists in onion fields of western United States. The purpose of this research was to quantify the duration of volunteer potato interference on yield and market grade of onion as well as potato tuber production. Volunteer potato interference caused a 5% yield loss before onions reached the two-leaf stage, at two of three locations. Relative to weed-free plots, onion bulb diameter was reduced as duration of interference increased, resulting in smaller proportions of marketable bulbs. Volunteer potato produced daughter tubers shortly after emergence, which explains, in part, weed persistence despite removal of shoots with contact herbicides, cultivation, and hand-weeding in onion. Significant losses in onion yield and bulb diameter are likely given current volunteer potato management systems.