Weed Seedling Density Research Articles

Impact of Rotational Sequence Selection on Weed Seedbank Composition in Australian Broadacre Crops

The use of competitive crops in successional rotations has been shown to reduce the growth and establishment of annual weeds by the depletion of the weed seedbank in broadacre cropping systems. However, the impact of specific crop rotational sequences contributing to weed seedbank density has not been quantified in the Riverina region of southern Australia. Trials were established in two locations in 2014–2018 to quantify the impact of selected annual rotations featuring grain, pulse, and pasture crops on weed infestation and seedbank dynamics with a focus on winter and summer annual weeds. The weed seedbank dynamics were evaluated by a twice-annual soil sampling regime (at planting and harvest), followed by soil sample screening for weed propagule germination and seedling establishment in a subsequent controlled-environment screening performed from 2014–2020. The weed seedling density decreased in the cereal rotations in years experiencing average to above-average rainfall, as crops established a dense canopy leading to reduced weed establishment and fecundity. Several rotational treatments were effective in suppressing the weed propagule numbers over time, including those using dual-purpose cereals only or a canola break-crop along with the cereals. Rotational selection can be an important and cost-effective tool in integrated weed management systems when applied over multiple growing seasons.

Justification of elements of rice cultivation technology

The purpose of the research is to identify the impact of sprinkler irrigation in rice crop rotation on rice productivity and soil fertility of irrigated lands of the Krasnodar region. To achieve this goal, the tasks of studying the density of weed seedlings after sprinkler irrigation, the content of water-soluble salts and humus in the soil of rice fields, and the reaction of an intensive variety of rice cultivated after irrigation and drainage techniques in rice fields were completed. Material and methods. Field studies were carried out on the Kuban irrigation system of the Krasnodar territory, which is the most typical in terms of soil conditions for the western climatic zone of the region, with various variants for sprinkler irrigation after major planning of basins. An intensive of Rapan rice variety was used. The methods of the Federal Research Center for Rice, the Kuban State Agrarian University, and Russian standards were applied. Conclusions, the obtained results of the conducted studies prove the effectiveness of sprinkler irrigation in rice crop rotation, increase soil fertility, rice productivity, and contribute to the production of environmentally friendly products without herbicides treatment.

Vertical Distribution of Nutsedge (Cyperus spp. L.) and Bahiagrass (Paspalum notatum L.) Seed Bank in Rice Growth Cycle

Weed management in rice continues to be a major challenge to the success of rice growers in northern Iran. Field experiments were conducted at Sari Agricultural Sciences and Natural Resources University to investigate the spatial distribution of weed seeds in the rice growth cycle in 2010 and 2011. Transplanting was done on June 6 in both years. Samples for seedbank analysis were collected 10 days before transplanting and emerged weed density was determined on three different dates during the growing season. Results indicated that nutsedge (Cyperusspp) and bahiagrass (Paspalum notatum) were the two most abundant weed species. The vertical distribution of weed seeds decreased by depth from 0.1 to 0.3 m, while weed pressure was the highest at the 0–0.1 m soil depth. There was no relationship between soil weed seedbanks (at different depths) and emerged weed populations, suggesting that weed seedbank data are not good predictors of weed seedling densities. Nevertheless, Kriging maps indicated that the spatial distribution of weed seeds was in accordance with seedling germination pattern. Also the regression coefficient for 0–0.1 m soil depth was R2= 0.17 and R2= 0.34 for relation between nutsedge and bahiagrass seedlings and their seedbank in 2010 and also, R2= 0.18 and R2= 0.05 in 2011, respectively. Therefore, results achieved from this depth can be used to predict the relationship between nutsedge and bahiagrass seedlings densities and weed seedbanks. The results of this study provide an option for the farmers growing rice to understand the dynamics of weed populations in a cost effective way.

Timing of Tillage as a Driver of Weed Communities

Tillage is a foundational management practice in many cropping systems. Although effective at reducing weed populations and preparing a crop seedbed, tillage and cultivation can also dramatically alter weed community composition. We examined the impact of soil tillage timing on weed community structure at four sites across the northeastern United States. Soil was tilled every 2 wk throughout the growing season (late April to late September 2013), and weed seedling density was quantified by species 6 wk after each tillage event. We used a randomized complete block design with four replicates for each tillage-timing treatment; a total of 196 plots were sampled. The timing of tillage was an important factor in shaping weed community composition and structure at all sites. We identified three main periods of tillage timing that resulted in similar communities. Across all sites, total weed density tended to be greatest and weed evenness tended to be lowest when soils were tilled early in the growing season. From the earliest to latest group of timings, total abundance decreased on average from 428±393 to 159±189 plants m−2, and evenness increased from 0.53±0.25 to 0.72±0.20. The effect of tillage timing on weed species richness varied by site. Our results show that tillage timing affects weed community structure, suggesting that farmers can manage weed communities and the potential for weed interference by adjusting the timing of their tillage and cropping practices.

Integrated management of Bromus diandrus in dryland cereal fields under no‐till

SummaryAs herbicides have limited effect in controlling Bromus diandrus in no‐till dryland cereal fields, the integration of chemical and cultural methods needs to be investigated. A field study was carried out in Lleida (Spain) during 2008–09, 2009–10 and 2010–11 seasons, in a no‐till winter cereal field integrating delayed crop sowing with herbicides in a barley–wheat–wheat rotation. Three crop sowing dates were considered: D1, mid‐October; D2, mid‐November; and D3, early December, and the herbicides mesosulfuron‐methyl plus iodosulfuron‐methyl‐sodium were applied in wheat. Weed density, cumulative emergence and fecundity were estimated for each sowing date. In all three seasons, a significant reduction in the cumulative emergence of B. diandrus as compared to D1 was observed in D2 (82.0, 97.5 and 98.1%) and D3 (80.8, 98.7 and 97.2%). In addition, a significant decrease in weed density and seed rain was observed across all sowing dates and seasons. The herbicide used in wheat was more effective under delayed sowing, due to lower weed density and presence of less developed weed seedlings. After three seasons, the populations of B. diandrus were completely depleted in D2 and D3. This study demonstrates the possibility of eliminating brome infestations in dryland cereal fields in no‐till systems through the integration of cultural and chemical strategies.

Efecto de la cobertura de rastrojos en la germinación del arroz (Oryza sativa L.) y principales malezas asociadas.

Crop residues effect on the germination of rice (Oryza sativa L.) and its major weeds. Three simultaneous experiments were conducted in El Pelon de la Bajura Farm, Guanacaste, Costa Rica in 2003 to determine the degree of interference caused by varying amounts of previous rice crop (Oryza sativa L.) residue on the emergence of rice and associated weeds. Nine coverage treatments of CR1113 crop residues (0 to 9 t/ha) were applied to measure effects on rice and weed germination. The associated weeds included several of the most frequent in flooded rice: Oryza sativa, Echinochloa colona, Cyperus spp., Fimbristylis spp., Ludwigia spp. and Heteranthera limosa. In the first two experiments, inverse relationships were established between the degree of coverage and the density of emergent weed seedlings (R2>0.89) and the degree of coverage and the percentage of rice germination (R2=0.86), respectively. Using bean residue (Phaseolus vulgaris) in the third experiment but no suppressing effect on the germination of rice was observed, possibly due to its rapid decomposition. Although the germination of rice was not affected even at the highest level of residues, similar long-term trials should be conducted to evaluate the possible impact of residue decomposition, allelopathy and herbicide carry-over effects after various consecutive rice production cycles.

Effects of Initial Seed-Bank Density on Weed Seedling Emergence during the Transition to an Organic Feed-Grain Crop Rotation

The transition period to certified organic production can present a significant weed management challenge for growers. Organic certification requires that prohibited fertilizers and pesticides must not have been used for 36 mo before harvest of the first organic crop. Understanding how organic management practices and initial weed seed-bank densities affect weed population dynamics during the transition period may improve weed management efficacy and adoption of organic practices. We examined how tillage systems (full or reduced) and cover crop species planted during the first transition year (rye or a mixture of timothy and red clover) affect the seedling densities of three common annual weed species, common lambsquarters, velvetleaf, and foxtail spp., during the 3-yr transition period. Weed seeds were applied in a one-time pulse at the beginning of the study at three densities, low, medium, and high (60, 460, and 2,100 seeds m−2, respectively), and cumulative seedling densities of each species were assessed annually. Treatment factors had variable and species-specific effects on weed seedling densities. In general, the full-tillage system, with an initial cover crop of timothy and red clover, resulted in the lowest density of weed seedlings following seed-bank augmentation. There was little consistent association between the initial densities of applied weed seeds in the weed seed bank at the start of the transition and weed seedling densities at the end of the transition period. This suggests that when multiple crop and weed cultural management practices are employed during the organic transition period, initial failures in weed management may not necessarily lead to persistent and intractable annual weed species management problems following organic certification.

A 2-Year Small Grain Interval Reduces Need for Herbicides in No-Till Soybean

This study measured weed interference in soybean and corn as affected by residue management tactics following a sequence of oat and winter wheat. Residue management tactics compared were conventional tillage, no-till, and no-till plus cover crops. Treatments were split into weed-free and weed-infested conditions; prominent weeds were green and yellow foxtail and common lambsquarters. Grain yield of soybean did not differ between weed-free and weed-infested conditions with no-till, whereas weeds reduced yield 25% in the tilled system. Corn responded inconsistently to treatments, with more than 40% yield loss due to weed interference in 1 yr with all treatments. Cover crops did not improve weed management compared with no-till in either crop. Seedling emergence of the weed community differed between tillage and no-till; density of weed seedlings was fivefold higher with tillage, whereas seedling emergence was delayed in no-till. The initial flush of seedlings occurred 2 to 3 wk later in no-till compared with the tilled system. Designing rotations to include cool-season crops in a no-till system may eliminate the need for herbicides in soybean to manage weeds.

Evaluation of an algorithm for automatic detection of broad-leaved weeds in spring cereals

Lack of automatic weed detection tools has hampered the adoption of site-specific weed control in cereals. An initial object-oriented algorithm for the automatic detection of broad-leaved weeds in cereals developed by SINTEF ICT (Oslo, Norway) was evaluated. The algorithm (“WeedFinder”) estimates total density and cover of broad-leaved weed seedlings in cereal fields from near-ground red–green–blue images. The ability of “WeedFinder” to predict ‘spray’/‘no spray’ decisions according to a previously suggested spray decision model for spring cereals was tested with images from two wheat fields sown with the normal row spacing of the region, 0.125 m. Applying the decision model as a simple look-up table, “WeedFinder” gave correct spray decisions in 65–85% of the test images. With discriminant analysis, corresponding mean rates were 84–90%. Future versions of “WeedFinder” must be more accurate and accommodate weed species recognition.

Effects of Dairy Manure and Weed Management on Weed Communities in Corn on Wisconsin Cash-grain Farms

A reason given by cash-grain farmers for not using manure from neighboring livestock operations is that manure may cause greater field weediness. To address this concern, trials were established in corn on 11 cash-grain farms, in which manure from six nearby dairy farms was spread for the first time in at least 10 yr. A split-plot design was used in which manured and nonmanured treatments were established as whole-plots, and split-plot treatments were either with or without the farmer's regular weed control. In the multisite analysis, weed seedling density at the time of corn emergence was not greater in the manured vs. nonmanured treatments. At 7 to 8 wk following planting, weed density was not greater in the manured plots. Just before corn canopy closure, weed biomass also did not differ between manured and nonmanured treatments. Although neither weed species richness nor species diversity differed significantly between manured and nonmanured treatments, these measures did have significant environment-by-manure interactions, indicating that weed species distributions responded differently to manure across the different trial environments. However, farmers' weed control practices were highly successful in both the manured and nonmanured plots. Large portions (280 m2) of all whole plots were visually inspected for introduced weed species after all weed control practices had been completed. The manured treatments did not differ significantly in the set of species observed, suggesting that manure did not introduce new weed species. Thus, this exploratory study showed that, contrary to some farmers' concerns, an application of dairy manure neither increased field weediness nor required alterations in the farmers' weed control programs.Nomenclature: Corn, Zea mays L.

Modeling spatial and temporal dynamics of Chenopodium album L. under the influence of site-specific weed control

Experiments were conducted on four arable fields in order to study the spatial and temporal dynamics of weed populations in a 4-year crop rotation under the influence of site-specific weed control from 1997 until 2003. Winter wheat (ww), winter barley (wb), maize and sugar beet (sb) were rotated in the experimental fields. The objective of the study was to adapt a modeling tool based on Zwerger and Hurle [1990. Untersuchungen zur Abbildungsgüte simulierter Befallsverläufe bei Unkräutern. (Experiments for closeness of simulated weed infestation runs). J. Plant Diseases Prot. 97, 133–141] to forecast weed population dynamics taking into account site-specific weed control. For weed mapping, a regular 15×7.5 m grid was established in all fields. Weed seedling density was counted before and after post-emergent herbicide application and before harvest in a 0.4 m 2 quadrate frame placed at all grid intersection points. Application maps were created to direct a GPS-controlled patch sprayer. The patch sprayer varied the herbicide dosage and mixture depending on the information in the application maps. Seed production of surviving weeds and seed mortality by predation and fatal germination was assessed in field studies. Data that were needed for the model and not assessed in the experiments were taken from literature. All data, including site-specific weed control, were entered in the weed population model. Distribution of Chenopodium album L. in two fields was predicted based on previous years weed distribution maps and compared to the observed data. In both fields weed density of C. album did not increase during the 6 years of site-specific weed control. Predicted and observed density values were significantly correlated using Pearson's correlation coefficient. Modeling improves our understanding of spatial and temporal dynamics of weed population and thus can be included in decision algorithms for patch spraying.

Recursive density equivalents: an improved method for forecasting yield loss caused by mixed weed populations

Simple models that can forecast yield loss from weed seedling density at crop emergence are useful tools for both research and practice. In 1985 Cousens presented the rectangular hyperbolic curve as a solution to this problem for the one-weed species case (Cousens 1985a). To address the multi-weed species case, the present theoretical paper investigates two published models and develops a third model, termed ‘recursive density equivalents’. The models were analysed and evaluated based on their biological rationale and using already published data. The earlier models were both found to rely on biologically unrealistic assumptions. The new model avoided additional assumptions, providing a neutral method of summarizing the Cousens curves for many species. Recursive density equivalents were found to be additive in a more intuitive fashion than the ‘density equivalents’ introduced earlier. An over-estimation bias was found to be inherent in the earlier density equivalents model, increasing with species richness. The new model corrected for this bias when checked against one year's field data but for another year, both models over-estimated markedly. All three models were found to be too simple to accommodate all possible modes of intra- and inter-specific competition, yet the new model is an improvement, as it agrees better with the biological principles of crop-weed competition.

Interaction of multiple disturbances: importance of disturbance interval in the effects of fire on rehabilitating mined areas

Abstract Multiple disturbance regimes are increasingly common as novel anthropogenic disturbances are added to existing natural disturbances. However, it is generally unknown whether simultaneous or sequential effects of different forms of disturbance are predictable from the independent effects of each disturbance. This study examines the short‐term effects of sequential disturbance by mineral sand‐mining followed by fire in a forest community in south‐eastern Australia. Four combinations of disturbance were sampled: unburned mined, burned mined, unburned forest (unmined) and burned forest (unmined, with between‐fire interval matching the disturbance interval between mining and fire of the burned mined treatment). All combinations were sampled approximately 12 months following fire on the burned sites. The impact of fire after mining depended on disturbance interval. Sites burned 0.5–2.4 years since mining had fewer native vascular plant species than unburned mined sites of the same mined age, whereas sites with 10–16 years or 20–26 years between mining and fire had greater native species richness than unburned mined sites of the same age. Burning 20–26 years after mining brought native species richness within the range of burned forest. For both unmined and mined sites native seedling densities increased with burning, and with longer disturbance intervals. Weed species richness and weed seedling densities were greater on mined sites than in forest, and burning mined sites elevated weed seedling densities further, particularly for short intervals. Both disturbance interval and fire intensity are likely to have contributed to these results, as intensity on mined areas increased with interval, and at 20–26 years post‐mining was equivalent to unmined forest. These results suggest that fire could be used to promote rehabilitation of these mined areas after at least 10 years, but should be excluded from earlier stages of post‐mining regeneration. However, other sources of spatial and temporal variability should be considered in addition to interval and intensity, as variation among mined areas was correlated with post‐fire weather conditions and available weed sources. Finally, the combined effects of mining and fire could not be predicted from knowledge of the disturbances operating separately, indicating that effects of multiple disturbance may be synergistic rather than additive.

How good is your weed map? A comparison of spatial interpolators

Recent interest in describing the spatial distribution of weeds and studying their association with site properties has increased the use of interpolation to estimate weed seedling density from spatially referenced data. In addition, farmers and consultants adopting elements of site-specific farming practices are using interpolation methods for mapping weed densities as well as soil properties. This study was conducted to compare the performance of four interpolation methods, namely inverse-distance weighting (IDW), ordinary point kriging (OPK), minimum surface curvature (MC), and multiquadric radial basis function (MUL), with respect to their ability to map weed-seedling densities. These methods were evaluated on data from four weed species, velvetleaf, hemp dogbane, common sunflower, and foxtail species, of contrasting biology and infestation levels in corn and soybean production fields in Nebraska. Mean absolute difference (MAD) and root mean square (RMS) between the observed point sample data and the estimated weed seedling density surfaces were used to evaluate the performance of the interpolation methods. Four neighborhood search types were compared within each interpolation method, and Search3 (12 to 16 neighboring locations) generated an interpolated surface with the smallest MAD and RMS indicating the highest precision. IDW with a power coefficient of p = 4 gave the smallest MAD and RMS, as did a test with an elliptical search and no anisotropy. The level of precision of all four interpolation methods was very poor for weed species with low infestation levels (> 75% of field weed-free; MAD ranged from 100 to 187% of the observed mean density), whereas precision was improved for weed species with high infestation levels (< 25% of field weed-free; MAD ranged from 45 to 85%). No single interpolator appears to be more precise than another. Implications of this study indicate that grid sample spacing and quadrat size are more important than the specific interpolation method chosen.

Effect of the Presence or Absence of Corn on Common Lambsquarters (Chenopodium album L.) and Barnyardgrass [Echinochloa crus-galli (L.) Beauv.] Emergence1

A 3-yr study was conducted to establish if the presence of corn had an effect on the emergence patterns and total weed seedling density under growing conditions in southwestern Québec. Weed seedling emergence was monitored in permanent quadrats throughout the growing season in the presence and absence of growing corn. Common lambsquarters and barnyardgrass were prevalent in most site-years. The presence of corn did not affect the patterns of common lambsquarters and barnyardgrass emergence nor their total weed seedling density except in 1994. Corn canopy was probably not sufficiently developed to affect light levels or soil temperature needed for weed germination and, consequently, seedling emergence. In 1994, in the absence of corn, some soil crusting was observed on a fine-textured soil, and the total number of seedlings was reduced. The results of these weed emergence studies in corn can be extended to other crops growing with wide row spacing and relatively slow canopy closure similar to those of grain corn.Nomenclature: Barnyardgrass, Echinochloa crus-galli (L.) Beauv. #3 ECHCG; common lambsquarters, Chenopodium album L. # CHEAL; corn, Zea mays L. ‘Pioneer 3921’.Additional index words: Amaranthus retroflexus L., AMARE, crop competition, redroot pigweed, weed density, weed seedling emergence.Abbreviations: CHU, corn heat units; PAR, photosynthetically active radiation.

Long‐term tillage and crop rotation effects on weed seedbank size and composition

Size and composition of the weed seedbank was assessed after 12 years of application of four tillage systems in two crop rotations. Mouldboard and chisel ploughing at 45 cm, minimum tillage at 15 cm and no tillage were compared in continuous winter wheat and a pigeon bean/winter wheat 2‐year rotation. Weed control was based upon post‐emergence herbicide application. Weed seedling emergence from soil samples taken at 0–15, 15–30 and 30–45 cm depths was assessed in a non‐heated glasshouse for 12 months. The tillage system influenced weed seedbank size and composition to a much greater extent than crop rotation. Total weed seedling density was higher in no tillage, minimum tillage and chisel ploughing plots in the 0–15, 15–30 and 30–45 cm layers respectively. Density in the whole (0–45 cm) layer did not differ significantly among tillage systems. With no tillage, more than 60% of the total seedlings emerged from the surface layer, compared with an average 43% in the other tillage systems. Crop rotation did not influence either weed seedbank size or seedling distribution among soil layers, and only had a small influence on major species abundance. The weed seedbank was dominated (>66%) by Conyza canadensis (L.) Cronq. and Amaranthus retroflexus (L.), which thrived in chisel ploughing and no tillage respectively. Results suggested that crop rotation and substitution of mouldboard ploughing by non‐inversion tillage (especially by minimum tillage) would not result in increased weed problems, whereas use of no tillage might increase weed infestations because of higher seedling recruitment from the topsoil.

Cultural Strategies Reduce Weed Densities in Summer Annual Crops

Producers in the central Great Plains are seeking alternative strategies to manage weeds because of herbicide resistance, narrow profit margins, and a lack of registered herbicides in some crops. Thus, we evaluated the impact of cultural systems in winter wheat and tillage on weed dynamics in corn, sunflower, and proso millet planted the year following wheat harvest. Weed seedling densities were 25 to 30% lower in a no-till system compared with minimum-till with a sweep plow. With no-till, cultural systems that produced more crop residue reduced weed densities an additional 15 to 30%, compared with the conventional system. Cultural system effect was eliminated in dry years and by tillage. Weed biomass was 10-fold less in proso millet than in corn. Crop residue management, critical for successful cropping in semiarid regions, also will help weed management by reducing weed density in summer annual crops, especially in no-till systems.

Weed Population and Crop Yield Response to Recommendations from a Weed Control Decision Aid

AbstractSelecting among the diverse options available to manage weeds requires varied knowledge. This study field‐tested the performance of a decision aid model that integrates biological and economic factors to make weed control recommendations. The model was parameterized using data from the literature and subjected to sensitivity analysis. Tactics generated from the resulting model were compared with standard‐herbicide weed control in continuous corn (Zea mays L.) having a long‐term history of various tillage and herbicide application regimes. The model recommended preemergent and postemergent weed control based on weed seed and weed seedling densities, respectively. Using standard‐herbicide weed control resulted in fewer weed seeds in the soil each year compared with model‐based weed control. Variation among model‐based weed control treatments applied to plots with different management histories was eliminated over the course of the study as weed populations shifted in response to weed control practices. The result was a 98% relative abundance of foxtail (Setaria spp.) seedlings after 3 yr of model‐based treatments, compared with 70% in standard‐herbicide treatments. In 1994, the model reduced herbicide use and weed control treatment costs, but often reduced corn yields and net economic returns. In 1995, model‐based treatments maintained or increased corn yields and net returns. In 1996, however, model‐based treatments consistently reduced corn yields and net returns. Variability in control treatment effectiveness and weed‐crop interaction greatly affected the performance of the model. The use of decision‐aid models in weed management is still a developing technology. Interactions of the weed seed bank, weed emergence, treatment effectiveness, weed‐crop interference, and environmental conditions are very complex. The model could become a valuable tool for producers if consistency of weed control were improved by better understanding and modeling of threshold levels and accounting for weed seed production and by adding data on weed emergence, seed production, yield loss, and control efficacy.

Multi-Year Evaluation of Model-Based Weed Control Under Variable Crop and Tillage Conditions

Abstract Selecting effective weed management options requires biological, ecological, and economic information. This study compared model-based to standard-herbicide weed control in a corn (Zea mays L.)/soybean [Glycine max (L.) Merr.] rotation that had a long-term history of different tillage and weed management practices. The model integrates weed population dynamics, herbicide efficacies, and economic information to evaluate preplant incorporated (PPI) or preemergence (PRE) weed control options based on weed seed bank size and postem-ergence (POST) strategies based on weed seedling densities. There were fewer weeds in standard-herbicide compared with model-based treatments. No-tillage had the greatest numbers of weeds 3 out of 4 years. Soybean yield was reduced the first year of the study in several treatments receiving model-based weed control and the third year in all model-based treatments. Corn yields were greatest in reduced tillage. Resuits of using model recommendations to control weeds were mix...

Influence of velvetleaf (Abutilon theophrasti) and common sunflower (Helianthus annuus) density variation on weed management outcomes

Interactions between initial weed seedling density and postemergence herbicide and mechanical weed control were studied in two field experiments conducted between 1994 and 1996. Increasing seedbank densities of velvetleaf (0 to 500 seed m–2) in soybean or common sunflower (250 to 2,500 seed 1.3 m–2) in corn or soybean were established at Lincoln and Mead, NE, respectively. Emerged seedlings were treated with increasing intensities of weed control from none to bentazon alone or with interrow cultivation. A positive linear relationship between initial seedling density and density of surviving seedlings was consistently observed. As initial seedling density increased, more survivors were present after treatment. As intensity of weed control increased, the number of seedling survivors decreased. Resulting reproductive fitness decreased with increasing management intensity but remained positive when regressed against surviving seedling densities. Weed management outcomes were dependent on initial seedling density, such that the absolute number of survivors increased, while proportion of survivors appeared constant within the density ranges studied. These research findings emphasize the need to account for weed infestation level when assessing efficacy of weed management systems and provide evidence that patchy weed distributions may persist in part because of the need for considerably higher management intensities in high density patch centers.