Suppress Weed Growth Research Articles

Competitiveness of Early Vigour Wheat (Triticum aestivum L.) Genotypes Is Established at Early Growth Stages

Weed competitiveness in wheat (Triticum aestivum L.) has previously been shown to be positively associated with shoot biomass. This study evaluated the impact of increased early shoot vigour on the weed competitiveness of Australian wheats. Breeding lines generated for early shoot vigour were top-crossed with two commercial wheat cultivars (Yitpi and Wyalkatchem) and the resulting high vigour lines (HV lines) were assessed for early growth and weed pressure in the field. These lines were directly compared with their parental lines, other commercial cultivars, and the tall heritage cultivar, Federation. Moreover, rye (Secale cereale L.) or triticale (× Triticosecale) was included in each trial as a positive control for vigour. The association between shoot growth and vigour and weed suppression was evaluated over 3 years in the cereal belt of south-eastern Australia during contrasting seasons. The HV lines consistently displayed greater leaf area, ground cover, and canopy light interception in both dry and wet seasons and suppressed weed growth significantly in contrast to commercial cultivars. Light interception at the first tiller stage, and ground cover at the end of tillering were identified as the most important variables for predicting weed suppression. This study demonstrated the enhancement of competitiveness in commercial wheat through the selection for early vigour, and identified traits that best predicted weed suppression.

The combination of organic and inorganic fertilizers influence the weed growth, productivity and soil fertility of monsoon rice.

Synthetic fertilizer and herbicides encompass the largest share in nutrient and weed management on food grain crops that create serious environmental issues. Integrated nutrient and non-chemical weed management approaches may help to reduce the chemical load in the environment, maintaining higher weed control efficiency and yield. A field experiment was conducted for two consecutive monsoon seasons during 2015 and 2016 in farm fields to develop a profitable and sustainable rice production system through integrated nutrient and weed management practices. A varied combination of nutrients either alone or integrated with chemical and non-chemical weed management were tested on transplanted rice in a factorial randomized block design with three replications. The results showed that the integration of concentrated organic manures with chemical fertilizer effectively inhibited weed growth and nutrient removal. Integration of nutrient and weed management practices significantly enhanced 9% biomass growth, 10% yield of the rice crop along with 3-7% higher nutrient uptake. Brassicaceous seed meal (BSM) and neem cake also had some influence on weed suppression and economic return. Thus, the integrated nutrient and weed management practices in rice cultivation might be an effective way to achieve economic sustainability and efficient rice cultivation in eastern India. Shortages of farmyard manure and vermicompost could be supplemented by BSM and neem cake in the integrated module.

Caffeic Acid, an Allelochemical in Artemisia argyi, Inhibits Weed Growth via Suppression of Mitogen-Activated Protein Kinase Signaling Pathway and the Biosynthesis of Gibberellin and Phytoalexin.

Artemisia argyi is widely distributed in Asia, and it often becomes the dominant population in the field because of its strong ecological niche competitiveness. Allelochemicals secreted by plants are generally considered an important reason for their dominance in ecological competition. In this study, the allelochemicals in A. argyi were screened by a series of experiments and their mechanisms were explored via transcriptomics. First, the inhibitory effects of A. argyi on Echinochloa crusgalli, Setaria viridis, Portulaca oleracea and Amaranthus retroflexus were evaluated. Then, we carried out a qualitative and quantitative analysis of the chemical composition of the aqueous extract of A. argyi to screen for potential allelochemicals that can inhibit weed growth. Four potential allelochemicals were quantified: neochlorogenic acid (5-CQA), chlorogenic acid (3-CQA), cryptochlorogenic acid (4-CQA), and caffeic acid (CA). Coincidentally, their allelopathic effects on weeds seemed to be identical to their content, in the order CA>4−CQA>5−CQA>3-CQA. These findings suggested that CA might be the main allelopathic compound in the aqueous extract of A. argyi. Subsequently, the allelopathic effect and molecular mechanism of CA on S. viridis leaves were investigated. The physiological results showed that CA significantly induced reactive oxygen species (ROS) production, led to malondialdehyde (MDA) accumulation, and disrupted enzyme activities (POD, SOD, CAT) in S. viridis leaves. Moreover, transcriptome results revealed that CA inhibited S. viridis growth by downregulating multiple genes involved in gibberellin (GA) and phytoalexin biosynthesis and Mitogen-activated protein kinase (MAPK) signaling pathways. In addition, differentially expressed genes (DEGs) related to the biosynthesis and signaling pathways of phytohormones were verified by Quantitative Real-Time PCR (RT-qPCR). Taken together, this study may be the first to identify allelochemicals and explore their molecular mechanism about A. argyi. Importantly, the ecological advantages of A. argyi could be applied to ecological regulation and the development of botanical herbicides.

Response of weeds and rice yield to Italian ryegrass as a cover crop and planting density in organic farming

AbstractOrganic farming has been receiving increased attention in the agriculture sector; however, Japanese organic farming often requires intensive labor, and the yield is lower compared with the conventional rice (Oryza sativa L.) system. In this study, we examined the effects of planting density (12.7 vs. 24.2 plant m−1) and cover crop (Italian ryegrass [Lolium multiflorum Lam.] vs. winter fallow) on organic rice production in central Japan. A 2‐yr experiment was conducted under organic management in a paddy field at the Center for International Field Agriculture Research & Education, Ibaraki University in 2019 and 2020 using a split‐plot design with four replications. Rice yields were 25 and 6.8% higher when Italian ryegrass was used as the cover crop under sparse planting conditions than under dense planting conditions in 2019 and 2020, respectively. The interaction between cover crop and planting density was significant across the 2 yr. Although there was no significant difference in weed biomass during the rice cultivation period, sparse planting and winter fallow resulted in greater weed biomass than dense planting and Italian ryegrass, respectively. The contribution of nitrogen (N) derived from Italian ryegrass showed a significant difference between 2019 and 2020 but not between sparse and dense planting. Although cover‐crop‐derived N contribution to organic rice production was different between the 2 yr, the use of Italian ryegrass as a cover crop at sparse planting density can improve rice yield and suppress weed growth in central Japan.

Weed suppression versus water use: Efficacy of cover crops in water‐limited agroecosystems

AbstractWinter cover crops (CC) may facilitate weed management by inhibiting weed seed germination and seedling emergence and suppressing weed growth within the cash crop. In southern New Mexico, with scarce winter precipitation and limited irrigation water, producing sufficient CC biomass for effective weed suppression while conserving water resources is challenging. This study assessed the water requirement to produce a CC with enough biomass for weed suppression benefits during cash crop growth at two locations in New Mexico. Three winter CC species, barley, Austrian winter pea and mustard, grown singly and in a three‐way mix, under three differential irrigation treatments (one, two or three irrigations after emergence) were evaluated for their weed‐suppressive potential. Maize was planted as a cash crop four weeks after winter CC termination. Number of irrigations had no effect on the CC and weed biomass production. All CCs had lower weed density prior to maize planting compared with fallow. Barley and the three‐way mix reduced weed density by 56–96% and 68–95%, respectively. All CC treatments had lower weed biomass at the end of critical period for weed control in maize compared with fallow. Weed biomass at maize harvest did not differ between treatments. The maize yield was consistently higher in conventionally managed, weed‐free subplots, than in unsprayed weedy subplots, suggesting that CCs did not suppress weeds throughout the maize growing season. Except for barley, CCs did not cause reductions in maize yield compared with fallow. Overall, the study suggested that with adequate winter precipitation, weed‐suppressive winter cover crop stands can be produced with just one irrigation at seeding and one supplemental irrigation, making them a viable option in water‐limited agroecosystems.

A Rice Ancestral Genetic Resource Conferring Ideal Plant Shapes for Vegetative Growth and Weed Suppression.

To maximize crop growth, crops need to capture sunlight efficiently. This property is primarily influenced by the shape of the crops such as the angle, area, and arrangement of leaves. We constructed a rice (Oryza sativa L.) inbred line that displayed an ideal transition of plant shapes in terms of sunlight receiving efficiency. During vegetative growth, this line exhibited tiller spreading with increased tiller number, which formed a parabolic antenna-like structure. The architecture probably improved light reception efficiency of individuals compared with the recurrent parent. The line achieved not only acceleration of the vegetative growth, but also significant suppression of weed growth under the canopy. The increased light reception efficiency of the line has consequently reduced the amount of incident light to the ground and supplied significant competitiveness against weeds. The spread tillers became erect from the entry of the reproductive growth phase, adaptively sustaining light reception efficiency in thicker stands. The line carries a small chromosomal segment from Oryza rufipogon Griff., a putative progenitor of Asian cultivated rice. The introduced chromosome segment had little effect on grain yield and quality. Our results shed light on potentials hidden in the wild rice chromosome segment to achieve the valuable traits.

Leaching Potential of Phosphite Fertilizer in Sandy Soils of the Southern Coastal Plain, USA

Novel biotechnology on transgenic plants capable of metabolizing phosphite (Phi), a reduced form of P, could improve the effectiveness of P fertilizers and reduce the P footprint in agriculture with the benefit of suppressing weed growth. However, potassium Phi (K-Phi) salts used as fertilizer are highly soluble in water. At the same time, sandy soils of the Southern Coastal Plain are vulnerable to leaching losses resulting from long-term Pi fertilizer application. We performed a replicated leaching trial using five soil materials that included three surface and two subsurface layers from cultivated topsoil (Ap horizon) with contrasting Phi and Pi sorption capacities. Each soil received three treatments K-Phi at rates 0 (control), 24, and 49 kg P ha−1 and leached twice with de-ionized water. All K-Phi-treated soils leached Phi except for the controls. A phosphorus saturation ratio (PSR) calculated from P, Al, and Fe in acid extracts indicated increasing environmental risk of Phi leaching in soils with lower Phi and Pi sorption capacities at rising rates of applied K-Phi. Because plants rapidly absorb Phi, further studies on the environmental impact of K-Phi fertilizer use should include the interaction of plants with soil properties and soil microbial activity at optimal Phi application rates for growing transgenic plants able to use Phi as a nutrient source.

Soil physical quality influenced by winter plants

The biomass production by cover plants provides soil protection against erosion and weed control in the winter period, while the effect of cover crops on the parameters of physical soil quality helps in root growth and water storage. The objectives of the present study were to evaluate the influence of winter plants on the physical quality of the soil. The experiment consisted of unifactorial treatments, composed of different winter plants: vetch (Vica sativa L.), forage radish (Raphanus sativus L.), black oat (Avena strigosa Schreb.), rye (Secale cereale L.), wheat (Triticum aestivum L.) and control treatment. The experimental design was randomized blocks, with four replications per treatment. The parcels consisted of 34 lines implanted with a disc seeder and spaced 17 cm and 10 m long, comprising an area of ​57,80 m2 per parcel. Sowing densities were 40 kg ha‑1 for vetch, 20 kg ha-1 for forage radish, 60 kg ha-1 for rye, 150 kg ha-1 for wheat and 90 kg ha-1 for black oat. The control treatment consisted of the vegetation that emerged spontaneously. The parameters evaluated were plant green mass, weed occurrence, apparent density, gravimetric moisture and soil penetration resistance. With the vetch cultivation there was a reduction in the density of the soil in its surface layer, compared to the control treatment and the other cover crops. Wheat increased gravimetric soil moisture retention. Forage radish was superior to the other cover crops in terms of biomass production, totaling 59.91 t ha-1, as well as being the only cover crop that reduced soil penetration resistance, in the layer from 0 to 40 cm of ground. Vetch reduced the density of the soil in its surface layer, and also the resistance to penetration, from 21 cm of depth. Compared to the control treatment, cover crops were efficient in suppressing weed growth.

Lignocellulose mulch increases the economic benefit of Chinese chestnut by suppressing weed and ameliorating soil properties

The yield of Chinese chestnut relies on multiple factors including soil, fertilizer, irrigation, and pest management. Hence, it is necessary to develop a simple and cost-effective strategy that can simultaneously modulate the above factors. Mulch films can largely influence the aforementioned factors. In this work, a grinding machine was used to fragment branches, chestnut shell, and involucres into 3-10 cm pieces, and the resulting lignocellulose mulch was applied to cover the soil surrounding Chinese chestnut trees. A field trial found that lignocellulose mulch ameliorated soil properties by increasing soil moisture and soil carbon. Moreover, lignocellulose mulch suppressed weed growth and inhibited chestnut blight, and eventually improved the quality and yield of chestnuts. Cost-benefit analysis showed that the mulch increased profit by 42% in three years compared with the control group. It is concluded that lignocellulose mulch is a viable alternative to plastic mulch, especially for perennial woody plants such as chestnut trees. This work provides an alternative strategy for the management of chestnut and other perennial trees.

Significance to the Horticulture Industry

Significance to the Horticulture Industry

Identifikasi Senyawa Metabolit Ekstrak Akar Padi dan Potensi Alelopati terhadap Gulma Echinochloa crus-galli dan Monochoria vaginalis

Allelopathy plays an important role in weed control because it reduces dependence use on synthetic herbicide and labor. Some rice varieties release chemical compounds that can inhibit weed growth. The objective of this research was to identify compounds and to determine the rice allelopathic potential of rice root extract. The experiment was conducted in Regional Health Laboratorium Jakarta and ICRR’s greenhouse, West Java. Identification of metabolite compounds in 10 rice root extracts used GCMS. The experiment in the greenhouse used a split plot design with four replications. The main plot was weeds (Echinochloa crus-galli and Monochoria vaginalis), while the subplot was the roots of 10 swamp rice varieties and control. The rice roots were extracted by the maceration method using 80% methanol and evaporated by a rotary evaporator. The root extract was diluted distilled water at a 50% concentration (w/v) and applied to weeds. The experimental unit was 3 pots planted with 5 weed seeds. The research identified 88 compounds in rice root extract and the highest peak area was stigmasterol compound. The inhibitory of growth and dry weight of weeds varied, between 27-44%. Inpara-3, Inpara-4, Inpara-7, Inpara-8, and Inpara-10 were able to inhibit weeds greater and belong to one cluster. The five swamp rice can be chosen to be developed in paddy fields that were dominated by Echinochloa crus-galli and Monochoria vaginalis.

Management of Bio-Waste by the Paper Mulch

Mulch is a type of protective covering placed on or spread over the soil surface that helps to conserve soil moisture, suppress weed growth and enrich the soil. The paper mulch is the most complete mulch and has numerous beneficial effects upon the soil and plants. This mulch which is produced from office waste paper, newspaper and wrapping papers, conserves soil moisture, is effective at suppressing and inhibiting weed growth, enhances agro-ecosystem health by improving the air and water movement through the soil; providing moist conditions thereby promoting micro-organisms and worm populations; promoting plant growth and product, promoting leaf litter build up and helping to improve the pH balance in the soil.

Weed control efficacy of combined application of grass pea and mustard crop residues in T. aman rice

Among different methods of weed control, allelopathy could lead to reduced labor costs and increased efficiency, without any adverse effects on the environment. In this regard, an experiment was conducted at the Agronomy Field Laboratory, Bangladesh Agricultural University, Mymensingh to evaluate the allelopathic potential of grass pea and mustard crop residues on weed suppression and crop performance of transplanted aman rice. The experiment consisted of three cultivars of T. aman rice viz., Binadhan-7, BRRI dhan49 and BR11 and five different level of crop residues such as no use of crop residues, grass pea crop residues @ 2.5 t ha-1, mustard crop residues @ 2.5 t ha-1, combined use of grass pea and mustard crop residues @ 1 t ha-1 of each and hand weeding. All crop residues applied in the experiment suppressed weed growth and inhibition at satisfactory level. The experiment was laid out in a randomized complete block design with three replications. Weed population, weed dry weight and percent inhibition of weed were not significantly influenced by the interaction effect of crop residues (grass pea and mustard) and cultivars. BR11 produced the highest grain and straw yield among the treatment combination. The highest numbers of tillers hill-1, numbers of grains panicle-1, 1000-grain weight, grain yield, straw yield were observed in hand weeding, followed by combined application of grass pea and mustard crop residues @ 1 t ha-1 of each treatment. The highest grain and straw yield (4.81 t ha-1 and 7.65 t ha-1) was observed in hand weeding along with variety BR11 and the second highest (4.19 t ha-1 and 7.36 t ha-1) was obtained from combined use of grass pea and mustard crop residues @ 1 t ha-1 of each. The results of this study indicate that hand weeding followed by combined application of grass pea and mustard crop residues @ 1 t ha-1 of each showed potential activity to suppress weed growth.

Efikasi Kombinasi Herbisida Metil Metsulfuron dan Asam Asetat pada Lahan Perkebunan Kelapa Sawit (Elaeis gueenensis Jacq.) Menghasilkan

On of the obstacles that resulted in a decrease in palm oil production was the presence of weeds. Controlling need to be done to suppress weed growth. Controlling using a mixture of methyl methulfuron herbicide and acetic acid herbicide is on way to weed control. This research was conducted in Lampung State Polytechnic. This study used a factorial randomized block design with 2 factor and each treatment combination was repeated 3 times. The first factor is the methyl methulfuron herbicide 20% with 3 level doses of 0 g.ha-1, 45 g,ha-1, and 75 g. ha-1 second factor is acetic acid herbicide 20% with 3 level doses of 0 ml.ha-1, 225.000 ml.ha-1, and 315 ml.ha-1. the result showed that the combination of methyl methulfuron herbicide 75 g.ha-1 and acetic acid herbicide 315.000 ml.ha-1 effective weed dry weight up to 5.50 grams at 5 WAA and able to reduce weed cover percent to 8% at 6 WAA. the dominance weed that arises after the application of the methyl methulfuron herbicide and acetic acid is Asystasia gangentica, Paspalum conjugatum , Panicum dichotomyflorum, Stachytarpeta indica, dan Imperata cilindrica.

Inhibitory Effects of Brassicaceae Cover Crop on Ambrosia artemisiifolia Germination and Early Growth

Several cover crops (CCs) exert allelopathic effects that suppress weed growth. The aim of the present study was to evaluate the effects of aqueous extracts containing different concentrations [0, 0.5, 1, 2.5, 5, 7.5 and 10% (w/v)] of Brassicaceae CCs (Sinapis alba, Raphanus sativus, Camellina sativa) and of the CCs Fagopyrum esculentum and Guizotia abyssinica on germination and early growth of Ambrosia artemisiifolia L. The allelopathic effects were species and concentration-dependent. C. sativa, for example, caused the greatest potential to inhibit germination, shoot, radicle length and fresh seedling weight, whereas S. alba and R. sativus inhibited germination and early growth of A. artemisiifolia only at concentrations ≥7.5%. In contrast, no inhibition was observed when aqueous extracts of F. escultneum and G. abyssinica were added at any of tested concentration. Liquid chromatography-tandem mass spectrometry detected 15 phenolic compounds in Brassicaceae CCs with the highest content (µg/g) of vanillin (48.8), chlorogenic acid (1057), vanilic acid (79), caffeic acid (102.5) and syringic acid (27.3) in C. sativa. Our results suggest that C. sativa is the most allelopathic CCs and that the fruits of C. sativa are the plant organs richest in allelochemicals.

Analysis Methods of Common Herbicides in Biological Material and Research Progress.

Herbicides are a kind of chemical or biological agents that can effectively destroy or inhibit weed growth. Because of the widespread and frequent use of herbicides, herbicide poisonings have often been reported. At present, the main species reported to have caused poisoning are paraquat, diquat, glyphosate, and glufosinate. The main instrumental analysis method is LC-MS. This paper reviews the research progress on analysis methods of common herbicides in biological material and their application, summarizes the sample pretreatment and instrumental analysis situation of qualitative and quantitative analysis of herbicides in biological material, and collects test data of actual poisoning cases, to provide reference for clinical diagnosis and treatment and forensic identification of herbicide poisoning.

Allelopathic effect of Artemisia argyi on the germination and growth of various weeds

Allelopathy means that one plant produces chemical substances to affect the growth and development of other plants. Usually, allelochemicals can stimulate or inhibit the germination and growth of plants, which have been considered as potential strategy for drug development of environmentally friendly biological herbicides. Obviously, the discovery of plant materials with extensive sources, low cost and markedly allelopathic effect will have far-reaching ecological impacts as the biological herbicide. At present, a large number of researches have already reported that certain plant-derived allelochemicals can inhibit weed growth. In this study, the allelopathic effect of Artemisia argyi was investigated via a series of laboratory experiments and field trial. Firstly, water-soluble extracts exhibited the strongest allelopathic inhibitory effects on various plants under incubator conditions, after the different extracts authenticated by UPLC-Q-TOF-MS. Then, the allelopathic effect of the A. argyi was systematacially evaluated on the seed germination and growth of Brassica pekinensis, Lactuca sativa, Oryza sativa, Portulaca oleracea, Oxalis corniculata and Setaria viridis in pot experiments, it suggested that the A. argyi could inhibit both dicotyledons and monocotyledons not only by seed germination but also by seedling growth. Furthermore, field trial showed that the A. argyi significantly inhibited the growth of weeds in Chrysanthemum morifolium field with no adverse effect on the growth of C. morifolium. At last, RNA-Seq analysis and key gene detection analysis indicated that A.argyi inhibited the germination and growth of weed via multi-targets and multi-paths while the inhibiting of chlorophyll synthesis of target plants was one of the key mechanisms. In summary, the A. argyi was confirmed as a potential raw material for the development of preventive herbicides against various weeds in this research. Importantly, this discovery maybe provide scientific evidence for the research and development of environmentally friendly herbicides in the future.

Rice yields and the effect of weed management in an organic production system with winter flooding

ABSTRACT Winter flooding of paddy rice production is characterized by flooding of paddy fields during the winter fallow season. It has attracted attention in terms of its ecological function, supporting the biodiversity of paddy field ecosystems. Therefore, recent winter flooding in Japan has been conducted by organic farming. However, it is not well documented how organic farming with winter flooding affect the productivity of rice. We conducted field experiments to examine changes in rice yield in organic farming with winter flooding compared with those in conventional and organic farming over the period of 5 and 9 years. The yields in organic farming with winter flooding were lower than those in conventional farming but were almost the same as those in organic farming. We found a trend that shows the relative yield of organic farming with winter flooding compared to that of conventional farming increased during the first several years after the conversion from conventional farming to organic farming with winter flooding, but that it decreased after several years. This trend may be caused by the flourishing of weeds during continuous organic farming with winter flooding. Therefore, we tested four weed control methods: rice bran application, mechanical weeding, repeated puddling, and side-row fertilizer application. Although each method suppressed weeds to certain extents, some combinations of different weeding methods more effectively suppressed weed growth, thereby resulting in enhanced rice yields. We found a trend in rice yield and a possibility of combining several weed control methods in organic farming with winter flooding.

English

Crop canopy architecture is known to affect weed performance. Field experiments were conducted to examine the effect of altered crop canopy architecture and light interception on growth and development of wild proso millet and giant foxtail, two problematic weed species. Crop canopy architecture was manipulated by planting two sweet corn varieties contrasting in canopy architecture (Bonus-has a dense leaf canopy and Sprint-has an open leaf canopy) at two row spacings (51-cm and 76-cm rows). Results showed that sweet corn variety, rather than row spacing, altered crop canopy architecture, which in turn altered photosynthetically active radiation (PAR) and red:far-red light ratio (R:FR) received by both weeds. The competitive Bonus canopy had a higher (P<0.05) PAR and R:FR than Sprint at anthesis and harvest. Bonus also more effectively suppressed weed growth and development than Sprint, and weeds growing on Bonus plots had reduced tiller numbers, reduced biomass, lower population densities, and reduced seed production (P<0.05). These responses were attributed to the Bonus canopy having a higher canopy area index, which intercepted more light resulting in lower PAR and R:FR received by both weeds. This study suggests that crop variety selection is an important consideration for weed suppression in row-cropping systems. Key words: Crop canopy architecture, light interception, photosynthetically active radiation, red:far-red ratio, row spacing, sweet corn, wild proso millet, giant foxtail.

Differences in Weed Suppression between Two Modern and Two Old Wheat Cultivars at Different Sowing Densities

Crop losses to weeds can be exacerbated in modern agricultural systems because modern crop cultivars have high population yields but low individual competitiveness. High density cropping systems offer the possibility of effectively suppressing weeds by increasing the initial size-asymmetric advantage of crops over the weeds. We tested this hypothesis in an outdoor mesocosm experiment with two old (Cultivar Heshangtou (HST) and Jinbaoyin (JBY)) and two modern (Xihan2 (XH2) and Xihan3 (XH3)) cultivars of spring wheat (Triticum aestivum L.), grown in a uniform pattern at four sowing densities under high weed pressure. Two annuals (Brassica napus and Linum usitatissimum) were used as model weeds sown at the same density in all treatments. Weed growth decreased and wheat yield increased with increasing crop density for all the cultivars, although yield levelled off at the highest densities. The old cultivars suppressed weeds better than the new cultivars at low density, reflecting the decline in individual competitiveness in modern cultivars. At high crop density, however, the modern XH3 suppressed the weeds as well as the old cultivars, supporting the hypothesis that traits that promote weed suppression are different at low vs. high density. Increasing crop density can be an effective way to suppress weed growth in many agricultural systems, and there is great potential for developing genotypes that can do this and produce high yields much better than the cultivars currently available.