Growth of seedlings of Agropyron repens L. Beauv. and Agrostis gigantea Roth. in wheat and barley: effect of time of emergence, nitrogen supply and cereal seed rate

As part of a programme of work evaluating the role of seeds in regenerating or initiating infestations of Agropyron repens and Agrostis gigantea, the growth of the weeds was analysed in cereal crops in two experiments. The first experiment investigated the effects of time of planting the weed seedlings (simulating different times of emergence), nitrogen supply and cereal seed rate in winter wheat and the second, the same factors in spring wheat and spring barley. In winter wheat, delaying planting of the weeds from autumn until spring greatly decreased shoot growth and almost completely prevented rhizome formation. Nitrogen fertilizer increased the weight of shoots of both species planted at both times but whereas it increased the amount of rhizome produced by Agropyron it decreased that of Agrostis. Without nitrogen Agrostis had twice as much rhizome as Agropyron but with nitrogen Agropyron had twice as much as Agrostis. Decreasing the cereal seed rate had little effect on rhizome weight when nitrogen was not given but it allowed twice as much rhizome to be produced when it was supplied. However, more longer rhizomes were formed at the smaller than at the larger seed rate with both amounts of nitrogen. In spring cereals, late planting decreased the shoot growth of Agrostis more than that of Agropyron, and of Agropyron in barley more than in wheat, especially at the smaller seed rate. Nitrogen increased shoot weight of Agropyron in wheat but had little effect in barley; it decreased that of Agrostis in barley. On average, rhizome growth was decreased by nitrogen, by increasing the seed rate and by delaying planting. Agropyron rhizomes were heavier in wheat than in barley but those of Agrostis were heavier in barley than in wheat. Agropyron produced most rhizome in thinlysown wheat given nitrogen, but Agrostis most in thinlysown barley without nitrogen. The two treatments had an equal number of rhizomes longer than 100 cm. The agricultural significance of the interaction of the various treatments is briefly discussed.     

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

As 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.     

Avena sterilis and Lolium rigidum infestations hamper the recovery of diverse arable weed communities

Intensification of agricultural practices has severely reduced weed diversity in arable fields, which affects the delivery of ecosystem services. However, in parallel, some species have benefited from intensive farming and have vastly increased their abundance, as is the case for Lolium rigidum and Avena sterilis in cereal fields. These highly competitive species severely reduce yields but can also compete with other weed species, and, when less intensive practices are applied, they might limit the recovery of weed diversity and the success of arable species reintroductions. A gradient of infestation was established in a winter wheat field in Catalonia (north‐eastern Spain) by sowing seeds of both species at three different densities to test their effects on the abundance, diversity and composition of the natural weed community. The emergence of seeds and the survival and biomass of transplanted seedlings of two rare species, Agrostemma githago and Vaccaria hispanica, were also evaluated. Avena sterilis and L. rigidum infestations reduced the diversity, abundance and biomass and changed the composition of the natural weed community, even at low infestation densities. Moreover, infestations of both species affected the overall performance of A. githago and V. hispanica. This study reveals that A. sterilis and L. rigidum are highly competitive and that their infestations might hamper the recovery of diverse weed communities. Their densities should be considered when selecting suitable sites for promoting diversity and reintroducing rare species.     

Winter annual grassy weeds increase over‐winter mortality in autumn‐sown wheat

Over‐winter mortality, that is, winterkill, reduces cereal crop competitive ability and yield. While management and environmental variables are known to affect winterkill, the extent to which weeds contribute to increased winterkill is largely unknown. Winter annual weeds may increase winterkill through resource competition and by increasing incidence of and damage from plant pathogens that cause winterkill. We evaluated the impact of summer annual (Avena fatua) and winter annual (Bromus tectorum) weeds on the over‐winter survival rate of winter wheat over three winters, during which plots were covered with snow. Pink snow mould (Microdochium nivale), a winterkill pathogen known to infect B. tectorum and winter wheat, was common in wheat stands. In weed‐free treatments, mortality rates were initially near zero, but increased by nearly 45% in each subsequent winter, presumably due to an increase in snow mould disease in continuously cropped winter wheat. Whereas A. fatua infestation had no impact on crop survival rates, winter wheat survival in B. tectorum‐infested plots was 50% less than the weed‐free control in the second and third years of this study. Among B. tectorum‐infested plots, winter wheat over‐winter survival declined with increasing weed seed produced in the previous summer. Overall, this study demonstrated that winter annual weed infestations can reduce crop stand densities below replanting thresholds by reducing fall‐sown cereal winter survival. The effects of winter annual weeds on winter wheat may be meditated by increased proliferation of snow mould disease.     

Differences between spring wheat cultivars in tolerance to <Emphasis Type="Italic">Fusarium</Emphasis> seedling blight under organic field conditions

Use of Fusarium-infected seed for cereal crops results in a reduced plant density due to seedling blight. This is especially a problem in organic agriculture, for which currently no practical seed disinfection methods are available. In the present paper we investigated whether spring wheat cultivars differ in tolerance to seedling blight in vivo, whether the possible differences could be linked to cultivar differences in initial growth rates, and whether differences in weed infestation were related to differences in emergence. Seed six spring wheat cultivars (Melon, Lavett, SW Kungsjett, Epos, Pasteur, Thasos), containing three Fusarium infection levels were obtained and sown in two field experiments in 2006 and 2007 and in an outdoor pot experiment in 2007. Results indicated that the six spring wheat cultivars differed in their tolerance to seedling blight, and consequently in the percentage of emergence of their seeds. The relative levels of tolerance to seedling blight of the six cultivars were robust in the three experiments performed. No clear relationship between initial growth rates and tolerance was found. In our experiments, no early and homogenous weed pressure was present, but in the 2007 field experiment a relationship between initial seedling emergence and weed infestation after anthesis was determined. Based on the presented results we suggest that additional to resistance to Fusarium head blight (FHB), differences in tolerance to seedling blight should also be considered during selection of wheat cultivars for organic agriculture.     

A COMPARISON OF THE GROWTH AND COMPETITION BEHAVIOUR OF SEEDLINGS AND PLANTS FROM RHIZOMES OF AGROPYRON REPENS (L.) BEAUV. AND AGROSTIS GIGANTEA ROTH

Summary. Seedlings and plants derived from single-node rhizome fragments of Agropyron repens and Agrostis gigantea were grown in au unheated glasshouse, separately or together with wheat ( cv. Kolibri), in sandy loam soil in well-spaced pots, adequately watered and moderately fertilized. Samples of crop and weeds were taken for growth analysis in mid- May, late June and early August (when the wheat was ripe).
On average, wheat decreased the weight of weed shoots by 84% and of rhizomes by 77%, but the weeds decreased the weight of wheat shoots by only 7% and of grain by 13%. Without wheat, seedlings of both weed species had, by late June, grown as much as plants from rhizomes, but with wheat, the weed seedlings were throughout most of the experiment more susceptible to competition than were plants from rhizomes. There was no simple relationship between the final dry weights of the weeds and the amount they decreased wheat yield: although Agropyron seedlings in competition with wheat were much lighter than Agrostis from rhizomes, they decreased grain yield of wheat as much, suggesting that they competed more intensely for a limiting factor, possibly nitrogen.
It is concluded that the faster initial growth rate of wheat seedlings relative to the weeds from rhizomes and a larger initial seed reserve relative to the weed seedlings enabled the wheat to dominate the weeds.
Comparaison de la croissance et comportement compétitif de plantules et de plantes issues de rhizomes d'Agropyron repens ( L.) Beauv. et d' Agrostis gigantea Roth     

Agronomic practises for weed control in turmeric (Curcuma longa L.)

Weeds are the main problem with turmeric (Curcuma longa L.) cultivation where herbicides are not allowed. This is because herbicides cause water contamination, air pollution, soil microorganism hazards, health hazards, and food risks. Considering turmeric's medicinal value and the environmental problems caused by herbicides, various agronomic practises have been evaluated for non‐chemical weed control in turmeric. One additional weeding is required before turmeric emergence and weed infestation is much higher when turmeric is planted in February and March, as compared to April, May or June planting. A similarly higher yield of turmeric is achieved when it is planted in February, March, and April, compared to late plantings. Weed emergence and interference are not affected by planting depth, seed size, planting pattern, planting space, ridge spacing, and the row number of turmeric until 60 days after planting. This is because turmeric cannot develop a canopy structure until then. Thereafter, weed infestation reduces similarly and significantly when turmeric is planted at depths of 8, 12, and 16 cm, compared to shallower depths. The yield of turmeric at these depths is statistically the same, but the yield for the 16 cm depth is difficult to harvest and it tends to decrease. Turmeric grown from seed rhizomes (daughter rhizomes) weighing 30–40 g reduces weed infestation significantly and obtains a significantly higher yield compared to smaller seeds. The mother rhizome also can suppress weed infestation and increase the yield markedly. Around 9% weed control and 11% higher yield are achieved by planting turmeric in a triangular pattern compared to a quadrate pattern. The lowest weed infestation is found in turmeric grown in a 20 or 30 cm triangular pattern and the highest yield is obtained with the 30 cm triangular pattern. Turmeric gown on two‐row ridges spaced 75 cm apart shows excellent weed control efficiency and obtains the highest yield. This review concludes that turmeric seed rhizomes of 30–40 g and/or the mother rhizome could be planted in a 30 cm triangular pattern at the depth of 8–12 cm on two‐row ridges spaced 75–100 cm apart during March to April in order to reduce weed interference and obtain a higher yield. Mulching also suppresses weed growth and improves the yield. The above agronomic practises could not control weeds completely; biological weed management practises could be integrated in turmeric fields using rabbits, goats, sheep, ducks, cover crops or intercrops.     

Influence of intra-row cruciferous surrogate weed growth on crop yield in organic spring cereals

In Northern Europe, inter-row hoeing has become a popular tactic for controlling weeds in organic cereals. Hoeing is highly effective and can be implemented from crop emergence until stem elongation to maintain a nearly weed-free inter-row zone. However, hoeing has a lesser effect on weeds growing in the intra-row zone, where crop–weed proximity results in heightened competition. In the hoed cereal system, it is investigated whether tall-growing, competitive, cruciferous weeds in the intra-row zone affect crop biomass, yield and thousand kernel weight (TKW). An additive experimental design is employed to enable the fitting of rectangular hyperbolas, describing and quantifying the effects of increasing intra-row surrogate weed density on crop growth parameters. Regressions were studied under the influence of crop (spring barley and spring wheat), row spacing (narrow [12.5 or 15.0 cm] and wide [25.0 cm]) and nitrogen rate (50 and 100 kg NH₄-N/ha). Cruciferous surrogate weeds were found to impact crop yield and quality severely. For example, ten intra-row plants/m² of surrogate weed Sinapis alba reduced grains yields by 7%–14% in spring barley and by 7%–32% in spring wheat with yield losses becoming markedly greater in wheat compared to barley as weed density increases. Compared to wheat, barley limited yield and quality losses and suppressed intra-row weed growth more. Row spacing did not have a consistent effect on crop or weed parameters; in one of six experiments, the 25 cm row spacing reduced yields and increased intra-row weed biomass in wheat. Nitrogen rate did not affect crop or weed parameters. Results warrant the implementation of additional tactics to control intra-row weeds and limit crop losses.     

Growth of Elymus repens (L.) Gould and Agrostis gigantea Roth. at different light intensities

Elymus repens (L.) Gould and Agrostis gigantea Roth. raised from rhizomes both responded to reduced light intensity by increased stem length, while the number of aerial shoots was reduced. The weight of the aerial parts was not influenced by a 50% reduction of the daylight intensity, but a further reduction of light caused a significant decrease in weight. The production of new rhizomes was more influenced by shading than were the aerial shoots. The consequence was an increase in the shoot/rhizome ratio. The food reserve per bud measured as inter-node weight in E. repens and A. gigantea was reduced only with intensive shading, and the vitality of the rhizomes appeared independent of light intensity. Intensive shading in early as compared to late summer caused a reduction in the number and weight of aerial shoots, but not in the weight of new rhizomes. Light intensities equal to those found in a spring wheat crop allowed more E. repens growth than light intensities equal to those in a spring oat crop. E. repens raised from seeds and grown at light intensities equal to those found in a cereal crop, showed insignificant rhizome production.     

A review of the effects of crop agronomy on the management of Alopecurus myosuroides

This study reviews 52 field experiments, mostly from the UK, studying the effects of cultivation techniques, sowing date, crop density and cultivar choice on Alopecurus myosuroides infestations in cereal crops. Where possible, a statistical meta‐analysis has been used to calculate average responses to the various cultural practices and to estimate their variability. In 25 experiments, mouldboard ploughing prior to sowing winter cereals reduced A. myosuroides populations by an average of 69%, compared with non‐inversion tillage. Delaying drilling from September to the end of October decreased weed plant densities by approximately 50%. Sowing wheat in spring achieved an 88% reduction in A. myosuroides plant densities compared with autumn sowing. Increasing winter wheat crop density above 100 plants m^?2 had no effect on weed plant numbers, but reduced the number of heads m^?2 by 15% for every additional increase in 100 crop plants, up to the highest density tested (350 wheat plants m^?2). Choosing more competitive cultivars could decrease A. myosuroides heads m^?2 by 22%. With all cultural practices, outcomes were highly variable and effects inconsistent. Farmers are more likely to adopt cultural measures and so reduce their reliance on herbicides, if there were better predictions of likely outcomes at the individual field level.     

两种小麦孢囊线虫在河南省郑州的侵染动态比较研究

 近年来, 小麦孢囊线虫病已成为我国小麦生产上的重要病害之一。掌握病原线虫的侵染动态是病害防控基础。本文在田间条件下, 对两种孢囊线虫—禾谷孢囊线虫(Heterodera avenae)和菲利普孢囊线虫(H.filipjevi)在河南郑州的侵染动态进行了比较研究, 结果显示:小麦出苗后2周即可发现孢囊线虫的二龄幼虫侵入到小麦根内, 4周后少量二龄幼虫发育为三龄, 6周后根内幼虫数量达到第一次高峰, 同时发现少量四龄幼虫。小麦出苗60 d后, 由于温度较低, 根内各虫态数量基本维持稳定;在120 d后, 温度逐渐回升, 根内二龄幼虫数量逐渐增加, 幼虫数量的第二次高峰出现在小麦出苗后150 d左右, 但入侵幼虫数量明显少于第一次。此后根内幼虫陆续发育为白雌虫和孢囊, 白雌虫数量高峰出现在小麦出苗后180 d后。H.filipjevi三龄、四龄幼虫及白雌虫出现的时间均比H.avenae的早一周。     

Johnsongrass (Sorghum halepense) growth characteristics as related to rhizome length

Growth characteristics of johnsongrass [Sorghum halepence(L) Pers] grown in the field from rhizomes 2.5, 5, 10, 15, 20, or 25 cm long were studied in a sandy loam soil for 2 years. Plant height, number of leaves per plant, number of tillers per plant, and fresh weight of new rhizomes and shoots were significantly dependent on the length of the planted rhizome 20, 40, 60, or 80 days after planting. All growth characteristics increased significantly as the length of planted rhizome increased from 2.5 cm to 10 cm to 25 cm Growth characteristics of Johnsongrass plants grown on rhizomes of adjacent lengths (differing by 5 cm) generally were not significantly different. Longer rhizomes (15, 20, or 25 cm) initiated new rhizome growth much earlier (about 20–30 days) than shorter rhizomes (2.5, 5, or 10 cm) Although all rhizome lengths showed a parallel growth potential, the lunger rhizomes were capable of more and faster growth, especially early after planting. It is suggested that Johnsongrass plants associated with longer rhizomes in the field as a result of limited tillage, coupled with their faster growth rate, are expected to interfere with crop production earlier than plants on shorter rhizomes unless controlled.     

The effect of controlling Alopecurus myosuroides Huds. and Avena fatua L. individually and together, in mixed infestations on the yield of wheat

Mixed infestations of Alopecurus myosuroides and Arena fatua growing in wheat were controlled individually or together in three experiments. Difenzoquat and ciofop-isohutyl were applied at the early tillering or early stem extension stages of the crops. Early control of both species resulted in significantly higher yields than later control, even though weed emergence was incomplete at the early applications. Herbicides, re-applied at the second date, improved the control of wild-oats hut not of black-grass; yields were not enhanced by this second application Halving the dose of herbicide gave little reduction in weed control or crop yield at the early date, but there was a greater response to dose with the later application. Yields were lower where only one weed was controlled. This work shows the need for broad spectrum control early in the life of the crop to safeguard yield where black-grass, and wild oats occur together in large numbers.     

AGROPYRON REPENS (L.) BEAUV.—SOME EFFECTS OF RHIZOME FRAGMENTATION, RHIZOME BURIAL AND DEFOLIATION

Summary. A factorial experiment with couch grass ( Agropyron repens (L.) Beauv.) grown in boxes examined the effects of rhizome fragmentation, planting depth and shoot removal on the survival of rhizome pieces, new rhizome growth and rhizome carbohydrate reserves.
Burial to 4 in. depth in sandy loam soil led to the death of 54% of 1 in. long rhizome pieces and 28% of 3 in. pieces. With all the segment lengths tested deeper planting decreased the proportion of buds which produced shoots.
Shoot removal every 14 days decreased the dry weight and carbohydrate content of the planted rhizomes and prevented new rhizome growth. Segments 1 or 3 in. long lost their carbohydrate reserves more quickly than 9 in. pieces. Rhizomes planted at 4 in. depth contained less carbohydrate after establishment than shallow-planted material, and produced less new rhizome growth.
IS Agropyron repens (L.) Beauv.–Quelques effets de la fragmentation et de l'enfouissement du rhizome et de la defoliation     

Increased density and spatial uniformity increase weed suppression by spring wheat

It has been hypothesized that increased crop density and spatial uniformity can increase weed suppression and thereby play a role in weed management. Field experiments were performed over 2 years to investigate the effects of the density and spatial arrangement of spring wheat (Triticum aestivum) on weed biomass and wheat yield in weed-infested fields. We used three crop spatial patterns (normal rows, random and uniform) and three densities (204, 449 and 721 seeds m⁻²), plus a fourth density (1000 seeds m⁻²) in the random pattern. Increased crop density reduced weed biomass in all three patterns. Weed biomass was lower and crop biomass higher in wheat sown in the random and uniform patterns than in normal rows in both years. At 449 seeds m⁻², weed biomass was 38% lower in the uniform and 27% lower in the random pattern than in rows. There was evidence of decreasing grain yield due to intraspecific competition only at 1000 seeds m⁻². The results not only confirm that increasing density and increasing crop spatial uniformity increase the suppression of weeds, but also suggest that a very high degree of spatial uniformity may not be necessary to achieve a major increase in weed suppression by cereal crops. Rows represent a very high degree of spatial aggregation. Decreasing this aggregation increased weed suppression almost as much as sowing the crop in a highly uniform spatial pattern. While the random pattern produced as much crop biomass and suppressed weeds almost as well as the uniform pattern, the uniform pattern gave the highest yield.     

Enhanced weed‐crop competition effects on growth and seed production of herbicide‐resistant and herbicide‐susceptible annual sowthistle (Sonchus oleraceus)

Enhanced crop competition could aid in the management of annual sowthistle (Sonchus oleraceus L.), a dominant weed of Australian cropping systems. A two‐year pot study was conducted to evaluate the effect of wheat (Triticum aestivum L.) planting densities (0, 82, and 164 wheat plants/m²) on growth and seed production of glyphosate‐resistant (GR) and glyphosate‐susceptible (GS) biotypes of annual sowthistle. Without competition, both biotypes produced a similar number of leaves and biomass, but the GS biotype produced 80% more seeds (46,050 per plant) than the GR biotype. In competition with 164 wheat plants/m², the number of leaves in the GR and GS biotypes was reduced by 62 and 61%, respectively, in comparison with the no‐competition treatment, and similarly, weed biomass was reduced by 78 and 77%, respectively. Compared to no‐competition treatment, the seed production of GR and GS biotypes was reduced by 33 and 69%, respectively, when grown with 82 wheat plants/m², but increasing wheat density from 82 to 164 plants/m² reduced the number of seeds only in the GS biotype (81%). Both biotypes produced greater than 6,000 seeds per plant when grown in competition with 164 plants/m², suggesting that increased crop density should be integrated with other weed management strategies for efficient control of annual sowthistle.     

Modelling the economics of controlling Avena fatua in winter wheat

A simple mathematical model of the life-cycle of Avena fatua L. is described and used to consider the financial consequences to the farmer of controlling A. fatua infestations in winter wheat. The likely economic benefits of applying herbicides in different cultivation regimes are investigated. The sensitivity of the model to variations in herbicide performance, straw burning, initial weed infestation and the value of the wheat crop is tested. The model predicts that the highest long-term benefits will be obtained when a herbicide is applied every time wild oats exceed a density of between 2 and 3 seedlings m^?2. Whether or not this results in a significant financial saving over spraying every year depends on the initial level of infestation and on the cultivation method. Whether straw is burnt or not is likely to be of little economic significance.     

Weed Control in Berseem using Stale Seed-bed,EPTC, and MCPB

Abstract

A field experiment was conducted in 1973 and 1974 at Udaipur, India to evaluate the selective weed control efficacy of stale seed-bed prepared with paraquat (1 kg/ha) or by cultivation, pre-planting incorporation of EPTC (1.5 kg/ha), and post-emergent application of MCPB (0.5 kg/ha). Two crop protectants, NA and activated carbon, were also field tested as seed treatments against injury by EPTC. It was found that stale seed-bed prepared by desiccation of weed seedlings with paraquat a day before planting berseem (Trifolium alexandrinum L.) and pre-planting incorporation of EPTC were both effective in significantly reducing weed growth and boosting yields of berseem. Berseem seeds coated with activated carbon before planting provided appreciable protection to the crop against EPTC, but NA stunted berseem growth. A combination of stale seed-bed and EPTC caused maximum reduction in weed growth. Post-emergent MCPB, though efficient in controlling weeds, was highly phytotoxic to the crop. Chenopodium spp. and Phalaris minor were lower in net energy content than berseem.     

Control of Elymus repens by rhizome fragmentation and repeated mowing in a newly established white clover sward

Control of perennial weeds, such as Elymus repens, generally requires herbicides or intensive tillage. Alternative methods, such as mowing and competition from subsidiary crops, provide less efficient control. Fragmenting the rhizomes, with minimal soil disturbance and damage to the main crop, could potentially increase the efficacy and consistency of such control methods. This study's aim was to investigate whether fragmenting the rhizomes and mowing enhance the control of E. repens in a white clover sward. Six field experiments were conducted in 2012 and 2013 in Uppsala, Sweden, and Ås, Norway. The effect of cutting slits in the soil using a flat spade in a 10 × 10 cm or 20 × 20 cm grid and the effect of repeated mowing were investigated. Treatments were performed either during summer in a spring‐sown white clover sward (three experiments) or during autumn, post‐cereal harvest, in an under‐sown white clover sward (three experiments). When performed in autumn, rhizome fragmentation and mowing reduced E. repens shoot biomass, but not rhizome biomass or shoot number. In contrast, when performed in early summer, rhizome fragmentation also reduced the E. repens rhizome biomass by up to 60%, and repeated mowing reduced it by up to 95%. The combination of the two factors appeared to be additive. Seasonal differences in treatment effects may be due to rhizomes having fewer stored resources in spring than in early autumn. We conclude that rhizome fragmentation in a growing white clover sward could reduce the amount of E. repens rhizomes and that repeated mowing is an effective control method, but that great seasonal variation exists.     

Weeding and nitrogen effects on farmers' wheat crops in semi-arid Morocco

The effects of three weeding systems with and without top-dressed nitrogen were examined in 40 experiments on bread wheat and durum wheat planted by farmers in the Chaouia (semi-arid area of Morocco) in 1984–1985 and 1985–1986 growing seasons. In both years, hand-weeding to simulate collection of forage reduced weed numbers by 30% and removed 63% of the weed dry weight. Treatment with 2, 4-D removed 66% of the weeds and reduced weed dry weight by 82%, in 1985–1986. Hand-weeding for forage produced 427 kg ha^?1 weed dry matter in both years, but wheat grain yields were 179 kg ha^?1 lower than with 2.4-D treatments. Over both years, the cost of each kg weed forage was 0·43 kg grain yield loss. Without weeding grain yields were 130 kg ha^?1 lower than 2, 4-D treatments. Weed control with 2,4-D increased wheat grain yields over both non-weeded and hand-weeded treatments by an average of 154 kg ha^?1. Overall, there were no significant effects of nitrogen on wheat or weed yields nor interactions between top-dressed nitrogen and weeding systems. A total of 157 weed species belonging to 29 botanical families were identified on the 40 experimental sites over both years; 89% were dicotyledons. Papaver rhoeas L. (common poppy), 2, 4-D susceptible plant, was the most annual weed in wheat fields in Chaouia.