Shade reduces growth and seed production of Echinochloa colona,Echinochloa crus-galli,and Echinochloa glabrescens

Echinochloa species are problematic weed species in direct-seeded rice systems in Asia. Because of concern about the continuous use of single herbicides, cultural weed management strategies need to be developed to maintain the sustainability of direct-seeded rice systems. However, the design of such strategies requires an understanding of the differential responses of weeds to shade caused by crop interference. The effects of shade on growth and seed production of Echinochloa colona, Echinochloa crus-galli, and Echinochloa glabrescens were determined. Weeds of three Echinochloa species were grown continuously in full sunlight or in 50% or 25% of full sunlight, or started in full sunlight and transferred to 50% or 25% of full sunlight at 21 days after sowing. The results suggested that changes in shade regime did not affect the plant height of E. colona and E. glabrescens; however, shade reduced the height of E. crus-galli. Compared with the plants grown in full sunlight, 75% of continuous shade reduced E. crus-galli height by 22%. Shade reduced leaf, total shoot, and root biomass and seed production in all the weed species, if occurred during the early growth of the weeds. The weeds responded with increased leaf biomass ratio when grown in shade. Compared with full sunlight, continuous shade of 75% increased leaf biomass ratio by 90% in E. colona and this value was 25% in the other two species. The results of this study show that shade can reduce weed growth and seed production of Echinochloa species but it should not be considered as a stand-alone strategy to manage these weeds in rice. This highlights the need for the integration of other weed management strategies to achieve complete control of these species.     

Effects of water regime,nitrogen fertilization,and rice plant density on growth and reproduction of lowland weed Echinochloa crus-galli

Direct-seeded rice systems are increasing in Asia as farmers respond to the high labor cost and shortage of water. Echinochloa crus-galli is one of the most problematic and competitive weeds in direct-seeded rice systems. Because of concerns about excessive herbicide use, there is an interest in developing cultural weed management strategies. However, the design of such strategies requires a better understanding of the weed response to crop density, nutrition, and water regime. A study was therefore conducted in pots to determine the effect of water (flooded and aerobic), nitrogen (N) fertilization (0, 100, and 200 kg N ha⁻¹), and rice density [0, 4 rice plants (≈20 kg seed ha⁻¹), and 16 rice plants (≈80 kg seed ha⁻¹)] on the growth and reproduction of E. crus-galli. When grown alone, the growth and seed production of E. crus-galli were higher in flooded conditions than in aerobic conditions. However, no such differences were observed when E. crus-galli was grown with rice interference. E. crus-galli growth and seed production increased with increases in N rate. Irrespective of water regime and N rate, the growth and seed production of E. crus-galli declined with increases in rice density. At 100 kg N ha⁻¹, for example, E. crus-galli shoot biomass and seed production decreased by 84–86% and 82–87%, respectively, when grown with 16 rice plants compared with its growth without rice interference. The results suggest that growth and seed production of E. crus-galli can be greatly reduced by increasing rice seeding rate. However, there is a need to involve other weed management strategies to achieve complete control of E. crus-galli and other weed species.     

Effect of emergence time,inter- and intra-specific competition on growth and fecundity of Echinochloa crus-galli in dry-seeded rice

Since 2005, the evolution and spread of herbicide-resistant Echinochloa crus-galli biotypes have posed a serious threat to crop production in the Philippines. A comprehensive knowledge of E. crus-galli ecology and fecundity is fundamental in managing different biotypes of this weed. It was hypothesized that (a) high weed plant density produces more biomass and fertile seeds per unit area, (b) rice interference reduces the biomass and fecundity of the weed, and (c) a delay in weed emergence reduces the soil seed bank. In 2013, experiments were conducted in the wet season (WS) and dry season (DS), to understand the effect of E. crus-galli densities (40 and 80 plants m⁻²) on its growth, survival, and fecundity, with varying emergence times of 2, 15, 30, and 45 d after rice emergence (DARE). Relative to the weed plants grown without rice interference, E. crus-galli growth and seed production was lower in the presence of rice. Percent survival and plant height of E. crus-galli declined in a linear manner in the DS, and declined in a quadratic manner in the WS. Tiller number, inflorescence number, inflorescence biomass, and shoot biomass per plant declined in an exponential manner, with a delay in emergence of each cohort relative to rice. Across rice seeding rate, weed density, and emergence time, there was a linear relationship (y = 110x − 272 in the DS and y = 100x − 220 in the WS) between E. crus-galli shoot biomass and the number of seeds plant⁻¹. Relative to the late-emerging weed cohorts, E. crus-galli seed production (1320–1579 seeds plant⁻¹), 1000-seed weight (2.2–2.9 g), and seed yield (2808–2334 kg ha⁻¹) were higher when seedlings emerged with the crop (2 DARE). None of the seedlings that emerged 45 DARE produced viable seeds. Seed germination of the first two cohorts (2 and 15 DARE) ranged from 84 to 91%. The delay in emergence of E. crus-galli beyond 30 DARE reduced the percentage of germinable and viable seeds, and increased the percentage of non-viable seeds produced plant⁻¹. The results suggest that cultural weed management approaches that delay the emergence of E. crus-galli can reduce weed biomass and seed production, and is thus valuable for preventing seed rain to the seed bank by noxious weed biotypes in the field.     

Effects of mechanical and chemical methods on weed control,weed seed rain and crop yield in maize,sunflower and soyabean

Eight field experiments with maize (Zea mays L.), sunflower (Helianthus annuus L.) and soyabean (Glycine max (L.) Merr.) were carried out in central Italy in order to evaluate the effects of mechanical and chemical methods (spring-tine harrowing, hoeing, hoeing-ridging, split-hoeing, finger-weeding, herbicides in the row + inter-row hoeing, herbicides broadcast) on weed control, weed seed rain and crop yield. The choice of chemical and mechanical treatments in maize and soyabean compared to sunflower, required to be managed more carefully in order to maximize the weed control reducing yield losses. A global rating of weed control methods, based on their weed control efficacy, was obtained as useful means to assist farmers and technicians to choose the more appropriate weed control method. The combination of herbicides intra-row and hoeing inter-row gave best efficacy (on average 99% of weed control), with a 50% reduction in the chemical load in the environment. Hoeing-ridging gave good results, both inter- and intra-row (on average 93% of weed control); this method was also effective in reducing competitive ability and seed production of uncontrolled weeds. Split-hoeing or finger-weeding showed some limitations giving satisfactory results only when combined. Harrowing gave lowest weed control, although when combined to other mechanical methods, can help achieve a better efficacy.     

Ecological studies on Echinochloa crus-galli and the implications for weed management in direct-seeded rice

Echinochloa crus-galli, a C₄ grass, is one of the world’s most serious weeds. Weed management decisions for this species can be derived from knowledge of its seed biology. Studies were conducted to determine the effects of light on germination; seed burial depth and rice residue on emergence and growth; and flooding time and depth on emergence, survival and growth of this species. Light stimulated seed germination but it was not an absolute requirement for germination. The proportion of seeds germinating was greatest for seeds placed on the soil surface (92%), and emergence declined with increasing burial depth in soil; no seedlings emerged from the depth of 8 cm. A burial depth of only 0.4 cm reduced seedling emergence by 50%. Seedling emergence and seedling biomass were reduced by the addition of high level (6 ton ha⁻¹) of rice residue to the soil surface. Early and deep flooding significantly suppressed growth of E. crus-galli seedlings. In flooded conditions, with increased water depth the weed allocated more biomass to shoots at the expense of roots. The information gained from this study could contribute to improve weed control approaches. Soil inversion by tillage to bury weed seeds below their maximum depth of emergence, use of crop residue as mulch and early flooding of the crop could serve as important tools for managing E. crus-galli and other weed species with similar germination requirements. These management options, however, would need to be compatible with other crop management requirements.     

Competitiveness of rice (Oryza sativa L.) cultivars against Echinochloa crus-galli (L.) Beauv. in water-seeded production systems

Developing more competitive rice cultivars could help improve weed management and reduce dependency on herbicides. To achieve this goal, an understanding of key traits related to competitiveness is critical. Experiments were conducted at Gelemen and Bafra districts of Samsun province in Turkey between 2008 and 2009 to measure the competitiveness of rice cultivars against Echinochloa crus-galli, a problematic weed in rice fields. Five rice cultivars (Osmancık, Kızılırmak, Karadeniz, Koral and Neğiş) and five E. crus-galli densities (0, 5, 10, 20, and 30 plants m⁻²) were used. Koral produced significantly more tillers than the other cultivars irrespective of E. crus-galli densities and reduced E. crus-galli tiller production by about 29.5% at Gelemen and 15.8% at Bafra at the highest weed density. E. crus-galli interference reduced rice height and there was a density dependent relationship. Koral was the most competitive cultivar; it maintained high biomass accumulation in early growth stages and suffered smaller reductions in plant height in the presence of E. crus-galli, compared to the other cultivars. In the absence of weed competition, Koral and Neğiş produced the highest yields at both locations. Stepwise regression analyses of the combined data from both years showed tillering capacity, early growth crop biomass, and plant height were critical traits related to competitiveness. These traits should be considered by plant breeders in their efforts to develop rice cultivars with enhanced competitiveness against weeds. Development of such cultivars could substantially reduce herbicide and labor inputs for rice production.     

Herbicidal control of Solanum elaeagnifolium Cav. in Australia

Solanum elaeagnifolium Cav. is considered as one of the worst weeds of crop and pasture systems in temperate Australia. Effective long-term control is difficult due to the extensive root system. Field experiments were conducted at two locations in south-eastern Australia between 2006 and 2008 to examine a range of herbicides for control of S. elaeagnifolium on seed production and root regrowth. Herbicide performance was affected by herbicide, weed growth stage and environmental factors. Pyridine herbicides, such as pre-packed mixtures of aminopyralid + fluroxypyr and triclopyr + picloram + aminopyralid were the most effective and consistently reduced within-season aerial growth by 60–90% in both seasons. Overall control using glyphosate-based treatments was generally reduced due to emergence of new stems following herbicide application. Three picloram-based treatments provided the best and most consistent long-term control on root regrowth after two seasons, reducing stem emergence by 45–88%, especially with a late application of herbicides. The efficacy of residual herbicides such as atrazine or imazapic + imazapyr depends on rainfall conditions. Seedset control was best achieved with herbicides applied at the start of flowering stage, with no viable seed produced following treatments of 2,4-D amine + picloram and triclopyr + picloram + aminopyralid. These two treatments also significantly reduced viable seed production when applied at the early berry stage. The results indicate that an application at early flowering followed by a late application in autumn is necessary to effectively control the seedset (seedbank) and the root regrowth (rootbank) of S. elaeagnifolium.     

Integrated effect of allelochemicals and herbicides on weed suppression and soil microbial activity in wheat (Triticum aestivum L.)

To evaluate the allelopathic effects of major crops and weeds, studies were conducted during 2011–12 and 2012–13 by utilizing water extracts of allelopathic plants namely rice (Oryza sativa L.), Parthenium hysterophorus L., Phragmites australis Cav., and Datura alba L. with reduced rates of fenoxaprop-p-ethyl and bromoxynil plus MCPA to control weeds. Application of Phragmites australis and Parthenium hysterophorus along with lower rates of fenoxaprop-p-ethyl and bromoxynil plus MCPA showed promising results by controlling weeds and improving yield. Parthenium hysterophorus extract with half of the recommended dose of fenoxaprop-p-ethyl and bromoxynil plus MCPA reduced weed density by 51 and 50% during year 1 and year 2, respectively, compared with the control. Phragmites australis extract with half of the recommended dose of fenoxaprop-p-ethyl produced grain yield (5.7 and 6.1 t ha⁻¹ during year 1 and 2, respectively) in wheat. However, these results were also at par with Parthenium hysterophorus and Datura alba extracts in combinations with half the recommended doses of the above mentioned herbicides. The study of microbial activity showed higher amount of mineralizable carbon in D. alba with half the recommended dose of fenoxaprop-p-ethyl treated plots (0.073 g during both the years). The lowest amount of mineralizable carbon (0.035 and 0.030 g during year 1 and 2, respectively) was observed in the control plots. The presence of allelopathic plants in field crops and subsequent mixing in soil by tillage may create problems in crop production. Therefore, further studies are suggested to fully explore all the possible interactions among allelochemicals and herbicides.     

Effect of herbicide application on weed flora under conservation agriculture in Zimbabwe

Increased challenges of weed control in the smallholder farming sector of southern Africa have often resulted in small yields. The objective of this study was to evaluate the effects of different weed control strategies on weed flora and composition under conservation agriculture (CA) systems in Zimbabwe. This study was conducted at three on-station trial sites namely Domboshawa Training Centre (DTC), University of Zimbabwe farm (UZ farm) and Henderson Research Station (HRS) in a maize–soybean rotation for four seasons from 2009–2010 to 2012–2013 seasons. Hand weeding was done whenever weeds were 10 cm tall or 10 cm in circumference for weeds with a stoloniferous growth habit. Weed identification was done up to the weed species level, and the Shannon–Weiner diversity and evenness index was used to determine the response of weed flora to herbicides. Results showed that there were more weeds in the early years which decreased gradually until the final season. Weed species diversity was not affected by herbicide application and the results indicated that weed species diversity was small in CA systems. Annual weed species constituted a greater proportion of species, and species richness decreased with the duration of the study. Richardia scabra L. and Galinsoga parviflora Cav. were the most common dominant weed species at all sites and in all seasons. Moreover, herbicide application had no effect on the evenness of weeds in the plots but site characteristics had a significant effect on the distribution of weed species (weed species evenness). The results presented in this study suggest that herbicide application facilitates a depletion of weed seed bank/number of weeds over time. Thus, herbicide application in CA has potential to reduce weed density, species richness and species diversity in the long term which may lead to more labour savings and larger yields.     

Modelling the population dynamic and management of Bromus diandrus in a non-tillage system

A cohort-based population model was developed to simulate the population dynamics and management of Bromus diandrus. Model parameters were derived from our experiments and from published sources. Individual and integrated management strategies were simulated. More than 85% of B. diandrus seeds emerged within the first cohort. In the absence of any control the seed-bank population grew until reaching an equilibrium at density of 17,324 seeds m⁻². Results pointed to the difficulty in controlling this weed with individual control tactics. All integrated programmes simulated resulted in long-term reductions in the seed bank. Simulations showed that the combination of pre-emergence and post-emergence herbicides or combination of autumn shallow cultivation and post-emergence herbicides are the best techniques to employ in integrated weed management (IWM) programmes in cereal. A sensitivity analysis indicated that B. diandrus is particularly vulnerable to small changes in the fecundity of the first cohort. Consequently, it is important to find strategies which can reduce the effect of the first cohort, because this is a clue to the control of this weed.     

Effect of herbicides on weed management in dry-seeded rice sown under different tillage systems

In India, dry-seeded rice (DSR) production systems are rapidly replacing conventional rice production systems due to various advantages. DSR systems can be managed under zero-till (ZT) conditions or after a preparatory tillage, often referred to as conventional tillage systems (CONT). Although previous reports indicate the contribution of tillage to weed suppression, the effect of one-time preparatory tillage in a DSR system could vary depending on the dominant weeds in the system, vertical seed distribution and the weed seed dynamics. A study was conducted to test the efficacy of ZT and CONT and their interaction with herbicide treatments on the weed population dynamics and rice grain yield in 2010 and 2011. Tillage systems did not affect weed emergence, weed biomass, tiller production and crop yield. However, herbicide treatments varied in their efficacy on individual weeds. Hand-weeding treatments and pendimethalin combined with hand weeding did not effectively control Cyperus rotundus L. and Panicum maximum Jacq. (a perennial grass weed with underground parts). The herbicide combination of metsulfuron and chlorimuron was effective in controlling C. rotundus but not grass weeds. This indicates the need for sequential applications of herbicides for grass weed control or integration of hand weeding to achieve broad-spectrum weed control. Apart from hand weeding (three times), treatment with penoxsulam–cyhalofop and pendimethalin followed by (fb) hand weeding resulted in low weed density, high tiller production and grain yield. The study clearly indicates that tillage does not always lead to weed suppression compared with ZT, and herbicides must be chosen based on the dominant weeds in a system. The results of this study are pertinent as herbicide-resistant weeds are rapidly evolving under continuous herbicide selection pressure, which warrants studies on enhancing productivity through low-input, environmentally friendly and sustainable production technology.     

Management of herbicide-resistant Phalaris minor in wheat by sequential or tank-mix applications of pre- and post-emergence herbicides in north-western Indo-Gangetic Plains

Development of cross resistance or multiple cross resistance in Phalaris minor in wheat will continue to increase, as the weed develops mechanisms of resistance against new herbicides. This weed is a major threat to wheat productivity in north-western India, and as such needs to be addressed with integrated weed management approaches, including crop and herbicide rotations, herbicide combinations along with cultural and mechanical methods. Three field experiments were conducted during 2008–09 to 2012–13 along with large plot adaptive trials during 2012–13 with the objective to evaluate the efficacy of sequential applications of pendimethalin applied pre-emergent followed by clodinafop, sulfosulfuron, or pinoxaden applied post-emergent and tank-mix applications of metribuzin with these post-emergence herbicides for the management of herbicide-resistant P. minor in wheat. Clodinafop 60 g ha⁻¹ or sulfosulfuron 25 g ha⁻¹ at 35 days after sowing (DAS) and pendimethalin 1000 g ha⁻¹ as pre-emergence did not provide consistently effective control of P. minor in wheat. An increase in the dose of clodinafop from 60 to 75 g ha⁻¹ and of sulfosulfuron from 25 to 30 g ha⁻¹ also did not improve their efficacy to a satisfactory level. However, pinoxaden 50 g ha⁻¹ provided effective control (97–100%) of P. minor but not of broadleaf weeds. The tank-mix application of metribuzin with clodinafop 60 g ha⁻¹ or sulfosulfuron 25 g ha⁻¹ at 35 DAS and the sequential application of pendimethalin 1000 g ha⁻¹ or trifluralin 1000 g ha⁻¹ just after sowing followed by clodinafop 60 g ha⁻¹ or sulfosulfuron 25 g ha⁻¹ at 35 DAS provided 90–100% control of P. minor along with broadleaf weeds in wheat, thus resulting in improved grain yields (4.72–5.75 t ha⁻¹) when compared to clodinafop 60 g ha⁻¹ (3.85–5.60 t ha⁻¹) or sulfosulfuron 25 g ha⁻¹ alone (3.95–5.10 t ha⁻¹). The efficacy of mesosulfuron + iodosulfuron (a commercial mixture) 14.4 g ha⁻¹ against P. minor was not consistent across the experiments and over the years. The ready-mix combination of fenoxaprop + metribuzin (100 + 175 g ha⁻¹) at 35 DAS provided effective control of weeds but its varietal sensitivity needs to be determined before its use in field conditions. The tank-mix or sequential application of herbicides would be a better option than their applications alone to manage the serious problem of herbicide-resistant P. minor in wheat.     

The critical period for weed control in dry-seeded rice

The critical crop-weed competition period in a dry-seeded rice system is an important consideration in formulating weed management strategies. Field experiments were conducted in the summer seasons of 2012 and 2013 at the Punjab Agricultural University, Ludhiana, India, to determine the extent of yield loss in two different rice cultivars (PR 114 and PR 115) with different periods of weed interference. Twelve weed control timings were used to identify critical periods of weed competition in dry-seeded rice. PR 114, a long-duration rice cultivar (145 d) having slower initial growth than PR 115 (125 d), was more prone to yield losses. In both years, 100% yield loss was observed where weeds were not controlled throughout the season. In weed-free plots, the grain yield of PR 114 was 6.39–6.80 t ha⁻¹, for PR 115, it was 6.49–6.87 t ha⁻¹. Gompertz and logistic equations fitted to yield data in response to increasing periods of weed control and weed interference showed that, PR 114 had longer critical periods than PR 115. Critical weed-free periods to achieve 95% of weed-free yield for PR 114 was longer than for PR 115 by 31 days in 2012 and 26 days in 2013. Weed infestation also influenced the duration of critical periods. Higher weed pressure in 2012 than in 2013 increased the duration of the critical period of crop-weed competition in that year. The identification of critical crop-weed competition periods for different cultivars will facilitate improved decision-making regarding the timing of weed control and the adoption of cultivars having high weed-suppressing abilities. This will also contribute to the development of integrated weed management in dry-seeded rice systems.     

Row spacing and weed control timing affect yield of aerobic rice

Field experiments were conducted during the wet season of 2009 and dry season of 2010 to determine the effects of row spacing and timing of weed control on weed growth and yield of aerobic rice. Ten weed management treatments were used to identify critical periods of weed competition with aerobic rice grown in three different row spacings (15-cm, 30-cm, and as paired rows 10-20-10-cm). Dominant weed species during both growing seasons were Rottboellia cochinchinensis, Digitaria ciliaris, Echinochloa colona, and Eleusine indica. Rice grown in 30-cm rows had greater weed biomass and less grain yield than in 15-cm and 10-20-10-cm rows; weed growth and grain yields were similar between 15-cm and 10-20-10-cm rows. Rice yields in the wet season ranged from 170 kg ha⁻¹ where weeds were not controlled throughout the crop duration to 2940 kg ha⁻¹ in weed-free treatment, indicating a 94% yield loss with uncontrolled weed growth. Similarly in the dry season, plots with no weed control (140 kg ha⁻¹) compared to weed-free plots (3640 kg ha⁻¹) indicate a 96% yield loss with no weed control. Gompertz and logistic equations were fitted to yield data resulting from increasing durations of weed control and weed interference, respectively. Critical periods for weed control in the wet season, to obtain 95% of a weed-free yield, were estimated as between 18 and 52 days after sowing (DAS) for crops in rows at 15-cm, 20-51 DAS at 10-20-10-cm, and 15-58 DAS at 30-cm. These intervals in the dry season were 17-56 DAS for crops in rows at 15-cm and 17-60 DAS at 10-20-10-cm and 15-64 DAS at 30-cm. Durations of the critical periods in the wet season were 31 days at 10-20-10-cm, 34 days at 15-cm and 43 days at 30-cm, while in the dry season, these were 43 days at 10-20-10-cm, 39 days at 15-cm and 49 days at 30-cm. In both seasons, crops in the wider spacing (30-cm) were vulnerable to weed competition for the longest period. The information gained from this study suggests that the aerobic rice yields better in 15-cm rows and 10-20-10-cm arrangements than in 30-cm rows and there is very little benefit of weed control beyond 8 weeks after sowing.     

Weed emergence as affected by maize (Zea mays L.)-cover crop rotations in contrasting arable soils of Zimbabwe under conservation agriculture

Weed control in smallholder farming systems of sub-Saharan Africa is labour intensive or costly. Many researchers have therefore advocated for the use of cover crops in weed management as an affordable alternative for smallholders. Cover crops may be grown in rotations to suppress weeds and reduce the reliance on herbicides. The use of cover crops creates microenvironments that are either conducive or inhibitive to the emergence of certain weed species. A study, initiated in 2008 in contrasting soils at four different locations of Zimbabwe, investigated the effect of maize (Zea mays L.)-cover crop rotations on the emergence of weeds that showed dominance in those soils. Weed assessments were however, carried out from 2011 to 2014. The weed species Galinsoga parviflora Cav., Commelina benghalensis L., and Richardia scabra L. showed dominance in all four locations with weed densities as high as 500 plants m⁻² being recorded for R. scabra L. in a sandy soil. Maize-cover crop rotations resulted in higher densities of Bidens pilosa compared with maize monocropping (control treatment) due to its high nitrogen (N) requirement to produce more seeds. On the other hand, the integration of cover crops such as pigeon pea [Cajanus cajan (L.) Millsp.] that had poor shading qualities, due to large gaps or spaces and slower initial growth, had limited effects on competitive weeds such as Cyperus esculentus L. which tend to dominate exhausted soils. The density of C. esculentus was 38% greater in maize–pigeon pea rotations compared with the control treatment. Variability between seasons and sites affected emergence of all weeds in the present study, which masked long-term trends. The results suggest that there is need to identify the germination and emergence requirements of specific weeds and select cover crops best suitable for their control. The study provides useful information for farmers and advisors on the best cover crops for control of certain problematic weeds in different soil types of Zimbabwe.     

Weed control in sunn hemp and its ability to suppress weed growth

Sunn hemp is a tropical, herbaceous annual legume that has potential as a cover crop during the summer in temperate climates. Due to the recent increased interest in sunn hemp breeding and seed production for temperate climates, there is a need for weed control in sunn hemp production. No herbicide product currently on the market specifically identifies sunn hemp as a tolerant crop. The aims of this research were 1) to evaluate herbicides with the intent of identifying a herbicide program that can assure near weed free sunn hemp intended for seed harvest and 2) to demonstrate and quantify sunn hemp-weed suppression. Pre-emergence applied treatments consisted of pendimethalin alone, imazethapyr alone, and pendimethalin plus imazethapyr. Pendimethalin alone provided consistent effective weed control and maximum sunn hemp biomass, but when yellow nutsedge was present, imazethapyr was required for effective control and greater sunn hemp biomass. The combination of pendimethalin and imazethapyr was detrimental to sunn hemp biomass yield. Results also established that sunn hemp is tolerant of 2,4-DB applied post-emergence, but was not necessary for weed control in these studies because of the lack of broadleaf weed pressure. In a separate study with variable sunn hemp densities, weed biomass reductions of ≥50% were obtained with sunn hemp densities of only 20 to 50 plants m⁻². This degree of weed suppression obtained from relatively modest sunn hemp densities is likely indicative of the ability of sunn hemp to grow faster and taller than other plants.     

Long-term perennial weed control strategies: Economic analyses and yield effect in hazelnut (Corylus avellana)

Weeds limit hazelnut productivity through competition and interference. Field experiments were conducted from spring 2010 through 2013 to evaluate string trimming alone or combined with herbicides in hazelnut orchards to control mugwort (Artemisia vulgaris L.), purple nutsedge (Cyperus rotundus L.), and burning nettle (Urtica urens L.). Treatments were mowing with a string trimmer (ST) alone, or ST followed by glyphosate, glyphosate + diflufenican, and glyphosate + carfentrazone-ethyl. These combinations also were applied with pendimethalin and oxyfluorfen as pre-emergence applications. The experiments were conducted in Fatsa-Ordu, Turkey, on a sandy clay soil with multi-stemmed trees (ocak). The combination treatments improved weed control compared to ST alone. Glyphosate plus carfentrazone-ethyl application 15 days after ST was the most effective treatment for control of these weeds. This combination was more effective in reducing seed bank reserves of A. vulgaris, C. rotundus and U. urens than herbicides applied alone or in mixtures throughout all seasons. Hazelnut yield was not significantly affected by herbicide treatments in 2010 or 2011. Hazelnut yield increased during the latter half of the experimental period, in 2012 and 2013. In a mixed population of A. vulgaris, C. rotundus and U. urens, 89 plants per m² caused 12.1% yield loss. When the density increased to 256 plants per m², yield losses increased to 29.7%. Hazelnut treated with ST followed by glyphosate plus carfentrazone-ethyl had the highest financial return. Post-emergence weed management systems in hazelnut should include ST followed by glyphosate plus carfentrazone-ethyl applications for maximum returns.     

Sustainable weed management in conservation agriculture

Sustainable crop production is necessary to ensure global food security and environmental safety. Conservation agriculture (CA) is gaining popularity around the globe due to its sustainable approaches such as permanent soil cover, minimal soil disturbance, planned crop rotations and integrated weed management. Weed control is the biggest challenge to CA adoption. Weed ecology and management is different in CA than in conventional agriculture. In CA, weeds expression, seed bank status, distribution, dispersal mechanisms, diversification, growing patterns and competition trends are complex and differ from conventional systems. It is due to reduced tillage of the soil and the flora that thrives in CA. Reduced tillage systems affect the efficacy of herbicides and mechanical weed control measures. So, it is an important task to find out the differences and to fabricate new management options. In this review, changing weed dynamics have been framed. A novel aspect of this review is the comprehensive account of sustainable weed management strategies in relation to CA. Modified tillage operations, improved cultural practices, bioherbicides, chemical herbicides, allelopathy, and crop nutrition have been identified as suitable weed management tools. None of these offers complete control but the integration of these tools in suitable combinations works efficiently. Weeds dominating CA and their responses to CA components are highlighted. For example, small seeded and perennial weeds are more abundant in CA. The role of herbicide resistance in weeds and herbicide tolerant (HT) crops in CA is also highlighted. Allelopathy and crop nutrition are discussed as modern weed management tools for CA. A detailed account of weed responses to fertilizer management options is also given. Integrated weed management compatible to cropping patterns and climatic conditions offers the best results in CA. Future efforts must be directed towards the optimization and integration of these weed management practices.     

Weed management in no-till winter wheat (Triticum aestivum L.)

In general, effective weed control in no-tillage systems is based on the use of herbicides. However, the development of appropriate weed management strategies can help to reduce the amount of herbicides applied.