Selectivity and weed control efficacy of pre- and post-emergence applications of clomazone in Southern Brazil

During the 2006/07 and 2008/09 growing seasons in Southern Brazil, we evaluated crop selectivity and weed control efficacy of clomazone on rice when applied alone or in a mixture with other pre- and post-emergence herbicides (BRS Querência variety). All herbicide treatments caused some degree of rice injury during both years; however, in no case was the injury still visible 21 days after application. Rice injuries were observed when application rates exceeded the recommended dose, and particularly when the herbicide was applied pre-emergence. Density reduction and panicle sterility served as measures of rice injury. Echinochloa crus-galli was the primary weed; it reduced rice yields by approximately 50% compared treated plots. In both growing seasons, clomazone herbicide (400 g ai ha⁻¹) controlled the weed 87.0%–99.6%, and it provided 8.06 t ha⁻¹ to 9.44 t ha⁻¹ of rice yield.     

Weed control efficacy and winter wheat safety of a novel herbicide HW02

HW02, a pyruvate dehydrogenase inhibitor, is a newly developed herbicide for broadleaf weed control in wheat, maize and turf in China. Greenhouse and field experiments were conducted to evaluate its efficacy against weeds and safety to winter wheat. In the greenhouse experiment, this herbicide had higher activities than 2,4-D against Descurainia sophia (L.) Schur., Amaranthus retroflexus L., Capsella bursa-pastoris (L.) Medic., and Malachium aquaticum (L.) Fries.. When it was applied at late tillering stage of winter wheat in spring, the herbicide provided weed biomass reduction of 98%–100% at the rates 225–525 g a.i. ha⁻¹ and was safe to the crop at the rate of up to 900 g a.i. ha⁻¹. These results showed HW02 could be an alternative herbicide for resistant weed management because its mode of action is different from herbicides presently used.     

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.     

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.     

Management of complex weed flora in dry-seeded rice

Dry-seeded rice has been introduced as an alternative to puddled hand-transplanted rice in the north Indian states of Punjab and Haryana. In dry-seeded rice, weed flora tends to be more diverse and weeds emerge in several flushes during the crop growth cycle and substantial yield reductions due to weed competition are quite common. The efficacy and compatibility of tank mixtures of different herbicides for the control of diverse weed flora in dry-seeded rice was evaluated in field experiments during the summer seasons of 2012 and 2013. The tank mixture of fenoxaprop with ethoxysulfuron improved the control of Echinochloa crus-galli and Echinochloa colona by 43–69% as compared to fenoxaprop alone while the tank-mix of azimsulfuron with fenoxaprop was antagonistic and reduced the control of Leptochloa chinensis by 86% as compared to fenoxaprop alone. Addition of azimsulfuron or ethoxysulfuron to bispyribac did not improve the control of grass weeds as compared to bispyribac alone. Weed control with the mixture of bispyribac and fenoxaprop varied over the two years. In 2012, bispyribac and fenoxaprop mixture was antagonistic for the control of Dactyloctenum aegyptium, Acrachne racemose, and L. chinensis but in 2013, there was no apparent antagonism and the addition of bispyribac to fenoxaprop reduced grass weed biomass as compared to fenoxaprop alone. In 2013, there was a strong negative correlation (r = −0.95, P < 0.001) between weed dry matter at 45 days after sowing and rice grain yield. According to the linear regression, rice crop is likely to produce no grain yield when weed dry matter exceeds 400 g m⁻². Over the two seasons, fenoxaprop-ethoxysulfuron tank-mix produced similar grain yields (5.6–6.2 t ha⁻¹) to the weed-free check (5.6–7.1 t ha⁻¹). At the farmer fields, rice grain yield in the plots treated with pendimethalin followed by post-emergence bispyribac or a tank-mix of fenoxaprop + ethoxysulfuron ranged from 6.2 to 7.7 t ha⁻¹ as compared to 5.3–5.6 t ha⁻¹ in the plots treated with pendimethalin alone. The tank mixture of fenoxaprop with bispyribac needs further evaluation as this mixture has the potential to effectively control aerobic and aquatic grasses in dry-seeded rice. Single hand weeding prevented crop yield loss from weeds that escaped herbicide treatments only when it was performed within six weeks of sowing.     

Effect of pre-emergence herbicides and timing of soil saturation on the control of six major rice weeds and their phytotoxic effects on rice seedlings

The study evaluated the effects of pre-emergence herbicides and their rates [oxadiazon (0.5 and 1 kg ai ha⁻¹), pendimethalin (1 and 2 kg ai ha⁻¹), and pretilachlor with safener (0.6 kg ai ha⁻¹)], and time of soil saturation establishment after herbicide application [1, 3, 5, and 7 days after spray (DAS)] in controlling the six major rice weeds, and their phytotoxic effects on rice seedling growth. All herbicides provided 100% control of Echinochloa colona, Echinochloa crus-galli, Leptochloa chinensis, Cyperus iria, and Amaranthus spinosus. Murdannia nudiflora was 100% controlled by oxadiazon and pretilachlor with safener, but poorly controlled (22–75%) by pendimethalin. Pendimethalin at 2 kg ai ha⁻¹ was more effective than at 1 kg ai ha⁻¹ in reducing the biomass of the stem, leaf, and root of M. nudiflora irrespective of timing of soil saturation. Rice plant height was reduced to a maximum (77–96%) by pendimethalin at 2.0 kg ai ha⁻¹ followed by oxadiazon at 1.0 kg ai ha⁻¹ (38–70%) compared to the non-treated control. In contrast, the tallest rice plants were observed in the non-treated control and those treated with pretilachlor with safener which had 80–100% rice plant survival. The lowest rice plant survival of 0, 6, 7, and 16% was found in the soil applied with pendimethalin at 2 kg ai ha⁻¹ and saturated at 1, 3, 5, and 7 DAS, respectively, which was followed by oxadiazon at 1 kg ai ha⁻¹. All herbicides except pretilachlor with safener reduced SPAD values with early soil saturation, which improved with delay in soil saturation timing. Pendimethalin at 2 kg ai ha⁻¹ reduced the SPAD values of rice plants by 100–164% relative to the non-treated control and produced the highest phytotoxicity symptoms. Pendimethalin also reduced rice shoot biomass more than oxadiazon, which was compounded by early soil saturation after herbicide application. Pretilachlor with safener was the only herbicide that exhibited low phytotoxic symptoms on rice plants and did not reduce leaf, stem, root, and shoot biomass of rice. Percent reduction in rice leaf, stem, root, and shoot biomass by the different herbicides was in the order of pendimethalin 2 > oxadiazon 1 > pendimethalin 1 > oxadiazon 0.5 > pretilachlor with safener 0.6 kg ai ha⁻¹. Each herbicide treatment reduced rice growth parameters as soil saturation was delayed in the order of 1 DAS > 3 DAS > 5 DAS > 7 DAS. The study suggests that soil water content and herbicide rates are important factors in influencing herbicide phytotoxicity in rice. The application of herbicides should be avoided when the soil is too wet, and irrigation should be delayed at least one week after herbicide application.     

Winter cover crops influence Amaranthus palmeri establishment

Winter cover crops were evaluated for their effect on Amaranthus palmeri establishment and growth in cotton production. Cover crops examined included rye and four winter legumes: narrow-leaf lupine, crimson clover, Austrian winter pea, and cahaba vetch. Each legume was evaluated alone and in a mixture with rye. Cover crop biomass in monoculture was greatest for rye and lupine (>6750 kg ha⁻¹), while clover, pea, and vetch were less and ranged from 2810 to 4610 kg ha⁻¹. Cover crop biomass was more than doubled when rye was mixed with clover or vetch relative to the legume monoculture. In early-June, A. palmeri densities were 46 seedlings m⁻² in the non-disturbed areas between cotton rows in the fallow, while populations were <4 seedlings m⁻² with rolled vetch or pea and 18 and 29 seedlings m⁻² in rolled clover and lupine. Rye and legume mixtures reduced A. palmeri densities to <3 seedlings m⁻², while rye monocultures had 8 seedlings m⁻². There were no differences in A. palmeri densities (≥144 plants m⁻²) in the cotton row among cover crop treatments. By late-June, rye and winter pea controlled A. palmeri in the row middle >80% relative to the non-cover crop fallow treatment, while control from clover, vetch and lupine ranged from 64 to 70%. The relationship between A. palmeri control in between cotton rows and cover crop biomass was described by a log-logistic regression model with 4530 kg ha⁻¹ providing median weed control (Bio₅₀); predicted A. palmeri control was 25, 50, and 75% from 2950, 4900, and 8600 kg ha⁻¹ cover crop biomass, respectively. However, A. palmeri plants in the cotton rows prevented yield production in the absence of herbicides. Where A. palmeri was controlled with herbicides, the highest yields occurred following rye, with lower yields following lupin/rye mixture and treatments including pea. Management of herbicide resistant weed species requires diverse management tactics; this may include high-biomass cover crops to reduce weed establishment between crop rows. However, greater research effort is needed to devise weed management options for the crop row that do not rely exclusively on the diminishing array of herbicide tools.     

Herbicide options for effective weed management in dry direct-seeded rice under scented rice-wheat rotation of western Indo-Gangetic Plains

Farmers' participatory field trials were conducted at Madhuban, and Taraori, the two participatory experimental sites/locations of the Cereal Systems Initiative for South Asia (CSISA), a collaborative project of IRRI and CIMMYT in Karnal district of Haryana, India, during Kharif (wet season) 2010 and 2011. This research aimed to evaluate preemergence (PRE) and postemergence (POST) herbicides for providing feasible and economically viable weed management options to farmers for predominant scented rice varieties. Treatments with pendimethalin PRE fb bispyribac-sodium + azimsulfuron POST had lower weed biomass at 45 days after sowing (DAS). At Madhuban, highest grain yield of scented basmati rice (3.43 t ha⁻¹) was recorded with the sequential application of pendimethalin PRE fb bispyribac-sodium + azimsulfuron POST. However, at Taraori, yields were similar with pendimethalin or oxadiargyl PRE fb bispyribac-sodium and/or azimsulfuron POST. Applying oxadiargyl by mixing with sand onto flooded field was less effective than spray applications in non-flooded field. The benefit-cost ratio of rice crop was higher with herbicide treatments at both sites as compared with the non-treated weed-free check except single PRE and POST applications and sequential application of oxadiargyl PRE fb oxadiargyl PRE. In a separate experiment conducted at Nagla and Taraori sites, scented rice cultivars' ('CSR 30′ and 'Pusa 1121′) tolerance to three rates of azimsulfuron (15, 25, and 35 g ai ha⁻¹) was evaluated over two years (2010 and 2011). CSR 30 (superfine, scented) was more sensitive to higher rates (35 g ai ha⁻¹) of azimsulfuron as compared to Pusa 1121 (fine, scented). Crop injuries were 8 and 28% in case of CSR 30; 5 and 15% in Pusa 1121 when applied with azimsulfuron 25 and 35 g ai ha⁻¹, respectively. Azimsulfuron applied at 35 g ai ha⁻¹ reduced yield in both cultivars but in CSR 30 yield reduction was twofold (11.5%) as that of Pusa 1121 (5.2%).     

Herbicide and winter flood treatments for controlling volunteer rice off-season

Field experiments were conducted to study the efficacy of 12 herbicide treatments for volunteer rice control with, or without, winter-flooding in Stuttgart and Rohwer, Arkansas, USA over two years (2012–13 and 2013–14). Herbicides were applied either in the fall or at 35 d prior to planting rice in the spring. Commercially harvested Clearfield™ long-grain inbred rice 'CL152' was used as volunteer rice seed, broadcasted and lightly incorporated in October, 2012 and 2013. 'Jupiter' (medium-grain inbred, conventional rice) was planted in May as the rice crop. Winter-flood was initiated soon after the fall herbicide treatments were applied and terminated in February. Winter-flood reduced volunteer rice germination by 34% in 2013 and by 40% in 2014. Some fall herbicide treatments, without winter flood, generally caused more injury to the rice crop planted in the spring than the winter-flooded treatments. Fall application of pyroxasulfone (0.12 kg ha⁻¹), flumioxazin (0.14 kg ha⁻¹), and sulfentrazone (0.34 kg ha⁻¹) as well as pre-plant application of pyroxasulfone (0.12 kg ha⁻¹) and 2,4-D (2.24 kg ha⁻¹), resulted in lower volunteer rice infestation, averaged over flood treatments. Pre-plant application of 2,4-D (2.24 kg ha⁻¹), sulfentrazone in the fall (0.34 kg ha⁻¹) and pyroxasulfone pre-plant (0.12 kg ha⁻¹) injured the rice crop by 20%, 23%, and 47%, respectively. Fall application of pyroxasulfone (0.12 kg ha⁻¹) followed by a lower rate of 2,4-D (1.12 kg ha⁻¹) 35 d pre-plant caused minimal (6%) crop injury and did not reduce yield. This treatment provided better volunteer rice control (73%) than pyroxasulfone alone at 0.12 kg ha⁻¹ applied in the fall (64%). To evaluate the overwintering potential of hybrid and non-hybrid volunteer seeds, these seed types were planted at three depths (0, 7.5, 15 cm) in flooded and non-flooded conditions in a buried-pot experiment at Stuttgart and Rohwer over 2 years. Winter-flood reduced rice germination by 50% in 2013–14 and 40% in 2014–15 (averaged over seed type and burial depth), after 160 d and 130 d of burial, respectively. After the winter, the viability of hybrid seed (germinable + dormant) was higher (13 and 53%) than that of non-hybrid seed (8 and 27%) in both years.     

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.     

Managing Meloidogyne incognita and Bemisia tabaci with thiacloprid in cucumber crops in China

Field trials were conducted to determine the potential use of thiacloprid for integrated Meloidogyne incognita and Bemisia tabaci B biotype control in cucumber (Cucumis sativus Linn.) in China. The following five treatments were evaluated: three thiacloprid doses (7.5, 15, and 30 kg ha⁻¹), an avermectin treatment (7.5 L ha⁻¹) and an untreated control. All thiacloprid application rates were effective for reducing the M. incognita and B. tabaci B biotype populations. M. incognita was reduced by 51.0%∼86.7% on 60th day and B. tabaci B biotype was reduced by about 37.2%∼95.3% within 21 days, respectively. In addition, greater thiacloprid doses resulted in fewer nematodes and whiteflies. Over two successive years, the cucumber plants that were treated with thiacloprid at a dose of 15 kg ha⁻¹ had the greatest plant height, plant vigor and marketable yield, which were 134.1 cm, 91, 1514.3 g plant⁻¹, respectively in 2010–2011 and 151.9 cm, 93, 1651.4 g plant⁻¹, respectively in 2011–2012. In addition, thiacloprid was superior to avermectin. The results of this study demonstrated that thiacloprid could be used in cucumber production for the integrated control of M. incognita and B. tabaci B biotype. Furthermore, a dose of 15 kg ha⁻¹ of thiacloprid was recommended for controlling nematode and whitefly populations according to the control effect and marketable cucumber yield.     

Control of broadleaf weeds with post-emergence herbicides in four barley (Hordeum spp.) cultivars

Limited information is available on control of broadleaf weeds in barley and response of barley cultivars to herbicides. Field experiments were conducted from 2007 to 2009 to evaluate post-emergence herbicides for control of broadleaf weeds in four barley cultivars. Herbicide treatments included 2,4-D sodium salt at 500 g ai ha⁻¹, carfentrazone-ethyl at three rates (15, 20 and 25 g ai ha⁻¹), and metsulfuron-methyl at 4 and 5 g ai ha⁻¹. The results suggested that density of broadleaf weeds was not affected by barley cultivars in 2007 and 2008, but it was influenced in 2009. Application of carfentrazone-ethyl or metsulfuron-methyl at all the rates was effective to reduce density and biomass of broadleaf weeds in all the years. A variable response was observed for yield attributes among barley cultivars. Barley grain yield was similar in all barley cultivars in 2007; however, higher yield was recorded in ‘DWRUB 52’ in 2008 and 2009 compared to other cultivars. All herbicide treatments were usually effective to secure higher barley yields in all the years and there was a significant interaction between barley cultivars and weed management treatments. Hand hoeing was not as effective as herbicide treatments to reduce density and biomass of broadleaf weeds; however, barley yield was usually comparable with herbicide treatments. Results also revealed that there was no significant herbicide injury on any barley cultivar during three year experiments. It is concluded that carfentrazone-ethyl and metsulfuron-methyl are additional tools for broadleaf weed control in barley. However, more research is required to evaluate efficacy of these herbicides as a tank mix partner that may increase weed control spectrum in barley.     

Spring-applied saflufenacil and imazapic provided longer lasting Euphorbia esula L. control than fall applications

Euphorbia esula is a serious weed problem in North American rangeland and pasture. Saflufenacil is a new herbicide being primarily developed for pre-plant and pre-emergence broadleaf weed control in several field crops. Imazapic is commonly used for E. esula control as a fall treatment, because spring applications do not provide satisfactory control and may cause grass injury. Field experiments were conducted during the spring and fall of 2007 and 2008 at O'Neill, Nebraska, USA with the objective to describe dose–response curves of saflufenacil and imazapic applied alone and tank-mixed in order to determine the best ratios of the two herbicides for E. esula control. The response of E. esula to saflufenacil for each imazapic treatment was evaluated in terms of plant density reduction over time, based upon DR₉₀ (effective dose that provides 90% density reduction). In general, saflufenacil or imazapic applied alone did not provide satisfactory long-term E. esula control, regardless of application timings. Overall, E. esula control increased when saflufenacil was applied with imazapic, especially as the doses of both herbicides increased. In the spring study, a 90% density reduction of E. esula for 24 months after treatment (MAT) was achieved with saflufenacil at 127 g ha⁻¹ tank-mixed with 105 g ha⁻¹ of imazapic. When applied in the fall, a significantly higher saflufenacil dose (418 g ha⁻¹) was needed in a tank-mix with 105 g ha⁻¹ of imazapic to obtain 90% density reduction for up to 23 MAT. This result indicates that spring applications of imazapic plus saflufenacil provided better E. esula control than fall treatments.     

Genetic inheritance of cytochrome P450-mediated metabolic resistance to chlorsulfuron in a multiple herbicide resistant Lolium rigidum population

Field evolved resistance to acetolactate synthase (ALS)-inhibiting herbicides in a multiple resistant Lolium rigidum population (VLR69) is known to be mainly due to enhanced rates of herbicide metabolism, likely involving cytochrome P450 monooxygenases. The present study investigates genetic inheritance of P450-mediated metabolic resistance to the ALS-inhibiting herbicide chlorsulfuron. To this end, a P450-mediated, metabolism-based resistant sub-set of VLR69 was carefully selected using plant vegetative cloning, appropriate herbicide screen test and the known P450 inhibitor malathion. Both intermediate and near-dominant nuclear-encoded phenotypic resistance traits were observed in 14 reciprocal F₁ families. The segregation of phenotypic chlorsulfuron resistance in ψ-F₂ families was analysed using genetic inheritance models involving one or two loci. The results from four ψ-F₂ families revealed complex patterns of genetic inheritance of P450-mediated metabolic resistance in genetically diverse and cross-pollinated species L. rigidum: multiple loci are likely involved and interact with herbicide rates and environmental conditions in mediating the resistance phenotype.     

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.     

Maximizing yields in rice–groundnut cropping sequence through integrated nutrient management

Integrated use of organic and inorganic fertilizers can improve crop productivity and sustain soil health and fertility. The present research was conducted to study the effects of application of green manures [sesbania (Sesbania aculeate Poiret) and crotalaria (Crotalaria juncea L.)] and farmyard manure on productivity of rice (Oryza sativa L.) and its residual effects on subsequent groundnut (Arachis hypogaea L.) crop. Rice and groundnut crops were grown in sequence during rainy and post-rainy seasons with and without green manure in combination with different fertilizer and spacing treatments under irrigated conditions. The results showed that application of green manures sesbania and crotalaria at 10 t ha⁻¹ to rice compared to no green manure application significantly increased grain yield of rice by 1.6 and 1.1 t ha⁻¹, and pod yields of groundnut crop succeeding rice by 0.25 and 0.16 t ha⁻¹, respectively. There was no significant difference between the application of crotalaria or farmyard manure at 10 t ha⁻¹ on grain yields of rice, but pod yields of subsequent groundnut crop were greater with application of green manure. There was no significant effect of different spacing 20×15,15×15,15×10 cm² (333 000; 444 000; 666 000 plant ha⁻¹, respectively) on grain yield of rice. Pod yields of groundnut were significantly greater with closer spacing 15×15 cm² (444 000 plants ha⁻¹) as compared to spacing of 30×10 cm² (333 000 plants ha⁻¹). Maximum grain of rice was obtained by application of 120:26:37 kg NPK ha⁻¹ in combination with green manures, whereas maximum pod yield of groundnut was obtained by residual effect of green manure applied to rice and application of 30:26:33 kg NPK ha⁻¹ in combination with gypsum applied to groundnut crop.     

Yield and agronomic performance of maize hybrids resistant to the maize weevil Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae)

This study evaluated improved maize hybrids (Zea mays L.) with varying level of resistance to the maize weevil, Sitophilus zeamais Motschulsky, for yield and agronomic traits for two seasons. A total of 22 improved maize hybrids and three commercial standards were tested. Out of the 22 tested, two hybrids CKPH08035 (7.4–9.9 t ha⁻¹) and CKPH08039 (7.3–9.8 t ha⁻¹) significantly out yielded the commercial standards WH505 (8.8 t ha⁻¹) and BH140 (5.5 t ha⁻¹). In addition to yield, the improved hybrids also possess desirable traits including good plant height, good plant and ear aspects and good husk cover. The hybrid CKPH08004 had the lowest Dobie index of susceptibility and was regarded as resistant to S. zeamais. Weevils fed with the resistant hybrids produced low numbers of F₁ generation weevils, had a high median developmental time and a low percentage of grain damage and grain weight loss. An increasing number of F₁ generation resulted in an increasing grain damage and grain weight loss. We found an inverse relationship between the susceptibility index and percent mortality. However, the numbers of F₁ generation, percent grain damage and grain weight loss were positively correlated with the susceptibility index. The use of resistant maize hybrids should be promoted in managing S. zeamais in stored maize under subsistence farming conditions in Africa.     

Evaluation of potential biocides for control of the earthworm Eukerria saltensis (Oligochaeta: Ocnerodrilidae), a pest of rice in southern Australia

The earthworm Eukerria saltensis can cause severe crop establishment problems in aerially sown rice grown on heavy clay soils in southern Australia. Damage occurs indirectly through destabilization of the topsoil, increased water turbidity, and mobilization of soil nutrients into the water column which leads to increased algal growth. We investigated the possibilities for chemical control of E. saltensis using laboratory bioassays and a series of field trials involving either the use of enclosures in flooded crops or soil incorporation of pesticides into rice fields during fallow periods or shortly before flooding. The four most toxic compounds in 7 day soil/water laboratory bioassays were carbofuran, acetamiprid, bendiocarb and lambda-cyhalothrin which provided corrected mortalities of 86–100% at 2 mg a.i. L⁻¹. Other compounds that showed some level of efficacy (corrected mortality >20% at one or more rates) were imidacloprid, esfenvalerate, thiacloprid, niclosamide and alpha-cypermethrin. Twenty-six of the 38 pesticides evaluated failed to produce mean corrected mortalities >6% at application rates of up to 2 mg a.i. L⁻¹. Eight trials were conducted in flooded rice crops using small stainless steel enclosures and carbofuran, thiodicarb, niclosamide and bendiocarb at rates of 1 and 2 kg a.i. ha⁻¹. Trials were assessed 8–14 days after chemical application. None of these treatments produced a statistically significant decrease in Eukerria biomass, although consistent downward trends in response to higher treatment rates were evident in 2 trials (one with carbofuran and one with bendiocarb). Three trials with liquid pesticides watered into fallow rice fields were conducted with carbofuran (0.5, 1.0 and 5.0 kg a.i. ha⁻¹) and thiodicarb (0.94 and 1.87 kg a.i. ha⁻¹) however only the 5.0 kg a.i. ha⁻¹ carbofuran treatment provided significant (P < 0.05) levels of control. Preflood soil applications of liquid carbofuran, thiodicarb and niclosamide (2 kg a.i. ha⁻¹), granular carbofuran and granular ethoprophos (0.5–2 kg a.i. ha⁻¹) also did not provide statistically significant levels of control, although the 2 kg a.i. ha⁻¹ liquid and granular carbofuran treatments did provide moderate levels of suppression (49–84%). Although further field trials with compounds such as acetamiprid and lambda-cyhalothrin may prove valuable, our results suggest chemical control of E. saltensis may be difficult to achieve with environmentally acceptable pesticides applied at economically viable rates. Cultural approaches such as appropriate crop rotations and landforming to ensure uniformly shallow water should continue to form the basis of Eukerria management programs.     

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.     

Rice straw mulching and nitrogen response of no-till wheat following rice in Bangladesh

Wheat (Triticum aestivum L.) cultivation in no-till soil of a postrice harvest field utilizes residual soil moisture and reduces the time period from rice harvest to wheat seeding in intensive rice-wheat cropping systems. Some of the major constraints in no-till wheat production are high weed infestation, poor stand establishment due to rapid drying of topsoil and low nitrogen use efficiency (NUE). A field experiment was conducted at the research farm of the Wheat Research Centre, Dinajpur, Bangladesh, for two consecutive years to overcome those constraints, to evaluate rice straw as mulch, and to determine the optimum application rate of nitrogen (N) for no-till wheat. The treatments included 12 factorial combinations of three levels of mulching: no mulch (M₀), surface application of rice straw mulch at 4.0 Mg ha⁻¹ that was withdrawn at 20 days after sowing (M₁), the same level of mulch as M₁ but allowed to be retained on the soil surface (M₂), and four nitrogen levels (control 80, 120 and 160 kg ha⁻¹). Rice straw mulching had a significant effect on conserving initial soil moisture and reducing weed growth. Root length density and root weight density of wheat were positively influenced both by straw mulching and N levels. N uptake and apparent nitrogen recovery of applied N fertilizer were higher in mulch treatments M₁ and M₂ as compared to M₀. Also mulch treatment of M₁ and M₂ were equally effective at conserving soil moisture, suppressing growth of weed flora, promoting root development and thereby improved grain yield of no-till wheat. N application of 120 kg ha⁻¹ with straw mulch was found to be suitable for no-till wheat in experimental field condition.