Total Weed Density Research Articles

Optimizing herbicidal efficacy of glyphosate isopropylamine salt through ammonium sulphate as surfactant in oil palm ( Elaeis guineensis) plantation in a rainforest area of Nigeria

A randomized complete block field trial was conducted over 2 years to evaluate the herbicidal efficacy of glyphosate isopropylamine salt (Roundup ®) applied singly at 1.41 kg a.e. ha −1 or in combination with ammonium sulphate (AMS) as surfactant at 0.5, 1.0, 1.5, and 2.0% (wt/v) in a 5-year old oil palm plantation of the Federal University of Technology, Akure located in the rainforest vegetation zone of Nigeria. Assessment of herbicidal efficacy based on the Henderson-Tilton formula indicated that glyphosate applied singly or in combination with varying concentrations of AMS proved highly effective in controlling most of the grasses and broadleaved weeds prevalent in the experimental plots. Herbicidal efficacy on total weed density, weed fresh weight as well as on weed dry weight was found to increase in the order of increasing concentration of AMS. Regressing percentage herbicidal efficacy ( Y) against increasing concentration levels of AMS ( X) indicated significant ( P ⩽ 0.001 ) positive relationships with an average correlation coefficient ( r) of +0.95 in both years. These results confirm the potential of AMS as an effective surfactant that can be exploited in glyphosate-based weed management schemes in the sub-humid tropical environment.

Relationships Between Soil Characteristics and Weeds

Information technologies, such as the global positioning system and geographic information system, provide new opportunities for improving the efficiency of weed management, thereby resulting in a reduction in financial and environmental costs. Thus, an evaluation of data of systematic weed surveys carried out repeatedly at locations identified by geographical coordinates allows the establishment of relationships between weed associations and soil properties. Our quantitative survey targeted a 53‐ha agricultural field at Baracska, Hungary, with a total of 122 sampling sites. Soil properties (pH, texture, organic carbon, humus, and macro‐ and microelement contents [altogether 24 parameters]) were determined and weeds (frequency and density for 27 species) were recorded at the sampling sites. A distinct negative association between the crop yield (tightly linked to levels of nitrogen, phosphorus, and potassium fertilizers in the soil) and the total weed density at the sampling sites was demonstrated by principal component analysis of our data, indicating a good management of the project area that successfully increased the crop plant's competitiveness with weeds.

Improving the Management of Dicot Weeds in Peanut with Narrow Row Spacings and Residual Herbicides

Narrow row spacings in peanut (Arachis hypogaea L.) production suppress spotted wilt and promote rapid canopy closure, improving competitiveness with weeds. Trials were conducted from 1999 to 2001 to determine if weed suppression in narrow row spacings, in conjunction with new residual herbicides supplemented with nonresidual herbicides, improved weed control and reduced herbicide use. Within each row spacing were three levels of weed management using the residual herbicides imazapic {(±)‐2‐[4,5‐dihydro‐4‐methyl‐4‐(1‐methylethyl)‐5‐oxo‐1H‐imidazol‐2‐yl]‐5‐methyl‐3‐pyridinecarboxylic acid}, diclosulam [N‐(2,6‐dichlorophenyl)‐5‐ethoxy‐7‐fluoro[1,2,4]triazolo[1,5‐c]pyrimidine‐2‐sulfonamide], sulfentrazone {N‐[2,4‐dichloro‐5‐[4‐(difluoromethyl)‐4,5‐dihydro‐3‐methyl‐5‐oxo‐1H‐1,2,4‐triazol‐1‐yl]phenyl]methanesulfonamide}, and flumioxazin {2‐[7‐fluoro‐3,4‐dihydro‐3‐oxo‐4‐(2‐propynyl)‐2H‐1,4‐benzoxazin‐6‐yl]‐4,5,6,7‐tetrahydro‐1H‐iso‐indole‐1,3(2H)‐dione}. Minimal weed management was ethalfluralin [N‐ethyl‐N‐(2‐methyl‐2‐propenyl)‐2,6‐dinitro‐4‐(trifluoromethyl)ben‐zenamine] alone for annual grass control. Moderate weed management was ethalfluralin, a residual herbicide, and 2,4‐DB [4‐(2,4‐dichlorophenoxy)butanoic acid]. Intense weed management was the moderate system for each residual herbicide, plus paraquat (1,1′‐dimethyl‐4,4′‐bipyridinium ion), bentazon [3‐(1‐methylethyl)‐(1H)‐2,1,3‐benzothiadiazin‐4(3H)‐one 2,2‐dioxide], and acifluorfen {5‐[2‐chloro‐4‐(trifluoromethyl)phenoxy]‐2‐nitrobenzoic acid}. Peanut seeded in narrow rows had quicker canopy closure than peanut seeded in wide rows. Densities of individual weeds species were not affected, although total weed densities were lower in narrow rows than wide rows. Narrow row spacings with residual herbicides did not reduce herbicide use compared with wide row spacings. Yields were 12% greater in narrow rows than wide rows. While narrow row spacings did not affect individual weed species and reduce herbicide use, narrow row spacings supplement herbicides by reducing the total number of weed escapes.

Winter Wheat Cultivar Characteristics Affect Annual Weed Suppression

Thirteen hard red winter wheat cultivars were evaluated for their ability to suppress summer annual weeds in grain production systems near North Platte, NE, from 1993 through 1997. ‘Turkey’, a 125-yr-old landrace selection, suppressed both broadleaf and grass weeds more than other cultivars. Some relatively new cultivars, such as ‘Arapahoe’, ‘Jules’, ‘Pronghorn’, and ‘Vista’ suppressed summer annual grasses almost as well as Turkey. Total weed density was negatively correlated with number of winter wheat stems/m2, mature winter wheat height, and lodging. Weed density after wheat harvest was positively correlated with delay in winter wheat seeding date and was negatively correlated with precipitation 0 to 30 d after winter wheat seeding, during tillering, tillering to boot stage, and heading to maturity stage. Mean air temperature 0 to 30 d after wheat seeding was positively correlated with weed density. In the spring, weed density was positively correlated with temperatures during the tillering stage, tillering to boot stage, and heading to maturity stage. Stinkgrass and witchgrass densities were positively correlated with severity of wheat leaf rust. The highest grain-producing cultivars included three medium height cultivars ‘Alliance’, Arapahoe, and ‘Niobrara’. Alliance wheat produced 53% more grain than Turkey, and the other two produced 43% more grain.

EFFECT OF NO-TILLAGE AND RYE MULCH ON OCCURRENCE OF WEEDS AND APHIDS AND ON YIELDS OF CABBAGE, CARROT AND RED BEET

EFFECT OF NO-TILLAGE AND RYE MULCH ON OCCURRENCE OF WEEDS AND APHIDS AND ON YIELDS OF CABBAGE, CARROT AND RED BEET

The Effect of Natural Mulches on Crop Performance, Weed Suppression and Biochemical Constituents of Catnip and St. John's Wort

Because of expanding markets for high-value niche crops, opportunities have increased for the production of medicinal herbs in the USA. An experiment was conducted in 2001 and 2002 near Gilbert, IA, to study crop performance, weed suppression, and environmental conditions associated with the use of several organic mulches in the production of two herbs, catnip (Nepeta cataria L.) and St. John's wort (Hypericum perforatum L. 'Helos'). Treatments were arranged in a completely randomized design and included a positive (hand-weeded) control, a negative (nonweeded) control, oat straw, a flax straw mat, and a nonwoven wool mat. Catnip plant height was significantly greater in the oat straw than the other treatments at 4 wk through 6 wk in 2001; at 4 to 8 wk in 2002, catnip plant height and width was significantly lower in the negative control compared with the other treatments. Catnip yield was significantly higher in the flax straw mat than all other treatments in 2001. In 2002, St. John's wort yields were not statistically different in any treatments. All weed management treatments had significantly fewer weeds than the non-weeded rows in 2002. Total weed density comparisons in each crop from 2 yr showed fewer weeds present in the flax straw and wool mat treatments compared with positive control plots. There was no significant weed management treatment effect on the concentration of the target compounds, nepetalactone in catnip and pseudohypericin-hypericin in St. John's wort, although there was a trend toward higher concentrations in the flax straw treatment.

The Effect of Natural Mulches on Crop Performance, Weed Suppression and Biochemical Constituents of Catnip and St. John's Wort

Because of expanding markets for high-value niche crops, opportunities have increased for the production of medicinal herbs in the USA. An experiment was conducted in 2001 and 2002 near Gilbert, IA, to study crop performance, weed suppression, and environmental conditions associated with the use of several organic mulches in the production of two herbs, catnip (Nepeta cataria L.) and St. John's wort (Hypericum perforatum L. ‘Helos’). Treatments were arranged in a completely randomized design and included a positive (hand-weeded) control, a negative (nonweeded) control, oat straw, a flax straw mat, and a nonwoven wool mat. Catnip plant height was significantly greater in the oat straw than the other treatments at 4 wk through 6 wk in 2001; at 4 to 8 wk in 2002, catnip plant height and width was significantly lower in the negative control compared with the other treatments. Catnip yield was significantly higher in the flax straw mat than all other treatments in 2001. In 2002, St. John's wort yields were not statistically different in any treatments. All weed management treatments had significantly fewer weeds than the non-weeded rows in 2002. Total weed density comparisons in each crop from 2 yr showed fewer weeds present in the flax straw and wool mat treatments compared with positive control plots. There was no significant weed management treatment effect on the concentration of the target compounds, nepetalactone in catnip and pseudohypericin–hypericin in St. John's wort, although there was a trend toward higher concentrations in the flax straw treatment.

Impact of Rye Cover Crop and Herbicides on Weeds, Yield, and Net Return in Narrow-Row Transgenic and Conventional Soybean (Glycine max)1

A field study was conducted during 1999, 2000, and 2001 at Stoneville, MS, on a Dundee silty clay loam to determine the impact of a rye cover crop with one or two postemergence (POST) herbicide applications on weed control, yield, and net return in narrow-row glyphosate-resistant, glufosinate-resistant, and conventional soybean systems. Cover crop systems included no–cover crop conventional tillage (CT), no–cover crop no-tillage (NT), and rye NT, all with early POST (EPOST), EPOST followed by late POST (LPOST), and no-herbicide weed management. Weed control and net return among glyphosate-resistant, glufosinate-resistant, and conventional soybean systems were similar. One POST ($111/ha) application of herbicides was more profitable than two POST ($79/ha) applications regardless of soybean cultivar and cover crop system. Rye residue reduced total weed density by 9 and 27% and biomass by 19 and 38% compared with no–cover crop CT and NT, respectively. In the rye cover crop, input costs were higher because of the additional cost of seed, planting, and rye desiccation. The additional cost resulted in a lower net return with the rye cover crop ($29/ha) compared with the no–cover crop CT ($84/ha) or NT ($87/ha) system, even though soybean yield in the rye cover crop system was comparable to that from the no–cover crop CT and NT systems. These results showed that because of additional cost, rye cover crop–based soybean production was less profitable compared with existing no–cover crop–based production systems.Nomenclature: Acifluorfen; bentazon; chlorimuron; clethodim; glufosinate; glyphosate; barnyardgrass, Echinochloa crus-galli (L.) Beauv. #3 ECHCG; browntop millet, Brachiaria ramosa (L.) Stapf # PANRA; hemp sesbania, Sesbania exaltata (Raf.) Rydb. ex A. W. Hill # SEBEX; pitted morningglory, Ipomoea lacunosa L. # IPOLA; prickly sida, Sida spinosa L. # SIDSP; sicklepod, Senna obtusifolia (L.) Irwin and Barneby # CASOB; smooth pigweed, Amaranthus hybridus L. # AMACH; rye, Secale cereale L. ‘Elbon’; soybean, Glycine max (L.) Merr. ‘DP 3588’, ‘DP 5806 RR’, ‘A 5547 LL’.Additional Index words: Conventional tillage, herbicide, integrated weed management, mulch, net return, no-tillage, transgenic soybean, weed biomass, weed density.Abbreviations: CT, conventional tillage; EPOST, early postemergence; LPOST, late postemergence; NT, no-tillage; POST, postemergence; WAP, weeks after planting.

Going Organic Changes Weed Population Dynamics

Organic agriculture is growing in importance worldwide. In the United States, the rate of increase of organic growers was estimated at 12% in 2000. However, many producers are reluctant to undertake the organic transition because of uncertainty of how organic production will affect weed population dynamics and management. The organic transition has a profound impact on the agroecosystem. Changes in soil physical and chemical properties during the transition often impact indirectly insect, disease, and weed dynamics. Greater weed species richness is usually found in organic farms but total weed density and biomass are often smaller under the organic system compared with the conventional system. The improved weed suppression of organic agriculture is probably the result of combined effects of several factors including weed seed predation by soil microorganisms, seedling predation by phytophagus insects, and the physical and allelopathic effects of cover crops.

Weed control efficacy of different post-emergence herbicides in mungbean (Vigna radiata) in hot arid regions

A field experiment was carried out during the rainy (Kharif) season of 2017 to 2019 at Jodhpur, Rajasthan to find the herbicide effective for mungbean [Vigna radiate (l.) R. Wilczek] in arid regions. The treatments comprised pre-emergence and post-emergence herbicides along with hand-weeding, weed-free, and unweeded. Results re- vealed that, weed-control treatments brought about a 48.973.3% reduction in total weeds density and 46.8 80.1% reduction in dry weed weight at harvesting as compared to unweeded control. Post-emergence application of propaquizafop + imazethapyr @125 g a.i./ha, being at par to other imazethapyr treatments and hand-weeding, resulted in significantly lowest total weed density (24.1/m2) and total weed dry weight (66.6 g/m2) with highest weed-control efficiency (80.1%) and showed the lowest values of weed index (18.4). Moreover, post-emergence application of clodinafop-propargyl + sodium acifluorfen @ 312.5 g a.i./ha also exhibited weed-control efficiency (73.2%) and weed index (21.0) at par with other imazethapyr treatments and hand-weeding. Propaquizafop + imazethapyr @ 125 g a.i./ha, being at par with clodinafop-propargyl + sodium acifluorfen @ 312.5 g a.i./ha and weed-free recorded significantly higher crop dry weight (542 g/m2), pods/plant (24.7), 1,000-seed weight (55.2 g), seed yield (840 kg/ha), and stover yield (2,563 kg/ha). Application of propaquizafop + imazethapyr @125 g a.i./ha also registered highest gross returns (`58.08 103/ha) and net returns (`42.58 103/ha) which were comparable to returns recorded under clodinafop-propargyl + sodium-acifluorfen @ 312.5 g a.i./ha. Propaquizafop + imazethapyr @ 125 g a.i./ha being comparable with clodinafop-propargyl + sodium-acifluorfen @ 312.5 g a.i./ha was also found superior in terms of impact assessment indices.

Influence of integrated weed-management practices on productivity and profitabil- ity of wet-seeded rice (Oryza sativa)

A field experiment was conducted at Coimbatore during 2000-2001 and 2001-2002 to study the effect of seeding methods (surface and anaerobic), in-situ incorporation of dhaincha (Sesbania aculeata) and time of pretilachlor-plus application on productivity and profitability of wet-seeded rice (Oryza sativa L.). Treatments in- cluded two seeding methods, viz. surface wet seeding and anaerobic seeding, with two intercropping levels, viz. sole rice and rice + dhaincha; and four weed-control treatments, viz. pretilachlor-plus @ 0.30 kg/ha 2 days after sowing (DAS) followed by (fb) 1 hand-weeding (HW) at 45 DAS, pretilachlor-plus @ 0.30 kg/ha 5 DAS fb 1 hand- weeding at 45 DAS, hand-weeding twice at 20 and 45 DAS, and unweeded check. Surface and anaerobic drill seeding were comparable in terms of weed density, growth and productivity of rice. Conjoint cropping of rice + dhaincha and incorporation of the latter at 37 DAS using con0 weeder proved better in terms of reducing the total weed density, increasing the crop growth, productivity (5.1 tlha) and weed-smothering efficiency (25.5%) of wet- seeded rice. Pre-emergence application of pretilachlor-plus @ 0.30 kg/ha on 2 DAS + hand-weeding at 45 DAS registered lower total weed density (53.6/m2) and higher weed-control efficiency, as well as markedly improved the growth and yield parameters and grain yield (5.6 ttha). Anaerobic seeding, rice + dhaincha and pretilachlor-plus at 2 DAS gave better profit (Rs 13,892lha). It was concluded that anaerobic seeding, dual cultivation of rice + dhaincha and pretilachlor plus @ 0.30 kg /ha on 2 DAS + hand-weeding at 45 DAS is an efficient method for im- proving weed control, productivity and profitability of wet-seeded rice.

Weed dynamics and productivity of chickpea (Cicer arietinum) under pre- and post-emergence application of herbicides

A field study was conducted during the winter (rabi) season of 201113 at Kanpur, Uttar Pradesh, to assess the performance of post-emergence application of quizalofop-ethyl in combination with pre-emergence application of pendimethalin on chickpea (Cicer arietinum L.). The treatments comprised 5 doses of quizalofop-ethyl (50, 75, 100, 125 and 150 g/ha) in combination with pendimethalin @ 1.25 kg/ha, and pendimethalin @ 1.25 kg/ha fol- lowed by (fb) manual weeding. The broad-leaf weeds like Coronopus dedymus, Melilotus officinalis and Chenopo- dium album were dominant. In case of grassy weeds, Phalaris minor was the most dominant weed. Significant re- duction in total weed density and weed dry weight was recorded under application of pendimethalin @ 1.25 kg/ha fb quizalofop-ethyl @ 100150 g/ha and pendimethalin @ 1.25 kg/ha fb manual weeding. Weed-control indices also showed improvement under these treatments. The poor crop-weed competition due to effective control of weeds under these treatments resulted in higher nodulation and yield. Similarly, higher net returns and benefit: cost ratio were recorded in pendimethalin @1.25 kg/ha fb quizalofop-ethyl @ 125 g/ha.

Conservation tillage and weed management for improving productivity, nutrient uptake and profitability of soybean (Glycine max) grown after wheat (Triticum aestivum)

A field experiment was conducted during 2010 and 2011 at New Delhi to study the performance of soybean [ Glycine max (L.) Merrill] grown after wheat [ Triticum aestivum (L.) emend Fiori & Paol] under four tillage and crop establishment practices, viz. conventional tillage (CT)flat-bed, CTraised-bed, zero tillage (ZT)flat-bed and ZT raised-bed along with four weed management options, viz. unweeded control, pendimethalin @ 0.75 kg/ha as pre- emergence (PE) + hand weeding (HW), pendimethalin @ 0.75 kg/ha as PE + imazethapyr @ 75 g/ha as post- emergence (POE), and wheat straw mulch @ 5 t/ha + imazethapyr @ 75 g/ha as POE. Total weed density and dry matter was comparatively higher under ZT than CT, but adoption of chemical + cultural weed control methods led to 79.5-82.5% weed control efficiency. Seed yield of soybean was equal under CTraised-bed, CTflat-bed and ZTraised-bed, which was 11.7% more than ZT flat-bed. Similarly, pendimethalin + HW, pendimethalin + imazethapyr, and wheat straw mulch + imazethapyr resulted in almost similar weed control, and thus gave compa- rable seed yield, which was 39.142.7% higher than unweeded control. Weed and crop biomass followed oppo- site trends, and the seed yield decreased by 0.2 t/ha for an increase of 100 g/m2 in weed dry weight. Concentra- tion of N, P and K in seed and stover of soybean was not influenced but the uptake was highest under CTraised- bed, which was on par with ZTraised-bed. Nutrient uptake was highest under pendimethalin + HW, which was significantly higher than under pendimethalin + imazethapyr, and wheat straw mulch + imazethapyr. The highest net benefit:cost was under ZTraised-bed and pendimethalin + imazethapyr or pendimethalin + HW, followed by CTraised-bed under the same weed control treatments. It was concluded that soybean can be grown under per- manent raised-bed with pre- and post-emergence herbicides for realizing higher productivity and profitability.

Effect of nitrogen and weed management on seed productivity of forage pearl millet (Pennisetum glaucum)

A field experiment was conducted during rainy (Kharif) season of 2015 to find out the effect of different nitrogen levels and weed control methods on seed productivity of forage pearl millet [Pennisetum glaucum (L.) B.] The re- sult indicated that increase in nitrogen level lowered the total weed density and weed dry-weight over control and significantly improved yield attributes and seed yield of forage pearl millet.There was reduction of 34.7 and 17.2 and 17.1 and 15.2% in seed and stover yield respectively at 0 and 50 kg N/ha compared to 100 kg N/ha. Density of Cyperus rotundus was significantly lower in pendimethalin [pre-emergence (PE) + halosulfuron [Post-emer- gence (POE) and atrazine (PE) + halosulfuron (POE) at 25 DAS whereas pendimethalin (PE) + 1 hand-weeding and atrazine (PE) + 1 (HW) at 25 days after sowing (DAS) effectively controlled broad leaf weeds. The treatments, viz. pendimethalin (PE) + 1 HW at 25 DAS and atrazine (PE) + 1 HW at 25 DAS recorded lower weed density and weed dry-weight at 40 DAS with lower weed index and higher weed-control efficiency. There was reduction of 41.6 and 38.2% in seed yield in weedy check compared to pendimethalin (PE) + 1 HW at 25 DAS and atrazine (PE) + 1 HW at 25 DAS respectively. Maximum net returns and B: C ratio was recorded with pendimetalin (PE) + 1 HW fol- lowed by atrazine (PE) + 1HW.

Effect of weed and fertilizer management on weed control and productivity of onion (Allium cepa)

An experiment was conducted to examine the effect of weed management and plant nutrition practices on weed biomass, growth parameters and bulb yield of onion ( Allium cepa L.). Weed management practices included alone application of herbicides, viz. pendimethalin, oxyfluorfen and fluazipop-p-butyl, their combination with hand weeding, weed free and weedy check. The crop was fertilized with three levels viz., 75% RDF, RDF (100:50:50 NPK kg/ha) and 125% RDF. The results indicated that weed management and fertilizer levels had a significant ef- fect on weed population dynamics and onion bulb crop. The total weed density decreased significantly with appli- cation of pendimethalin 1 kg/ha or oxyfluorfen 0.24 kg/ha + one hand weeding at 40 days after transplanting (DAT) during both the seasons of investigation. Echinochloa ssp., Trianthema portulacastrum, Digera arvensis Forsk. Physalis minima L. and Cynodon dactylon (L.) Pers. were found as major weeds in the crop. Higher onion bulb yield (38.0 t/ha) was recorded with pendimethalin 1 kg/ha + one hand weeding at 40 DAT. The increase in yield was 83.7% compared to the yield obtain in weedy check. Increasing level of fertilizer applications increased the to- tal biomass of grassy and broad leaves weeds. Application of 125% RDF significantly improved bulb yield and in- crease in yield was 19.4 and 10.5 % over 75% RDF and RDF respectively. On the basis of interaction, combina- tion of pendimethalin 1 kg/ha fb 1 hand weeding at 40 DAT and 100 % RDF was most productive (39.8 t/ha) and profitable (Net return `2,69,422/ha and benefit: cost ratio 7.85).

Productivity of winter (rabi) onion (Allium cepa) as influenced by sole and sequential application of herbicides

A field experiment was conducted during the winter (rabi) seasons of 201415 and 201516 to study the effect of sole and sequential application of different herbicides on weed control in onion (Allium cepa L.). Sequential ap- plication of pendimethalin @ 750 g/ha at 3 days after transplanting (DAT) + oxyfluorfen @ 100 g/ha at 20 DAT controlled the grasses, sedges and broad-leaf weeds most efficiently and was at par with oxadiargyl @ 90 g/ha at 3 DAT + oxyfluorfen @ 100 g/ha at 20 DAT. Weed competition resulted in about 54.8% yield loss of onion in weedy check plot. The lowest values of total weed density (18.6/m 2), dry weight (6.8 g/m 2), weed index (6.2%) and the highest values of weed control efficiency (89.2%), bulb yield (21.89 t/ha) and benefit: cost ratio (2.84) were registered with sequential application of pendimethalin @ 750 g/ha at 3 DAT + oxyfluorfen @ 100 g/ha at 20 DAT. In weedy check, weeds removed 23.9 kg N, 3.8 kg P and 27.6 kg K/ha.

Weed management in rabi groundnut (Arachis hypogaea) for Konkan region of Maharashtra

A field experiment was conducted at Agricultural Research Station, Shirgaon, Tal. Dist. Ratnagiri (MS) on the lateritic soil during rabi 2009-12 to evaluate post emergence herbicides in rabi groundnut (Arachis hypogaea L.). The experiment comprised of twelve treatments of weed control replicated thrice in Randomized Block Design (RBD). The various weeds observed in groundnut field during rabi season were Digitaria sanguinalis (L.) Scoup, Eleusine indica (L.) Gaertn., Echinochloa crusgalli (L.) Beauv. and Cyperus difformis (L.) among the narrow leaved weeds were more rampart. The broad leaved weeds like Leucas aspera Spreng., Cleome viscose (L.), Amaranthus viridis (L.), Euphorbia hirta (L.), Eclipta prostrate (L.), Physalis minima (L.), Alternenthera sessils (L.), and Convolvulus arvensis (L.) marked their presence in good numbers. Post emergence application of quizalofop- p-ethyl @ 50 g a.i./ha along with pre emergence pendimethalin @ 1.0 kg a.i./ha gave significantly lower total weed density (52.1/m2), weed dry weight (12.1g/m2) and higher weed control efficiency (91.3%), which was at par with post emergence application of imazethapyr @ 75 g a.i./ha along with pre emergence application of pendimethalin @ 1.0 kg a.i./ha. Application of quizalofop-p-ethyl @ 50 g a.i./ha as a post emergence along with pre emergence application of pendimethalin @ 1 kg a.i./ha significantly increased the pod yield, haulm yield and kernel yields (2.57, 2.83 and 1.90 t/ha, respectively) and was at par with post-emergence application of imazethapyr @ 75 g a.i./ha in groundnut. Highest net returns ( 29,700/ha) and benefit: cost ratio (1:1.68) were obtained with application of pre-emergence application of pendimethalin @ 1 kg a.i./ha along with one hand weed- ing at 30 to 35 DAS followed by combination of pre-emergence application of pendimethalin with quizalofop-p- ethyl @ 50 g a.i./ha ( 26,551/ha and 1:1.55, respectively) and with imazethapyr @75g a.i./ ha ( 23,499/ha and 1:1.47, respectively).

Effect of application of post-emergence herbicides at different levels of available soil moisture content in irrigated wheat (Triticum aestivum)

A field experiment was conducted during the winter ( rabi) season of 200809 and 200910 at Jabalpur, Madhya Pradesh, to study the effect of post emergence herbicides (isoproturon @ 0.75 kg/ha, clodinafop @ 0.06 kg/ha and clodinafop followed by 2,4-D @ 0.5 kg/ha) against weeds under different available soil-moisture regimes (ASM) (100%, 95%, 90%, 85% and 80%) on weeds, nutrient depletion by weeds and uptake by crop and the grain yield and economics of wheat [ Triticum aestivum (L.) emend. Fiori & Paol]. Herbicidal application at 100% available soil moisture resulted in significantly lowest weed density and total dry weight of weeds during both the years and hence lowered the nutrient depletion by weeds and increased the uptake by the crop. The presence of 100% available soil moisture registered significantly higher grain yield of wheat (6.1 t/ha) and proved significantly supe- rior to 85 and 80% ASM. Post-emergence application of clodinafop followed by 2,4-D caused significantly lowest total weed density (7.8/m2) and dry weight (5.1 g/m2), which resulted in production of higher grain yield as well as net monetary returns over isoproturon, clodinafop and weedy check. Maximum benefit: cost ratio was obtained with 100% available soil moisture along with application of isoproturon.

Effects of Soil Amendments on Herbicide Efficacy and Leaching1

Field experiments were conducted in 1997 and 1998 to evaluate the effects of gypsum (GYP), anionic polyacrylamide (PAM), and dolomitic lime (DL) on atrazine and acetochlor efficacy and leaching. Surface-applied treatments of PAM (20 kg/ha), GYP (1,000 kg/ha), PAM + GYP (20 + 1,000 kg/ha), and DL (1,000 kg/ha), plus an unamended control, were evaluated at two locations, i.e., West Lafayette, IN (sites A and B) and Bourbon, IN (sites C and D). Sites A and C were evaluated in 1997 and 1998, while sites B and D were evaluated only in 1998. West Lafayette experiments were on a Raub silt loam (fine-silty, mixed, mesic, aquic Arguidolls) soil, and Bourbon experiments were on a Rensselaer silt loam (fine-silty, mixed, mesic, Typic Arguidolls) soil. Atrazine and acetochlor efficacy was reduced on GYP-amended plots at site A in 1997 where the total weed density was significantly higher (P = 0.10) compared with all other treatments. The results were not significant at this site in 1998; however, weed density tended ...

Tillage intensity and crop rotation affect weed community dynamics in a winter wheat cropping system

Development of improved weed manage ment systems requires more knowledge on how various weed species respond to changing agronomic practices. A long-term study was conducted to determine weed population responses to various tillage intensities and crop rotations in a winter wheat (Triticum aestivum L.) dominated cropping system. Weed density and species composition differed with tillage, rotation, year, and date of sampling within years. Weed community dynamics were most affected by year-to-year differences in environmental conditions, followed by crop rotation, and then tillage intensity. Russian thistle (Salsola iberica Sennen & Pau) and kochia [Kochia scoparia (L.) Schrad.] densities increased in years of low rainfall and above average temperatures. Winter annual weeds such as downy brome (Bromus tectorum L.) and flixweed [Descurainia sophia (L.) Webb ex Prantl], as well as the perennial weed dandelion (Taraxacum officinale Weber in Wiggers), increased in years where higher than average rainfall was received in fall or early spring. Continuous winter wheat facilitated a dense downy brome infestation to develop over time. Trifluralin is not efficacious on stinkweed (Thlaspi arvense L.) or Canada thistle [Cirsium arvense (L.) Scop.] and its use in canola resulted in an increase in these species in a winter wheat-canola rotation. Total weed densities were often greater in zero tillage than in either minimum or conventional tillage. Russian thistle, downy brome, kochia, and redroot pigweed (Amaranthus retroflexus L.) were associated with zero tillage while wild buckwheat (Polygonum convolvulus L.), lamb’s-quarters (Chenopodium album L.), flixweed, and wild mustard (Sinapis arvensis L.) were associated with conventional tillage. Perennials such as dandelion and perennial sowthistle (Sonchus arvensis L.) were associated with zero tillage but Canada thistle was associated with conventional tillage. Information will be utilized to implement more effective weed management programs in winter wheat production systems. Key words: Conservation tillage, fallow, multivariate analyses, weed populations, weed shifts, zero tillage