Effect of Weeding Regime and Plant Spacings on Weed Growth and Performance of Transplanted Rice

Abstract

Effect of weeding regime (unweeded control, hand weeding once, 4 weeks after transplanting (w.a.t.) and hand weeding twice, 4 and 7 w.a.t.) and different plant spacings (20 × 2.5 cm, 20 × 5 cm, 20 × 10 cm, 20 × 15 cm and 20 × 20 cm) on weed growth and performance of transplanted rice were tested in a split-plot design. Grain yield and number of panicles were not significantly different in both weeding treatments from the unweeded control at 20 × 2.5 to 20 × 10 cm spacings, showing that, at closer spacings weed control may not be necessary to increase grain yield. The number of weeds at harvest was significantly lower in the weeded plots than the unweeded control at all spacings used. Weed weight at harvest was significantly affected by weeding regime at all spacings except at 20 × 2.5 cm, where no significant difference was observed between the weeded and the unweeded plots. Plant spacings significantly affected the grain yield and weed weight, but did not affect the panicle number and weed counts of transplanted rice. At 20 × 2.5 cm, grain yield was significantly better than that at 20 × 15 cm or 20 × 20 cm. A simple trend of increase in grain yield along with the decrease in spacing between plants was observed in terms of actual grain yield.     

Weed competition in irrigated cotton (Gossypium barbadense L.) and groundnut (Arachis hypogaea L.) in the Sudan Gezira

Losses of crop yield due to weed competition in unweeded plots averaged nearly 60% of weed-free yields in cotton and 70% in groundnuts. Weed competition was not directly related to weed groundcover but was dependent on the seasonal growing conditions. The critical period of weed competition in both crops was the 6 weeks between 4 and 10 weeks after crop emergence. During this period cotton could tolerate up to 25% weed groundcover without appreciable loss in crop yield. Groundnuts could tolerate not more than 10% weed cover before yield loss occurred. A main factor in achieving standards of weed control within these limits was preventing the early growth of monocotyledonous weed species: pre-sowing application of trifluralin and benfiuralin provided this over a wide range of growing conditions.     

Weed infestation and tea growth under various weed management methods in a young tea (Camellia sinensis[L.] Kuntze) plantation

A field experiment was conducted in the low country of Sri Lanka, during the period 1994–1995 to investigate the severity of weed infestation and tea growth in relation to weed management methods in newly established tea ( Camellia sinensis [L.] Kuntze). Manual weeding (hand and slash weeding) at various intervals was compared with various herbicides, with or without mulching. Weed control with herbicides was superior to that of hand weeding at 6-week intervals or more. Weed control with oxyfluorfen at 0.29 kg ai ha⁻¹ + paraquat at 0.17 kg ai ha⁻¹ or glyphosate at 0.99 kg ai ha⁻¹ + kaolin at 3.42 kg ha⁻¹ were superior. Plots unweeded for 12 weeks or more produced significantly greater ( P  < 0.05) weed biomass than plots unweeded for 6 weeks. Although the least weed dry weight ( P  < 0.05) and the greatest number of weed species were recorded with hand weeding at 2 week intervals, there was no particular benefit on tea growth when compared with hand weeding at 6 and 12 week intervals. Inter row mulching in chemically treated plots was more favorable for tea growth than no mulching, while living weed cover in unmulched slash weeded plots suppressed tea growth. A combination of mulching and herbicides, particularly oxyfluorfen and paraquat, followed by hand weeding at least every 6–8 weeks was considered the most appropriate weed management system for young tea.     

Weed competition in spring-planted strawberries

Annual weeds germinating after planting strawberry (Fragaria chiloensis (L.) Duch. cv. Cambridge Favourite) in late March had no effect on crop growth if removed by late May. Dense weed cover thereafter severely inhibited stolon growth, virtually eliminating it if allowed to remain beyond mid-August. Shading by weeds inhibited leaf production and caused etiolation of existing leaves. New leaves appeared shortly after weed removal and few plants died unless weed cover persisted for most of the growing season. Further weed germination was allowed on some plots. Although not removed until late autumn, these weeds only had adverse effects on crop growth where initial weeding had occurred before mid-June. In one experiment, delaying weed removal until 6 July, 31 August or 2 November in the first year reduced fruit yield in the second (weed-free) year by 34%, 54% and 67% respectively. In a later experiment, competition from weeds until July or later in the first growing season gave fruit yields similar to those in the first experiment, but totally weed-free plots and those kept clean after weeding in mid-June produced less fruit than plots which remained weedy between mid-June and mid-August. It is suggested that competition from uncontrolled stolon growth in this experiment severely inhibited crown and hence truss production on plots which did not suffer weed competition. Unless left untouched until early September, weeds had less adverse effect on truss production than the stolons which they displaced. The results are interpreted in relation to improving the efficiency of weed control techniques.     

Critical period of weed competition in three vegetable crops in relation to management practices

The critical period of weed competition was determined in three vegetable crops: early cabbage (Brassica oleracea var. capitata L.), pickling cucumbers (Cucumis sativus L.), and field-seeded processing tomatoes (Lycopersicon esculentum L.). There were significant interactions between weed-removal treatments, year, and row width. Cabbage yields were reduced if plots were not kept weed-free for at least 3 weeks after transplanting or if weeds which emerged with the crop were allowed to remain longer than 4–5 weeks, Cucumber yields were reduced if plots were not kept weed-free for up to 4 weeks after seeding or if plots remained weed-infested longer than 3–4 weeks. Higher crop population densities (narrower row widths) in cabbage and cucumbers resulted in smaller plants, earlier competition from weeds, and therefore a shorter period that the crop could remain weed-infested without suffering reduced yields. Yields of direct-seeded tomatoes were reduced if plots were not kept weed-free for up to 9 weeks after seeding or if weeds which emerged with the crop were allowed to remain longer than 5 weeks. In each crop the timing of the critical period of competition was verified by weed removal only during this interval. There was a true critical period in direct-seeded tomatoes, but not in cabbage or cucumbers where a single weeding was sufficient to prevent yield losses.     

Weed interference and control in white yam (Dioscorea rotundata Poir)

The climbing growth habit of white yam (Dioscorea rotundata) coupled with its inability to shade the ground completely at any stage of its growth and development makes it very susceptible to weed interference. The critical period of weed interference in white yam was between the 8th and 16th week after planting (w.a.p.) for yam planted at the onset of rains. Keeping yam plants weedy for 16 w.a.p. or beyond significantly reduced tuber yield; keeping them weed-free for the same period resulted in a significant increase in tuber yield. A minimum of three weedings within 16 w.a.p. are necessary to minimize yield reduction caused by weeds. The lowest weed weight and highest crop yield from herbicide treatments were obtained where a mixture of fluometuron and metolachlor each at 2.0 kg a.i./ha was used for pre-emergence weed control.     

Chemical weed control in rainfed upland rice in Nigeria

Abstract

Two field experiments on chemical weed control in Faro 41 upland rice (Oryza sativa L.) variety were conducted at a rainforest site near the National Cereals Research Institute, Amakama Substation in 1989 and 1990. The herbicides tested were a coformulated mixture of pretilachlor and dimethametryne at 1.5, 2.0 and 2.5 kg a.i./ha, a co‐formulated mixture of piperophos and propanil applied at 3.16 and 3.95 kg a.i./ha, and Oxadiazon at 1.0 kg a.i./ha. Two hand weedings and a ‘no weeding’ treatment were included. The herbicides were applied 5 days after planting. All were safely selective to the crop. Most provided adequate weed control through 8–12 weeks after planting. Weeds controlled included Cynodon dactylon, Commelina benghalensis, Dlgitaria horizontalis, Eleusine indica, Panicum maximum and Pennisetum purpureum as grass weeds. The broadleaf weeds were Emilia sonchifolia, Ageratum conyzoides, Portulaca oleraceae, Richardia brasiliensis and Ipomoea Involuncrata. The sedges Mariscus alternifolius and Cyperus esculentus were encountered in the plots. Pretilachlordimethametryne at 2.5 kg a.i./ha had the best weeding score. Twoyear average grain yields of 1.7–2.6 t/ha were obtained from the herbicide treatments. With only 0.4 t/ha from the unweeded treatment, yield losses of more than 80% were recorded.     

Influence of fallow management systems and frequency of cropping on weed growth and crop yield

The influence of weeds on maize intercropped with cassava was evaluated in three fallow management systems and four cropping frequencies from 1989 to 1996 in Ibadan, Nigeria, West Africa. Fallow management systems consisted of natural bush, Leucaena leucocephala hedgerows and Pueraria phaseoloides fallow. Frequencies of cropping were continuous cropping, 1 cropping year alternating with 1, 2 and 3 years of uncropped fallow. Shrubs and climbers contributed 60–70% and herbs (predominantly weeds) 30–40% to the total dry matter produced in all treatments. Weed dry matter and seedbank increased with time in all treatments but was higher in natural bush fallow by the fifth and sixth years and in continuously cropped plots. Weed seed density increased with time in the continuously cropped plots and in plots cropped after 1 or 2 years of fallow but decreased with time when the fallow period was up to 3 years. Maize grain yield decreased over time in both unweeded and weeded plots irrespective of treatment with the exception of the weeded P. phaseoloides fallow treatment. Cassava tuber yield decreased over time in unweeded plots in all treatments while tuber yield increased in weeded P. phaseoloides fallow treatment and remained relatively constant in L. leucocephala and natural bush fallow plots. The results from this study suggest that planted fallow involving legume species is more effective in weed management in the long term than natural fallow. Fallow period was beneficial to crop yield and yield improvement increased with the length of the fallow cycle, particularly for cassava.     

Punch planting, flame weeding and stale seedbed for weed control in row crops

Punch planting is introduced as a new method to reduce weeds within rows in organically grown crops. In this method a hole is punched in the soil, and a seed is dropped into it, without seedbed preparation and soil disturbance outside the hole. In 2 years, punch planting with flame weeding, normal planting with flame weeding and normal planting without flame weeding were compared in fodder beet for five planting dates. Each planting date represented a lag‐period since establishment of the stale seedbed. Over all planting times and years, punch planting with flame weeding reduced intra‐row weed densities by 30% at the two to four leaf stage of fodder beet compared with normal drilling with flame weeding. Punch planting with flame weeding also reduced intra‐row weed densities by 50% compared with normal drilling without flame weeding. In general, there was no improved performance of punch planting with flame weeding over years by later planting, but delayed planting reduced intra‐row weed densities significantly. Over 2 years, 240 day degrees Celsius (4 weeks) planting delay reduced intra‐row weed densities in the range of 68–86% depending on plant establishment procedure. Punch planting with flame weeding offers a promising method of weed control in organic farming.     

Interference by the weed Parthenium hysterophorus L. with grain sorghum: Influence of weed density and duration of competition

Two sets of field experiments were conducted at two sites (lowland and intermediate altitude) for 2 years in eastern Ethiopia to determine the influence of parthenium weed ( Parthenium hysterophorus ) density and duration of competition on grain yield of sorghum. In the first set of experiments, target weed densities of 0, 3, 7, 13, 27, 53 and 100 plants m -2 were used. Yield loss was severely affected by parthenium weed density, peaking at 97% at the lowland site in 2000. At this site, even very low density (e.g. three plants m -2 ) resulted in a high yield loss (69%). Owing to differences between sites and years, however, it was not possible to specify meaningfully the threshold densities for weeding. In the critical weed-free period experiments, four parthenium weed-infested and four weed-free periods from emergence to harvesting of sorghum were maintained by hand hoeing. The critical periods for weed control, i.e. the period over which weeding had the greatest benefit on yield, were 19 - 69 and 40 - 57 days from emergence of sorghum in 1999 and 2000, respectively, at the intermediate altitude (assuming an acceptable loss of 10%). In the lowland, however, it ranged directly from emergence to 61 and 66 days, indicating more severe competition at this site. The substantial variation in yield and yield loss between sites and years illustrates the problems of attempting to give well-established, accurate recommendations for threshold densities and critical periods in small-scale, rain-fed agriculture.     

Weed control in rose-scented geranium (Pelargonium spp)

Abstract: Field investigations were carried out during 1999 and 2000 to identify effective chemical/ cultural methods of weed control in rose-scented geranium (Pelargonium spp). The treatments comprised pre-emergence applications of oxyfluorfen (0.15, 0.20 and 0.25 kg AI ha(-1)) and pendimethalin (0.50, 0.75 and 1.00kg AI ha(-1)), successive hand weeding, hoeing and mulching using spent of lemon grass (at 5 tonnes ha(-1)) 45 days after planting (DAP), three hand-weedings 30, 60 and 90 DAP, weed-free (frequent manual weeding) and weedy control. Broad-leaf weeds were more predominant than grass and sedge weeds, accounting for 85.8% weed density and 93.0% weed dry weight in 1999 and 77.2% weed density and 93.9% weed dry weight in 2000. Unrestricted weed growth significantly reduced geranium oil yield, by 61.6% and 70.6% in 1999 and 2000, respectively. Pre-emergence application of pendimethalin (0.75-1.00 kgAI ha(-1)) or oxyfluorfen (0.25 kg AI ha(-1)), successive hand-weeding, hoeing and mulching and three hand-weedings were highly effective in reducing weed density and dry weight and gave oil yield comparable to the weed-free check. Application of oxyfluorfen (0.15 or 0.20 kg AI ha(-1)) and pendimethalin (0.50 kg AI ha(-1)) were less effective in controlling the weed species in geranium. None of the herbicides impaired the quality of rose-scented geranium oil measured in terms of citronellol and geraniol content.     

Response of onion (Allium cepa L.) plants to fertilizers, weed competition duration, and planting times in the central Jordan Valley

The competitive ability of onion with weeds and the effects of weeds on onion crop growth and yield were investigated in three field experiments carried out in the central Jordan Valley during the 1997–1998 growing season. Fertilizer application to the onion plants in the presence of weeds significantly lowered the onion yield and reduced the bulb diameter, compared to the unfertilized, weed-infested onion crop. Weed competition and onion yield reduction increased with an increase in the fertilizer rate. All weed-free treatments with or without fertilizer gave a significantly higher onion yield than any of the fertilized, weedy plots. The highest yield of onion was obtained from the weed-free plots with a moderate application of fertilizer. Weed competition reduced the growth, bulb yield, and size of onion in the plots established from bulbs, seedlings, and seeds when compared to the relevant weed-free controls. The effect increased with competition duration and was more pronounced in direct-seeded onion than in the other two types of planting material. However, onion grown from bulbs or seedlings gave better growth, bulb weight, and number and was more competitive than the direct-seeded onion. The results showed that the minimum number of days of weed competition needed for a significant reduction in onion growth was 42 days when propagated from bulbs or seedlings and 21 days after direct-seeding. Onion grown from bulbs tolerated weed competition better and produced a higher bulb yield than that obtained from direct-seeded or transplanted onion, irrespective of the planting dates. December was found to be the best planting time for onion that was grown from bulbs and seedlings, while November was the best planting time for direct-seeded onion, provided the plots were weed-free throughout the growing season.     

Study on the effect of four herbicides with and without applied phosphorus on weed control and seed yield of fenugreek (Trigonella foenum‐graecum L.)

Abstract

Field experiments were conducted at Jobner (Rajasthan) during the winter seasons of 1982 and 1983 to evaluate certain physical and chemical weed control systems in fenugreek at two levels of applied phosphorus. The experiments comprised four herbicides (fluchloralin, pendimethalin, thiobencarb, and chloramben) at two levels each, manual weeding at three levels; and an unweeded check. The second factor, namely, application of phosphorus was evaluated at 0 and 40 kg P₂O₅/ha. The soil of the experiment site was loamy sand, containing 0.16% organic carbon. The results showed that amongst the herbicides, preemergent pendimethalin at 0.75 kg/ha controlled the weeds most effectively and gave 8.91 q/ha fenugreek seed yield, which was more than twice the seed yield obtained from the unweeded check plots. The twice hoed plots were found to give 1.32 q/ha higher seed yield than the pendimethalin herbicide treatment, but the benefit‐cost ratio was found higher for the herbicidal treatment. Application of phosphorus at 40 kg P₂O₅/ha was found to bring about significant increase in the seed yield of fenugreek by 59 kg/ha over control, without any interaction with the weed control treatments.     

Evaluation of herbicides for maize production in three ecological zones of Nigeria

Abstract

Maize cultivation in Nigeria has increased rapidly in the last few years as fertilizers have become more readily available to farmers. Without the use of herbicides however, the area of land that can be brought under maize production will be limited. The following herbicides were evaluated in three ecological zones of Nigeria: atrazine and mixtures of atrazine and simazine, atrazine and metolachlor and atrazine and cyanazine. All herbicide treatments were applied at the rate of either 1.0 or 2.0 kg a.i./ha. The plots that received 1.0 kg a.i./ha also received one supplementary hand weeding. All treatments gave yields comparable to the weed free control, with the exception of the unweeded higher rate of the atrazine and cyanazine treatment which gave the lowest grain yield as a result of poor weed control.     

Weed competition in willow coppice crops: the cause and extent of yield losses

Growth in 2-year-old willow Salix spp., grown in the short-rotation coppice (SRC) system on agricultural land, was compared in 30 weeded and 30 unweeded plots in each of 2 years after cutting. Non-destructive assessment methods of both crop and weed biomass were used. Coppice growth in year I was greater in the weeded plots than in the unweeded plots. In year II, coppice growth was not different between plots so that, over the 2-year study period, the coppice yield reductions with weeds reflected the losses in year I only. There was considerable variation in the amount of weeds in the unweeded plots. The relationship between the volume of weeds present and the extent of the coppice yield reduction over 1 and 2 years after cutting are described by linear models. Soil moisture and nutrient content, when measured in mid-summer, were not different between plots in either year. In year I, mid-summer coppice height was greater in the weedy plots, while stem numbers in both years and canopy density in year II were lower in the weedy plots. These results indicate that tall weeds competing for light and space in the first year of growth, rather than moisture or nutrient stress, caused fewer (and taller) stems to grow from the coppice stools, leading to the observed reductions in biomass.     

Problems of herbicide assessment in peanuts in Jamaica

Delays of 40 or 60 days in weeding peanuts (Arachis hypogaea L.) gave lower yields and fewer pods per plant but did not affect seed number per pod. Yield, pod number per plant, seeds per pod and mean weight per seed were all less in unweeded plots. In three herbicide trials crop yields were not closely correlated with crop vigour scores made several weeks before crop maturity, or with weediness scores. Correlations between yields and weed dry weights were better, but certain high-yielding herbicide treatments gave poor weed control and in some cases had low crop vigour scores. Most yield differences reflected differences in pod number per plant, with additional smaller compensating or additive effects on the other components. Certain herbicides apparently gave high mean seed weights without diminishing seed numbers per pod. Pre-emergence alachlor was the most promising herbicide, combined with preplant incorporated vernolate if nutgrass was serious. Napropamide and metobromuron merit further testing.     

Competition from weeds and their control in direct-seeded rice

In direct-seeded upland rice (Oryza sativa L.) yield reductions due to weed competition ranged from 42 to 65% in field experiments conducted in eastern Utter Pradash, India. The most critical period, when crop losses due to weed competition were most severe, ranged from 10 to 20 days after emergence. Yields generally continued to increase, however, as the length of the weed-free period increased. The weed flora consisted of various grasses, sedges and broadleaved species. The most effective herbicide treatment evaluated was a pre-emergence application of alachlor followed by a post-emergence application of propanil or one mechanical weeding.     

Herbicide Research on Groundnut and Sorghum under Farmer Conditions in the Indian Semi-arid Tropics

Abstract

Plots 17 × 5 m were laid out in farmers' fields in three villages. Treatments (replicated thrice) included atrazine (0.5 or 1.0 kg a.i./ha) on sorghum and nitrofen (0.75 and 1.5 kg a.i./ha) on groundnuts with or without hand-weeding or farmers normal weed control. Groundnuts were unfertilized, sorghum received 20 or 80 kg N/ha. Cooperating farmers were allocated plots for traditional weed control, other operations were carried out by research staff. Some plots were discounted because farmers withdrew cooperation or did not participate correctly or because of flooding. In groundnuts nitrofen alone was inferior to nitrofen + one hand-weeding. In sorghum there were no differences between high and low fertilizer regimes. Atrazine gave superior yields to farmers' weed control. All treatments were better than the unweeded control. Generally farmers fields had low weed populations due to good, timely control and low soil fertility. Herbicides are not economic at present. Problems associated with research in farmers fields included: selection of farmers who would participate correctly, variability between different farmers' weeding practices and between different fields due to previous crops and cultural practices; lack of control of farmers weeding operations and the distance of experimental plots from the research station. The authors suggest that small experiments with only 4-6 treatments are easier for participating farmers to comprehend, selecting suitable size and shape of plots is important and that if many farmers are involved the number of replicates can be reduced.     

Effect of initial herbicide treatment and planting material on woody weed development and the growth of Eucalyptus nitens and Eucalyptus regnans

A research study of establishment techniques in plantations of Eucalyptus nitens (Deane et Maiden) Maiden and Eucalyptus regnans F Mueller was assessed for growth at age 12 years. Biomass of trees and woody weeds was determined in the 13th year to evaluate the long-term effect of herbicide treatment on plots established with optimum seedling tree and site preparation. Eucalyptus regnans produced only 60% of the biomass of E. nitens. Under-storey woody weed biomass under E. regnans comprised 18–30% of the total biomass compared with 6% for E. nitens plots. There was less total under-storey weed biomass under the herbicide-treated plots, but a similar weed leaf biomass. Under-storey weed leaf biomass contributed 14–40% of the total leaf biomass on the plots. Despite under-storey weed biomass being substantially greater on the no-herbicide plots sampled, this competition had not generally reduced growth of the trees compared with the herbicide-treated plots. Suitable site preparation, providing weed-free conditions at the time of planting, resulted in woody weed control adequate to establish seedlings and allow full growth without the use of herbicides, given suitable seedling material. Although pre-planting herbicide treatment was not necessary for optimum growth of E. nitens grown from bare-root transplants, it did improve growth of slower-growing planting stock.     

Effects of inter-row hoeing and fertilizer placement on weed growth and yield of winter wheat

Inter‐row hoeing is known to control tap‐rooted and erect weed species more effectively in winter wheat than weed harrowing. However, little is known about its effectiveness for use in the spring in winter wheat grown at wide row spacing (240 mm) under the influence of different placement of fertilizer. Two field experiments, one in 1999 and one in 2000, were conducted to study the influence of fertilizer placement, timing of inter‐row hoeing, and driving speed on the weeding effect on different weed species and crop growth. Placement of fertilizer below the soil surface improved crop growth and grain yield in both years compared with placement on the surface, but the more vigorous crop did not give any better suppression of the weeds surviving hoeing. Timing was not important in one experiment, whereas hoeing twice beginning in early April was more effective in the other experiment where weed growth over the winter had been vigorous. Driving speed had no influence on either the weeding effect or the yield, except for one case where increasing speed reduced the control of well‐developed weeds. Compared with unweeded reference treatments, inter‐row hoeing reduced total weed biomass by 60–70% and tap‐rooted and erect weed species in particular by 50–90%. Sowing at 240 mm row spacing yielded less than 120 mm (Danish standard), and inter‐row hoeing for winter wheat needs to be adapted to narrower row spacing to avoid such yield decreases.