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1.
Spring-planted raspberries (Rubus idaeus L. cv. Malling Jewel) were exposed to competition from annual weeds for various lengths of time during the first growing season. Weeds germinating following crop planting in late March had no effect on numbers of new canes produced provided weed removal occurred by early June. The importance of preventing competition from these weeds during the critical period of cane emergence (June/July) was demonstrated. Dense weed cover reduced cane growth and, if weeds were left beyond late June, caused considerable mortality of planting material. Weed growth also frequently reduced cane height. In the second year, all plots were maintained free of weeds. Fruit yields showed effects of weeds similar to or greater than those indicated by total cane growth in the previous year. Height of new canes was unaffected by previous weeding treatments, but the numbers of new canes produced continued to show severe effects of initial competition from weeds. Allowing further weed growth to develop after initial weeding had no additional effect on crop survival or cane numbers in the first year. In one experiment, however, a reduction in cane height due to weeds germinating in June was followed in the second year by a reduction in the numbers of new canes produced.  相似文献   

2.
Early growth and nutrient content of crops and weeds from weed-free and weedy no-tillage maize (Zea mays L, cv. TZB), cowpea (Vigna unguiculata (L) Walp. cv. VITA-5) and maize/cowpea intercrop at populations of 40000, 50000 and 30000 + 40000 plants ha?1 grown on a loamysand Oxic Ustropept in a subhumid tropical location were monitored in the early and late 1979 cropping seasons. In the first 6 weeks of growth in the early season, cropping pattern had no effect on weed growth; weeds did not suppress crop growth significantly until 5–6 weeks after sowing and total crop dry weights were not affected by cropping pattern. Three weeks after sowing, weeds from weedy crop plots had taken up two to four times as much nutrient (N, P, K, Ca + Mg) as was taken up by corresponding weed-free crops. In the late season, weed dry weight 6 weeks after sowing was depressed in the intercrop compared to monocultures and dry-matter production of the intercrop was higher than those of monocultures. The resource use index (RUI), defined as the amount of an environmental resource used by a weed-free crop divided by the combined amount of the same resource used by the corresponding weedy crop and the associated weeds, increased with age of crop and was higher for the intercrop than the monocultures only in the late season.  相似文献   

3.
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.  相似文献   

4.
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.  相似文献   

5.
Competition between annual weeds and vining peas (Pisum sativum L.) at five target population densities between 11 and 194 plants/m2 was examined by means of periodic destructive sampling of weedy and weed-free plots. A further area of each plot was cut and vined to assess yields. Weeds impaired vegetative development, particularly by reducing tillering in low density crops. This resulted in weedy plots having fewer pods per plant at harvest but a lower proportion of flat pods than weed-free plots. Weeds had no effect on numbers or weights of peas in full pods nor on tenderometer values of samples of vined peas. Adverse effects of weeds on the growth of individual crop plants decreased with increasing crop density. However, at lower crop densities many of the additional pods on weed-free plots contributed little to vined yield, while at higher densities, direct or indirect effects of weeds increased the problem of maintaining sufficient photosynthetic area during pod swelling to prevent pod abscission and poor ovule development. Regression analysis of yield on crop density and of yield on numbers of pods per plant showed that vined yield per hectare was reduced by weeds by a constant amount across the range of densities and numbers of pods examined. Vining throughput was also reduced in weedy as compared with weed-free crops, even on high density plots where little or no weed vegetation remained at harvest. In general, weed presence had effects similar to those caused by increasing crop density, but without the additional contribution to yield made by extra plants. Higher density crops suppressed weeds very effectively but were no less vulnerable to yield loss than those of lower density; they therefore merit just as much attention to effective weed control as crops suffering more visibly from competition by weeds.  相似文献   

6.
The effects of weed removal at five dates after planting the crop were examined and compared with weed-free and unweeded controls. The results revealed that the total weed population increased up to 6 weeks after planting and then decreased drastically in both the years. Total dry weight of weeds (at weeding and at haulm-cutting) was greatest in the unweeded control, followed by weeding at 10 weeks after planting. In both years, maximum yield was obtained where plots were kept weed-free, followed by weeding at 4 and 6 weeks after planting. The remaining treatments, including weeding at 2 weeks after planting, resulted in significant reductions in tuber yield. In unweeded control plots the tuber yield of potato was reduced by 40–43%.  相似文献   

7.
Double-cropped soybean after winter cereals is the most common soybean production system in the eastern Mediterranean region of Turkey. Weeds are among the main obstacles to double-cropped soybean. A study was conducted in 2002 and 2003 to determine the critical period of weed control (CPWC) for double-cropped soybean. The treatments consisted of either allowing weeds to infest the crop for increasing durations after sowing, or maintaining plots weed-free for increasing durations after sowing. The Gompertz and logistic equations were fitted to relative yields representing the critical weed-free period and the critical time of weed removal, respectively. Johnsongrass (Sorghum halepense), common cocklebur (Xanthium strumarium) and field bindweed (Convolvulus arvensis) were the dominant weeds. For 5% crop loss level, the CPWC was almost all season long, whereas it was from V1 to R6-R7 growth stages for 10% yield loss level. These findings indicate that pre-sowing or pre-emergence control methods should be applied in the region to avoid greater crop losses.  相似文献   

8.
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.  相似文献   

9.
In Northern Europe, inter-row hoeing has become a popular tactic for controlling weeds in organic cereals. Hoeing is highly effective and can be implemented from crop emergence until stem elongation to maintain a nearly weed-free inter-row zone. However, hoeing has a lesser effect on weeds growing in the intra-row zone, where crop–weed proximity results in heightened competition. In the hoed cereal system, it is investigated whether tall-growing, competitive, cruciferous weeds in the intra-row zone affect crop biomass, yield and thousand kernel weight (TKW). An additive experimental design is employed to enable the fitting of rectangular hyperbolas, describing and quantifying the effects of increasing intra-row surrogate weed density on crop growth parameters. Regressions were studied under the influence of crop (spring barley and spring wheat), row spacing (narrow [12.5 or 15.0 cm] and wide [25.0 cm]) and nitrogen rate (50 and 100 kg NH4-N/ha). Cruciferous surrogate weeds were found to impact crop yield and quality severely. For example, ten intra-row plants/m2 of surrogate weed Sinapis alba reduced grains yields by 7%–14% in spring barley and by 7%–32% in spring wheat with yield losses becoming markedly greater in wheat compared to barley as weed density increases. Compared to wheat, barley limited yield and quality losses and suppressed intra-row weed growth more. Row spacing did not have a consistent effect on crop or weed parameters; in one of six experiments, the 25 cm row spacing reduced yields and increased intra-row weed biomass in wheat. Nitrogen rate did not affect crop or weed parameters. Results warrant the implementation of additional tactics to control intra-row weeds and limit crop losses.  相似文献   

10.
In a long-term cropping systems trial comparing organically and conventionally managed systems, organic maize production sustained crop yields equal to conventional methods despite higher weed levels. In 2005 and 2006, an experiment nested within the trial was conducted to gain insight into this apparent crop tolerance to weed competition. Density of mixed weed species was experimentally manipulated to achieve a broad range of weed infestation levels. Under standard management conditions, all cropping systems produced equivalent maize yields, even though weedy plant biomass in the organic treatments was between fourfold and sevenfold greater than in the conventionally managed maize. Increased yield capacity, evidenced when plots were maintained weed-free, and enhanced crop competitiveness, were the main pillars of this apparent crop tolerance to weed competition in the organic systems. Increased soil resource availability and a faster relative crop growth rate in the organic systems probably contributed to these factors, which play an important role in buffering crop fitness during years of less than ideal weed control. Simultaneously, the experiment illustrated the poor efficacy of mechanical weed management in the organic systems, which is the main reason organic maize did not out-yield conventional maize under standard management conditions.  相似文献   

11.
Critical periods of weed competition in cotton in Greece   总被引：1，自引：0，他引：1  
Four experiments were conducted in central Greece during 1997 and 1998 to determine the late-season presence of weeds in cotton (Gossypium hirsutum L.) and the critical times for removing weeds. Experiments were conducted in natural, heavily infested cropland. The presence of weeds for more than 3 weeks after crop emergence caused significant reductions in crop growth and lint yields. However, weeds that emerged 11 weeks or more after crop emergence did not adversely impact yields. Total weed biomass increased with increasing time prior to weed removal. A weed-free period of 11 weeks after crop emergence was needed to prevent significant reductions in cotton height, biomass, number of squares, and yield. These results indicated that postemergence herbicides or other control measures should be initiated within 2 weeks after crop emergence to avoid significant yield reduction. For greater efficiency, soil-applied herbicides in cotton should provide effective weed control for at least 11 weeks. Curvilinear regression equations were derived to describe the relationship between critical periods of weed presence and cotton growth and fruit development.  相似文献   

12.
Most herbicide applications to sugar beet (Beta vulgaris L.) are made to the whole crop area, but there is the opportunity to restrict applications to the crop row, decreasing the usage of herbicide by up to 70%. However, this would require greater use of mechanical weed control between rows. Experiments were performed in two seasons to evaluate the weed control performance of a novel, vision‐guided, inter‐row hoe in sugar beet crops grown on a peat fen soil. Hoe lateral placement was within ±30 mm. A precise hoeing and band spraying treatment was compared with overall herbicide use, and with treatments in which the herbicide applications were replaced by hand weeding to minimize competition between crop and weeds. Two hoe passes were made in each season, at crop growth stages of two and 10–12 true leaves in the first season and four and eight true leaves in the second season. Plant population density was not affected by treatment, indicating that none of the treatments caused crop plant loss. Use of the guided hoe controlled weeds better than overall spraying. Crop yields were not significantly different between treatments, indicating that weed control prevented competition with the crop in all treatments.  相似文献   

13.
Summary Co-ordinating herbicide applications with the suppressive ability of the crop has the potential to improve weed control and optimize herbicide use in water-seeded rice. However, the successful integration of herbicide applications and crop development depends on the timing and duration of competition between rice and weeds. The critical period of competition between rice and Echinochloa species was examined in field and glasshouse experiments from 1996 to 2000. In 1999 and 2000, Echinochloa species seeded 30 days after rice in field experiments did not survive and rice yields were not reduced when plots were kept weed-free for 30 days or longer. In a basin experiment conducted in 1998, E. phyllopogon seeded with the crop was unaffected by light competition alone but the relative importance of shading by the crop increased when E. phyllopogon was seeded after rice. Management strategies that delay the germination or growth of Echinochloa species might confer a competitive advantage to rice and reduce the need for herbicide applications. However, yields in the field experiments were reduced by at least 18% after only 30 days of competition in both years, suggesting that it may be difficult to integrate currently available herbicides with crop growth in water-seeded rice.  相似文献   

14.
Linear regression of dry weight of weeds against crop density, together with the use of diversity indices and principal component analysis were used to derive information about changes in the behaviour of annual weeds over the growing season and in response to a wide range of crop densities in vining peas Pisum sativum L. Using linear regression it was possible to quantify reductions in weed dry weights per unit increase in crop plant density The ‘weed losse’ factor was acceptably consistent between experiments. Indices examining richness and evenness showed that numbers of weed species declined with increasing crop density and as the season progressed, but although species evenness became less at successive sampling dates the presence of a pea crop, whatever its density, did not radically alter the composition of the weed flora. Principal component analysis demonstrated that although there was competition within the weed flora, the crop did not replace the dominant weed species on high density plots, but reduced growth of all weed species alike.  相似文献   

15.
Echinochloa colona and Trianthema portulacastrum are weeds of maize that cause significant yield losses in the Indo‐Gangetic Plains. Field experiments were conducted in 2009 and 2010 to determine the influence of row spacing (15, 25 and 35 cm) and emergence time of E. colona and T. portulacastrum (0, 15, 25, 35, 45 and 55 days after maize emergence; DAME) on weed growth and productivity of maize. A season‐long weed‐free treatment and a weedy control were also used to estimate maize yield and weed seed production. Crop row spacing as well as weed emergence time had a significant influence on plant height, shoot biomass and seed production of both weed species and grain yield of maize in both years. Delay in emergence of weeds resulted in less plant height, shoot biomass and seed production. However, increase in productivity of maize was observed by delay in weed emergence. Likewise, growth of both weed species was less in narrow row spacing (15 cm) of maize, as compared with wider rows (25 and 35 cm). Maximum seed production of both weeds was observed in weedy control plots, where there was no competition with maize crop and weeds were in rows 35 cm apart. Nevertheless, maximum plant height, shoot biomass and seed production of both weed species were observed in 35 cm rows, when weeds emerged simultaneously with maize. Both weed species produced only 3–5 seeds per plant, when they were emerged at 55 DAME in crop rows spaced at 15 cm. Infestation of both weeds at every stage of crop led to significant crop yield loss in maize. Our results suggested that narrow row spacing and delay in weed emergence led to reduced weed growth and seed production and enhanced maize grain yield and therefore could be significant constituents of integrated weed management strategies in maize.  相似文献   

16.
Using a previous model as a base, data derived in field trials in wheat ( Triticum aestivuort L.) and bailey ( Hordeum vulgare L.) were assessed to estimate the yield penalty, and resulting reduction in economic benefit, from progressive spraying of herbicides up to late crop tillering. Compared with early post-emergence application, yield penalties from delayed spraying began at early tillering. For median values of weed-free yield and weed density in the data set. the loss in potential yield increase when spraying at late tillering compared with early post-emergence was 71%, Crops with higher weed-free yield potential and with greater initial weed density showed a proportionately (as well as absolutely) larger yield penalty from a moderate delay in spraying, indicating an earlier and more intense onset of competition with weeds.  相似文献   

17.
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.  相似文献   

18.
H. M. LAWSON 《Weed Research》1972,12(3):254-267
Summary. The presence of weeds during autumn and winter had no effect on the growth of transplanted spring cabbage provided they were removed before rapid growth of crop and weeds began in early spring. Weeds left beyond this time competed with the crop, resulting in smaller marketable heads. Increasingly severe competition affected internal head quality, reduced the numbers of plants producing heads and resulted in the death of a proportion of the crop plants. The main weed species responsible for crop loss was Stellaria media , which survived winter frosts and grew rapidly in early spring to fill all available ground space, dominating the weed flora and shading the crop foliage.
Application of propachlor at planting time failed to give sufficient control of S. media to avoid crop loss, although the onset of competition was delayed. Trifluralin gave excellent control of S. media and resistant species were kept in check by the crop.
Comparison of cropped and uncropped plots showed that the crop exerted considerable competitive pressure on the growth and development of weeds particularly where this had been reduced or delayed by herbicide treatment. The presence or absence of the crop did not, however, affect the relative proportions of the weed species, except on plots treated with trifluralin, where the crop suppressed Capsella bursa-pastoris.
Compétition des mauvaises herbes dans les choux de printemps repiqués  相似文献   

19.
Summary. In 3 years and in three nurseries, experimental plots sown with conifer seed were weeded by hand at intervals from 1½ to 12 weeks. Assessments of the seedlings at the end of each year showed a reduction in numbers and height only on plots left for 12 weeks between successive weedings. The total time taken to weed plots during the growing season was least for plots weeded at intervals of 3-4 weeks and greatest for plots weeded at the longest intervals. Data on the total weight of weeds, the total number of weeds, the species composition and the stage of weed growth at weeding are also given and discussed.
Essais de désherbage dans les pépinières  相似文献   

20.
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.  相似文献   

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