Competition between annual weeds and vining peas grown at a range of population densities: effects on the crop

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.     

速除不同施用时间对直播稻田杂草的防除效果

水稻直播是金华市推广的主要水稻轻型栽培技术．但因杂草危害严重．阻碍了该技术的全面推广。50％速除WP是江苏省农科院开发的除草剂．该除草剂对直播稻田禾本科、莎草科及阔叶草均具有较高的防效。水稻播种当天、播种后第1d、第2d和第3d用药．对杂草的综合防效很高．只是最后一次施药后15d对禾本科杂草的防效较差。但对其他杂草的防效达到98％以上；药后40d后对禾本科杂草的防效也达到98％以上。用量80g／667m^2和60g／667m^2，不同用药时间对杂草鲜重防效均表现优良．无显著差异．尤以播后第3d用药效果最佳。在播种当天和播后第1d用药．对秧畦上有渍水的畦面出苗有轻微影响．其他时间用药对水稻安全。     

Competition between annual weeds and vining peas grown at a range of population densities: effects on the weeds

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.     

Selective regulation of germination and growth of annual weeds by crop residues

Residues from mature, harvested crops of sorghum (Sorghum bicolor Moench.), sunflower (Helianthus annuus L.), oilseed rape (Brassica napus L.), wheat (Triticum aestivum L.) and field pea (Pisum sativum L.), exhibited selective effects on weed germination and growth under field conditions. Weed species in the study included Avena fatua L., Avena sterilis ssp. ludoviciana (Durieu) Nyman, Echinochloa crus-galli (L.) Beauv., Phalaris aquatica L., Phalaris paradoxa L., Lolium perenne L., Vulpia myuros (L.) Gmel., Hibiscus trionum L., Polygonum aviculare L., Bilderdykia convolvulus (L.) Dumort. and Lamium amplexicaule L. All crop residues tested, and in particular wheat and pea residues, promoted the germination and growth of A. fatua and A sterilis ssp. ludoviciana. Other grass weeds, however, were inhibited by the presence of crop residue, the extent of inhibition being dependent on residue type. Germination response of dicotyledonous weed species was also a function of residue type, H. trionum numbers were significantly higher in plots where oilseed rape, sorghum or sunflower residue had been incorporated, while L. amplexicaule was inhibited by these residue types and stimulated by pea and wheat residues.     

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.     

Gap colonization by weeds in a wheat crop grown under different cultivation regimes

The effects of tillage systems (mouldboard plough, chisel, disk and non-tillage, over 3 years) and gap openings during August and October of 0, 0.30 m × 0.30 m and 0.45 m × 0.45 m on the weed community were investigated in a wheat (Triticumaestivum L.) crop. Weed flora composition and species abundance were recorded in August, September and November and the data analysed with MULVA programs and non-parametric tests. The tillage system was more important than the timing or gap size on the weed floristic composition, and the changes in weed communities were evident within a 3-year period in spite of herbicide use. Less disturbing tillage systems (non-tillage and chisel plough) allowed the build-up of a more diverse community, whereas the most disturbing one (mouldboard plough) prevented high diversity in the weed community.     

Effect of the sowing date on the growth of hairy vetch (Vicia villosa) as a cover crop influenced the weed biomass and soil chemical properties in a subtropical region

Weeds emerge throughout the year in agricultural fields in subtropical regions. The weed suppression and improved soil fertility resulting from a living mulch of hairy vetch were investigated. Hairy vetch was sown in October and in December 2006. The fallow condition was without the sowing of hairy vetch, with the weeds allowed to grow naturally. The biomass of the top parts (BOT) of hairy vetch increased from February to April and then decreased in May on both sowing dates. The BOT of hairy vetch sown in October was significantly higher in February, March, and April than that sown in December. Hairy vetch sown in October and harvested from February to April varied from 372–403 × 10⁻³ kg m⁻², with weed suppression percentages of 62.8% in comparison with the fallow plots. The fixed C, N, P, and mineral uptake of hairy vetch showed similar patterns to its biomass. The nitrate (NO₃-N) content increased from February to May for the soils in the October and December plots, in contrast to the fallow plots. Moreover, the NO₃-N and available N of the October and December soils sampled from February to May were higher than that of the fallow soils. In subtropical agriculture, hairy vetch should be sown in October in order to achieve a higher biomass for suppressing weeds effectively and improving the soil fertility, mainly N.     

浙江省水稻直播田杂草发生规律与防除策略

1996～ 2 0 0 0年在浙江省水稻直播田开展了杂草发生规律调查和农美利应用技术研究。调查表明 ,浙江省水稻直播田杂草共 4 1科 77属 131种和 2变种。根据杂草发生频率、密度和危害综合分析 ,稗草等 15种为优势种群 ,杂草群落中各种群的组成及其比率随地区、时间及耕作栽培制度而变化。杂草于水稻播种后 3～ 4d开始出土 ,至第 7d(单季晚稻 )或第 15～ 2 1d(早稻 )达到高峰 ,第 4 2～ 70d时又出现一个较小的出草高峰。禾本科草出土较早 ,其次为阔叶草 ,莎草和部分阔叶草出土最迟。田间试验表明 ,农美利、扫特、杀草丹、去稗安、拜田净、千金、威霸、二氯·苄对直播稻田杂草具有优异的防除效果。     

Effect of crop density on competition by wheat and barley with Agrostemma githago and other weeds

The effect of Agrostemma githago L. and other naturally occurring weeds on biomass production and grain yield was studied in winter wheat and winter barley. Naturally occurring weeds had only a negligible effect on barley, but reduced wheat grain yield by 10% at a quarter of normal crop density. The interaction between the cereals and A. githago was studied in additive series employing different crop densities. Growth of this weed species was strongly dependent on crop density, which was more important for controlling weed growth than it was for obtaining a normal grain yield. Wheat and especially barley had a better competitive ability than A. githago. Wheat and A. githago utilized resources for growth better when grown in mixture than when grown in pure stands as the relative yield totals were significantly larger than unity.     

直播稻田杂草的生态特点和控制技术研究

近年来,随着直播稻种植面积不断扩大和栽培技术不断改革,田间草相也随生态条件的不同而发生了变化。水稻前期干、湿栽培,十分有利老草复活和新草的萌发生长。直播稻田杂草危害已成为阻碍直播稻优质高产和大面积推广应用的主要障碍。为了明确直播稻田杂草的生态特点和杂草萌发规律,科学制定防除策略,积极探索直播稻田杂草的化除技术,安全、有效、经济地将杂草危害损失控制在最低限度,我们于2003年开展了直播稻田杂草的生态特点和防除技术研究,初步摸清直播稻田出草规律,得出化除配套技术,并进行了大面积推广应用,取得了显著的灭草、增产效果…     

Weed species composition of maize fields in Germany is influenced by site and crop sequence

During the last decade, maize has become the crop with the second largest acreage in Germany. Therefore, agricultural advisors and the plant protection sector are interested in an overview of the weed species composition in maize fields, their determining factors and trends. From 2001 to 2009, a weed survey was conducted in 1460 maize fields throughout Germany. Data on crop management and soil characteristics were collected via farmer questionnaires. Principal component analysis and redundancy analysis were used to analyse patterns in weed species composition. The late spring and summer germinating species Chenopodium spp., Echinochloa crus‐galli and Solanum nigrum occurred with high densities and frequencies, but their occurrence was determined by different factors. Other frequent weed species were those that typically accompany autumn‐sown crops. The variation in species composition was significantly related to environmental factors (9.1% explained variance), particularly geographical latitude and precipitation, and management factors (4.7% explained variance), particularly crop sequence. The relative importance of these factors seems universal, when compared with surveys in other crops and regions. The factor ‘year’ was of minor importance (0.9% explained variance). Over the 9‐year period, no changes in weed species composition could be determined. The results suggest that despite the limited impact of crop management on weed species composition, farmers can use crop sequence to suppress individual species. The survey furthermore sets a baseline against which future changes can be measured in a landscape of rapidly changing agricultural land use.     

The phytotoxicity potential of olive processing waste on selected weeds and crop plants

The effect of sun-dried OPW (olive processing waste) on weeds and crop plants, was investigated at the Adnan Menderes University Research and Application Farm between 2006 and 2007. Sun-dried OPW was placed in pots in doses of 9, 18, 27, 36, 45 and 54 grams per pot, which is equivalent to doses of 1, 2, 3, 4, 5 and 6 kg m⁻²; pots with no OPW served as controls. In these experiments, ten seeds each of wild oat (Avena fatua), sterile oat (Avena sterilis), blackgrass (Alopecurus myosuroides), perennial ryegrass (Lolium perenne), yellow sweetclover (Melilotus officinalis), redroot pigweed (Amaranthus retroflexus), jimsonweed (Datura stramonium), faba bean (Vicia faba), pea (Pisum sativum), and sesame (Sesamum indicum) were sown in pots; for common lambsquarters (Chenopodium album), seedlings were planted in pots. Seedlings of both weeds and crop plants were counted in order to assess the effects of sun-dried OPW on plant emergence. One plant was left per pot for observation of the effects of sun-dried OPW treatments on weed and crop plant growth. The results showed that OPW can be used to suppress the growth of all the weeds listed above, in pots containing V. faba, P. sativum and S.indicum plants and without any negative effects on crop growth.     

Competition between weeds and spring wheat for 15N-labelled nitrogen applied in pig slurry

The changes in weed:crop competition as affected by the interaction of slurry distribution pattern with crop sowing pattern was examined, using the parameters dry matter (DM) production, nitrogen (N) uptake and recovery of applied N in spring wheat and weeds. Pig slurry enriched with isotopic nitrogen (¹⁵N) was applied either fully incorporated or in concentrated bands. The two slurry distribution patterns were combined with either crop density or distance between the slurry band and seed row. Spring wheat and weeds were sampled separately seven times during the season. A high and fast crop recovery of applied N coincident with a low recovery in weeds may be obtained by at least three management elements: sowing the crop with a high seed density, sowing the crop row close to the band-applied slurry N, and early sowing. The effects on crop DM, N-uptake and ¹⁵N recovery of a high crop density and a narrow distance between the slurry band and crop row appear clearly at the beginning of the spring wheat elongation phase. For weeds the effects were most pronounced for ¹⁵N recovery, and using DM as the only response variable may cause insignificant results. However, methods for N application may be part of a strategy controlling weeds, but to obtain satisfactory weed control the N management needs to be supplemented with chemical or mechanical weed management.     

Spray drift as influenced by meteorological and technical factors

BACKGROUND: The objective of this study was to investigate spray drift from a conventional field sprayer as influenced by meteorological and technical factors, and to provide spray operators with data on which to base sound judgements when applying pesticides. The study was conducted in grazing fields and cereal crops. RESULTS: Interpreting the results from 15 field trials under varying meteorological conditions using different boom heights and driving speeds indicates that, during normal spraying conditions, the most decisive factors influencing the total spray drift (TSD) will be boom height and wind speed, followed by air temperature, driving speed and vapour pressure deficit. One important finding was that TSD (within the encompassed range of meteorological conditions and a boom height of 0.4 m) could be expressed as a simple function of the fraction of droplets ≤ 100 µm. In cereal crops: TSD = 0.36 + 0.11× [fr. (d ≤ 100 µm)] and in grazing fields, TSD = 1.02 + 0.10× [fr. (d ≤ 100 µm)]. In most cases a fraction of the airborne drift passed over the 6 m sampling mast located 5 m downwind of the spray swath. CONCLUSIONS: Under specified conditions, the present results indicate a simple relation between the total spray drift and volume fractions of droplets ≤ 100 µm. Given the nozzle type, it was concluded that the most decisive factors determining TSD are wind speed and boom height. Evaluating the relative importance of the meteorological and technical factors contributes to increasing knowledge in this field of research. Copyright © 2011 Society of Chemical Industry     

Competitive interactions between chick-pea genotypes and weeds

Growing chick‐pea in sustainable systems requires the use and development of more competitive genotypes which can complement the effects of reduced input weed control. A 2‐year study assessed the competitive ability of 13 genotypes grown in either the presence or absence of weeds, in a split‐plot design including the weeds in pure stands. Crop and weed density, phenology, relative biomass of crop (RB_c) and weeds (RB_w), crop yield characters, crop biometric traits in the absence of weeds, relative biomass total of mixtures (RBT) and crop competitive ability (C_b = ln RB_c/RB_w) were recorded. Lines C136, C120, C101 and C106, and cultivars Pascià, Visir and Sultano gave the best seed yield in the absence of weeds (1.8–2.0 t ha^?1 DM). Weeds reduced yield by 75% and 83% in C136 and C133 and by 87–97% in the other genotypes. Weed biomass in mixture (mainly Chenopodium album) averaged 4.42 t ha^?1 DM. Chick‐pea genotypes C136 and C133 were the most competitive, but weeds were more competitive than any of the chick‐peas. C_b was correlated directly to the height of first fertile pod (r² = 0.84) and inversely to the insertion angle of primary branches to the vertical (r² = 0.77). Intergenotypic variation for competitive ability could be exploited in integrated weed control using more competitive genotypes, or used in breeding programmes aimed to develop highly competitive cultivars on the basis of easily screenable characters.     

Assessment of competition between crops and weeds

A two-species model was used to summarize results of four experiments with two component mixtures of barley (Hordeum vulgare L.), peas (Pisum sativum L.), Chenopodium album L. and Sinapis alba L. grown in pots in greenhouses. The results, covering a wide range of plant densities both in mixtures and pure stands, showed that the model was not always able to describe the relationship between the yield of a species and the densities of itself and its companion species. The deviations from the model were in all instances greatest for the least competitive species. The model that quantifies competition and niche differentiation appeared to be too general because competition between species was not independent of the wide plant density ranges used here. The results are discussed in relation to possible improvements of the model and an analogy between the principles of assessing crop weed competition and the assessment of the relative potency of herbicides in bioassay studies is put forward.     

Asymptomatic weeds are frequently colonised by pathogenic species of Fusarium in cereal‐based crop rotations

Several Fusarium species cause harmful cereal diseases, such as fusarium head blight and crown rot, which, during pathogenesis, may result in significant grain yield and quality losses. Several species of agricultural weed are believed to be alternative and reservoir hosts for Fusarium spp.; however, studies have not comprehensively evaluated those weed species in cropping systems that may harbour these fungi. The objective of this study was to determine weed species in cereal‐based crop rotations that are asymptomatically colonised by Fusarium spp. We sampled all species of weed present in fields that were managed under six different crop sequences in 2015 and 2016. The study yielded 2326 single‐spore isolates of Fusarium spp. derived from various organs of asymptomatic weeds. Isolates were identified morphologically and then confirmed using PCR with species‐specific primers and/or sequencing of tef1α gene fragments. Isolates of nine Fusarium spp. were obtained from 689 of the 744 individuals collected that represented 56 weed species. Each weed species harboured at least one species of Fusarium, and >80% were colonised by 3–9 Fusarium spp. In total, we identified 27 dicotyledonous weed species that were previously undocumented as Fusarium hosts and 251 new weed × Fusarium species combinations were revealed. Consequently, there is a greater risk of negative Fusarium impacts on cereal crops than was previously thought. We suggest effective weed management and inversion soil tillage may help mitigate these impacts.     

The movement of paraquat as influenced by the partition coefficient of surfactants between water and leaf wax

“Lissapol” NX and “Lubrol” L, used to improve the uptake of paraquat into plants were found in earlier work to reduce its movement. Several series of surfactants with widely varying solubilities in water were partitioned between cabbage wax and water. A marked correlation was found between the effect of surfactants on the movement of paraquat and the amount of surfactant partitioning into the wax. It is concluded that although surfactants increase the uptake of paraquat into leaves, this increase is offset by reduced movement following penetration of surfactants into leaf tissue. Surfactant partition into wax reduces the degree of penetration, but there is no evidence how surfactants in leaf tissue reduce movement.     

农田杂草抗药性及其检测鉴定方法

杂草的抗药性是杂草综合治理中存在的重大难题之一,本文根据国内外已报道的文献,对农田杂草抗药性的现状与发展,抗药性杂草产生的原因和机理以及抗药性杂草的检测鉴定方法作一综述。     

Glutamine synthetase activity and ammonium accumulation is influenced by time of glufosinate application

Time of glufosinate application impacts weed control. Although leaf angle of velvetleaf significantly contributes to the time of day (TOD) effect, it is not the sole reason for reduced efficacy. Absorption and translocation of glufosinate, glutamine synthetase (GS) activity, and ammonium accumulation were investigated as possible physiological components of the TOD effect. Absorption and translocation were not associated with a decrease in glufosinate efficacy. GS activity, ammonium accumulation, and plant biomass were influenced by the time of glufosinate application. Velvetleaf GS activity quickly diminished during the light period and remained high during the dark period following glufosinate treatment. GS activity was higher in plants treated at 10:00 pm than in those treated at 2:00 pm 12 HAT. With little GS inhibition during the dark period, ammonium accumulation occurred only during the light period. At 72 HAT, ammonium concentration was nearly 1.5-fold greater in plants treated at 2:00 pm versus those treated at 10:00 pm with 160 g/ha glufosinate. Plant biomass of plants treated with 160 g/ha glufosinate at 10:00 pm was greater than those treated at 2:00 pm at 72 HAT. Increasing the application rate from 160 to 320 g/ha removed these differences in GS activity, ammonium accumulation, and plant biomass. These results demonstrate that GS activity and ammonium accumulation are physiological processes involved in the TOD effect.