Modelling the population dynamics of Papaver rhoeas under various weed management systems in a Mediterranean climate

The demography of the annual dicotyledonous weed Papaver rhoeas and the efficacy of different management practices were studied during three consecutive years in winter cereals in the north‐east of Spain. These data were used to estimate the parameters of a weed life cycle model that was used to describe the population dynamics of this species and to predict the effect of various control strategies and integrated weed management (IWM) scenarios. Without control, the annual rate of increase was 40 (λ_t), and the minimum control level required to maintain the population stable was 99% of the emerged plants. The annual application of post‐emergence and/or pre‐emergence herbicides did not prevent the growth of the population. Using various cultural control tactics (delayed seeding, harrowing and fallow) resulted in different trends in the overall population depending on the techniques and combinations analysed. Simulations showed that delayed seeding, fallow and pre‐emergence herbicides are the best techniques to employ in IWM programmes, always using a combination of these and other more common practices (i.e. post‐emergence herbicides). Sensitivity analysis indicated interaction between the parameters and that the model was especially sensitive to seed losses and also to fecundity, seedling survivorship and emergence. The study shows that new strategies should be sought to control these parameters. To develop IWM programmes for P. rhoeas, the combination of two or more control strategies is required.     

Chloris polydactyla (L.) Sw., a perennial Poaceae weed: Emergence, seed production, and its management in Brazil

Experiments were conducted to evaluate the plant emergence and seed production of Chloris polydactyla and the efficacy of herbicides for its control. The plants emerged mainly when the seeds were placed on the soil surface at ≤ 3 cm depth. Isolated plants produced a great amount of seeds. The pre-emergence herbicides, acetochlor, atrazine + simazine, s-metolachlor, alachlor, and trifluralin, were effective for C. polydactyla control. The postemergence herbicides, clodinafop-propargil, haloxyfop-methyl, clethodim, fluazifop- p -butil, tepraloxydim, sethoxydim, and quizalofop- p -tefuril showed satisfactory control of the plants at a 20 cm height with six leaves. During the flowering stage (85 cm plant height), only glyphosate was effective in controlling C. polydactyla .     

茶园间作功能植物对茶小绿叶蝉的调控作用

为研究间作功能植物对茶园主要害虫茶小绿叶蝉的影响,于2017—2018年在福建省泉州市安溪县茶园间作白三叶Trifolium repens L.、金花菜Medicago hispida Gaertn.、金盏菊Calendula officinalis L.,以自然留养杂草茶园为对照,用网捕法采集茶小绿叶蝉并于室内计数,镜检剥查法调查其茶梢着卵量。结果表明,在4种不同生境管理茶园网捕茶小绿叶蝉总个体数及每月个体数均无显著差异;茶小绿叶蝉个体数分别在2017年8月与2018年6月达到高峰。茶梢各节间着卵量不同,主要产卵在顶芽之下第2～5节间,以第4节着卵量最多。间作金盏菊茶园茶小绿叶蝉在茶梢第1节着卵量显著高于间作白三叶和金花菜茶园。不同生境管理茶园茶小绿叶蝉在茶梢第4节着卵量从大到小依次为间作金盏菊(8.13)、间作金花菜(7.50)、自然留养杂草(7.17)和间作白三叶茶园(6.57)。不同时间段4种不同生境管理茶园茶小绿叶蝉在茶梢各节之间的着卵量存在差异,且均在9月上中旬着卵量达到高峰。在茶园间作功能植物,短期内未见其显著降低茶小绿叶蝉网捕量和茶梢着卵量的效应。     

Cover crops and mulches influence weed management and weed flora composition in strip‐tilled tomato (Solanum lycopersicum)

This study was conducted in the Mediterranean environment of Central Italy from 2011 to 2013 with the aim of evaluating the effects of winter cover crops and their residues on weed composition in a cover crop‐tomato sequence. Treatments consisted of five soil managements (three cover crop species ‐ hairy vetch, phacelia, white mustard, winter fallow mulched with barley straw before tomato transplanting and conventionally tilled soil), two nitrogen fertilisation levels (0 and 100 kg N ha^?1) and two weed management levels (weed free and weedy) on tomato. Cover crop residues were arranged in strips on the soil surface and then used as beds for transplanting the tomato seedlings in paired rows. Rotary hoeing was performed in the bare strips between paired tomato rows. At tomato harvesting, the weed aboveground biomass and density was higher in nitrogen‐fertilised tomato than unfertilised tomato, except in hairy vetch and barley straw that showed similar values. Hairy vetch used as a cover crop and dead mulch was the most suppressive species with the highest production of residues, while phacelia and mustard were not suitable for controlling weeds. The tomato yield was high in nitrogen fertilised and weed‐free treatments, except in barley straw mulch, which showed similar values among the weed management treatments. The mulch strips caused variations in weed species composition that was mainly composed of perennial ruderal weeds, while in tilled soil, the weed flora was dominated by annual photoblastic weeds.     

Peanut (Arachis hypogaea) response to weed and disease management in northern Ghana

Weeds and diseases can reduce peanut (Arachis hypogaea L.) yield or increase cost of production to maintain acceptable yield. While herbicides and fungicides have limited availability in many areas of Ghana and currently are too expensive for resource-poor farmers, control by these pesticides can have a major positive impact on peanut yield. Field experiments were conducted during the rainy seasons of 2009 and 2010 in northern Ghana to determine the effects of herbicide and hand weeding in combination with fungicides on pest management and peanut yield. Peanut pod yield was often more highly correlated with disease severity and canopy defoliation resulting from early leaf spot (caused by Cercospora arachidicola Hori) and late leaf spot (caused by Cercosporidium personatum (Berk. & M.A. Curtis) Deighton) than weed biomass. In some instances, less disease and canopy defoliation were observed when weeds were not controlled effectively compared with increased weed management through hand weeding or herbicide. Two hand weedings or applying pendimethalin preemergence with one hand weeding in combination with 4 applications of triadimefon and chlorothalonil resulted in the lowest weed density and canopy defoliation and often resulted in the highest peanut yield.     

Influence of weed management measures on glyphosate resistance and endophyte infection in naturalized Italian ryegrass (Lolium multiflorum)

Recently, glyphosate‐resistant Italian ryegrass (Lolium multiflorum Lam.) was found on rice paddy levees in a western region of Shizuoka Prefecture, Japan. Naturalized populations of Italian ryegrass are frequently infected with fungal Epichloë endophytes. Endophytes often confer benefits to their host grasses. This study investigated the influence of five weed management treatments on glyphosate resistance and endophyte infection in Italian ryegrass that was growing on paddy levees where glyphosate‐resistant individuals were dominant. The weed management treatments were: (i) mowing once before the grass flowered; (ii) mowing once during flowering; (iii) mowing twice during flowering; (iv) glyphosate application before flowering; and (v) no treatment. The seeds were collected from the treatment plots in 2013 and 2014. The seeds were examined for endophyte infection and the seedlings that had been grown from the seeds were tested for the frequency of glyphosate resistance. The seedlings that had been derived from the glyphosate treatment showed higher frequencies of glyphosate resistance than those seedlings that had been derived from all the other treatments. Endophytes were found in all populations of the seeds from the paddy levees, with higher infection rates in the seeds that had been derived from the glyphosate treatment and the twice‐mowed treatment. There was a significant relationship between the endophyte infection frequency in the seeds and glyphosate resistance in the seedlings that had been grown from the same populations. The results indicate that where glyphosate herbicides are frequently used, selection for glyphosate‐resistant Italian ryegrass occurs, and along with this, the frequency of endophyte infection also increases.     

The development of tea blister caused by Exobasidium vexans in tea (Camellia sinensis) correlates with the reduced accumulation of some antimicrobial metabolites and the defence signals salicylic and jasmonic acids

Blister blight (causal agent, Exobasidium vexans) is an economically devastating disease of tea (Camellia sinensis). To determine what metabolite changes occur with tea blister that could be linked to disease progression, metabolomic approaches were used on E. vexans infected tea from a Darjeeling (India) plantation. Samples were classified according to disease phenotypes, i.e. either healthy or at one of three stages of disease progression. Initial metabolite fingerprinting using Fourier transform infrared (FTIR) spectroscopy indicated that metabolite changes could be related to disease stage. Electrospray ionization mass spectrometry (ESI‐MS) highlighted caffeine and flavonoid metabolism changes as disease progressed. High‐performance liquid chromatography (HPLC) with online photodiode array detection and electrospray ionization‐tandem mass spectrometry (HPLC‐PDA‐ESI/MSⁿ) was used to characterize the caffeine, flavan‐3‐ol, flavone and flavonol profiles. There were increases in quercetin and kaempferol glucosides, kaempferol triglycosides and some catechin‐class antioxidants, but also substantial reductions in apigenin and myricetin glycosides and, particularly, caffeine as disease progressed. The content of important defence hormones, salicylic acid and jasmonic acid, was also reduced in blister blight diseased samples. Thus, E. vexans infections perturb defence signalling and reduce many potentially antimicrobial compounds, such as caffeine, to aid disease progression.     

A novel pre‐emergence herbicide (Diclosulam) as an environmentally friendly weed management option in peanut and its phytotoxicity evaluation

A two‐season field experiment was conducted to evaluate the efficacy of diclosulam compared with recommended doses of pendimethalin and oxyfluorfen for weed management in peanut. Persistence of diclosulam in oil, de‐oiled cake, haulm of peanut, and soil was also studied. Diclosulam 22 and 26 g a.i. ha^?1, and a weed‐free check had a high pod yield due to more mature pods and their mass. Pre‐emergence application of diclosulam 26 g a.i. ha^?1 provided better weed management and enhanced peanut growth and yield with high net returns. Phytotoxicity studies indicated that the diclosulam application did not cause any phytotoxic symptoms (vein clearing, epinasty, hyponasty, wilting, and injury) on leaf tips and leaf surface of peanut. Diclosulam residues in peanut viz. oil, de‐oiled cake, haulm, and soil were below the detection level after harvesting of peanut from the experimental field. Further, germination percentage and seed cotton yield of cotton crop cultivated after peanut were also not affected significantly.     

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.     

Propanil‐resistant barnyardgrass [Echinochloa crus‐galli (L.) Beauv.] in Sri Lanka: Seedling growth under different temperatures and control

Experiments were conducted to (i) evaluate the efficacy of propanil formulations available in Sri Lanka in controlling Echinochloa crus‐galli; (ii) study the seedling growth of propanil‐resistant (R) and ‐susceptible (S) biotypes of the weed under different temperatures; (iii) quantify the level of resistance in R biotypes and; (iv) to suggest alternative control measures for R biotypes. Field studies showed that retail propanil formulations (36% a.i., EC) applied at 2.7 kg a.i. ha^?1 gave less than 30% control of E. crus‐galli collected from several locations of the north dry zone of Sri Lanka. Chemical analysis revealed that there was no adulteration of propanil formulations at the retailer level. Growth studies conducted in controlled environments indicated that per cent germination and seedling growth of R and S biotypes were similar at the day/night temperature regimes imposed. However, per cent germination for plants grown under a 34/31°C (day/night) regime was 27–29% higher compared to those grown at 28/24°C. At the higher temperature regime, R and S biotypes reached the 2–3 leaf stage five days earlier, and the 4–5 leaf stage seven days earlier. The ED₅₀ values from the dose–response experiments indicated that the R biotype was four times more resistant to propanil than susceptible ones. The resistance index (RI) did not vary significantly under different temperature regimes. Quinclorac (25% a.i., SC) applied at 200 g a.i. ha^?1 and bispyribac‐sodium (10% a.i., SC) applied at 30 g a.i. ha^?1 (recommended dosages) successfully controlled propanil‐resistant biotypes of E. crus‐galli. Conversely, oxadiazon and propanil (8% and 23% a.i., EC, respectively) applied at 280 + 805 g a.i. ha^?1 did not result in satisfactory control.