Is the current state of the art of weed monitoring suitable for site‐specific weed management in arable crops?

Weed monitoring is the first step in any site‐specific weed management programme. A relatively large variety of platforms, cameras, sensors and image analysis procedures are available to detect and map weed presence/abundance at various times and spatial scales. Remote sensing from satellites or aircraft can provide accurate weed maps when the images are obtained at late weed phenological stages. Cameras located on unmanned aerial vehicles (UAVs) have been shown to be adequate for early‐season weed detection in a variety of wide‐row crops, providing images with relatively high spatial resolutions. Alternatively, weed detection/mapping systems from ground‐based platforms can achieve even higher resolutions using a variety of non‐imaging and imaging technologies. These ground systems are suited, in some cases, for real‐time site‐specific weed management. Despite this rich arsenal of technologies, their commercial adoption is, apparently, low. In this study, we describe the state of the art of remotely sensed and ground‐based weed monitoring in arable crops and the current level of adoption of these technologies, exploring major constraints for adoption and trying to identify research gaps and bottlenecks.     

The utility of the ‘Arable Weeds and Management in Europe’ database: Challenges and opportunities of combining weed survey data at a European scale

Over the last 30 years, many studies have surveyed weed vegetation on arable land. The ‘Arable Weeds and Management in Europe’ (AWME) database is a collection of 36 of these surveys and the associated management data. Here, we review the challenges associated with combining disparate datasets and explore some of the opportunities for future research that present themselves thanks to the AWME database. We present three case studies repeating previously published national scale analyses with data from a larger spatial extent. The case studies, originally done in France, Germany and the UK, explore various aspects of weed ecology (community composition, management and environmental effects and within-field distributions) and use a range of statistical techniques (canonical correspondence analysis, redundancy analysis and generalised linear mixed models) to demonstrate the utility and versatility of the AWME database. We demonstrate that (i) the standardisation of abundance data to a common measure, before the analysis of the combined dataset, has little impact on the outcome of the analyses, (ii) the increased extent of environmental or management gradients allows for greater confidence in conclusions and (iii) the main conclusions of analyses done at different spatial scales remain consistent. These case studies demonstrate the utility of a Europe-wide weed survey database, for clarifying or extending results obtained from studies at smaller scales. This Europe-wide data collection offers many more opportunities for analysis that could not be addressed in smaller datasets; including questions about the effects of climate change, macro-ecological and biogeographical issues related to weed diversity as well as the dominance or rarity of specific weeds in Europe.     

What criteria are relevant for predicting the invasive capacity of a new agricultural weed? The case of invasive American species in France

In Europe, exotic species are assessed for their potential threat only after they have already become weeds. To test hypotheses underlying risk assessment procedures, 274 North and South American exotic species naturalized in France were compared to differentiate environmental from agricultural weeds and to characterize weeds of several crops. Most agricultural exotic weeds belonged to the Asteraceae and the Poaceae, but proportionally to the total number of invasive species from a family the most successful families were the Amaranthaceae, Euphorbiaceae and Poaceae. Weed status in North and South America was the best predictor of agricultural weed status in France, and a pre-1900 date of introduction was associated with a greater likelihood of having become a major weed. The characteristics of 78 species present in field crops were examined in relation to management practices. In annual crops, the life-cycle compatibility of weeds appeared to be the main factor of selection. Exotic species differed in their C4 photosynthesis pathway in maize and rice. In vineyards, many ecological strategies are possible because the habitat is heterogeneous. Intrageneric comparison of exotic and native species showed a superior relative growth rate and higher biomass production under nutrient-rich conditions for exotics. However, it is still difficult to find a predictive function that fits well with all observed cases of weed invasion.     

Changes in sediment discharge in a sediment-rich region of the Yellow River from 1955 to 2010： implications for further soil erosion control

The well-documented decrease in the discharge of sediment into the Yellow River has attracted considerable attention in recent years. The present study analyzed the spatial and temporal variation of sediment yield based on data from 46 hydrological stations in the sediment-rich region of the Yellow River from 1955 to 2010. The results showed that since 1970 sediment yield in the region has clearly decreased at different rates in the 45 sub-areas controlled by hydrological stations. The decrease in sediment yield was closely related to the intensity and extent of soil erosion control measures and rainstorms that occurred in different periods and sub-areas. The average sediment delivery modulus(SDM) in the study area decreased from 7,767.4 t/(km2?a) in 1951–1969 to 980.5 t/(km2?a) in 2000–2010. Our study suggested that 65.5% of the study area with the SDM below 1,000 t/(km2?a) is still necessary to control soil deterioration caused by erosion, and soil erosion control measures should be further strengthened in the areas with the SDM above 1,000 t/(km2?a).     

Weed or not a weed? Density,perceptions and management of Chromolaena odorata (Asteraceae) in West Africa: Voices from Ghana

The status (weed or beneficial shrub) of Chromolaena odorata in West Africa has been a major subject of debate since its introduction in the 1930s. Its negative impacts on agriculture and biodiversity are clear. However, indigenous people have harnessed several benefits of the plant, making management strategies less straightforward. Using indigenous voices in Ghana, the current perceptions of C. odorata in West Africa were assessed. Here, 90 respondents in three regions of Ghana were interviewed, using questionnaires, on aspects relating to the abundance, perceptions and management of C. odorata in their communities. Overall, results showed that the density of C. odorata had declined. The majority of the respondents considered C. odorata as a fallow shrub, a medicinal plant or both. However, impacts on crop production and injuries incurred during physical control were also highlighted. The local uses of the plant in Ghana included treating fevers and injuries, and as a fallow shrub for soil nutrient replenishment. Although most of the respondents classified C. odorata as a useful shrub in Ghana, they also highlighted the use of local farming tools such as cutlasses for the slash of the plant. The use of herbicides for the control of C. odorata was rare and not applied specifically for C. odorata. In conclusion, local awareness programmes on the deleterious impacts of C. odorata on ecosystem functioning and livelihoods are required for its effective management in West Africa.     

Powdery mildew of Arabidopsis thaliana: a pathosystem for exploring the role of silicon in plant–microbe interactions

Silicon (Si) has been used in agriculture to protect plants against disease for hundreds of years and its prophylactic effects in monocots and dicots are well documented. The mechanisms by which Si exerts its protective effects in planta, however, are uncertain and presently the subject of debate. In this study, we sought to determine if Arabidopsis thaliana could be used to clarify the role of Si in plant–pathogen interactions. Accordingly, X-ray microanalysis mapping, light microscopy, scanning and transmission electron microscope techniques were used to examine the leaves of Si− fed A. thaliana plants inoculated with the powdery mildew fungus, Erysiphe cichoracearum. The results of this study demonstrate for the first time, that A. thaliana is a species that absorbs Si and that the incidence of powdery mildew disease for Si− fed plants is significantly lower compared to control plants. In particular, treatment with Si appeared to induce the production of an electron-dense, fungitoxic substance that accumulated within and around the collapsed fungal haustoria of infected epidermal cells within the leaves of disease-resistant plants. These results with Arabidopsis corroborate recent observations in other non-related species and support the emerging theory that the mechanisms by which Si imparts resistance to plants are complex and are not entirely explained by the traditionally proposed role of Si as a reinforcer of mechanical resistance. Collectively, the findings of the present study have established the Arabidopsis thaliana-Erysiphe cichoracearum pathosystem as a valid model to investigate the role of Si in plant–microbe interactions.     

First record of the impact of the parasitism of Cecidochares connexa (Diptera: Tephritidae) by a solitary larval ectoparasitoid in West Africa: Cause for concern?

Journal of Plant Diseases and Protection - Cecidochares connexa is currently the only effective biological control agent of Chromolaena odorata an invasive weed in West Africa. Recently, an...     

Gamma radiation sensitivity of the eggs, larvae and pupae of Indian meal moth Plodia interpunctella (Hübner) (Lepidoptera: Pyralidae)

BACKGROUND: This study focused on determining the minimal effective gamma radiation dose that prevents commodity damage caused by the Indian meal moth Plodia interpunctella (Hübner). The study was also designed to assess the effect of releasing either partially sterilized males alone or both partially sterilized males and females on the reproductive potential of P. interpunctella populations. RESULTS: The dose of radiation required to prevent larval emergence from irradiated eggs was 350 Gy, and the same dose was also required to prevent adult emergence from mature larvae. A dose of 300 Gy was not able to prevent adult emergence from irradiated pupae. The dose at which 100% sterility was achieved in treated females mated to treated males was 300 Gy for the parental generation of irradiated pupae. Fertility of the parental males from irradiated pupae was 48.17% at 300 Gy in treated males crossed with untreated females, but male progeny of irradiated male parents had a residual fertility of 11.06% at the same dose. CONCLUSION: F(1) males from irradiated pupae were more sterile than parental males. To prevent larval emergence from irradiated eggs, a dose of 350 Gy is required. The same dose is required to prevent the larvae from reaching the adult stage.     

(Q)SAR tools for the prediction of mutagenic properties: Are they ready for application in pesticide regulation?

The assessment of human health risks resulting from the presence of metabolites in groundwater and food residues has become an important element in pesticide authorisation. In this context, the evaluation of mutagenicity is of particular interest and a paradigm shift from exposure‐triggered testing to in silico‐based screening has been recommended in the European Food Safety Authority (EFSA) Guidance on the establishment of the residue definition for dietary risk assessment. In addition, it is proposed to apply in silico predictions when experimental mutagenicity testing is not possible due to a lack of sufficient quantities of the pesticide metabolite. This, combined with animal welfare and economic considerations, has led to a situation where an increasing number of in silico studies are submitted to regulatory authorities. Whilst there is extensive experience with in silico predictions for mutagenicity in the chemical and pharmaceutical industry, their suitability in pesticide regulation is still insufficiently considered. Therefore, we herein discuss critical issues that need to be resolved to successfully implement (Quantitative) Structure‐Activity Relationship ((Q)SAR) as an accepted tool in pesticide regulation. For illustration purposes, the results of a pilot study are included. The presented study highlights a need for further improvement regarding the predictivity and applicability domain of (Q)SAR systems for pesticides and their metabolites, but also raises other questions such as model selection, establishment of acceptance criteria, harmonised approaches to the combination of model outputs into overall conclusions, adequate reporting and data sharing. © 2020 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.     

Field efficacy of permethrin and fenvalerate applied as sprays to cattle for control of Boophilus microplus (Canestrini) (Acari: Ixodidae) in the eradication program in Puerto Rico∗

Abstract

Permethrin applied as a spray to cattle at 0.025% or 0.05% effectively controlled Boophilus microplus (Canestrini) by the third day post‐treatment, but only provided < 60% control within 1 day post‐treatment with both concentrations. Percentage control did not drop below 90% until day 28 for 0.025% and day 31 for 0.05% permethrin; percentage control did not fall below 92% for 0.025% fenvalerate until after day 24–25; and at 0.05%, fenvalerate provided 95% control until day 28. A multiple treatment (spray applied every 2 weeks) with permethrin (0.05%) provided greater than 96% control of B. microplus after the initial treatment and 100% control by day 56. We concluded that although both chemicals have potential in an eradication program, they are not satisfactory for use at a quarantine line because both acaricides provided less than 100% control within 1 day post‐treatment.     

MoTlg2, a t-SNARE component is important for formation of the Spitzenkörper and polar deposition of chitin in Magnaporthe oryzae

T-SNAREs are a family of conserved proteins involved in intracellular transport of membrane-coated cargo among subcellular compartments. In this study, we identified a putative t-SNARE gene, MoTLG2, in Magnaporthe oryzae via insertion mutagenesis. Deletion of MoTLG2 resulted in slower vegetative growth and less conidiation relative to the wild-type strain, but the ΔMotlg2 null mutant was as virulent as the wild-type strain. MoTlg2 has 30% overall amino acid identity with Saccharomyces cerevisiae Tlg2, and rescued the defect of monensin de-sensitivity in the yeast strain where TLG2 had been deleted. More importantly, apical regions of the hyphae of the ΔMotlg2 null mutant were only weakly stained by FM4-64, which was reported as an excellent vesicle tracer, suggesting that the Spitzenkörper was not well formed in the ΔMotlg2 null mutant. In addition, more uneven lateral deposition of chitin was observed in the cell wall of vegetative hyphae of the ΔMotlg2 null mutant. Taken together, this study shows that the t-SNARE Tlg2 is important for both vegetative hyphal growth and conidiation, but dispensable for plant infection in filamentous fungi, and suggests that Tlg2 is important for formation of the Spitzenkörper and polar distribution of chitin.     

Invasion of Phytophthora infestans at the landscape level: how do spatial scale and weather modulate the consequences of spatial heterogeneity in host resistance?

Strategic spatial patterning of crop species and cultivars could make agricultural landscapes less vulnerable to plant disease epidemics, but experimentation to explore effective disease-suppressive landscape designs is problematic. Here, we present a realistic, multiscale, spatiotemporal, integrodifference equation model of potato late blight epidemics to determine the relationship between spatial heterogeneity and disease spread, and determine the effectiveness of mixing resistant and susceptible cultivars at different spatial scales under the influence of weather. The model framework comprised a landscape generator, a potato late blight model that includes host and pathogen life cycles and fungicide management at the field scale, and an atmospheric dispersion model that calculates spore dispersal at the landscape scale. Landscapes consisted of one or two distinct potato-growing regions (6.4-by-6.4-km) embedded within a nonhost matrix. The characteristics of fields and growing regions and the separation distance between two growing regions were investigated for their effects on disease incidence, measured as the proportion of fields with ≥1% severity, after inoculation of a single potato grid cell with a low initial level of disease. The most effective spatial strategies for suppressing disease spread in a region were those that reduced the acreage of potato or increased the proportion of a resistant potato cultivar. Clustering potato cultivation in some parts of a region, either by planting in large fields or clustering small fields, enhanced the spread within such a cluster while it delayed spread from one cluster to another; however, the net effect of clustering was an increase in disease at the landscape scale. The planting of mixtures of a resistant and susceptible cultivar was a consistently effective option for creating potato-growing regions that suppressed disease spread. It was more effective to mix susceptible and resistant cultivars within fields than plant some fields entirely with a susceptible cultivar and other fields with a resistant cultivar, at the same ratio of susceptible to resistant potato plants at the landscape level. Separation distances of at least 16 km were needed to completely prevent epidemic spread from one potato-growing region to another. Effects of spatial placement of resistant and susceptible potato cultivars depended strongly on meteorological conditions, indicating that landscape connectivity for the spread of plant disease depends on the particular coincidence between direction of spread, location of fields, distance between the fields, and survival of the spores depending on the weather. Therefore, in the simulation of (airborne) pathogen invasions, it is important to consider the large variability of atmospheric dispersion conditions.     

Phenotypic and genotypic changes in French populations of Phytophthora infestans: are invasive clones the most aggressive?

The main objective of this investigation was to test the ‘always more aggressive’ hypothesis, often advocated to explain lineage replacements in clonal populations of the potato late blight oomycete Phytophthora infestans. To this end, genotypic and pathogenicity data on 1274 French isolates of P. infestans, collected over the period 2001–2008, were analysed. Overall, the populations sampled showed limited genetic diversity, with four multilocus lineages (1_A1, 2_A1, 8_A1 and 13_A2) accounting for over 80% of the isolates collected. As in other West European countries, drastic changes in these dominant clonal lineages were observed over the course of the 8 years, particularly in the appearance and propagation of the clone 13_A2. However, invasiveness of clones was not associated with higher aggressiveness; on the contrary, dominant clones had generally low or moderate aggressiveness relative to others present at the same time within the same populations. This finding challenges the link between invasive behaviour and increased aggressiveness often assumed for this biotrophic pathogen, and could reflect the existence of a trade‐off between intra‐season and inter‐season transmission. This would be consistent with the concept of inclusive fitness, which involves the abilities to both reproduce and survive.     

Plant and veterinary disease diagnosis: a generic approach to the development of field tools for rapid decision making?

Rapid and accurate diagnostic tests make an important contribution to programmes to monitor and eradicate infectious diseases that impact animal and plant health. Using foot-and-mouth disease (FMD) and sudden oak death as examples, this review outlines recent progress to develop new field tools for detection of the infectious agents that cause high-impact livestock and plant diseases. The principal driver for this work is to develop tools that can be used locally to assist in decision making. Advances in this area have developed simple-to-use lateral-flow devices for the detection of FMD virus and the genus Phytophthora (including Phytophthora ramorum , the causal agent of sudden oak death and the related pathogen P. kernoviae ), as well as new hardware platforms to allow PCR testing for these agents by non-specialists in the field. Although developed for different diseases, the user requirements for rapid diagnostic tools for FMD and sudden oak death share many similarities. Using generic solutions to these challenging problems, it is now possible to imagine a new paradigm for how the collection and testing of samples to monitor the spread of important livestock and plant diseases might be achieved.     

Use of different plastics for soil solarization in strawberry growth and time–temperature relationships for the control of <Emphasis Type="Italic">Macrophomina phaseolina</Emphasis> and weeds

The aim of this study was to determine the effect of soil solarization on soilborne diseases, weeds and plant yields by using polyethylene film (30-μm-thick) containing different additives [ultraviolet (UV), ultraviolet + infrared (UV + IR), ultraviolet + infrared + anti-fog + anti-dust (UV + IR + AF + AD)], and used polyethylene film (260-μm-thick). Trials were conducted in commercial strawberry (Fragaria ananassa cv. ‘Camarosa’) fields in the town of Sultanhisar in Aydin province, Turkey, between 2007 and 2009. The highest soil temperatures at the depth of 10 cm under a polyethylene sheet containing UV + IR + AF + AD were 54°C in 2007 and 50.7°C in 2008. During the 2007 growing season, collapse and death of strawberry plants were not detected. At the end of the 2008 season (May–June), collapsed and dying strawberry plants were observed. Pure cultures of Macrophomina phaseolina and Rhizoctonia solani were isolated from affected roots and crowns of plants. Viability studies of M. phaseolina were conducted under various field conditions and temperatures and M. phaseolina sclerotia survived more than 18 days at 45°C. There was a sharp decline in M. phaseolina at 50°C, where it survived for 19 h but was completely killed at 20 h. It first lost viability after 17 h at 50°C and after 60 min at 55°C. In the field, solarization did not reduce the viability of M. phaseolina at a soil depth of 10 or 20 cm; however, a significant reduction (66%) in survival was determined at a soil depth of 5 cm. All treatments controlled Portulaca oleracea, Amaranthus spp., Digitaria sanguinalis, Echinochloa crus-galli, Veronica hederifolia, Raphanus raphanistrum, Setaria verticillata and Mercurialis annua at a rate of 100%, but no treatment was effective on Cyperus rotundus. The marketable fruit yield was 38,004 kg.ha⁻¹ for UV + IR, 35,834 kg.ha⁻¹ for UV-added polyethylene film and 35,368 kg.ha⁻¹ for used polyethylene sheet-covered plots, whereas it was 27,365 kg.ha⁻¹ for untreated control plots.