Potential uses of small unmanned aircraft systems (UAS) in weed research

Small unmanned aerial systems (UAS) with cameras have not been adopted in weed research, but offer low‐cost sensing with high flexibility in terms of spatial resolution. A small rotary‐wing UAS was tested as part of a search for an inexpensive, user‐friendly and reliable aircraft for practical applications in UAS imagery weed research. In two experiments with post‐emergence weed harrowing in barley, the crop resistance parameter, which reflects the crop response to harrowing, was unaffected by image capture altitude in the range from 1 to 50 m. This corresponded to image spatial resolution in the range from 0.3 to 17.1 mm per pixel. This finding is important because spatial resolution is inversely related to sensing capacity. We captured 20 plots comprising a total of about 0.2 ha in one image at 50 m altitude without losing information about the cultivation impacts on vegetation compared with ground truth data. UAS imagery also gave excellent results in logarithmic sprayer experiments in oilseed rape, where we captured 37 m long plots in each image from an altitude of 35 m. Furthermore, perennial weeds could be mapped from UAS images. These first experiences with a small rotary‐wing UAS show that it is relatively easy to integrate as a tool in weed research and offers great potential for site‐specific weed management.     

Simulating the effects of weed spatial pattern and resolution of mapping and spraying on economics of site-specific management

The economic benefits of using site‐specific weed management (SSWM) are related to the proportion of the field that is weed‐infested, the number of weed patches and the spatial resolution of sampling and spraying technologies. In this paper we simulate different combinations of these factors using parameter values obtained for Avena sterilis ssp. ludoviciana growing in Spanish winter barley crops. The profitability of SSWM systems increased as the proportion of the field infested by this weed decreased and when patch distribution was more concentrated. Under most of the conditions tested, positive net returns for SSWM were obtained when the weed‐infested area was smaller than 30%. The highest net return occurred using a 12 m × 12 m mapping and spraying resolution. The critical parameter that determined the economic viability of patch mapping and spraying resolution was the technology costs. The site specific strategy was economically superior to the standard strategy (overall herbicide application) in most cases. However, the differential between the two strategies decreased when the number of patches and the resolution of mapping and spraying increased, such that the highest net returns were obtained with a single patch covering 14% of the field and using a 12‐m mapping and spraying resolution; whereas the worst net returns were obtained for all patch numbers when 64% of the field was infested and a 3‐m mapping and spraying resolution was used.     

Practical experiences with a system for site-specific weed control in arable crops using real-time image analysis and GPS-controlled patch spraying

Information on temporal and spatial variation in weed seedling populations within agricultural fields is very important for weed population assessment and management. Primarily, spatial information allows a potential reduction in herbicide use, when post‐emergent herbicides are only applied to field sections with high weed infestation levels. This paper presents a system for site‐specific weed control in sugar beet, maize, winter wheat, winter barley, winter rape and spring barley. The system includes on‐line weed detection using digital image analysis, computer‐based decision making and Global Positioning System‐controlled patch spraying. In a 2‐year study, herbicide use with this map‐based approach was reduced in winter cereals by 6–81% for herbicides against broad leaved weeds and 20–79% for grass weed herbicides. Highest savings were achieved in cereals followed by sugar beet, maize and winter rape. The efficacy of weed control varied from 85% to 98%, indicating that site‐specific weed management will not result in higher infestation levels in the following crops.     

Innovation in mechanical weed control in crop rows

Weed control within crop rows is one of the main problems in organic farming. For centuries, different weed removal tools have been used to reduce weeds in the crop rows. Stimulated by the demand from organic farmers, research in several European countries over the last decade has focused on mechanisation using harrowing, torsion finger weeding and weeding with compressed air (Pneumat). Intelligent weeders are now being developed which offer more advanced ways to control weeds, including larger ones and to leave the crop plants unharmed. One of the first commercially available intelligent weeders, the Sarl Radis from France, has a simple crop detection system based on light interception, which guides a hoe in and out of the crop row, around the crop plants. The inclusion of innovative technologies, including advanced sensing and robotics, in combination with new cropping systems, might lead to a breakthrough in physical weed control in row crops leading to significant reductions, or even elimination, of the need for hand weeding.     

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.     

Development of chemical weed control and integrated weed management in China

More than 200 species of weeds are infesting main crop fields in China, among which approximately 30 species are major weeds causing great crop yield losses. About 35.8 million hectares of crop fields are heavily infested by weeds and the annual reduction of crop yields is 12.3–16.5% (weighted average). Along with rural economic development, approximately 50% of the main crop fields undergo herbicide application. Chemical weed control has changed cultural practices to save weeding labor in rice, wheat, maize, soybeans and cotton. At the same time, continuous use of the same herbicides has caused weed shift problems and weed resistance to herbicides. Consequently, integrated weed management in main crops is being developed.     

Real-time weed detection, decision making and patch spraying in maize, sugarbeet, winter wheat and winter barley

Information on temporal and spatial variation in weed seedling populations within agricultural fields is very important for weed population assessment and management. Most of all, it allows a potential reduction in herbicide use, when post‐emergence herbicides are only applied to field sections with weed infestation levels higher than the economic weed threshold; a review of such work is provided. This paper presents a system for site‐specific weed control in sugarbeet (Beta vulgaris L.), maize (Zea mays L.), winter wheat (Triticum aestivum L.) and winter barley (Hordeum vulgare L.), including online weed detection using digital image analysis, computer‐based decision making and global positioning systems (GPS)‐controlled patch spraying. In a 4‐year study, herbicide use with this map‐based approach was reduced in winter cereals by 60% for herbicides against broad‐leaved weeds and 90% for grass weed herbicides. In sugarbeet and maize, average savings for grass weed herbicides were 78% in maize and 36% in sugarbeet. For herbicides against broad‐leaved weeds, 11% were saved in maize and 41% in sugarbeet.     

Spatial distribution of weeds in arable crops: are current sampling and analytical methods appropriate?

This paper reviews the literature concerning the spatial distribution of weeds; highlighting the limitations of our current sampling and analytical methodologies, and suggesting how these inadequacies can be addressed. Most research studies have used discrete sampling, i.e. weeds are counted within a quadrat, on a grid basis. Few have mapped weeds at a whole-field scale, either with a resolution appropriate to spraying operations or key ecological processes. Statistical analyses used to describe the data can be divided into two main types, spatially implicit (also at the scale of the sampling unit) or spatially explicit, in which the location of individuals is included in the analyses. Spatially implicit methods can be strongly affected by quadrat size and mean density and are of doubtful benefit. More attention is required to address sampling resolution issues for spatially explicit methods. Our understanding of the formation and dynamics of spatial pattern, as well as predicting the consequences of site-specific management, can be improved with models. Unfortunately, most models consider only newly expanding patches and appear incapable of predicting spatial distributions when an area has been fully invaded. More detailed biological information is required if models are to become more realistic and informative. We also need to ensure that we understand the spatial processes in the context of the whole field environment, to optimize the success of site-specific weed management in the longer term.     

Influence of developmental stage and time of assessment on hot water weed control

Summary The influence of plant developmental stage in hot water weed control was studied on the test weed Sinapis alba in field experiments. The dose was measured as thermal energy in the hot water (kJ m⁻²) and the response as reduction in plant weight. The energy dose for a 90% reduction in plant weight was 340 kJ m⁻² at the two-leaf stage, which is one-third of the energy required for the same reduction at the six-leaf stage. Treatment at an early stage saves energy, increases the driving speed and lowers the costs. Hard surface areas with naturally developed weeds were used to study the required treatment interval and the influence of time of assessment on the reduction in weed cover. The required treatment interval was 25 d on average, which is similar to that of flame weeding. A longer lasting effect requires a higher energy dose. A 50% higher energy dose was needed to obtain a 90% reduction in weed cover that lasted for 15 d instead of 7 d. After 3–4 weeks, hardly any reduction could be recorded because of regrowth of perennial weeds. However, hot water weed control has a potential on urban hard surfaces and railroad embankments, especially where the use of herbicides is restricted.     

Non-chemical weed control on traffic islands: a comparison of the efficacy of five weed control techniques

The efficacy of five non‐chemical weed control methods for reducing weed cover on traffic islands was investigated in the growing season of 2004. Three trial sites were divided into six treatment areas which were treated with either flame, steam, hot air, hot water, brushes or left untreated. The treatments were carried out at regular intervals throughout the growing season. The percentage weed cover was measured every second week using a 75 × 75 cm quadratic frame with 100 squares. In the control areas, a rapid increase in weed cover was observed, whereas all treatments reduced weed cover. Hot water was the most effective method, although not significantly better than hot air or steam. Hot air treatment was more effective than brushing, whereas hot water was more effective than both flaming and brushing. The doses that were used were relatively high (150–355 kg ha^?1), partly because of the irregular shape of the traffic islands and the treatment intervals were quite short in comparison with those in similar studies. However, the treatments could keep down the weeds only to a certain extent. The present knowledge of the efficacy of various weed control methods, as well as an increase in our knowledge of adequate treatment intervals, supports an optimisation of hard‐surface weed control. Data and experience gained from these trials were used to develop further calibrated application studies.     

Integrated weed management: Quo vadis?

The different components of Integrated Weed Management (IWM), such as crop selection, crop husbandry, plant nutrition, crop protection, farm hygiene, and the site-specific conditions, all are factors having an influence on the successful adoption of the basic IWM concept. Farmers' field activities, directly or indirectly, affect germination and development of weeds as well as weed population dynamics. However, also important non-agronomic parameters indirectly affect weed management. They include farm structure, farmers' personal targets and preferences, the provision and communication of technical know-how, economics, but also demands from society and in the area of ecology. In the light of the many additional important influences and interactions, rather than thinking in terms of IWM, it seems appropriate to view crop production as a whole process, probably best defined as Integrated Crop Management (ICM). Boiling down the mass of information and outlining a rational, straightforward, easy-to-apply and cheap approach for the site-specific weed management is needed for the successful implementation of IWM principles within the framework of ICM.     

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.     

Use of mesotrione and tembotrione herbicides for post-emergence weed control in alkaloid poppy (Papaver somniferum)

Two field experiments were carried out a year apart on the alkaloid poppy (Papaver somniferum) in 2012 and 2013 in north-west Hungary, to assess the efficacy of mesotrione and tembotrione herbicides for post-emergence weed control. Our experiments tested (1) a single application of mesotrione at 144 g active ingredient (a.i.) ha^–1, (2) two separate applications of mesotrione at 144 g a.i. ha^–1, (3) a single application of tembotrione at 88 g a.i. ha^–1, (4) two separate applications of mesotrione at 88 g a.i. ha^–1, and (5) the combination of a single application of mesotrione at 144 g a.i. ha^–1 followed by a single application of tembotrione at 88 g a.i. ha^–1. Both non-treated and hand-weeded plots were used as controls. Among the most important weeds, Chenopodium album was most successfully controlled in the majority of the test treatments, but Fallopia convolvulus and Polygonum aviculare tolerated each herbicide application in 2012, likely due to the dry weather conditions. Because of the botanical similarity to the crop, none of the treatments proved to be significant against Papaver rhoeas. One dosage of tembotrione alone never reduced the dry weights of the target weed species or weed numbers significantly. The cuticular wax layer of the opium poppy can provide a natural defence against these herbicides, but some temporary phytotoxic yellowish discoloration occurred after tembotrione treatments. Our results show that mesotrione in combination with tembotrione is the most effective treatment and should be employed in poppy cultivation.     

我国农田杂草治理技术的发展

我国稻、麦、玉米、大豆及棉花等主要农作物农田杂草有580种,属于危害重而又难于防除的有17种,受杂草危害较重的农田有3 580万hm²,年平均受草害减产12.3％～16.5％(加权平均)。自1980年以来,全国化学除草面积以年增200万hm²的速度扩大,农田化学除草面积从20世纪70年代早期不到100万hm²扩大到近年来6 000万hm²。本文概述了我国农田主要作物杂草的发生危害、化学除草剂应用现状及其综合防治进展,并提出今后杂草防除的设想与建议。     

Critical periods for weed control in cotton in Turkey

Field studies were conducted over 4 years in south‐eastern Turkey in 1999–2002 to establish the critical period for weed control (CPWC). This is the period in the crop growth cycle during which weeds must be controlled to prevent unacceptable yield losses. A quantitative series of treatments of both increasing duration of weed interference and of the weed‐free period were applied. The beginning and end of CPWC were based on 5% acceptable yield loss levels which were determined by fitting logistic and Gompertz equations to relative yield data representing increasing duration of weed interference and weed‐free period, estimated as growing degree days (GDD). Total weed dry weight increased with increasing time prior to weed removal. Cotton heights were reduced by prolonged delays in weed removal in all treatments in all 4 years. The beginning of CPWC ranged from 100 to 159 GDD, and the end from 1006 to 1174 GDD, depending on the weed species present and their densities. Practical implications of this study are that herbicides (pre‐emergence residual or post‐emergence), or other weed control methods should be used in Turkey to eliminate weeds from 1–2 weeks post‐crop emergence up to 11–12 weeks. Such an approach would keep yield loss levels below 5%.     

Determining treatment frequency for controlling weeds on traffic islands using chemical and non‐chemical weed control

Many public authorities rely on the use of non‐chemical weed control methods, due to stringent restrictions on herbicide use in urban areas. However, these methods usually require more repeated treatments than chemical weed management, resulting in increased costs of weed management. In order to investigate the efficacy of four non‐chemical weed control methods and glyphosate treatment, experiments were carried out on traffic islands in the growing seasons 2005 and 2006. Three trial sites were each divided into six treatment areas, which were either treated with glyphosate, flame, steam, hot air/flame, hot water or left untreated. The treatments were carried out at regular, predetermined intervals throughout the growing season in 2004, whereas in 2005 and 2006 how many treatments that were required to keep weed cover below a predetermined acceptance level of 2% were investigated. Percentage weed cover was measured every second week using a 75 cm × 75 cm quadrat divided into 100 squares. On the control areas, a rapid increase in weed cover was observed, whereas weed cover could be kept below 2% by 2–7 treatments per year, depending on control method. On average, the following numbers of treatments per year were required: glyphosate 2.5, hot water 3, flames 5, hot air/flames 5.5 and steam 5.5 treatments. The results demonstrate that the weed control should be adjusted to the prescribed quality for the traffic islands by regularly assessing the need for weed control. They also show that tailored treatments can reduce the number of required non‐chemical treatments per year.     

基于农田养分管理的杂草生态防控策略

农田杂草是农田生态系统的一个组成部分,揭示杂草种群对养分管理模式的响应及其机制是进一步通过科学的养分管理来实现防控农田杂草的关键。为此,作者总结了农田养分管理与杂草的关系的研究进展、指出了存在的问题,并从农田杂草的重点防控对象、农田优势杂草种群和竞争临界期的确定以及杂草的生态化学计量学特征等方面对杂草生态防控策略进行了分析。在此基础上,作者提出了土壤营养调控假设,期望为制定农田杂草综合管理策略以及保护农田生态环境提供新的思路。     

Weed flora and weed management in established olive groves in Albania

Weed flora were surveyed during 2000 and 2001 in 10 established olive groves that were located in the area of Vlora, in south‐western Albania. The effectiveness of six weed management treatments (soil tillage, straw mulch, cover cropping [a mixture of rye with peas], and grazing, as well as glyphosate and diuron application) on the weed flora, olive yield, and fruit quality also were investigated in two locations during 2000, 2001, and 2002. More than 80 weed species were recorded, representing a total of 14 families, in which the families Poaceae, Fabaceae, Asteraceae, Ranunculaceae, and Rosaceae predominated. The glyphosate application provided the highest and most consistent level of weed control, whereas diuron achieved sufficient weed control. The straw mulch provided acceptable weed control but the cover crop and the grazing did not sufficiently control the weeds. The highest fruit and oil yields were produced by the trees treated with the straw mulch as a result of the highest mean fruit weight in each year, followed by the soil tillage treatment. However, the olive trees in the plots treated with glyphosate or grazing provided lower or equal, respectively, fruit and oil yields than did those in the untreated plots (control). The results indicated that certain non‐chemical weed control methods, such as straw mulch, can be implemented successfully in established olive groves, providing satisfactory control of weeds and promoting the highest fruit and oil yields.     

Arbuscular-mycorrhizal fungi: potential roles in weed management

The importance of interactions between arbuscular-mycorrhizal fungi (AMF) and weeds of agro-ecosystems is reviewed. Considerable evidence suggests that AMF can affect the nature of weed communities in agro-ecosystems in a variety of ways, including changing the relative abundance of mycotrophic weed species (hosts of AMF), and non-mycotrophic species (non-hosts). These effects may merely change the composition of weed communities without affecting the damage that these communities cause. However, it is quite plausible that interactions with AMF can increase the beneficial effects of weeds on the functioning of agro-ecosystems. Through a variety of mechanisms, weed:AMF interactions may reduce crop yield losses to weeds, limit weed species shifts, and increase positive effects of weeds on soil quality and beneficial organisms. If beneficial effects of AMF on the composition and functioning of weed communities can be confirmed by more direct evidence, then AMF could provide a new means of ecologically-based weed management. Intentional management will be required to increase diversity and abundance of AMF in many cropping systems, but these actions (e.g. conservation tillage and use of cover and green-manure crops) typically will confer a range of agronomic benefits in addition to potential improvements in weed management.     

Co‐operative versus non‐co‐operative farmers' weed control decisions in an agricultural landscape

This study presents a simple landscape model of the influence of seed dispersal on weed population dynamics between fields. In the model, three fields are interconnected through weed seed dispersal, where seed might move with field equipment, in irrigation water or may be wind‐dispersed. The model is intended to characterise the impact of field‐level weed management decisions on landscape‐level weed population dynamics. Two simple scenarios were studied. The first simulates farmers adopting common effective methods of control on each of the three fields. In the second scenario, farmers manage the weed population independently on each of the three fields. In the first scenario, weed populations were driven to extinction as might be expected with uniformly high levels of weed suppression in each of the three fields. In the second scenario, when the two nearest fields in the sequence experienced control, the weed population was driven to extinction in the second field but not in the first where weed populations were able to survive in spite of high levels of suppression. The results suggest that control measures within a field may not adequately reflect their impact on weed population dynamics when between field seed movement occurs. Another important result is the importance of proximity and spatial arrangement of fields and the resulting influence on weed population dynamics within a field.