Herbicide options for weed control in papaya

This paper reviews the literature on weeds and weed control in papaya. There is limited research on this topic, and nearly all of the research focuses on herbicides. Effective use of paraquat and glyphosate in papaya is dependent on avoidance of spray contact to green bark and foliage. Pre-emergence herbicide tolerance is dependent on papaya age, size and maturity, and soil type. Only one herbicide, oryzalin is shown to be tolerated by papaya immediately after transplanting. Herbicides such as diuron and oxyfluorfen with a broader spectrum of weed control generally injure young papaya, however they can be effectively used if the initial application of these herbicides is delayed until papaya attains certain size or maturity indices. There is a need for further research on weeds and weed control to improve the efficiency of papaya production     

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.     

Evaluation of finger weeder safety and efficacy for intra-row weed removal in irrigated field crops

Increased demand for pesticide-free food and the development of herbicide-resistant weed populations have created a need for non-chemical weed-control tools. A candidate mechanical tool for controlling weeds in the seeding line (intra-row zone) is the finger weeder. This study thus aimed to evaluate the safety and weed-control efficacy of the finger weeder in various irrigated field crops. Eight field trials were conducted in processing tomato, sweet corn, sunflower, cotton, and beetroot over 2 years. The finger weeder treatments were applied as the sole weed-control method (single or double treatments) and in combination with herbicides. A mini meta-analysis was used to evaluate the overall effect of the finger weeder treatments on crop stand and yield and on weed control efficacy. Weed density in the control not treated with herbicides nor a finger weeder ranged between 2 and 62 weeds m⁻². The finger weeder treatments resulted in a significant reduction in weed density, which ranged between 40% and 90%. The weed density following the double finger weeder treatment was not significantly different from that for the conventional herbicide-based treatment (p = 0.32) and could therefore be considered as an effective environmentally friendly alternative. Furthermore, a single FW treatment integrated with herbicide application gave better weed control than the conventional herbicide treatment (p = 0.04). This treatment was safe for the crops with no significant stand (p = 0.19) or yield (p = 0.29) reductions compared to commercial treatment. The results of this study demonstrate the promise of the finger weeder as an effective tool within integrated weed management systems for conventional agro-systems. The tool offers a rational weed-control solution for sustainable systems under irrigation.     

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.     

Weeds for weed control: Asteraceae essential oils as natural herbicides

The aim of this study was to test the botanical family of Asteraceae as a source of natural herbicides. Twenty Asteraceae species were collected during flowering time and evaluated in terms of the yield and quality of essential oils (germination inhibition and growth of weeds). Half the species showed a sufficient yield of essential oil (from about 0.1% to 1.43%) when testing these phytochemicals in vitro as germination inhibitors of two typical weeds, Amaranthus retroflexus and Setaria viridis. Despite the higher tolerance of S. viridis, the concentration of 100 μg L^?1 of essential oils of the two Artemisia species and Xanthium strumarium could totally inhibit germination. In addition, at 10 μg L ^?1, the same essential oils showed full inhibition of A. retroflexus seeds. A comparison of their effectiveness at suboptimal doses led to a further selection of the most promising sources of essential oils. After their chemical characterisation, the essential oils were tested as post‐emergence herbicides on seedlings of the above‐cited weeds. After spraying the weeds at different concentrations (10, 100 and 1000 mg L^?1) during two different phenological stages of weed seedlings (cotyledons and the third true leaf), the essential oils of Artemisia annua and X. strumarium showed the best performance. The essential oils of X. strumarium were then tested again on both weeds to monitor the dynamics of plant injury. A reduction in plant fresh weight (about 20%–30% after 10 days) and chlorophyll content (destroyed, after the same amount of time) was found, thus confirming the total and rapid effectiveness of these essential oils. In summary, A. annua and X. strumarium have elicited considerable agronomic interest and appear to be suitable as a source of essential oils to act as natural herbicides.     

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.     

Repeated grading of weed abundance and multivariate methods to improve the efficacy of on-farm weed control trials

We evaluated whether new information could be drawn from additional data collection and unconventional statistical analyses of an on-farm trial. First, we compared a conventional sampling method using a biomass estimate of weed abundance to repeated visual assessment of the percentage ground cover of weeds. The biomass was sampled once after the treatment, whereas the ground cover was repeatedly sampled once before weed control plus several occasions after weed control. Second, we contrasted the outcomes from analysis of variance ( anova ), taking samples from a single point in time with repeated measures (rm) anova and a multivariate method. As the outcomes and conclusions drawn were relatively similar, we conclude that the ground cover estimate of weed abundance was as reliable as the biomass estimate. The rm anova enabled us to follow the temporal trend in response to treatments in the most abundant species, including possible initial differences. Multivariate analysis went even further, by clearly displaying species-wise responses and treatment selectivity.     

The effect of crop,cultivation and seed addition for birds on surface weed seed densities in arable crops during winter

Weed seeds present an agronomic threat, but are also an important food resource for wildlife in winter. Weed seed densities on the soil surface in winter were examined from 1999 to 2002 in 105 fields on three different farms in UK. The effect of the preceding crop, cultivation, position within the field and the application of seed for birds (bird seed) on surface seed abundance and species composition was tested. Six or fewer species comprised c. 80% of the weed seeds. By January of each study year, the densities of seeds important for farmland birds (key seeds) were 73% or 87% lower compared with early winter on two of the farms, but were stable on the third where seeds were incorporated through cultivation. At the edge and mid‐field, seed densities only exceeded 400 m^?2 in 17%, 10% and 12% of fields for total, key and dicotyledonous seeds respectively. The preceding crop only affected seed densities at one site; stubbles of winter barley had fewer seeds compared with winter wheat or spring barley. Seed densities varied between the edge and mid‐field, but trends were inconsistent between sites. The density of the larger seeds (Atriplex patula, Viola arvensis, Polygonum aviculare and Chenopodium album) were reduced in fields receiving bird seed. The objectives of weed control and conservation may not be mutually exclusive because seed return was most reduced where the ground remained uncultivated through the winter, yet this also provided the best foraging opportunities for surface feeding seed predators.     

Weed species composition of conventional soyabean crops in Hungary is determined by environmental,cultural, weed management and site variables

The goal of this study was to identify factors determining weed species composition in soyabean crops in Hungary, where its expanding production faces difficult weed problems. The abundance of weed flora was measured in 262 fields across the country, along with 38 background variables. Using a minimal adequate model containing 24 terms with significant net effects, 21.6% of the total variation in weed species data could be explained. Plot location (edge vs core position, the single site variable in our analysis) was found to be the most important explanatory variable that was followed by a set of environmental (temperature, precipitation, altitude, soil texture, pH, Ca, K, Na and humus content), cultural (cultivar maturity, organic manure, fertiliser P and N, row spacing) and weed management (flumioxazin, pendimethalin, dimethenamid, propaquizafop, bentazone, quizalofop‐p‐ethyl, quizalofop‐p‐tefuril, linuron, thifensulfuron) factors. Variation partitioning revealed that environmental variables accounted for about four times more variance than cultural and about two and half times more than weed management variables. Chenopodium album, Ambrosia artemisiifolia, Hibiscus trionum, Echinochloa crus‐galli and Convolvulus arvensis were the most dominant and frequent weeds, but their abundance was influenced by different factors. The responses of weed species to the studied variables provide new information about their ecological behaviour, and our findings also can be used to develop better weed management strategies.     

Critical period for weed control in sesame production

Planning effective weed control in cropping systems requires exact appraisal of the weed intensity and duration of their competition with the crops. This 2‐year study was carried out in order to determine the critical weed control period in sesame fields. Related and relative crop yields were monitored and analyzed using a four‐parametric log‐logistic model. We recorded data from weed‐free plots and compared these with data from different periods of weed interference. In both the study years, the longer period of weed interference decreased the relative yield of sesame, whereas the yield was increased with increasing duration of the weed‐free period. A 51–78.7% decline in sesame yield was noted if the weeds were allowed to compete with the crop from planting to harvest. In the first year, the duration of the critical period for weed control (CPWC) was 177–820 growing degree days (GDD), which corresponded to 14–64 days after crop emergence (DAE), and between 170 and 837 GDD (13–64 DAE) in the second year; this was based on a 5% acceptable yield loss. The results of this study clearly elaborated that maintaining weed‐free conditions is compulsory from as early as the second week after the emergence of sesame plants, and this should be maintained at least until the ninth week to avoid sesame yield losses by more than 5%. These findings show that growers can benefit from CPWC to improve weed control in sesame production, including the efficacy of a weed control program and its cost.     

河西走廊玉米与豆科作物间作田化学除草及对作物安全性的研究

玉米与豆科作物复合种植是河西走廊地区重要的粮经作物栽培模式,杂草危害是该复合种植体系中普遍存在的重要问题。本文采用田间裂区试验设计的方法研究了5种除草剂(或配方)对玉米与3种豆科作物-大豆Glycine max、赤小豆Vigna umbellata和菜豆Phaseolus vulgaris间作田杂草的防除效果和对两类作物的安全性。结果表明,除草剂对杂草的防效为81.67%～91.55%,显著高于当地常规玉米单作的化学除草处理(P<0.05),5种药剂处理对苗期玉米无明显药害,而对3种豆科作物幼苗均有不同程度的不利影响。玉米收获期900 g/L乙草胺EC、900 g/L乙草胺EC+87.5%2,4-滴异辛酯EC和900 g/L乙草胺EC+10%唑嘧磺草胺SC 3种药剂处理条件下三种间作组合的玉米+豆科作物总产量均高于空白对照,且与各自的人工除草处理相当或更优;本试验5种药剂处理条件下玉米与3种豆科作物间作组合的玉米+豆科作物总产量均与玉米单作常规化学除草处理相当或更优。研究结果可为西北河西走廊地区玉米与豆科作物间作模式下田间杂草的安全、高效化学防除提供技术参考。     

我国芝麻田杂草防控现状及建议

本研究对我国主要芝麻产区杂草发生情况和防控现状进行了调查。结果显示, 我国芝麻田杂草共计31科86种, 使用的除草剂共15种, 普遍存在阔叶杂草难防控等问题。芝麻田杂草防控难与科研基础薄弱和可用除草剂品种严重不足有关。针对上述情况, 提出加大基础研究力度、重视除草剂筛选登记工作、加强抗除草剂育种、加速植保机械的研发及产业化、研究和推广注重芝麻田生态系统保护的标准化防控技术等建议。     

Integrating preventive and curative non‐chemical weed control strategies for concrete block pavements

Reduction in herbicide use in non‐agricultural areas is being imposed by a growing number of governments, triggering the development of alternative strategies for weed prevention and control. This study aimed to determine the weed preventive abilities of different paving types, the required treatment frequency of non‐chemical weed control scenarios on these pavements and the associated weed species composition. A test parking area, constructed with four concrete paving types, was sown with a mixture of dominant weed species. Six scenarios with repeated use of a single weed control method (brushing with waste removal, hot air, selective application of hot water and three scenarios with flaming) and two scenarios with alternating use of brushes and hot air were applied to control the weeds during two growing seasons. Treatments were applied at well‐defined intervention moments, based upon weed development. Over 2 years, the paving types differed in weed coverage (up to a fourfold difference) and required varying treatment frequency (up to a 11‐fold difference) with lowest values for pavings with porous pavers. Within most paving types, up to 28% lower treatment frequencies were found for selective application of hot water, as compared with all other single method scenarios. Shifts in weed composition occurred in plots treated repeatedly with the same technique. Paving type determined the chances for the establishment of different weed species and alternating non‐chemical control methods with different modes of action offered the best opportunity to keep weeds under control.     

Predicting the risk of weed infestation in winter oilseed rape crops

Chemical weed control before crop and weed emergence is a systematic practice in winter oilseed rape crops in France. It would be profitable both for farmers and the environment to predict the level of weed infestation early on in the growing season and to control weeds only when necessary using post‐emergence weed control. The objective of this paper was to develop and evaluate simple models to predict weed biomass in oilseed rape crops. The model input variables were related to weed population characteristics and farmers’ practices. The models can be used to classify oilseed rape plots into two categories: plots with a level of weed infestation above a threshold or those with level of weed infestation below a threshold. A data set including 3 years of experiments, conducted across several regions in France, was used to estimate the parameters and to evaluate the models. High values of sensitivity and specificity were obtained when weed biomass was predicted as a function of sowing date, type of soil tillage, soil mineral nitrogen, crop density, weed density at emergence, and main characteristics of the most abundant weed species. Model performance strongly decreased when input variables related to the weed population were not taken into account. The best models correctly classified 90% of the plots with high weed infestation and 64% of the plots with low weed infestation.     

Combining physical, cultural and biological methods: prospects for integrated non-chemical weed management strategies

Physical, cultural and biological methods for weed control have developed largely independently and are often concerned with weed control in different systems: physical and cultural control in annual crops and biocontrol in extensive grasslands. We discuss the strengths and limitations of four physical and cultural methods for weed control: mechanical, thermal, cutting, and intercropping, and the advantages and disadvantages of combining biological control with them. These physical and cultural control methods may increase soil nitrogen levels and alter microclimate at soil level; this may be of benefit to biocontrol agents, although physical disturbance to the soil and plant damage may be detrimental. Some weeds escape control by these methods; we suggest that these weeds may be controlled by biocontrol agents. It will be easiest to combine biological control with fire and cutting in grasslands; within arable systems it would be most promising to combine biological control (especially using seed predators and foliar pathogens) with cover‐cropping, and mechanical weeding combined with foliar bacterial and possibly foliar fungal pathogens. We stress the need to consider the timing of application of combined control methods in order to cause least damage to the biocontrol agent, along with maximum damage to the weed and to consider the wider implications of these different weed control methods.     

Recent advances in allelopathy for weed control: from knowledge to applications

Allelopathy is the biological phenomenon of chemical interactions between living organisms in the ecosystem, and must be taken into account in addressing pest and weed problems in future sustainable agriculture. Allelopathy is a multidisciplinary science, but in some cases, aspects of its chemistry are overlooked, despite the need for a deep knowledge of the chemical structural characteristics of allelochemicals to facilitate the design of new herbicides. This review is focused on the most important advances in allelopathy, paying particular attention to the design and development of phenolic compounds, terpenoids and alkaloids as herbicides. The isolation of allelochemicals is mainly addressed, but other aspects such as the analysis and activities of derivatives or analogs are also covered. Furthermore, the use of allelopathy in the fight against parasitic plants is included. The past 12 years have been a prolific period for publications on allelopathy. This critical review discusses future research areas in this field and the state of the art is analyzed from the chemist's perspective. © 2019 Society of Chemical Industry     

Reducing intrarow weed numbers in row crops by means of a biennial cultivation system

Intrarow weed emergence in row crops can be reduced by means of a biennial cultivation system that is based on an exhaustion of the weed seedbank in the upper soil layer of crop‐free bands established in a preceding cereal crop, year I, before the row crop, year II. In this study, a series of field experiments is presented focusing more specifically on the influence of prevention of weed seed shedding and of different cultivation tactics in the system on intrarow weed emergence in the bands in year II. As the system excludes inverting soil tillage between years I and II, the prevention of weed seed shedding in year I turned out to be a key factor in achieving the desired effect of the system. This was seen with spring barley grown in year I, but not with winter wheat, where the system actually resulted in an increase in intrarow weed numbers in spite of the measures taken in year I. Cultivating the crop‐free bands in spring barley in year I with conventional goose‐foot shares in order to enhance seed germination and mortality further had no significant effects regardless of time and intensity. Results from two other experiments, in which freshly shed weed seeds were incorporated into the soil, supported the finding that cultivating the bands was of no advantage.     

Evaluation of the allelopathic potential of Kava (Piper methysticum L.) for weed control in rice

Kava is a perennial pepper plant from the Oceanic region, which is commonly used as a drink by natives and for pharmacological purposes. Results of this study concluded that Kava has allelopathic potential and suppressed germination and growth of lettuce ( Lactuca sativa L), barnyardgrass ( E. crus-galli Beauv var. formosensis Ohwi.), and duck-tongue weed ( M. vaginalis Presl var. plantaginea Solms-Laub.) Moreover, Kava inhibited emergence of weeds in paddy soils. The inhibition of Kava became stronger as the applied concentration increased. In a greenhouse experiment, Kava had the greatest inhibition on emergence and weed growth in paddy soils when a dose of 1 ton ha⁻¹ of Kava was divided and applied at 3, 16, and 23 days after watering. Inhibition by Kava varied among weed species. Results from this study suggest that Kava might be useful for weed control in rice or reduce dependence on herbicide.