Biology of milk thistle (Silybum marianum) and the management options for growers in north-western Pakistan

Milk thistle ( Silybum marianum ) is cultivated as a medicinal plant but it also can be a troublesome weed. It is an annual or biennial herb that prefers high rainfall and fertile soils. Milk thistle has become a widespread weed in north-western Pakistan, where it causes yield reductions ≤37% in wheat and poses harvesting problems due to its thorny nature. Shortcomings in cultural practises, such as a low crop seed rate, wide row spacing, broadcast fertilizer, and limited crop rotation have contributed to milk thistle becoming a severe weed problem for farmers in this region. This paper reviews the biology of milk thistle and discusses the possible management options for its control, considering the socioeconomic conditions of farmers in Pakistan.     

The crucial role of information exchange and research for effective responses to biological invasions

Farmers have been fighting weeds and pests since the beginnings of agriculture, but the impacts of invasive alien species (IAS) on native species, habitats and ecosystem services have only been brought to the world's attention relatively recently. Invasive plants, also known as environmental weeds, constitute an insidious 'biological pollution'. Unlike many other types of pollution, they are not diluted in time but, on the contrary, can expand in numbers, density and geographical extent – often exponentially. This paper illustrates an increasing ability to fight back, using a number of case studies of good management practice, including prevention, ecosystem approaches, adaptive management and stakeholder involvement. It identifies some of the challenges inherent in managing IAS in complex situations and identifies areas where weed scientists and other researchers can increase their contributions. Crucially, communities, conservation groups, NGOs and agencies undertaking prevention and management activities need ready access to science-based biological and ecological information about target species, prevention strategies and management techniques, as well as case studies from other regions facing similar problems. Information exchange is a key component of effective responses to biological invasions. A number of global-scale information exchange mechanisms are described.     

The influence of water level and nutrient availability on growth and root system development of Myriophyllum aquaticum

Myriophyllum aquaticum is an aquatic plant of still or slow flowing waters. The species mostly occurs in its emerged growth form in dense stands, but submerged shoots can also be found. Due to its rapid growth, M. aquaticum is considered one of the most important aquatic weeds worldwide. In southern Europe, M. aquaticum occurs in irrigation and drainage systems, rice fields and lowland wetlands. In this study, root development and growth response of M. aquaticum to different water levels and nutrient availabilities were investigated in a rhizotron experiment under Central European climatic conditions. The species shows an ability to respond to drained soil conditions by a rapid root growth (up to >1 cm day⁻¹), resulting in a deep root system under drained conditions. In waterlogged soil, the root system spreads more horizontally. Root density increased with increasing nutrient availability. Root:shoot ratio increased significantly with decreasing nutrient availability. In addition, total shoot length, shoot biomass, root biomass and total biomass differed significantly between different water levels and different nutrient availabilities. Relative growth rate increased with increasing water level and nutrient availability. Shoot porosity was higher in nutrient rich substrate than in nutrient low substrate. Root porosity increased with increasing water level. In conclusion, M. aquaticum shows a high tolerance to different water levels, which may be important for future habitat conditions in waterbodies and wetlands in Central Europe under the impact of global change with increased water level fluctuations.     

An on-farm approach to investigate the impact of diversified crop rotations on weed species richness and composition in winter wheat

Weed species diversity may benefit from organic farming due to enhanced temporal diversification of crop species in a rotation and omission of herbicide applications. However, in intensively managed conventional systems, little evidence exists as to what extent diversified crop rotations contribute to higher weed species richness. Using an on-farm approach, the effect of crop rotation (organic, conventional diverse (CD) and conventional simple (CS) crop rotations) and weed control (with vs. without) on weed species richness, cover, community composition and crop biomass, was analysed in 24 winter wheat fields. Weed species with beneficial functions for invertebrates and birds were analysed separately. Weed species richness was higher in the organic crop rotation, but did not differ between CD and CS crop rotations. Weed control treatment reduced species richness in both conventional rotations, but not in the organic one. Redundancy analyses revealed that crop rotation intensity accounted for the largest part of the explained variation in weed species composition. Results from the study indicate that the maintenance of weed species richness and conservation of species with important ecological functions requires not only temporal diversification of crop species in the rotation, but also an adjustment of weed control strategies.     

Variation in seed dormancy and light sensitivity in Alopecurus myosuroides and Apera spica-venti

Variation in seed dormancy and light sensitivity was studied in Alopecurus myosuroides and Apera spica-venti . Seeds were collected from different populations, at different dates and from plants emerging in autumn or spring, and used in four experiments. In the first experiment, initial dormancy was investigated in light and darkness. In Expt 2, buried seeds were exhumed on 16 occasions, from September 1997 to March 2000, and germinated in light, in darkness and after a 5-s light exposure. In Expt 3, emergence was recorded for seeds sown in pots outdoors. In Expt 4, stratified seeds of A. myosuroides only were exposed to photon irradiance ranging from 0.1 to 25 600 μmol m⁻². Variation was high among seed collections, but both species showed winter annual dormancy patterns. Apera spica-venti germinated to high percentages in autumn but negligibly in spring. Alopecurus myosuroides germinated less in spring when tested in darkness and after a short light exposure and emerged poorly in spring, which reflected photo-desensitisation during cold stratification. We conclude that the peak of emergence in A. myosuroides , and to some extent in A. spica-venti , is largely regulated by exposure to light interacting with low-level dormancy. This offers valuable information regarding optimal timing of weed control measures.     

Fractal characterisation of plant canopies and application in spray retention modelling for arable crops and weeds

Fractal analysis can provide a unique mathematical tool to quantify the geometry of irregular and complex plant canopies. This study demonstrated that a single numerical fractal dimension (FD) value derived from an image taken from above the plant canopy could differentiate between and rank the canopies of a range of plant species. We also investigated the influence of canopy architecture and surface characteristics on spray retention. Multiple regressions were used to derive mathematical relationships and develop a spray retention model. It was discovered that the FD value can successfully be used to replace the statistically generated plant morphological factor (M_p4) used in a previous retention model, with the major advantage being that the retention model now only involves variables that can be readily measured. There is an excellent relationship ( R ² = 0.99) between actual spray retention per plant (μL) and that predicted by the model incorporating the FD. The spray retentiveness of the plant species studied was ranked using a numerical index based on plant canopy architecture and surface characteristics.     

新疆林木外来有害生物种类记述

林木外来有害生物对新疆林业和林果业生产造成巨大损失,对苹果棉蚜Eriosoma lanigerum(Hausm.)、苹果小吉丁Agrilus mali Matsumura、苹果蠹蛾Cydia pomonella(L.)、枣实蝇Carpomya vesnviana Costa、枣球坚蜡蚧Eulecanium gigantea(Shinji)、黄斑星天牛Anoplophora nobilis Ganglbauer、茶子透翅蛾Synanthedon tipuliformis Clerk、果树冠瘿病Agrobacterium tumefaciens (Smith and Townsend)Conn.等8种新疆林木外来有害生物种类的形态特征、生物学特性、在新疆的分布等进行了记述.     

240g·L~(-1)烯草酮乳油防除洋葱田禾本科杂草研究

为探讨烯草酮EC对禾本科杂草的防治效果,以洋葱品种红一号为试材,研究了240g·L~(-1)烯草酮EC加入3种专用助剂不同处理对禾本科杂草的防效。结果表明:240g·L~(-1)烯草酮EC180、240、300、600mL·hm-2+0.125%Amigo专用助剂各处理,对洋葱田禾本科杂草防效达89.7%~100%,240g·L~(-1)烯草酮EC16mL·hm-2+0.2%TM-4专用助剂处理,对洋葱田禾本科杂草防效达87.0%~99.5%,240g·L~(-1)烯草酮EC240mL·hm-2+0.05%力透专用助剂对禾本科杂草的株数没有防效,鲜重防效只有72.5%和78.7%。各处理均有一定的增产效果。推荐使用的最佳应用剂量范围为240g·L~(-1)烯草酮EC240~300mL·hm-2+0.125%Amigo专用助剂和240g·L~(-1)烯草酮EC240mL·hm-2+0.2%TM-4专用助剂。施药适期为移栽后洋葱苗4~5叶;稗草、野黍等禾本科杂草3~5叶期,施药方法为洋葱苗后茎叶喷雾。     

基于专利分析的作物病虫草害检测技术发展趋势研究

在专利文献统计分析的基础上,从时间属性、地域属性、专利权人属性和技术属性4个角度对国内外作物病虫草害检测技术进行研究,总结了该技术领域的专利技术发展状况以及未来发展趋势。结果表明:全球作物病虫草害检测技术正处于快速发展期,我国近年来在该技术领域研发成果较多;作物虫害和作物病害检测技术是该领域的重点研发技术;在我国,高校和科研院所构成该领域创新主体。对该领域的专利H指数、被引频次、核心专利等质量指标分析发现:国外企业掌握了该领域核心技术,国内高校院所和企业的专利质量有待提升。最后,从政府和企业两个层面,提出了我国进一步发展作物病虫草害检测技术的对策建议。     

Impact of climate change on the invasive traits of weeds

Invasive weeds degrade ecosystems and are a threat to plant and animal biodiversity. The literature on biological invasions suggests that only 10% of introduced species become invasive in a new host range. Most introduced plants do not become invasive in a new environment. The invasive behavior of a weed depends on the weed's genetic variability, biotic factors, and climatic factors with which it interacts. The climatic factors that affect the invasive traits of weeds include the atmospheric temperature, soil temperature, precipitation, evaporation, and CO₂ concentration. The biological traits that are influenced by a change in any one or more of these climatic factors include the pattern of assimilate partitioning, induction of dormancy or seed germination, herbivore tolerance, propagule production and distribution, variability of plant architecture, photosynthetic rate, and seedbank longevity. The impact of climate change on the invasive traits of certain weed species is reviewed.