The neotropical composite, Parthenium hysterophorus, has achieved major weed status in India and Australia within the past few decades. The reasons for its success as an alien invasive weed are discussed, particularly those relating to allelopathy, together with its effect on crop production, animal husbandry, human health and biodiversity. The actual and potential use of natural enemies as classical biological control agents is reviewed and the work undertaken over the last 20 years on screening and evaluating both insect and fungal agents is analysed. It is concluded that successful management of this weed can only be achieved by an integrated approach in which biological control, because of its cost effectiveness, environmental safety and sustainability, could play a significant role.

Parthenium hysterophorus: a review of its weed status and the possibilities for biological control.

Weed flora in arable fields of eastern Ethiopia with emphasis on the occurrence of Parthenium hysterophorus

This review provides an insight into alien plant invasion taking into account the invasion mechanism of parthenium weed (
 Parthenium hysterophorus
 L.). A multi-lateral understanding of the invasion biology of this weed has pragmatic implications for weed ecology and management.
 Biological invasions are one of the major drivers of restructuring and malfunctioning of ecosystems. Invasive plant species not only change the dynamics of species composition and biodiversity but also hinder the system productivity and efficiency in invaded regions. Parthenium weed, a well-known noxious invasive species, has invaded diverse climatic and biogeographic regions in more than 40 countries across five continents. Efforts are under way to minimize the parthenium weed-induced environmental, agricultural, social, and economic impacts. However, insufficient information regarding its invasion mechanism and interference with ecosystem stability is available. It is hard to devise effective management strategies without understanding the invasion process. Here, we reviewed the mechanism of parthenium weed invasion. Our main conclusions are: (1) morphological advantages, unique reproductive biology, competitive ability, escape from natural enemies in non-native regions, and a C3/C4 photosynthesis are all likely to be involved in parthenium weed invasiveness. (2) Tolerance to abiotic stresses and ability to grow in wide range of edaphic conditions are thought to be additional invasion tools on a physiological front. (3) An allelopathic potential of parthenium weed against crop, weed and pasture species, with multiple modes of allelochemical expression, may also be responsible for its invasion success. Moreover, the release of novel allelochemicals in non-native environments might have a pivotal role in parthenium weed invasion. (4) Genetic diversity found among different populations and biotypes of parthenium weed, based on geographic, edaphic, climatic, and ecological ranges, might also be a strong contributor towards its invasion success. (5) Rising temperatures and atmospheric carbon dioxide (CO2) concentrations and changing rainfall patterns, all within the present day climate change prediction range are favorable for parthenium weed growth, its reproductive output, and therefore its future spread and infestation. (6) Parthenium weed invasion in South Asia depicts the relative and overlapping contribution of all the above-mentioned mechanisms. Such an understanding of the core phenomena regulating the invasion biology has pragmatic implications for its management. A better understanding of the interaction of physiological processes, ecological functions, and genetic makeup within a range of environments may help to devise appropriate management strategies for parthenium weed.

What do we really know about alien plant invasion? A review of the invasion mechanism of one of the world's worst weeds

Invasive species are a growing problem for the world, both ecologically and economically. The impact of invasive species on native species and ecosystems has been immense. Invasion is considered to be an important driver of global change. The impact on economy by these species is evident. The cost of impact which invasive species cause is now estimated to range from millions to billions of dollars and eventually it would be severe for all ecosystems. The various aspects of invasion related to ecology and economy have been summarized to give an insight into the problem and presumed solutions to invasion. Prediction of invasiveness is intricate, but economic and ecological outcome, either good or bad of species invasion, will soon pervade all countries and societies.

Plant invasions : Emerging trends and future implications

Interference by the weed Parthenium hysterophorus L. with grain sorghum : influence of weed density and duration of competition

M. S. Sowerby

Papers

Allelopathic potential of the weed, Parthenium hysterophorus L., in Australia.