Centre for Agriculture and Bioscience International (CABI) on Wednesday issued a list of recommendations to fight the highly-invasive parthenium weed which can have significant impacts on human health, the environment, livestock production and health and crop yields.
The report "Parthenium: Impacts and coping strategies in Central West Asia," states that the aggressively-spreading weed, now classified as a "superior weed," is extremely prolific being capable of producing up to 30,000 seeds per plant - a key factor in its global spread to 48 countries including India and Pakistan.
CABI scientists say parthenium weed can cause severe allergic reactions in humans and livestock, may harbour malaria-carrying mosquitoes, displace native plant species and reduce pasture carrying capacities by as much as 80% to 90% where in India, for example, the cost of restoring grazing land is around USD 6.7 billion per annum.
The evidence note also highlights that parthenium weed can have a significant impact on crop yields - through direct competition as well as by inhibiting germination of seeds - where, for instance, in Ethiopia sorghum grain yield was reduced from 40 to 97 percent.
Abdul Rehman, Deputy Director Programme based at CABI's office in Pakistan, said, "Parthenium ranks in the top five weeds worldwide, is extremely prolific, and requires a management approach that will have to keep pace with its spread to limit its widespread impact on various facets of the economy and the social fabric of affected communities."
In Pakistan, substantial yield losses in maize have also been reported. A yield loss of 50 percent in maize was recorded at an infestation rate of 20 parthenium plants per square metre.
The current spread of parthenium, the scientists say, seems to be facilitated by the road network and water canal systems for irrigation and flooding events.
Rehman added, "Areas with low climatic suitability such as the south of Punjab are affected by the weed, as are other areas such as Sindh& Balochistan Province. Based on the likely expansion of parthenium following the irrigation network, the weed will likely spread towards the south-western part of Punjab, threatening Pakistan's cotton industry."
To try and mitigate the weed, of which the scientists said there is no single measure, CABI has listed in the report a number of recommendations which include - where possible - the use of more environmentally sustainable biological controls.
Steps to prevent parthenium arriving include increasing the inspection of vehicles, livestock, seed and feed to manage parthenium seed movement through its pathway as well as creating awareness at nurseries and floriculturists on weed identification, and to restrict the introduction of floral products from areas where the weed is present.
If parthenium has just arrived, regulators should facilitate the registration and promotion of biological control agents through classical and augmentative biological control efforts to prevent the weed becoming widespread. Where chemical control has to be used, it should be applied along roadsides, in public parks or on private properties where it is present.
Invaded countries should also be helped to develop and implement a parthenium management strategy to contain it and slow its further spread.
When parthenium has already arrived and is firmly established the advice includes declaring parthenium as a noxious plant and ensuring public and political support through sufficient budget allocation to manage it. CABI also suggests that the economic considerations for different control methods, including health and environmental impacts, also need to be accounted for.
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