Parthenium (Parthenium hysterophorus) is a genus of flowering plants in the aster family, Asteraceae, a new and potentially major weed, spreading exponentially in Pakistan especially in Punjab. The survey of various districts of the Punjab reveals that this weed is spreading rapidly in the rain-fed districts viz. Sialkot, Gujranwala, Sheikhupura, Lahore, Kasur, Hafizabad, Rawalpindi and Islamabad while the districts of southern Punjab viz. Multan, Bahawalpur and Bahawalnagar are either free or have very little infestation of this weed. It is an annual herb with a deep taproot and an erect stem that becomes woody with age. It normally germinates in spring and early summer, produces flowers and seeds throughout its life and dies around late autumn. With suitable conditions (rain, available moisture, mild temperatures) it can grow and produce flowers at any time of the year. Its seeds spread by water, vehicles, machinery, stock, feral and native animals and in feed and seed. It invades disturbed bare areas along roadsides, heavily stocked areas around yards and watering points. It also invades pastures, reduces beef production, affects cropping industries and competes with crops for nutrients and space. It also affects the human health in several countries. Hand weeding small areas is not recommended because there is a health hazard from allergic reactions. There is also a danger that mature seeds will drop off and increase the area of infestation.

Parthenium leaching as root exudates plays a pivotal role in allelopathic interference with surrounding plants. It has also been reported as a germination and radical growth inhibitor in a variety of dicot and monocot plants and it enters the soil through the decomposing leaf litter. Its burning in the fields can reduce germination, biomass growth, plumule and radical length of different crops. Poor fruiting of leguminous crops and reduction in chlorophyll content of crop plants can also be observed in P. hysterophorus-infested fields. It also serves as an alternative host for crop pests, such as scarab beetle: a pest of sunflower, functioning as an inoculums source.

It is a serious invasive weed of pasture systems, reducing the pasture productivity up to 90 per cent. Its invasion causes changes in above-ground vegetation and below-ground soil nutrient contents, disturbing the entire grassland ecosystem.

It also proves to be a damaging source for the human health. Dermatitis, a T cell-mediated immune injury, is caused by it. This disease manifests as itchy erythematous papules and papulovesicular lesions on exposed areas of the body. These effects have been related to the cytotoxicity of plant. Persons exposed to this plant for prolonged period manifest the symptoms of skin inflammation, eczema, asthma, allergic rhinitis, hay fever, black spots, burning and blisters around eyes. Diarrhea, breathlessness, choking and allergic bronchitis are also influenced by it. It causes severe health hazards in livestock. Systemic toxicity in cattle is introduced by it. Alopecia, loss of skin pigmentation, dermatitis and diarrhea has been reported in animals feeding on P. hysterophorus. Degenerative changes in the liver, kidneys and inhibition of liver dehydrogenases have been reported in buffalo and sheep.

The best form of weed control is prevention. Weed infestations should be treated when they are small. They should not be allowed to establish. Some steps for weed prevention include: checking of the property regularly for suspect plants, control of new infestations before they spread and become a major problem, weeds and garden wastes should not be dumped in bush or parkland, knowing the weed status of any products or materials you are receiving. This includes fodder, grain, gravel, machinery, mulch, packing material, sand, soil, stock, vehicles and water. The equipment, clothing, shoes, vehicles and machinery should be cleaned when leaving the natural habitats and camping areas. Vehicles, machinery and tools should be vacuumed or washed for the dirt and seeds.

A weed hygiene declaration should be requested from the suppliers. Grazing management is also an important control measure. This may require rehabilitation of poor pastures, followed by a sound grazing maintenance program. This could include: sown pasture establishment, overgrazing, fencing and burning. Controlling parthenium in cropland requires selective herbicide use and crop rotations.

Biological control of P. hysterophorus is currently done by a number of insect species and two rust pathogens, that have been introduced to control this weed: Epiblema strenuana (stem galling moth), Listronotus setosipennis (stem weevil), Zygogramma bicolorata (leaf beetle), Smicronyx lutulentus (seed weevil), Conotrachelus albocinereus (stem galling weevil), Bucculatrix parthenica (leaf feeding moth), Carmentia ithacae (root feeding moth), Stobaera concinna (sap feeding plant hopper), Platphalonidia mystica, Puccinia abrupta var. partheniicola (leaf rust).

The combined effects of biological control agents reduce the density parthenium thus increasing the grass production. For this reason, proper control measures should be implicated in order to control this noxious weed. This will dwindle its detrimental effects, thus escaping the biosphere of our planet and reducing the losses caused by it.



The authors are associated with the Department of Agronomy and Department of Botany, University of Agriculture, Faisalabad, Pakistan.

By Web Team

Technology Times Web team handles all matters relevant to website posting and management.