Bye-Bye Congress Grass, let us work with combined efforts for biological based integrated management of the weed

Dr Nameirakpam Irabanta Singh *

Congress grass/carrot weed/white top (Parthenium hysterophorus L.) has been rapidly spreading in the North East India and continually affecting our health, livestock, flora and environment. The writer already reported Congress grass menance in North-East India (The Sangai Express, June 26, 2018). In this article, he further focuses on biological based integrated management of parthenium in North-East India.

What is Parthenium?: Parthenium hysterophorus (Carrot weed, white top or Congress grass) is a herbaceous, erect and annual plant belonging to the family Asteraceae (Composotae). The origin of Parthenium is considered to be Mexico, America, Trinidad and Argentina. Parthenium was first notice in Pune (Maharashtra) in 1956.

It has now spread like a wildfire throughout India. It is a nuisance on the road sides, railway tracts, vacant lands, wastelands, industrial areas, on the side of open drainage system and irrigation canals besides invading agricultural crop and National parks.

How to Identify Parthenium? : Parthenium leaves look like Carrot leaves, hence it is known as carrot weed. It may attain a height of 1.5 to 2.0 metres. It is branched. Stems and leaves are covered with fine hairs. The flowers are white.

How Parthenium spreads? : It spreads through seeds. The weed has the potential of producing as high as 1,54,000 seeds. The seeds are very light in weight and easily carried or transported by wind, water or through various human activities. Parthenium has the capacity to regrow from the cut or broken parts. Its allelopathic effects coupled with the absence of natural enemies like insects and diseases are two important factors responsible for its rapid spread in North Eastern India.

Harmful effects of Parthenium : Parthenium is a poisonous pernicious, problematic, allergic and aggressive weed posing a serious threat to human beings and livestock. In India, including North East, this weed has been considered as one of the greatest source of dermatitis, asthma, nasal-dermal and nasal-bronchial types of diseases. Besides ill effects, it also causes several other problems like blockage of common pathways and reduces the aesthetic value of parks, gardens and residential colonies.

Parthenium also infests every type of crop, orchards, plantation and forest. It severely reduces the crop productivity besides loss to biodiversity and environment

Integrated Management of Parthenium : So far, no single method has proved satisfactory as each method suffers from one or more limitations such as impracticability, temporary relief, environmental safety, high cost etc. Therefore, it is necessary to adopt an integrated approach of Parthenium management by mixing/clubbing together all the methods as and when applicable.

1. Mechanical and manual method : Parthenium plants can be uprooted before flowering during monsoon when the soil is wet. Some sensitive persons may be allergic to Parthenium and hence recommended for use of polythene bag or hand gloves while uprooting Parthenium. Parthenium is not a problem of single individual but is a problem for whole community. Therefore, there is need to motivate colony residents, workers in industry and larger farms to uproot Parthenium in a collective way.

2. Use of biological control agents and how biological control works : Parthenium can be managed by its natural enemies like insects, fungi, competitive plants. Biological control is inexpensive and poses no threat to non-target organisms, environment and biodiversity. It is self perpetuating and can spread by its own. While other control measures require inputs periodically. It is to integrate with other control measures.

Biological control by Mexican beetle (Zygogramma bicolorata Pallister. Coleoptera: Chrysomelida) : The beetles were imported in 1982 from Mexico to Bangaluru (India). It was released in the field after detailed host specific test under quarantine conditions confirmed harmless in India.

Biology of Mexican beetles : Beetles are off-white or light reddish in colour with dark brown longitudinal markings on the elytra measuring about 6mm in length. Light yellow eggs are laid generally on ventral side of the leaves and hatch in 4-7 days. There are four instars. The grub feed 10-15 days on the leaves and mature enters into soil and pupates below upto 15 cm depth. Beetles emerged after 8-12 days. The beetle completes its life cycle in 17-32 days.

Insect completes 4-5 generations from June to October in natural conditions. The female can lay upto 2500 eggs during its life span. The beetle remain most active in the field during the rainy season between June to October but stages of Zygogramma bicolorata may be encountered in summer and winter season depending on the moisture and temperature.

Efforts of DBT/GOI Twinning Prohramme for NE India : So far, a total of 2,38,000 beetles had been released in the NE States (Manipur, Meghalaya, Arunachal Pradesh, Tripura, Nagaland and Sikkim) during 2015-17. The beetles were supplied by the Directorate of Weed Science Research (DWSR), Jabalpur through Principal Investigator, Collaborating Institute and jointly released along the P.I./Parent Institute, Manipur University.

After revisiting the places in the next year, beetles were recovered from one place in Guwahati (Assam) and two places in Imphal (Manipur). Recovery of bioagent at Guwahati and Imphal indicate the possibility of establishment of Zygogramma bicolorata in other parts of NE India. Therefore, it is necessary to take field observation at the forthcoming season, 2018. Field visit to Mizoram is yet to be undertaken.

Can beetles harmful to other crops : There is no chance or harming other crops as the beetles is host specific. It can not survive on food other than Parthenium.

How many beetles should be released? : Release of about 500 to 1000 beetles can bring about establishment and eventual control. More release means quicker establishment of the beetles. The least affordable approach is to introduce one or two release into infested areas and do nothing more.

Biological control by Cassia tora : Cassia tora (Chakoda in Hindi and Thounam macha in Manipuri) is capable to replace Parthenium by broadcasting of seeds during February – April in the Parthenium infested areas. Plenty of Cassia tora seeds may be collected early during October – November.

It is observed that Parthenium population was reduced 28% to 30% by broadcasting Cassia tora seeds in Parthenium growing areas. Further, Cassia tora strongly inhibited the dry matter production in Parthenium areas also. Thus, Parthenium infested sites have been managed by the used of this technique.

Conclusion : The best way for management of Congress grass from the North East India is biological based integrated management.