Parthenium hysterophorus L., commonly known as carrot weed, white top or --- congress grass in India,
In general, parthenium is a poisonous, pernicious, problematic, allergic and aggressive weed posing a serious threat to human beings and livestock.
values of parks, gardens and residential colonies.
Biological control is the intentional manipulation of natural enemies by man for the purpose of controlling harmful weeds. Biological control seldom means complete eradication of the unwanted organism, but rather maintaining its population at lower than average that would occur in the absence of the bio-control agent. Parthenium is mainly a weed of waste and fallow land, hence, biological control is the most economical and practical way to keep the weed under check.
Under the biological control programme, host specific bio agents from the native home of the weed are imported into other countries, where the weed had entered and became invasive. Biological control is inexpensive and poses no threat to non-target organisms, environment and biodiversity. It is self-perpetuating and can spreads by its own while other control measures require inputs periodically. It is easy to integrate with other control measures.Biological control by Mexican beetle (zygogramma bicolorata) in India
Based on well documented success by Mexican beetle, Zygogramma bicolorata Pallister (Coleoptera: Chrysomelidae) in other countries where they were introduced, beetles were imported in 1982 from Mexico to Bangalore. Detailed host-specificity tests under quarantine conditions confirmed the safety of Z. bicolorata to cultivated crops in the country. Thereafter, field releases were initiated in Bangalore and India.
DWSR also provides consultancy on Parthenium management to private and government agencies. DWSR released about 60 lakh beetles under consultancy programme in different blocks and circles of Nagpur region. To obtain the beetle culture free of cost, requests may be sent to Director DWSR in June–July.
The beetles can easily be collected from the established sites during June to September. Collection can be made in ordinary polythene or plastic containers that are perforated with a needle. Upper parthenium twigs without leaves should be placed inside the polythene to avoid the shrinking and to provide resting place for the insect. If the insects have to be carried over long distances, it is better to avoid leaves to prevent moisture condensation and fungal growth, which can cause insect mortality. Care must be taken to make the initial releases on small and succulent growth of parthenium in undisturbed areas away from human habitations. Initial release should be avoided in cultivated land because ploughing of land may disturb the pupation process hence poor survival and subsequent establishment. Low lying areas prone to water logging should also be avoided because pupation takes place in soil. The ideal time for carrying out releases will be June to August when plenty of fresh parthenium plants are available in nature. There is no benefit in undertaking releases between Novembers to May when they normally do not breed. However, during this period, beetle can be released over parthenium near the water sources
There are no chances or harming other crops as beetle is host specific. It cannot survive on food other than Parthenium. A controversy emerged on the feeding status of Z. bicolorata sunflower ended in 1999, based on the report of “Fact Finding Committee" constituted by Indian Council of Agricultural Research.
One adult was found to bring defoliation of a single parthenium plant in 6-8 weeks. Therefore, if releases are to be carried out at this rate, about 0.4. to 0.7 million insects will be required per hectare, as the weed density varies between 40 to 70 plants per square metre. In practice, it is neither possible nor necessary to release so many insects as they are capable of multiplying rapidly. Releases of about 500-1000 beetles can bring about establishment and eventual control. Once plants are eaten up in the release spot the insects migrate into adjacent areas. Taking this into consideration, a number of release spots can be selected in a particular place or city, which can act as a focal point.
More releases mean quicker establishment of the beetle, Therefore, for better control, do as many release as affordable during first couple years of introduction. This method reduces the time in years for the beetle to build up population and help the beetles to disperse fast. The least affordable approach is to introduce one or two releases into infested area and do nothing more.
Source:Directorate of Weed Research