Dr. R D Gautam, principal scientist and in-charge of the Plant Health Clinic, speaks to Down To Earth
"Biological control is the way out"
What are the various methods of managing invasive weeds?
The government generally comes to know about invasive weeds 10-15 years after they are introduced. By then, they are already spread over wide areas and their extinction becomes impossible. The only thing that can make a difference is the people's awareness. People should be informed as soon as a pest is intercepted by the quarantine department. In initial stages, a community approach with mechanical controlling methods - such as uprooting - is enough to overcome the probldem. Earlier, we could burn these weeds; now a days, however, because of environmental reasons, we do not have that option anymore. We cannot use chemicals either, as in some cases they may harm other useful plants as well. Bio-control methods are the only way out, but they are risky as the controlling agent may turn into a pest in the future. Therefore, we have to be very careful. For instance, in case of parthenium, we looked for a specific biological controlling agent that eats only parthenium and had to make sure it would not switch over to any other plant. We searched the parthenium's original habitat and some other countries where it is found, whose climate is similar to that of ours. Then we determine some useful biological controlling agents - insects, viruses, fungi - and import them. For this we have a protocol, which is different from that of the FAO.
What are the steps processes of importing biological controlling agents?
In India there is a nodal agency called the Project Directorate of Biological Control (PDBC), which is based in Bangalore. A scientist who wants to import a biological controlling agent has to first give all the information about the organism he wants to import - whether it is specific to a particular weed, and whether it can be multiplied in lab conditions. Biological controlling agents must be well tested. The organism should meet the ideal attributes of biological controlling agents. Their handling and release should also be hazard-free. For instance, scales and dust produced by certain insects can create health problems for us. All this information is to be submitted in a document to the PDBC, which then forwards the request to the Government of India. Then it goes to a committee generally headed by the chair of the ICAR, with a PPQ advisory representative as member secretary. After the committee's approval, the place from where the controlling agents are to be imported is decided and the import permit is given by the PPQ. After the import, the consignment is again checked by the PPQ, and handed over to the scientist, who then develops a protocol for its multiplication and release. The release is usually carried out in pocket conditions to make sure that no risk is involved.
How successful have these biological controlling methods been?
While searching for a controlling agent, we must keep in mind the fact that the climate of the country from which we are importing it should be similar to that of our own. Like in case of parthenium, Zycogramma Bicolorata, which is used as a controlling agents, was established successfully in Banglore, where climate is suitable for it. In the case of Delhi, however, it did not produce any good results due to the extreme temperatures in the city.
What is the ecological history of parthenium?
It is said that that parthenium came with a consignment of the wheat from Mexico. The parthenium seeds are also too small to intercept. The first report on parthenium came was from Pune. Initially, mechanical and chemical devices failed to get rid of the weed.
What are the health problems associated with parthenium weed?
Lots. It is harmful for people suffering from asthma. Its pollens cause pollenises. Some nervous disorders have also been reported. In forest areas, it causes dermatitis to rodents like rabbits.
Why was zycogramma bicolorata used as a controlling agent?
A good thing about zycogramma bicolorata is that it eats the parthenium weed only. It strikes at the plant's leaf, and the plant cannot survive without its leaf. There were a few reports that the insect was devouring sunflowers as well. After an inquiry by a government fact-finding committee, it was however found that the zycogramma bicolorata could not develop on sunflowers. Permission of its release was given. We released it in Delhi three years ago.
What is the current status of its introduction?
We have found mixed responses in north India. Now it is being introduced in some other parts of the country, like Karnataka, Madhya Pradesh, and in Jammu and Kashmir.
Can it switch over to any other plant?
After finishing parthenium, it can switch over to another plant, but the chances of its survival are low. Insect multiplication decreases according to the availability of food. Thus multiplication of zycogramma will decrease as the population of parthenium decreases.
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