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Measures to control lantana invasion

Last Updated : 11 September 2017, 18:29 IST

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There are many invasive species like lantana, eupatorium, parthenium and strobilanthes, which have destroyed the habitats of wild animals across the country. Many palatable species have gone missing as the composition of forests has undergone changes. Over the years, repeated fire in dry deciduous and moist deciduous forests has resulted in a thick growth of lantana camara. Important protected areas of South Karnataka like Bandipur and Nagarhole have been heavily invaded by lantana which has become a menace for forests and wild animals.

The spread of lantana in some of these areas is so intense that wild animals cannot pass through these patches quickly. For instance, tigers cannot run fast and hunt its prey easily. Additionally, the regular routes of animals like gaur and other ungulates through lantana patches look like tunnels. Degradation of habitat is the main reason for straying of wild animals in human areas, which leads to conflict.

No solution in sight

It has been observed recently in these Protected Areas, especially in Bandipur National Park, that an insect called Teleonemia scrupulosa stal (commonly known as lantana lace bug) has been attacking lantana plants, which is found to be defoliating and drying up in fairly big patches of the Protected Areas. This bug is observed to be three to four mm in length and 1.1 to 1.3 mm in width. The bug is dull to darkish brown in colour and is usually found on the ventral surface of young leaves. The infested leaves of lantana show typical dark brown to black, scorched or burnt patches caused due to the feeding of the bugs. It also attacks newly opened buds and flowers of lantana.

The bug was introduced in India from Australia in 1941 but was not released in the field, as the adult lantana lace bugs fed on teak flowers in quarantine. The culture was destroyed, but the bug is believed to have escaped quarantine. This bug is now found in northern, northeastern and southern part of our country. The bug can be found on 15 different plants, but except lantana and sesame, it does not damage other plants significantly. However, the production of sesame is observed to have suffered in East Africa. As the bug does not kill lantana plant outright, we cannot be too sure to have found a solution for lantana in our forests. It appears that the bug can only restrict the growth of the plant.

Recently, Union Minister for Environment, Forests and Climate Change Dr Harsh Vardhan expressed hope to find a scientific solution to the menace of the lantana camara’s excess growth. Weather the solution is biological or chemical, Forest Departments across the country have struggled for decades to contain the menace. Also, forest managers are enthusiastic and want to physically introduce the bug to eradicate the invasive lantana in areas still not affected by bugs.

However, as the bug is naturally spreading, we should not be hasty to introduce the lantana lace bug without observing its effect on other plant species. It is known to be attacking teak trees and can affect the production of agricultural crops like sesame in the vicinity of the forests. However, the bug is very useful and helps in biological control of lantana. Though recent studies indicate that the bugs don’t affect other species, it is necessary to commission long-term research to find how other native species are responding in areas where lantana is attacked by the bug.

Need for rigid protection

By now, forest managers are tired of physical removal of lantana. Corbett National Park in Uttarakhand developed a method of cutting this plant, inverting it upside down and leaving it on the same spot. This way the reproduction is kept in check and the regeneration becomes slow and sparse. It was further observed in the same area in Uttarakhand that if the exercise is annually repeated for five years in any particular area, unwanted lantana can be eradicated.

Of course, palatable grasses have to be artificially supplemented and the area has to be managed as grassland for a successful solution. Such a laborious and expensive exercise could not be undertaken across the length and breadth of the National Park and hence, the area could not become free from lantana.

Physical removal of lantana was also tried in many patches in Biligiriranganatha Swamy Temple Wildlife Sanctuary (BRT Wildlife Sanctuary) and Bandipur and Nagarhole National Parks. A part of this exercise was carried on the model that Corbett National Park followed. However, we have not seen concrete results here. In some patches, lantana bounced back with more vigour while in some other patches the area was taken over by parthenium, another invasive weed. Studies have also revealed that regeneration of other natural species did not take place in areas where lantana was physically removed.

In the circumstances, I only reiterate the suggestion that lantana infested forests require rigid protection from fire, grazing, encroachments, illicit felling, hunting etc. In a long run it will help the forests in succession towards more moist side; the composition of species would undergo change and may be severity of lantana would come down.

(The author is retired principal chief conservator of forests, Karnataka)

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Published 11 September 2017, 14:25 IST

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