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Field rats: a new cotton pest in riverine forests
The province of Sindh has three distinct physiographic regions — riverine and irrigated alluvial region, sandy eastern region (Thar desert), and rocky western region (Khirthar range). The land use in the riverine and irrigated region is related to agriculture and forestry.
According to Sindh forest department statistics: the riverine belt of the province comprises riverine forest spread over an area of 241,217 hectares. Among the dominant plant species in this tropical forest are Acacia nilotica and Prosopis spicigera. Other plant species prevalent in the forest are Populus eupharatica, Tamarix articulata and numerous herbs and shrubs. As a matter of fact, riverine forests lie within the protective embankment on either side of the River Indus.
Reportedly, riverine forests are managed on the clear felling silvi-culture system which is rational, economical, and sustainable in the flood plains of lower Indus.
Clear felled areas of riverine forest were fully regenerated and restocked a year later with natural inundation and manual seeding operation including aerial seeding with the help of the Central Plant Protection Department Karachi.
But, contrary to the facts mentioned above, a survey of the riverine forest area in districts Ghotki, Sukkur and Khairpur during Kharif 2003 and Rabi 2003-2004 by this reporter indicated that existing system of riverine forest management is not sustainable and likely to suffer steady deterioration with the passage of time.
Main reason is not only the absence of inundation water following the construction of barrages on the River Indus, but aslo failure of the Sindh Forest Department to stop illegal island crop cultivation in the riverine forest belt removing established forest vegetation and trees.
In this respect, it would be proper to mention here that during the early settlement of North America by the European colonists, agricultural crops were grown in small patches surrounded by large tracts of uncultivated land crops were like small island in a matrix of natural vegetation. As agriculture developed, this matrix of forest vegetation dwindled fast with the passage of time.
Unfortunately, today our riverine forests represent a similar scenario. Island crop cultivation is dwindling the riverine forest area.
During Kharif 2003 season, this writer had the privilege to keep on such island crop of cotton under regular surveillance since sowing till harvesting. Total acreage of this island crop was about five acres surrounded by tall bushy grass locally known as Burho. Long leaves of this bushy grass are used in rope preparation and also in hut building. Cotton crop cultivated as island crop in the riverine forest belt encountered both sucking as well as boll worm pest complex, but remain at low ebb requiring only two sprays of pesticides. The land lord concerned was happy with the situation, but to the surprise of both, the land lord as well as the very writer, cotton crop came under a sudden attack of field rats just a couple of days prior to its picking. Rodent species were found damaging the seed cotton (phutty) ready for picking. No damage of ripe or unripe cotton bolls were observed.
Close examination of phutty scattered in the cotton field indicated empty seed coats. It was evident that it was not the lint but the seed cornels which had been eaten by the rats. Besides, a good quantity of phutty was also seen on the path ways as well as near the burrow sites which were in numerous number at the base of Burho bushy grass in the fields contiguous with cotton field.
As per a conservative estimate, damage to seed cotton was in the range of 5 to 10 per cent. In spite of the fact that field rats have not been reported as a pest of cotton in the country particularly in Sindh hitherto, but the review of literature has indicated that one species of rat, Bandicota bengalensis, has been found as a pest of cotton in India.
According to a study undertaken to this effect at Tamil Nadu, India, the damage was observed in both the unripe and riped bolls. On an average rodents cause 55 per cent depredation.The damage was more in the unripe bolls than in the ripe bolls in the ratio 4:1. This may probably be due to higher palatability of unripe bolls.
The damaged bolls were found at the burrow entrance of the Bandicota bengalensis. And in a few instances the rodents had used the damaged bolls as plugging material for their burrows. However, from the aforementioned study at Tamil Nadu it was evident that rodent species which invaded cotton crop in the riverine forest belt of district Khairpur, when it was ready for picking of phutty (seed cotton), was other than the Bandicota bengalensis, which was of course, a matter of great concern.
A study undertaken at the Vertebrate Pest Control Centre of the PARC as well as the Zoological Survey Department Government of Pakistan, Karachi, has indicated the presence of Bandicota bengalensis species of rodents in Sindh. If the practice of cultivation of cotton as an island crop continues in the forest belt of River Indus, it is quite possible that these two or more species of field rats may pose serious threat to cotton crop also in the area other than the riverine cotton belt.
SUGGESTIONS
Since cotton is the backbone of the economy of our country, it is warranted that insurgence of rodents as a pest of cotton in the riverine forest belt should be taken into account by the quarters concerned both at provincial as well as federal levels.
Moreover, since control of rodents with toxic rodenticides may become lethal to the wild life species, particularly to hog deer, rabbits, barn owl, titter and other game birds found in the riverine forest. It is imperative that some sustainable approach should be adopted to handle this problem.
For the identification of rodent species found damaging cotton crop (seed cotton) in the riverine forest help of the concerned bodies may also be sounght for an invironment friendly-control of this problem.
The writer
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