IT was late 1980s when Ghorabari in Thatta district came under spotlight because of the appearance of a deadly alien disease — banana bunchy top virus.
Initially localised in a small patch of land, over time this disease spread to the entire banana growing areas. Now it causes yield losses worth millions of rupees annually.
Unfortunately again after about three decades, a new highly invasive aquatic weed has appeared in the vicinity of Gharo, Thatta, on coastal highways.
Presently this aquatic weed known as Salvinia molesta (kariba weed) is limited to a narrow water channel not more than 200 feet long and can easily be eradicated manually.
It is a pest of rice paddies. Review literature has indicated that habitat of kariba weed includes irrigation channels, lake, ponds, reservoir, river/streams
Originating in Brazil, this aquatic weed has spread throughout the world over past 50 years. Its presence has also been reported in Indus River without any details.
Salvinia molesta is one of world’s most noxious aquatic weeds. Recently it has also been added in the list of the world’s 100 most invasive species. Here it would be relevant to mention that water hyacinth too was alien to Pakistan several decades ago but after its introduction, it spread across the country because of ineffective plant quarantine regulatory service at the federal and its absence at the provincial level.
On Feb 26, this alien Salvinia molesta was detected by this writer in a water channel near coastal highways area in Gharo. The local farmers told this scribe that it initially had a patchy appearance but within a few months it has covered the entire channel 200 feet in length.
Farmers also complained that its fast growth is hindering water flow into their fields through water courses. Now there is no fish in the channel. Leaves of this aquatic weed are not eaten by their animals unlike water hyacinth.
Review literature has indicated that habitat of kariba weed includes irrigation channels, lake, ponds, reservoir, river/streams. It is a pest of rice paddies. In India studies on transplanted rice kariba weed was found to cause 12.5pc yield loss due to reduction in panicle bearing tillers.
Salvinia molesta also contributes to human health problem. Dense mats of this aquatic weed are an important plant host of many species of mosquitoes which cause encephalitis, malaria, dengue fever etc. Thatta, where this kariba weed presently exists, is basically a salinity affected area with sporadic vegetable cultivation.
If this highly invasive weed species is are allowed to spread it is quite likely that they may spread to the rice growing area of both lower and upper Sindh inflicting colossal damage not only to rice cultivation but fish farming and lotus cultivation undertaken in fresh water ditches and ponds.
To detect presence of this invasive aquatic weed, a detailed survey of the area should be undertaken by the Sindh’s agriculture department and to get rid of this menace an eradication campaign should be launched on a war footing.
The writer is an ex-entomologist of the Plant Protection Department, government of Pakistan
Published in Dawn, Business & Finance weekly, March 7th, 2016