Natural Suppression of the Aquatic Weed Salvinia molesta D.S. Mitchell, by Two Previously Unreported Fungal Pathogens

Salvinia molesta D. S. Mitchell (Salviniaceae), variously called giant salvinia, water fern or African payal, is a vegetatively reproducing, perennial, free-floating, aquatic weed, native to southeastern Brazil (Waterhouse and Norris 1987). It (hereafter called salvinia) is a very serious weed in most regions outside its native range (Harley and Mitchell 1981) including India. The purpose of this paper is to report on two fungal pathogens that were found to be the cause of a sudden decline in salvinia in Bangalore.(PDF has 4 pages.)

Vertebrates Removed by Mechanical Weed Harvesting in Lake Keesus, Wisconsin

Mechanical weed harvesting has been used to control nuisance vegetation in Lake Keesus since 1979. Fish, turtles, and amphibians often become entangled in the vegetation and are incidentally removed from the lake while harvesting weeds. Mechanical harvesting removed 2 to 8% of the standing crop of juvenile fish in harvested areas in Saratoga Lake, New York (Mikol 1985) and 32% of the fish population in harvested areas in Orange Lake, Florida, representing an estimated replacement value of $6000 per ha (Haller et al. 19890). Engle (1990) found mechanical harvesting removed 21,000 to 31,000 fish per year from Lake Halverson, Wisconsin, representing 25% of the fry in the lake. Little other current information has been published concerning aquatic vertebrate removal by mechanical weed harvesting in Wisconsin, though it is a commonly used management tool. Additionally, only Engle (1990) reported information on the removal of turtles relative to weed harvesting, but none on amphibians. The objective of this study was to document the number, species, and size of vertebrates removed by mechanically harvesting weeds in Lake Keesus.

Mechanical control of floating aquatic weed: Kainji Lake experience

The paper describes the uniqueness and invasiveness of water hyacinth (Eichhornia crassipes) on Lake Kainji (Nigeria). The mechanical blocking device design concept based on the Kainji Lake flooding regime is also highlighted. Water hyacinth coverage, that was over 23% at high water in level in 1994, was reduced to 0.75% in the same period in 2000. Although this feat cannot be wholly ascribed to mechanical control effort alone, the first year of the device's full operation more than 1.04 million kg of fresh weight of water hyacinth were trapped, collected and deposited in two separate dumping pits, each at about 1 km off the shoreline of either side of the Lake. On further analysis over a period of one year of uncleared inflow of water hyacinth indicated the effectiveness of the bloom. Recommendations are advanced for the use of such local but highly technical knowledge to control floating water hyacinth that is vastly taking over the intricate network of Nigerian water systems and within the West African sub-region

Weed control by adult and juvenile tilapia Tilapia rendalli in rainfed ponds

Two studies were conducted in consecutive years over the time period 14 January to 1 July to determine whether labor-savings and fish growth enhancement could be achieved by stocking Tilapia rendalli directly into ponds containing weeds left from a dry period. Six replicates 200 sq. m ponds located at the Malawi National Aquaculture Centre, Domasi were drained, left dry for 63 days and natural growth of weeds was allowed. All ponds were stocked with 200 T. rendalli fingerlings (study 1) or adults (study 2) averaging 4.6 g (40 mm TL) and 47.7 (130 mm TL), respectively. For T. rendalli juveniles, final standing stock, growth and offspring production were significantly (P<0.05) better in fed than in weedy ponds. Average weight of fingerlings were significantly (P<0.05) different between the two treatments. For T. rendalli adults, final standing stock, growth and offspring production were not affected by the presence of weeds.

Seasonal fluctuation in primary production in relation to the physicochemical parameters of two weed-infested ponds of Kalyani, West Bengal

Kalyani lake (P sub(1)), a weed infested recreational water body and a weed chocked derelict water body (P sub(2)) in the heart of Kalyani city of West Bengal were studied for a period of one year for their primary productivity and other physicochemical parameters. Very low primary productivity (GPP=360-1237mg C m super(-2) d super(-1); NPP=157-787 mg C m super(-2) d super(-1)) was recorded in P sub(2) in spite of having a high concentration of nutrients (PO sub(4)–P=0.052-0.260mg l super(- 1); NO sub(3)-N=0.110-0.412mg l super(-1)). On the other hand, moderate primary productivity (GPP=1687-3195mg C m super(-2) d super(-1); NPP=900-2700mg C m super(-2) d super(-1)) was found in P sub(1) with comparatively low range of nutrients (P0 sub(4)-P =0.010-0.058mg l super(-1); NO sub(3)-N=0.032-0.118mg l super(-1)). After studying the other physicochemical parameters (temperature, transparency, dissolved oxygen, free carbon dioxide, pH, alkalinity and macrophytic biomass), it was found that the overall hydro-biological conditions of the weed-chocked derelict water body (P sub(2)) is not congenial for biological production as compared to Kalyani Lake (P sub(1)). Kalyani Lake may be used for fish culture with proper management practices.

A new water weed, giant salvinia (Salvinia molesta), invades Lake Kyoga

Giant salvinia (Salvinia molesta) is an introduced invasive water weed in the tropics and subtropics It is a free floating weed that grows rapidly and forms extensive dense mats over still or slow moving waters.

Status of kariba weed (Salvinia molesta) infestation, its impacts and control options on Uganda’s water systems

Kariba weed (Salvinia molesta) is an invasive alien waterweed that was first recorded in Uganda in sheltered bays of Lake Kyoga in June 2013. This waterweed has become a common feature on Lake Kyoga and its associated rivers, streams and swamps, and has spread to other lakes notably Kwania and Albert in addition to Lake Kimira in Bugiri district.