Aquatic weed classification, environmental effects and the management technologies for its effective control in Kerala, India

Aquatic weeds,the unabated plants completing life cycle in water,are a serious menace to the environment.Dense colonies of aquatic weeds are observed in the southern regions of Kerala which mainly includes Ernakulam,Kottayam,Idukki and Alappuzha districts.The noxious aquatic weeds invade inland water masses,estuaries inshore regions of seas and are now abandoned.The rapid and excessive growth of aquatic weeds in varied and wide environmental condition limits the sustained performance of many drainage and irrigation system,reducing the productivity of agricultural land.Aquatic weeds are classified into emergent,floating and submerged weeds according to the various habitats.Many species are found in Kerala which were originally introduced into botanical gardens.The major aquatic weeds found in Kerala include Salvinia spp.,Eichhornia crassipes,Pistia stratiotes,Alternanthera spp.,Azolla,common duckweed,and Hydrilla verticillata.Reduction or elimination of aquatic weeds is possible through well planned management strategies which includes preventive and control(biological,physical,chemical,eco-physiological)measures.A successful weed control program depends on the resources available,the weeds present and the ability to carry out effective control methods.Operational research and/or pilot projects have to be initiated in the problematic areas on long term basis,using technical recommendations derived from research experiments.

Host Range and Virulence of a Fungal Pathogen for Control of Giant Salvinia (<i>Salvinia molesta</i>)

A teleomorph of the fungus Botryosphaeria rhodina (Berkeley et Curtis) von Arx, (Br) was evaluated as a bioherbicide for control of giant salvinia (Salvinia molesta D.S. Mitchell) under greenhouse conditions and in small-scale field trials. We found that fungal mycelium was highly infective and could be rapidly produced (48+ h) in soy flour-cornmeal liquid media contained in shake flasks or fermenters. A dew period was not required to achieve infection and mortality of inoculated plants. A surfactant (Silwet L-77, a polyalkyleneoxide modified heptamethyl-trisiloxane) incorporated in the fungal formulation was required for Br to infect and kill plants. Infection and mortality occurred rapidly (within 48 h after treatment), and re-growth of treated plants did not occur. In replicated field trials, Br controlled giant salvinia ~95%. Br also infected other plants, such as common salvinia (S. minima Baker), and Azolla filiculoides Lam., as determined in ongoing host range research. However, no symptomatology was observed on several economically important crop species, such as rice (Oryza sativa L.), corn (Zea mays L.), and several woody species such as bald cypress (Taxodium distichum L.) and loblolly pine (Pinus taeda L.) occurring in areas where giant salvina occurs that would be subject to contact with releases of Br. These results suggest that this teleomorph of Botryosphaeria rhodina has potential as a bioherbicide for controlling this onerous aquatic weed.