Salvinia molesta: An Assessment of the Effects and Methods of Eradication

Salvinia molesta is an invasive aquatic fern. It is now the second worse aquatic invader in the world. Since the 1930s, it has invaded most tropical and some temperate countries. S. molesta plants grow vegetatively and can increase in size rapidly. S. molesta can form thick mats of up to 1-meter-thick. There are a number of ways these thick mats negatively affect the environment: 1) reduce light to benthic organisms, 2) reduce oxygen in the water column for other organisms, 3) accumulate as organic matter at the bottom of the water column, 4) decrease nutrients for other organisms, and 5) change water flow. S. molesta not only degrade and alter ecosystems, infestations also increase public health concerns. Dense S. molesta mats are ideal breeding grounds for mosquitoes and other insects that carry vector-borne diseases. Countries are negatively affected economically because S. molesta hinder use of waterways. Recreational activities, tourism, fishing, and transportation are all impeded due to S. molesta infestations. Methods of control are: 1) physical control, 2) chemical control, and 3) biological control. A combination of two or more methods work best for complete eradication. Biological control is the method of choice in tropical areas. Australia was the first to implement biological control via Cyrtobagous salviniae. C. Salviniae have devastative effects on S. molesta plants because both adults and larvae feed on plant parts. Althought C. savliniae are very effective, they have some constraints: 1) temperature, 2) nutrients, and 3) S. molesata infestation growing stage. S. molesta can withstand lower temperatures than C. salviniae, so in temperate regions, C. salviniae are ineffective. These regions are where other methods of control, such as chemical control, are more effective. C. salviniae also require adequate nitrogen concentration for proper development. S. molesta infestations also need to be in the primary or secondary growing stage for C. salviniae to survive. Tungog Lake in Sabah, Malaysia is heavily infested with S. molesta plants that are in the tertiary growing stage. Mats must first be thinned out via chemical control or mechanical removal. C. salviniae then should be introduced to the lake. Other recommendations for control overall of S. molesta are: 1) more studies in temperate regions should be conducted at specific infestation sites, 2) increase public education to reduce use of S. molesta as an ornamental, and 3) ban cultivation sites and sales