Review Microbial agents for control of aquatic weeds and their role in integrated management Puja Ray* and Martin P. Hill Address: Department of Zoology and Entomology, Rhodes University, P.O. Box 94, Grahamstown 6140, South Africa *Correspondence: Puja Ray. Email: puja.ray@gmail.com Received: 14 May 2012 Accepted: 15 October 2012 doi: 10.1079/PAVSNNR20128014 The electronic version of this article is the definitive one. It is located here: http://www.cabi.org/cabreviews g CAB International 2013 (Online ISSN 1749-8848) Abstract Aquatic ecosystems throughout the world are threatened by the presence of invasive aquatic plants, both floating and submerged. Some of the aquatic species, such as water hyacinth (Eichhornia crassipes [Mart.] Solms), alligator weed, Alternanthera philoxeroides (Mart.), giant salvinia, Salvinia molesta D.S. Mitchell and water lettuce (Pistia stratiotes L.), Griseb. despite being relatively minor problems in their native range, have become major invaders of aquatic habitats in other parts of the world after having escaped from their natural enemies. Unchecked growth of aquatic vegetation is generally undesirable and reduces the value of the water resource. Despite adopting all control options including manual, mechanical, chemical and classical biological, the problem persists. The current weed management is oriented towards finding approaches that are effective in controlling the weed and reducing environmental contamination from herbicides. Plant pathogens have been gaining increasing attention and interest among those concerned with developing environmentally friendly, effective and compatible approaches for integrated manage- ment of the noxious weeds. This paper discusses some of the major microbial agents associated with aquatic weeds and their increasing role in integrated weed management. Keywords: Aquatic weeds, Biological control, Mycoherbicides. Introduction Aquatic plants grow and complete their life cycle in water. Some of them, after coming out of their native range, grow aggressively, causing significant ecological impacts on the environment, and associated cascading socio- economic effects causing harm to aquatic environment, directly or indirectly, and attain the status of a weed [1]. These invasive plants are largely anthropogenically spread, and their presence is typically an indication of the enrichment of waters through pollution, as a result of increasing urbanization, industries and agriculture [2]. Most of the world’s worst tropical aquatic weeds are native to the neotropics, a vast biogeographic area com- prising of South and Central America, the Caribbean and parts of Southern Mexico. Some of the species, such as water hyacinth, Eichhornia crassipes (Mart.) Solms, alligator weed, Alternanthera philoxeroides (Mart.) Griseb., giant salvinia, Salvinia molesta D.S. Mitchell and water lettuce, Pistia stratiotes L., despite being a relatively minor problem in their native range, have become major invaders of aquatic habitat in other regions of the world after having escaped from their natural enemies [3]. The presence of unwarranted aquatic vegetation influences the management of water in reservoirs, man- made canals, river systems and natural waterways, which amount to millions of kilometres/square kilometres of such water bodies around the world [4, 5]. Dense impenetrable infestations restrict access to water, often reduce the usefulness of aquatic bodies for pisciculture [6] and related commercial activities, the use of irrigation canals, navigation and transport, hydroelectric pro- grammes and tourism [7–9]. They greatly increase water loss through evapotranspiration when they completely cover the surface of a water body [10] and decrease light penetration, which affects the diversity and population of native aquatic flora and fauna in these habitats [11–12]. Aquatic weeds can assimilate large quantities of nutrients http://www.cabi.org/cabreviews CAB Reviews 2013 8, No. 014