At harvest , Common Lambsquarter plants of up to 1.8 m height were observed in the control treatment, linked to a very low CCL and associated, also, with a very low WSI. When weeds emerge together with the crop and are not controlled, crop competition ability is very low, as already found by Nelson and Thoreson , who determined reductions in yields of 54% when weeds emerged together with the crop and reductions of 16% when they emerged 3 weeks later; allowing the crop to better compete with them. When Clomazone 1.6 was applied, there was not an adequate control of Common Lambsquarter and Spiny Cocklebur, then CCL and WSI were low, when compared with the Clomazone 2.0 or the Clomazone + Metribuzin combinations . Lake Kyoga is a large shallow lake in Uganda of about 1720 km2 in area with mean depth of 3.6 m and maximum depth of 6 m About 9.3 million people inhabit Lake Kyoga Basin and their major economic activity is agricultural productivity practiced by 85% of the population Fishing is also carried out on the lake by an estimated 200,000 people and the lake is used for inland water transport as well as source of water for drinking and other domestic uses for most of the inhabitants in the lake basin Unfortunately, Lake Kyoga has been invaded by the free-floating aquatic weed, giant Salvinia molesta D.S. Mitchell with a high potential to infest the numerous satellite lakes in Kyoga Basin .
Therefore, there is an urgent need to collect baseline data and information on the extent of S. molesta infestation in the Kyoga Basin lakes . Salvinia molesta belongs to Order Hydropteridales, Family Salvinanceae and genus Salvinia with about 12 species which are all native to South America Salvinia molesta formally existed only in South America, but since the 1940s the weed has been dispersed by humans to different tropical and subtropical countries in Africa, Asia, and Australia as well as USA in the recent years . The plant is known by a number of common names such as giant Salvinia, Kariba weed, aquarium water moss, water fern, and giant azalea etc. These names often reflect the environment the weed inhabits or its invasiveness The weed is called “Nankabirwa” by locals in Uganda,vertical grow system due to lack of a native name . The free-floating S. molesta weed comprises of an underneath horizontal rhizome which lies close to the water surface . It has two types of leaves attached to each node of the rhizome. The submerged leaves of S. molesta are modified to perform the function of roots as the weed does not have true roots . S. molesta exhibits several morphological variations ranging from slender floating plant with less than 15-mm wide leaves to a robust plant having leaves up to 60-mm wide brought about by crowding and nutrient availability in the habitat The weed is capable of spreading easily over water bodies using its floating structures and even survives in unfavourable environments using the most suitable growth form .
It seemingly produces only sterile spores, hence reproduces entirely by vegetative means which can be extremely rapid under suitable conditions . For instance, S. molesta can double in biomass in 2 to 3 days under favourable conditions . This enables S. molesta to out-compete other plant species and completely cover the water surface with mats as thick as 1 m . Salvinia molesta has been recently added onto the list of the world’s 100 most invasive species and ranks second to water hyacinth Solms-Laub.The thick mat also severely reduces dissolved oxygen content in aquatic ecosystems sometimes resulting into fish kills For the case of Lake Kyoga, the thick mats of S. molesta on the lake have hampered activities such as abstraction of water by surrounding communities, watering of domestic animals, docking and boat take-off, bathing and swimming . Fortunately S. molesta weed has been successfully managed in other countries e.g. lake Moondara, Australia where the weed had threatened the biodiversity and the life of the lake . Studies in Australia showed that successful management of Salvinia molesta is achieved through integrated control strategies combining herbicide spraying, biological control agents and mechanical removal including the containment of the weed to keep some areas free of S. molesta . However, the best management practices for Salvinia in Africa can be found from those countries where the weed is non-native but has apparently not led to major disruptions to use of water resources as well as Senegal, Mauritania and South Africa among other countries where successful control by biological agent was achieved. The use of Cyrtobagous salviniae biological agent to control S. molesta in these countries was based on the outstanding success of Cyrtobagous salviniae in Australia and Papua New Guinea Nevertheless, planning a management strategy for S. molesta involves identification of the source of the infestation, mapping the infestation, identification and minimising sources of nutrients entering the water body .