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INTRODUCTION
Macrophytes are important in the operation of the ecosystems in which they occur, being capable of establishing a strong connection between the aquatic and terrestrial environment that surrounds them. Among their functions, one can mention the elimination of the excess of toxic and eutrophying substances from the water by retaining the material carried by erosion of terrestrial environments and the promotion of spatial and temporal heterogeneity, which contributes to a greater system diversity (Pitelli et al., 2008; Souza, 2013).
Considering only the aquatic environment, there are several examples of macrophytes that were introduced into new places. A classic example of that is the water hyacinth (Eichhorniacrassipes), a tropical America native plant that was introduced into several countries as an ornamental plant (Holm et al., 1977). In the new environments, the absence of the powerful natural enemies and the characteristics of water and the water bodies provide favorable conditions so that the water hyacinth would form great population densities (Olaleye et al., 1993).
According to Pitelli et al. (2008), the chemical control of aquatic plants is restricted to a few herbicides due to the restrictions imposed by the legislation to the environmental impact, to the market size and to the private sector, as well as to the application technology. The environmental restrictions are the most important factors because the waterways are used for several purposes such as source of water for human and animal consumption, irrigation of crops, leisure, navigation and generation of hydropower.
According to data from the World Bank, in 1990, E.crassipes already caused economic losses of around US$ 500 million dollars a year (Olaleye & Akinyemiju, 1996). Thus, the chemical control by herbicides is one of the alternatives for the handling of this macrophyte. However, it is still scarce to find information and even researches which aim to generate information on the efficiency and the application techniques of the herbicide products in aquatic environments.
In a terrestrial environment, spraying of herbicides into water is the most used means for taking and distributing the products to the plants that will be controlled. The applications are normally done with sprayers equipped with hydropower nozzles, in which the combination of the size of droplets produced by the spray nozzles, the application volume (L...