Biomass and productivity of water hyacinth and their application in control programs.

Water hyacinth is controllable if management programs take account of plant dynamics and factors that influence plant behaviour. The project for reclamation of water bodies in Mexico considered water hyacinth standing crop, coverage and growth. The method proposed served to characterise the initial population and monitor the control process. The growth model used was reliable in predicting the effective reduction in the weed in response to control pressure. Change in growth over an annual cycle was characterised by a sigmoid curve. The maximum relative percentage growth rate was 9.34%, with a duplication time of 7.4 days from April to June. During winter, growth decreased by up to 90%. In a dam, 144 t/ha/year of dry matter was produced, characteristic of water plants with a high nutrient content. The water hyacinth population can be reduced by 90% through water level management and mechanical destruction. For example, approximately 3600 t/day was removed over 181 days to reduce the infestation to manageable levels. Physical, chemical and biological methods are used to maintain these levels, but input of urban and industrial contaminants must be controlled for long term rehabilitation. OUTBREAKS of aquatic plants is the result of changes in the physical, chemical and biological conditions brought about by the uncontrolled flow of nutrients from urban, agricultural and industrial centres and in silt eroded from watersheds (Gutierrez et al. 1994). Water hyacinth is successful owing to its life cycle and survival strategies that have given it a competitive edge over other species. Its adaptability to little competed ecological conditions make eradication of this plant virtually impossible and control extremely difficult (Gutierrez et al. 1996). In Mexico, more than 40,000 ha were infested and specific management programs were needed. The Aquatic Weed Control Program (AWCP) was created in 1993 to combat the excessive presence of the weed in the nation’s watercourses. The aims of the AWCP included to: • reduce the weed to a manageable level and maintain this level through a maintenance program developed for the body of water; • use methods most suitable to ecosystem and water uses; • formulate an integral watershed program which will include the control and maintenance operations; and • establish biological control using insects and fungi. Under a national program to control the water hyacinth, guidelines to deal with the related environmental, social, technical and economic factors, and specific strategies to reduce coverage were developed. The environmental factors included the identification of the characteristics of the affected areas and the consequences of the proposed treatments. The social aspects embraced the stimulation of user awareness of the importance of water quality, the creation of organisations to coordinate user-sponsored control activities, and the awakening of the community identity. * Instituto Mexicano de Tecnologia del Agua, Paseo Cuauhnahuac 8532 colonia Progreso, Jiutepec, Morelos 62550, Mexico. Email: egutierr@tlaloc.imta.mx