A generally dramatic success in combating water hyacinth
infestation has been realised so far in Tanzania,
particularly in Lake Victoria. Water hyacinth is no
longer a menace in the Lake Victoria Basin. Biological
control has worked very well.
• The water hyacinth infestation in the Lake Victoria
has been reduced by over 70% over a period of 3
years.
• Data from ground survey in Lake Victoria has
revealed only localised water hyacinth infestations
and most of the landing beaches are weed-free.
• Plants estimated to contain approximately 30
million eggs of the weevils were placed in the field.
• Preliminary weevil impact data (7 months) from
stabilised water hyacinth mats have revealed a
significant reduction in plant population from 45 to
7 plants/0.5m2 (Fig 1).
• Through manual removal, more than 60 landing
beaches in Lake Victoria are kept water hyacinthfree.
• The reproductive index of water hyacinth in Lake
Victoria has fallen from 6 to an average 0.5 ramets
per plant (Fig 2).
• Both N. eichhorniae and N. bruchi have equally
established in release and recovery sites (adult
populations of up to 30 per plant) but the efficiency
of each species has yet to be determined.
• A survey has revealed the existence of eight water
hyacinth infested ponds in the Lake Victoria basin
with coverage ranging from less than 1 ha to 35.5 ha
and weevils have been released in some of them.
• Nitrogen and phosphorus have been identified as
important nutrients in Lake Victoria. They come
mainly from industrial, domestic and agricultural
effluents.
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