Control of Water Hyacinth with Neochetina spp. and Alternaria alternata in the Rift Valley of Ethiopia

Abstract

Water hyacinth [Eichhornia crassipes (Mart.) Solms] remains one of the worst
aquatic weeds worldwide. Its presence in Ethiopia was officially reported in Koka
Lake and Awash River about 60 years ago. A study was conducted for two years
to evaluate the integrated use of host-specific herbivorous weevil species
Neochetina eichhorniae and N. bruchi, and an indigenous fungal plant pathogen
(Alternaria alternata) for controlling water hyacinth in the lathhouse in the Rift
Valley of Ethiopia. Water hyacinth plants that grown in caged tanks were exposed
to one of eight treatments: control; only either of the weevil species (N.
eichhorniae or N. bruchi alone); the two weevil species (N. eichhorniae + N.
bruchi)\ the fungal spray (foliar application of A. Alternate); combination of the
weevils and fungal spray (N. bruchi, N. eichhorniae or N. bruchi and N.
eichhorniae + foliar fungal application). Water hyacinth plants that received the
two weevils combined with A. alternata showed a disease index (D l) of 90%
compared with Dl values of 70% and 60% recorded in N. bruchi combined with A.
alternata and N. eichhorniae with A. alternata, respectively. Application of both
weevils combined with A. alternate showed about 97% and 85% reduction in
number of new ramets and fresh weight, respectively. Thus, it is concluded that
application of the three agents together had an overall synergistic effect in
controlling water hyacinth.