Distribution of the water hyacinth(Eichhornia Crossipes) (mart) solms.] its carpet characteristics, some of its diseases and pests in the Winam gulf of lake Victoria

Abstract

The occurrence of the Water hyacinth (Eichhornia crassipes [Mart.] Sohns) in the Winam gulfhas created numerous negative attributes that make its control an urgent priority. Little has been reported about its carpet characters and the occurrence of the natural enemies that are known to occur with it in other water bodies. Since these natural enemies presented the most ideal source of viable biocontrol agents, investigations meant to establish their occurrence and distribution were desirable. Experiments were set up between 1995 and 2000 in selected beaches within the Winam gulf, aimed at establishing the distribution pattern, origin, carpet characteristics, disease types, disease causative agents and their suitability for use as biocontrol agents. Plants meant for the identification exercises were collected from 6 locations, and the characteristics exhibited by their roots, stems, leaves and inflorescence compared to those already described as Eichhornia crassipes [Mart.] Sohns-Laubach. The entry point of the water hyacinth was confirmed by conducting an investigation exercise at the Rusinga channel. In order to have a better understanding of the seasonal changes in the carpet sizes, a surveillance program that lasted four years was conducted twice a year (between June. 1995 and 1999 November) at Kisumu, Kobala, Homa-bay and Luanda-nyamasaria. The distribution of water hyacinth growth forms was determined by counting the number of each growth form that appeared out of 100 plants collected from Kisat bay, Dunga beach, Luanda Kotieno, Osodo bay, Nyakach bay and Sori bay. Carpet connectivity calculated as the difference in pressure when weights were added on a mesh wire measuring 0.434 m2 until the carpet submerged and the pressure on the same carpet that was required to submerge it after a complete disconnection. The standing population density was determined by counting the number of plants found within quadrants measuring 1m2 located at Dunga beach, Kisumu pier, Kusa, Kobala and Kendu bay, while the biomass density was determined when oven dried plant materials collected from quadrants xv measuring 1 m2 were weighed. The plant mass and rhizome length measurements were correlated, while the population density was correlated to biomass density within the same carpet. Water hyacinth plants showing disease symptoms whose causative agents were unknown were collected from the Winam gulf and brought to the Laboratory for isolation purposes. Potato Dextrose Agar (PDA) cultures of each pathogen were prepared and the disease causative organism isolated. Pathogenicity trials were conducted in accordance to Koch's postulates. When the counts for growth forms were complete, the larger growth form occurred 45.0% while the medium and small occurred at 34% and 21%. There was no correlation between the rhizome measurements and the fresh weight, but the correlation between the population density and biomass was highly significant with r2 = 0.9202. Six genera of filamentous fungi together with an unidentified number of bacterial forms found occurring with the water hyacinth in the Winam gulf. The isolated species include; Myrothecium roridium, Acremonium zonatum, Rhizoctonia solani, Fusarium sp., Cercospora sp. and Alternaria sp. The results obtained from this study have confirmed the occurrence of more than six water hyacinth phytopathogens that can be developed into mycoherbicides. They have shown that the water hyacinth distribution in the Winam gulf is seasonal, adopts secluded bays and mostly exhibit the large growth form. It is now clear that carpets measuring 0.434m2 in size that have a connectivity of288.4 Pa (pascal) are able to support a weight of 12.6 kg. only, with any additional weight causing them to submerge. The distribution of plant mass in the Winam gulfis normal except in locations that are subjected to external factors.