72 

 Materials and Methods 



Field applications were conducted on Lake Dexter, one of a chain of 

 lakes located on the St. Johns River, 6.7 km southeast of Astor, Florida. 

 The waterhyacinths appeared free of any disease, but did exhibit evi- 

 dence of moderate feeding by waterhyaci nth weevils, Neochetina spp. The 

 plants were growing in a large stand of Nuphar luteum which prevented 

 movement of the waterhyaci nth mat during the treatment period. 



Field evaluations were conducted in two phases. In phase one, the 

 experimental plots were 9.2 m x 3.0 m. Three experimental plots were 

 established in each of 17 separate 46.0 m x 3.0 m transects such that 

 each of the 51 9.2 m x 3.0 m plots were separated by an untreated plot. 

 The untreated plots served as buffer areas between treated plots. 

 Prior to treatment, three random 0.33 sq m samples were taken from the 

 plots to be treated. Plants within the 0.33 sq m samples were counted, 

 allowed to drain of excess water, and weighed to the nearest 0.05 kg in 

 order to determine pretreatment biomass and number per sq m. In phase 

 two, experimental plots were laid out as three separate 0.40 ha-plots 

 each separated by an untreated strip of waterhyacinths. Pretreatment 

 biomass determinations were not made because the efficacy of treatments 

 was based on visual evaluations of individual plants to obtain a propor- 

 tion of dead plants per plot. 



In phase one, the 51 individual plots were treated by use of an 

 airboat equipped with a tank-mix spray system calibrated to deliver a 

 spray volume of 467 1 /ha. Each plot was treated twice in order to 

 obtain a spray volume of 934 1/ha. Applications were made with a fixed 

 boom equipped with a single Delavan Type-D20 flooding nozzle. The boom 



