CONTROL OF SUBMERSED WEEDS BY GRASS CARP IN WATERLILY PRODUCTION PONDS

A 4 x 2 factorial randomized block experimental design was used to evaluate triploid grass carp (Ctenopharyngodon idella Val.) for submersed weed control in waterlily (Nymphaea spp.) production ponds. Two stocking levels (one carp per enclosure and two carp per enclosure) were evaluated and compared to that of hand harvesting and no control. The effect of weed growth and control on the growth of two waterlily types, hardy and subtropical, was also investigated. Waterlily plants in the untreated-control enclosures had significantly (P = <0.05) lower leaf area/plant and number of flowers than in any of the weed control treatments. Manual weed control (hand harvesting) allowed for the greatest amount of waterlily growth (leaf area) and was significantly different from the one-carp treatment but not from the two-carp treatment. The hand harvesting treatment resulted in lower weed biomass throughout the experiment; however, complete control was not achieved. In the one-carp and two-carp treatments, complete weed control was achieved in 60 and 40 weeks, respectively, after introduction of grass carp. Following complete weed elimination, grass carp in two of the enclosures damaged some waterlily plants, but overall, results indicated that with careful management, triploid grass carp can be used to control submersed aquatic weeds in waterlily production ponds.