CONTROL OF SUBMERSED WEEDS BY GRASS CARP IN WATERLILY PRODUCTION PONDS

A 4 x 2 factorial randomized block experimental design was used to eva luate triploid grass carp (Ctenopharyngodon idella Val.) for submersed weed control in waterlily (Nymphaea spp.) production ponds. Two stock ing levels (one carp per enclosure and two carp per enclosure) were ev aluated and compared to that of hand harvesting and no control. The ef fect 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 treat ments. 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 th e experiment; however, complete control was not achieved. In the one-c arp and two-carp treatments, complete weed control was achieved in 60 and 40 weeks, respectively, after introduction of grass carp. Followin g complete weed elimination, grass carp in two of the enclosures damag ed some waterlily plants, but overall, results indicated that with car eful management, triploid grass carp can be used to control submersed aquatic weeds in waterlily production ponds.