William T. Haller

Effects of heavy metals on water hyacinths (Eichhornia crassipes (Mart.) Solms)

Abstract Water hyacinths ( Eichhornia crassipes (Mart.) Solms) were exposed for 6 wk to solutions containing 0–5 mg/1 Ph, Cd or Cu. The metal concentrations and metal accumulations within plant tissues increased linearly with solution concentration in the order leaves

Influence of Hydrilla on Harvestable Sport-Fish Populations, Angler Use, and Angler Expenditures at Orange Lake, Florida

Abstract An infestation of hydrilla Hydrilla verticillata caused an 85% reduction in angler effort at Orange Lake, Florida, in 1977 when plant coverage exceeded 80% of the lake. Nonlocal anglers were only 3% of the total number of anglers fishing the lake in 1977, but were 37% of the anglers during 1978 and 1979, when hydrilla coverage was less than 19%. Although angler use of Orange Lake was greatly reduced during the peak 1977 hydrilla infestation, the number of fish caught per hour during 1977 was equivalent to or greater than that of all other study years for all species of sport fish. The almost complete plant coverage did not lower the population of harvestable largemouth bass Micropterus salmoides or black crappie Pomoxis nigromaculatus. Numbers of harvestable bluegill Lepomis macrochirus and redear sunfish Lepomis microlophus were, however, negatively correlated with hydrilla coverage. Reduction in angling caused a 90% loss in revenue from the Orange Lake sport fishery that is valued at approximat...

Fish harvest resulting from mechanical control of hydrilla.

Abstract Mechanical harvesting of the submersed weed hydrilla, Hydrilla verticillata (L.F.) Royle, in Orange Lake, Florida entangled fish in the cut vegetation resulting in their disposal with the weeds on shore. Three block-net samples in dense hydrilla indicated fish standing crops (mean ± SD) of 205,000 ± 35,000 fish/hectare and 460 ± 30 kg/hectare. The estimated loss of fish to mechanical harvesting represented 32% of fish numbers and 18% of fish biomass. Fish most susceptible to mechanical removal with hydrilla were juvenile sportfish and smaller species. The monetary replacement value of the fish lost was estimated at over

Documentation of landoltia (Landoltia punctata) resistance to diquat

6,000/hectare.

Hydrilla control with split treatments of fluridone in Lake Harris, Florida

Abstract Landoltia was collected and cultured from a canal in Lake County, Florida, where diquat was used repeatedly during the past 20–30 yr for duckweed control. Recent applications of diquat failed to provide adequate control of duckweed, and a new commercial formulation of diquat was suspected. The new formulation was not the cause of reduced efficacy. Static exposures (48 h) to various concentrations of diquat were used to compare the susceptibility of the Lake County landoltia accession to one never exposed to diquat. These static tests indicated that landoltia, from a population with no prior history of herbicide treatment, was extremely susceptible to diquat. The accession from Lake County, FL had developed resistance to diquat, and was also cross resistant to paraquat. The resistance factor was 50 for diquat and 29 for paraquat. The Lake County accession also exhibited reduced ion leakage after diquat exposure under light and dark conditions. This suggests the resistance mechanism to the bipyridylium herbicides in landoltia is independent of photosynthetic electron transport. This research documents the first aquatic plant species that has developed resistance to the bipyridylium herbicides. Nomenclature: Diquat, paraquat; duckweed, Lemna spp.; landoltia, Landoltia punctata (G. Meyer) D. H. Les and D.J. Crawford.

Phytoene and β-carotene response of fluridone-susceptible and -resistant hydrilla (Hydrilla verticillata) biotypes to fluridone

After several unsuccessful management efforts, a split treatment of fluridone was applied to the 6700 ha Lake Harris in March and June 1987, at a rate of 3.4 kg ha−1 (680 and 340 kg fluridone, respectively) to two 3 m deep, hydrilla-infested bays. Fluridone concentrations in the water were sampled following the June treatment. Average fluridone concentrations were 2.1 µg l−1 prior to this second application, and a maximum concentration of 30.2 µg l−1 was detected in the treated area on the day following application. Fluridone residues dissipated out of the plot quickly due to dilution but concentrations declined lake-wide more slowly, following a logarithmic model, with an estimated fluridone half-life of 97 days. Control of hydrilla in Lake Harris resulted from the long exposure (over 25 weeks due to the split application) to fluridone concentrations of 2 µg l−1, well below the maximum labelled rate of 150 µg l−1.

Utilization of Selective Removal of Grass Carp (Ctenopharyngodon idella) from an 80-Hectare Florida Lake to Obtain a Population Estimate

Abstract Fluridone has been widely used for control of the submersed aquatic weed hydrilla in Florida for over 25 years. Recently, some hydrilla biotypes were suspected of having developed resistance to fluridone. Laboratory studies were conducted to monitor changes in phytoene and β-carotene contents as a function of suspected susceptible and resistant hydrilla biotypes to fluridone treatment. Hydrilla shoot tips from each biotype were exposed to 5, 10, 15, 20, 30, and 50 μg L−1 fluridone. Higher β-carotene and lower phytoene content was observed in all resistant hydrilla biotypes compared with the susceptible. The susceptible biotype showed an increase in phytoene or a decrease in β-carotene content when treated with as little as 5 μg L−1 of fluridone, whereas much higher doses were needed for the resistant biotypes. EC50 β-carotene values of 9 and 63 μg L−1 fluridone were found in the susceptible and the most resistant biotype, respectively. Consistent levels of hydrilla injury occurred at phytoene/β carotene index values of 5.5–7 and occurred at exposure to 5–10 μg L−1 fluridone in susceptible and 50 μg L−1 in the most resistant biotype. A resistance factor (R/S) was calculated for each hydrilla biotype which ranged from as low as 2X (R1 and R2) to 7X (R5). Aggressive spread of fluridone resistant dioecious hydrilla in aquatic ecosystems can severely impact hydrilla management, and consequently cause substantial and long-lasting ecological and economic problems throughout the southern United States. Nomenclature: Fluridone; hydrilla, Hydrilla verticillata (L.f.) Royle HYLLI.

Mutations in Phytoene Desaturase Gene in Fluridone-Resistant Hydrilla (Hydrilla verticillata) Biotypes in Florida

Abstract Selective removal of grass carp was attempted in an 80-hectare Florida lake by means of a 0.1-mg/liter treatment of rotenone. A mark-recapture procedure was used to obtain a population estimate. Prior to the lake treatment, a field bioassay conducted in large polyethylene bags containing lake water and suspended in the lake, revealed that a 0.1-mg/liter concentration of rotenone killed grass carp but had little effect on sport fish. Fish collected from block nets set within the lake revealed lake-wide rotenone treatment removed more than half of the threadfin shad (Dorosoma petenense), grass carp, and golden shiners less than 100 mm. Appreciable numbers (20-50%) of largemouth bass (Micropterus salmoides), lake chubsuckers (Erimyzon sucetta), larger golden shiners, and redear sunfish (Lepomis microlophus) less than 100 mm were affected. Larger redear sunfish, bluegill (Lepomis macrochirus), warmouth (Lepomis gulosus), and black crappie (Pomoxis nigromaculatus) were abundant within the lake, as sho...

Cross-Resistance in Fluridone-Resistant Hydrilla to Other Bleaching Herbicides

Abstract Hydrilla is one of the most serious aquatic weed problems in the United States, and fluridone is the only U.S. Environment Protection Agency (USEPA)–approved herbicide that provides relatively long-term systemic control. Recently, hydrilla biotypes with varying levels of fluridone resistance have been documented in Florida. One susceptible and five fluridone-resistant biotypes of hydrilla varying in resistance levels were maintained in 950-L tanks under ambient sunlight and day-length conditions from September 2004 to September 2005 in absence of fluridone. Because fluridone is an inhibitor of the enzyme phytoene desaturase (PDS), the gene for PDS (pds) was cloned from fluridone-susceptible and -resistant hydrilla biotypes. Somatic mutations in amino acid 304 of hydrilla PDS are known to confer herbicide resistance. We determined pds sequence from these hydrilla biotypes at planting and 12-mo after planting. Two independent mutations at the arginine 304 codon of pds were found in the resistant hydrilla plants. The codon usage for arginine 304 is CGT, and a single point mutation yielding either serine (AGT) or histidine (CAT) was identified in different resistant hydrilla biotypes. There were no differences at codon 304 in the PDS protein of any hydrilla biotype 12-mo after planting. Several other mutations were also found in resistant pds alleles, though their possible role in herbicide resistance is unclear. Nomenclature: Fluridone; hydrilla, Hydrilla verticillata (L.f.) Royle HYLLI

Differential Herbicide Response among Three Phenotypes of Cabomba caroliniana

Abstract The development of fluridone resistance by hydrilla has significantly impacted hydrilla management, and research is ongoing to develop alternate herbicides for effective hydrilla control. We determined the potential cross-resistance in fluridone-resistant hydrilla to other bleaching herbicides norflurazon, mesotrione, and topramezone-methyl. Phytoene, β-carotene, and chlorophyll contents as a function of hydrilla biotype and herbicide treatment were evaluated. Hydrilla shoot tips were collected from fluridone-susceptible (S) and -resistant (R) biotypes and exposed to 5, 25, 50, 75, and 100 µg L−1 of herbicide. The susceptible biotype showed an increase in phytoene and a decrease in β-carotene and chlorophyll contents when treated with 5 µg L−1 fluridone, whereas higher doses of fluridone were required to affect these pigments in the resistant biotype. There was no difference in response by S and R biotypes to mesotrione and topramezone-methyl, with both biotypes showing significant affects on pigment contents at 5 µg L−1. Higher doses of norflurazon were required to affect these pigments in the R compared to the S biotype. The S biotype had EC50 values of 11.7, 12.2, and 4.7 µg L−1, whereas the R biotype had EC50 values of 56.6, 41.1, and 41.7 µg L−1 fluridone for phytoene, β-carotene, and chlorophyll contents, respectively. There was no difference in EC50 for phytoene, β-carotene, and chlorophyll values between the hydrilla biotypes for mesotrione and topramezone-methyl herbicides. In fluridone-susceptible and -resistant hydrilla biotypes, EC50 values for phytoene, β-carotene, and chlorophyll were 12.4 to 11.8, 10.2 to 13.2, and 3.1 to 4.6 µg L−1 mesotrione and 12.6 to 13.5, 13.3 to 11.9, and 4.6 to 5.7 µg L−1 topramezone-methyl, respectively. For norflurazon, S and R biotypes had EC50 values of 33.1, 45.4, and 40.6 µg L−1 and 84.6, 81.0, and 92.7 µg L−1 for phytoene, β-carotene, and chlorophyll, respectively. These studies confirmed negative cross-resistance of fluridone-resistant hydrilla to mesotrione and topramezone-methyl and a positive cross-resistance to norflurazon. Nomenclature: Fluridone; mesotrione; norflurazon; topramezone-methyl; hydrilla, Hydrilla verticillata (L.f.) Royle HYLLI.