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Title: US Department of Agriculture/Corps of Engineers cooperative aquatic plant control research--Annual report for FY 1982 : Biological and chemical control technologies
Authors: Aquatic Plant Control Research Program (U.S.)
United States. Department of Agriculture. Southern Region.
Keywords: Aquatic plant control
Biological control
Chemical control
Publisher: Environmental Laboratory (U.S.)
Engineer Research and Development Center (U.S.)
Description: Miscellaneous Paper
CHAPTER 1: The purpose of the study reported in this chapter was to compile a list of insects associated with hydrilla in the United States. The fauna associated with hydrilla was surveyed by taking 267 collections of hydrilla from 58 Florida locations and an additional 22 collections of hydrilla from 17 out-of-state locations. Most of the Florida collections were made using a quantitative sampler to provide data on the density of insects and other fauna and to compare these densities with hydrilla standing crop. The quantitative results from six ecologically and geographically different sites are analyzed and diacuased. Hydrilla biomass fluctuated greatly at any given site, and these fluctuations in biomass showed definite, predictable seasonal trends at only a few locations. Hydrilla biomass also varied greatly from location to location, peaking at 1013 g/m² (standing crop dry weight) at a clear, spring-fed river, while never exceedini 100 g/m² at an oligotrophic lake. Almost half of the 59,130 faunal specimens recorded during this survey were snails, with Goniobasis floridense being the moat abundant (over 12,000 specimens). Densities of G. floridense exceeded 3200 snails/m² of hydrilla mat at one lotic site. Snail densities generally appeared to track biomass density directly. At least 25 species of snails were recorded from hydrilla, but moat appeared to feed on the epiflora associated with hydrilla. Over 17,000 insects were collected and these comprised almost 200 species. Analysis of a species accumulation curve for the insects found in the 267 Florida collections indicated that additional collections would continue to add additional insect species, but that only 35 more insect species would be added for every 100 additional Florida collections. Insect densities tended to peak around March, but this was highly variable. The peak insect density observed was 2691 insects/m² at Lake Lochloosa, but almost all of these insects were several species of midges (Diptera:Chironomidae). Midges were the moat abundant insect group, comprising 57 percent of all insects collected. Some midge larvae in the genera Endochironomus and Glyptotendipes occasionally caused minor damage to hydrilla when they constructed burrows in hydrilla stems. Caddisflies (Trichoptera) comprised almost 25 percent of the insects collected. Of the 22 species of caddisflies, 5 species at least occasionally feed on hydrilla. Of these, Leptocerus americanus and Nectopsyche tavara were the moat abundant. A half-dozen species of moth larvae feed on hydrilla leaves. Of these Synclita obliteralis and Parapoynx diminutalis were the most numerous and damaging. Parapoynx diminutalis is the only species of U.S. insect which shows a definite preference in the field for feeding on hydrilla. CHAPTER 2: Thia chapter presents results of a biological control study of the Asian moth, Parapoynx diminutalis Snellen, for use against the problem aquatic plant, hydrilla. Biology and host range studies were conducted with P. diminutalis, a moth adventive in Panama and Florida. The eggs were deposited on the leaves and stems of hydrilla plants lying at the water surface. The larvae fed on the leaves and stems from tubular cases constructed from leaves. The larvae had spotted heads and feathery gills along their aides. The spotted heads distinguish them from native Parapoynx larvae, which are not spotted. A white cocoon was constructed inside a case attached to the stem from which the pupa obtained oxygen. Larval development was studied at different temperatures. Adults were found to mate the first night but not to begin ovipositing until the second night. The laboratory host range was studied in oviposition tests, larval no-choice development tests, and larval choice tests. There was little discrimination in small containers by ovipositing females and the larvae developed on at least 14 plant species. Young larvae, however, preferred hydrilla over most of the other test plants. Even though P. diminutalis was polyphagous in the laboratory, it has been found in the field almost entirely on hydrilla. Because of its broad host specificity, it is unlikely that this insect agent would ever be used as a biocontrol agent for hydrilla. No further work is recommended on importation of this species; this is the final report upon which that decision was based. CHAPTER 3: Thia chapter presents the results for FY 82 of an ongoing evaluation program of chemical formulations to determine their potential as aquatic weed control herbicides. During FY 82, 28 chemicals were evaluated in the laboratory, greenhouse, outdoor aquaria, or in the field. Sixteen of these were experimental including nine controlled release (CR) formulations. Two clay-pellet formulations of Poly (GMA) 2,4-D were subjected to advanced evaluations in outdoor aquaria. One of these formulations controlled watermilfoil within 4 weeks, and control was maintained throughout the 20 week experiment. Flowing water bioassys were conducted in the laboratory for various CR formulations of dichlobenil and fluridone. The dichlobenil-alginate granules effectively inhibited hydrilla regrowth from tubers and rootstocks when concentrations of dichlobenil in the flowing water were maintained at 0.04 mg/l or higher. Similar control of hydrilla regrowth was obtained in treatments with a CR formulation of fluridone to maintain 0.02 mg/l of the chemical in the flowing water. The experimental herbicide DPX-5648 continued to give promising results in field evaluations. Complete control of waterhyacinth was obtained with field treatment rates of 10 or 20 g a.i./ha. The persistence of the chemical in the aquatic environment is being investigated in a cooperative study with DuPont Company. Other experimental herbicides evaluated during the past year gave poor control of submersed aquatic plants in laboratory screenings. However, AC-925 showed promising results in greenhouse evaluations. Complete control of waterhyacinth and several other floating species was obtained 12 weeks after treatment with 0.11 kg/ha AC-925. The chemical AC-925 also gave adequate control of torpedograss at 0.28 kg/ha and alligatorweed at 0.56 kg/ha. Hygrophila polysperma (Roxb.) Anderson, Bacopa caroliniana (Walt.) Robins, and Cabomba caroliniana var. multiparita were shown to be tolerant to most aquatic herbicides at levels currently being used for hydrilla control. The selectivity in herbicide responses appeared to be partly responsible for the recent weed problems with these species in various locations previously infested by hydrilla. NOTE: This file is large. 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Appears in Collections:Miscellaneous Paper

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