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Title: US Department of Agriculture/Corps of Engineers cooperative aquatic plant control research--Annual report for FY 1981 : Biological and chemical control technologies
Authors: United States. Department of Agriculture.
Aquatic Plant Control Research Program (U.S.)
Aquatic Plant Management Laboratory (Fort Lauderdale, Fla.)
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: Classical biological control, i.e., the importation and establishment of a natural enemy (usually an insect) from the home range of the target pest, is a proven technique for controlling some terrestrial weeds. To date all the insects released to control aquatic plants in the United States have been imported from South America to control alligatorweed and waterhyacinth, both natives of South America. Currently, the United States has no scientists overseas working on biological control of aquatic plants. This is especially unfortunate in view of the long time periods necessary to discover, evaluate, import, and establish a new biological control agent. As a result of the lack of foreign exploration for natural enemies, there are now no exotic insects awaiting release for the other aquatic weeds in the United States. This includes the noxious plant hydrilla. In June 1980, the U.S. Department of Agriculture entered into a specific cooperative agreement with the University of Florida entitled "Foreign Search for Biological Agents to Control Aquatic Weeds." The initial searches focused on tropical Asia, which is considered by most experts to be the area of origin for hydrilla and which is an area where the insects associated with hydrilla are poorly known. During the visit to Asia, hydrilla was observed in all countries visited and firsthand knowledge was gained of requirements and difficulties for collecting and testing in each country. Progress was made in the overall project goal of locating possible biological control agents for hydrilla. Several species of a small aquatic weevil belonging to the genus Bagous were collected feeding on hydrilla in south-central India that appeared to be very promising natural enemies. Potential biological control agents for other aquatic plants were also noted during this trip. Much research has been done in Thailand with the moth Episammia pectinicornis, which is very destructive to waterlettuce, Pistia stratiotes, and which appears to be very specific to this floating aquaphyte. This trip was noteworthy not only because of these accomplishments, but also because there were several general indications that natural control agents exist in Asia: (A.) hydrilla usually becomes a problem only in recently formed (within the last 20 years) reservoirs; and (B.) on the relatively few occasions hydrilla was known to have been established for a long time, it was usually not the dominant macrophyte and was being outcompeted by native vegetation such as coon tail, or by more recently introduced plants such as waterhyacinth and Salvinia molesta. Thus, while hydrilla may have been abundant in some, usually newly formed, aquatic systems, where populations of its natural enemies may not have yet become established, in general, it appeared to be less abundant and less competitive than in Florida. In view of the tremendous expenditures currently required for partial, temporary control, it would appear highly advisable to more thoroughly investigate the natural enemies of hydrilla in these areas, in case some of them may prove useful in controlling this nuisance in the United States. CHAPTER 2: Sameodes albiguttalis, a pyralid moth species, was released in Florida for the biological control of waterhyacinth in 1977. Several populations became well established, most of which were in south Florida, and, by January 1979, the range of these populations began to expand. Within 18 months, S. albiguttalis could be found throughout the peninsular portion of the state. The moat dramatic dispersal period occurred during mid-summer 1979 when a range extension which averaged ca. 4 km/day occurred. After the dispersal phase, population intensities varied seasonally and geographically and were somewhat dependent upon the type of waterhyacinth plant present. When the data were analyzed in such a way as to remove the effects of plant type, the populations seemed to be higher in the south during the spring and summer than during the winter and fall. The reverse was true in the north and little seasonal variation occurred in the central part of the state. Once populations became established, they persisted throughout all areas of the state in spite of a very cold winter in the northern regions. CHAPTER 3: This chapter presents the results for FY 81 of an ongoing program to evaluate chemical formulations to determine their potential as aquatic plant control herbicides. The objective of this project was to expand evaluation research on the use of chemicals for aquatic weed management in an attempt to discover safer and more effective herbicides and growth regulators. Recently, several techniques of formulating effective chemicals within various polymer or matrix structures have been developed to provide controlled release over time, allowing a prolonged exposure of target plants to a sustained low concentration of a given herbicide. The effective use of controlled release herbicide formulations (CRHF) appears to hold great potential for long·term management of nuisance aquatic plant growth with much lees herbicide required for the same period of activity. During FY 81, our principal activity was to implement the protocol for evaluating CRHF's of MOE 2,4-D/GMA, Poly GMA 2,4-D, 2,4-D Kraft Lignin, and various formulations of diquat and dichlobenil. Progress on the implementation of the protocol as well as the results of the conventional herbicide evaluation program will be discussed in this chapter. The polymer GMA 2,4-D was shown to be efficacious in constancy of 2,4-D release in static tests. After an initial "wash-out" during the first few days posttreatment, release rates stabilized at approximately 2.6 mg 2,4-D/g polymer/day in reconstituted water. Complete control of watermilfoil (Myriophyllum spicatum L.) was obtained in flowing-water bioassays with poly GMA 2,4-D at treatment rates calculated to maintain constant levels of 0.05 and 0.10 mg/l 2,4-D in the flowing water. The experimental herbicides DPX-4189 and DPX-5648 provided complete control of waterhyacinth and several other floating and emergent plants at treatment rates of 0.010 to 0.020 kg/ha after 8 weeks posttreatment. The chemicals were taken up readily by both the foliage and roots of waterhyacinth. Also, severe growth retardation was observed at treatment rates of 0.02 to 0.05 kg/ha, suggesting their possible use in combination with a biological control agent in an integrated management program for hyacinth. DPX-4189 applied up to 20 mg/l did not inhibit hydrilla tuber germination. However, growth and development of the newly germinating sprouts were severely retarded by treatments of 0.01 mg/l or higher. Procedures have been developed for inducing tuber formation by hydrilla under controlled growth conditions in the laboratory. Preliminary evaluations indicated that the herbicides fluridone and DPX-4189 inhibited hydrilla tuber formation under experimental conditions, at treatment rates of 0.05 mg/l and 0.10 mg/l, respectively. The susceptibility of Hygrophila polysperma and Cabomba caroliniana var. multipartita to aquatic herbicides now available or under development was determined.
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Appears in Collections:Miscellaneous Paper

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