Development of Suitable Area-Wide Weed Management Practices for Improved Land Utilization (LS94-64)
Musk thistle, an introduced plant, is a noxious weed that impacts land utilization over a broad geographical region. This weed grows in many areas that are inaccessible and uneconomical for herbicide use or mowing. A multi-state project to develop and integrate a sustainable weed management program incorporating the release and establishment of two introduced thistle-feeding biological control agents was conducted with cooperators from Georgia, North Carolina, Tennessee, and Virginia. This multi-disciplinary (entomology, agronomy, and agricultural economics), multi-institution/agency (North Carolina Department of Agriculture, Tennessee Department of Agriculture, Tennessee Department of Transportation, University of Georgia, The University of Tennessee, and Virginia Polytechnic Institute and State University), and multi-state (Georgia, North Carolina, Tennessee, and Virginia) project involved research and extension entomologists, agronomists, agricultural economists, numerous grower and state organizations, and farmers.
This regional project emphasized farmer education and the functional integration of research technology for implementation of sustainable management of musk thistle into ongoing farm systems. The overall goal of this project was to develop and integrate a sustainable weed management program that incorporated the release and establishment of two introduced thistle-feeding biological control agents. These two agents feed specifically on thistle and pose no threat to agricultural crops. These biological control agents have been evaluated, and are established, in Virginia, where they effectively provide sustainable control of musk thistle. Research knowledge from previous studies in Virginia was transferred and developed into a practical, integrated sustainable management program for surrounding states. Once developed, this program can be easily adapted by personnel in other states for sustainable management of musk thistle. The specific objectives of this proposal were to:
1) establish and maintain on-farm field insectaries in Georgia, North Carolina, Tennessee, and Virginia for propagation of two introduced thistle-feeding biological control agents,
2) develop a distribution plan to provide biological control agents to landowners and agencies for release in thistle-infested areas,
3) develop and implement a regional educational program (through grower education days, field days, county meetings, publications, etc.) to improve public awareness of sustainable management systems using this program as a model [the educational program will be directed at numerous targets including farmers, landowners, schools, organizations, and state and federal agencies], and
4) assess the economic and environmental benefits of this type of sustainable weed management program.
During this project, more than 200,000 biological control agents (i.e., two types of plant-feeding weevils) were collected and redistributed on farmland and other musk thistle-infested lands in Georgia, North Carolina, Tennessee, and Virginia. More than 130,000 head weevils, Rhinocyllus conicus, and ca. 72,000 rosette weevils, Trichosirocalus horridus, were released into thistle-infested areas. In many of these areas, populations became established, reproduced, and moved into other thistle-infested areas. In addition, plant-feeding weevils were provided to cooperators in other states.
During the final year of this project, about 50,000 biological control agents were released against musk thistle at locations in Alabama, Georgia, North Carolina, Oklahoma, Tennessee, and Virginia. About 17,550 head weevils and 6,100 rosette weevils were collected and redistributed on thistle-infested farmland in Tennessee. Approximately 1,100 head weevils and 900 rosette weevils were collected in Tennessee and released on farmland in North Carolina. During 1997, 3,850 head weevils were collected in Virginia and released in Alabama, Oklahoma, and Virginia; 15,000 rosette weevils were collected in Virginia, and provided to cooperators in Oklahoma and Virginia. Head weevils (ca. 5,500) were collected and redistributed in Georgia. In 1997, weevils were released at 18 sites in 13 counties in Georgia, in 4 counties in North Carolina, at about 110 sites in 14 counties in Tennessee, and at several sites in 4-5 counties in Virginia. On-farm and off-farm demonstration sites and field insectaries were established and maintained in Georgia, North Carolina, and Tennessee. Two field insectaries also were maintained in Virginia for propagation of biological control agents.
Throughout this regional project, goals were outlined and discussed with numerous county extension agents and farmers, as well as at various grower meetings, field days, and scientific meetings. Cooperators worked closely with county extension agents and farmers to coordinate releases and to keep interested individuals informed of the status of the project. Because this program was relatively new to Georgia, North Carolina, and Tennessee, much continued effort was placed on contacting and explaining this project to county agents. Additional cooperators were aligned and field insectaries were designated. Information on this sustainable weed management program was distributed through various media outlets (e.g., letters, publications, field days, grower meetings, “Weevil Roundups/Rodeos”, radio and television programs, and professional meetings).
As part of the educational component of this project, “Weevil Roundups/Rodeos” were held each year in several counties in Georgia, North Carolina, and Tennessee. These activities, held on grower cooperator farms, were developed in cooperation with county agents. Farmers, other interested individuals, and several extension agents from other counties attended these field demonstrations. Participants received “hands-on” experience related to weevil identification, as well as identification of the types of damage caused by these biological control agents and a general overview of this sustainable program. The goals of this project were outlined, and questions were answered. At the conclusion of the program, participants received and/or could collect weevils to redistribute into other thistle-infested areas.
This environmentally safe and economically sound management program is expected to provide environmental, economical and social benefits. These include reduced herbicide use, improved pasture management, improved water quality, improved land value, reduced fossil fuel and labor costs, reduced impact on non-target organisms, reduced risk of exposure to herbicides, reduced herbicide residues, and reduced costs of weed management (e.g., in Missouri and Virginia, management agencies and farmers save from $750,000 to $1,000,000 annually in reduced herbicide use compared to previous conventional practices). Reducing musk thistle populations to lower levels will lead to an increase in available pasture and crop lands. Valuable efforts expended to control musk thistle could be allocated more effectively and efficiently on crop or livestock production. Establishment of this biological control system should provide a self-perpetuating, sustainable control system capable of being implemented over wide areas. This project should also reduce environmental pollutants, thereby protecting the environment and natural resources.
Management of weeds, such as musk thistle, using sustainable systems will demonstrate a positive approach to the current global concerns over environmental and groundwater contamination by pesticides.
Once established, these biological control agents can significantly impact populations of musk thistle. For example, densities of musk thistle have decreased dramatically (ca. 97%) in Tennessee since 1989 when initial large-scale releases were initiated. Similar reductions have now been observed in Georgia and North Carolina. In some areas in Tennessee, densities of musk thistle were too low to enable collections of head and rosette weevils. These low populations of musk thistle are a direct result of the impact of these biological control agents, which are well established in eastern Tennessee, and efforts are underway to enhance their establishment and distribution in middle Tennessee. The average number of seeds produced per plant also has been reduced. As the number of seeds decline, the available seed bank in the soil should also decline. Data suggest that the number of musk thistle plants and the number of seeds available in the soil are decreasing as a result of this project. As plant populations decline, fewer monumental efforts will need to be initiated to manage musk thistle over a large area. This decline in musk thistle should result in economical and environmental savings to farmers and other landowners. For example, Tennessee Department of Transportation estimated that they saved about 1-2 million dollars as a direct result of this project.
The economic savings to farmers also is high, estimated at $500,000 to $1,000,000 in Tennessee. A survey is underway to further evaluate the potential economic savings to growers in Tennessee. These plant reductions also should enable farmers and other land managers to better utilize their land. Future efforts will continue to focus on the redistribution of both species and on the education of growers and the public on integrated management of thistle weeds using biological control.
Impact of results
These two biological control agents contribute to sustainable control of musk and other exotic thistle pests. Using these two thistle-feeding weevils, farmers and landowners can better manage thistles in a nontoxic, nonpolluting manner that is sustainable. In addition, once established, the control agents disperse to attack thistles in adjoining areas. In many locales, such as the mountains, farmers cannot get equipment into their fields or they cannot afford to mow or spray thistles. This biological control program gives these farmers thistle reduction in the areas that may need it most. Successful sustainable management of musk thistle using biological control should enable farmers and other land managers to better use their land, redirect their resources, better utilize their time and labor, and improve productivity of their lands. Thus, a successful program would have tremendous economic and environmental impacts throughout a region. In addition, populations of R. conicus have not been shown to have much, if any, impact on nontarget plant species in these states. Nontarget plants will continue to be monitored to evaluate potential impact caused by R. conicus.
This program has demonstrated the effectiveness, ease of adoption and incorporation, and economic and environmental benefits of an integrated biological control program for successful area-wide sustainable management of musk thistle. This program also contributed to education of farmers and the general public as to the benefits of this type of program. Its success and educational benefits should encourage more use of biologically sustainable programs in these and other states.