Impact of Biological Control Agents on Musk Thistle Populations at the Indiana and Radford Army Ammunition Plants
by Phillip A. Lewis
U.S. Army Industrial Operations Command, Rock Island, IL
Abstract:
The musk thistle head weevil (Rhinocyllus conicus) and rosette weevil (Trichosirocalus horridus) were released at INAAP in 1987 and at RFAAP in the spring of 1978 to quell populations of musk thistle (Carduus nutans). Details of the release scenario, current thistle infestation and head weevil preponderance at each installation is reported. Impact on native thistle species will be assessed in future trips.
Introduction:
Musk thistle or nodding thistle (Carduus nutans) is an aggressive, invasive weed accidentally introduced from Europe into the U.S. in the 1800’s. This weed was first recorded in 1853 from Harrisburg, Pennsylvania and has since spread rapidly throughout North America, degrading pastures and rangelands. The head weevil Rhinocyllus conicus (Coleoptera: Curculionidae) was the first insect approved for the control of musk thistle in the U.S., with releases made in 1969 in Montana, Virginia and Nebraska. The rosette weevil Trichosirocalus horridus was imported from Italy, with the first field releases made in Virginia in 1974.
The U.S. Army Industrial Operations Command (IOC) is located in Rock Island, Illinois. The IOC is a U.S. Army Command that is responsible for the management of the U.S. Army Ammunition Plants, Depots and Arsenals located throughout the continental United States. The IOC has 36 installations in 29 states, covering over 650,000 acres. These installations have natural resources programs and projects that include fish and wildlife, forestry, agricultural outleasing, and wetlands.
Musk thistle is present at several IOC installations and estimates of chemical and mechanical control of the thistle range from $15-$60 per acre, depending on frequency of control required. In order to reduce control costs and comply with state noxious weed laws and avoid costly fines, releases of biological control agents have been made at IOC installations. Following are details of the original releases and current status of thistle and head weevil populations.
Indiana Army Ammunition Plant
This inactive ammunition plant, located in Clark County on the north shore of the Ohio River near Louisville Kentucky, once had a serious musk thistle problem which arose from the construction of a railroad spur in the late 1970’s. Having no native enemies, this aggressive weed flourished and infested 3,500 acres (1,000 heavily) of this 9,800 acre installation. Head and rosette weevils were introduced in 1987 to control the thistle (about 400 of each species) and 800 acres of the worst infested areas were sprayed with herbicide in 1989 (Figure 1).
Survey Methods and Results
Four areas were selected that had populations of musk thistle in the vicinity of the original release sites (Figure 1). Twelve plants were randomly inspected at each of these areas for the presence of the head weevil during the third week in July, 1998 (Table 1). Area 3 had a heavy, isolated infestation |