Weber State University
Department of Botany
Antelope Island Field Trip
Noxious and Invasive Weeds of Antelope
What is a Weed? Weeds are defined as plants out of place or as "a plant that interferes with management objectives for a given area of land at a given point in times" (J.M. Torell)
Weeds, plants that pose a threat to the welfare of a community, are placed into two major groups, noxious and invasive. Noxious weeds are plant species that tend to be especially injurious to public health, crops, livestock, or other properties. Invasive weeds are plant species that have the potential to spread rapidly and become noxious.
One of the most spectacular displays of spring wild flowers along the Wasatch front is provided by the weed species of plant called Dyer’s Woad (Isatis tinctoria). This prolific, yellow flowered species was introduced into Utah in the 1800's as a dye plant and has since spread and infests millions of acres in the valleys and hillsides of Weber, Davis, Box Elder, and Cache Counties in Utah. This "beautiful" display is not as innocent as it appears in its splendor when in full bloom. The problem: When Dyer’s Woad was introduced from Europe, the natural predators that helped Mother Nature maintain an ecological balance of the plant in its native habitat were left behind and upon its introduction had no natural predator to keep it in balance. In fact, it is allelopathic! The plant releases chemicals into the soil surrounding it which retard the growth and development of native plant species, giving it a competitive edge and allowing its rapid spread. Dyer’s Woad is not palatable to native or domestic animals so grazing does not help control it. So, Dyer’s Woad has spread throughout Utah, and surrounding states. What can we do to control it? Many communities have a day called "Bag of Woad Day" where community groups pull and bag the weed in the early spring so that it will not produce and spread by seeds. Because of environment issues and the fact that the plant occupies such an expansive area, many of which are difficult to reach, chemical herbicides are not always a desirable way to control it. Research is being done on a fungus predator that prevents the "weed" from producing flowers, hence no seeds are produced. The fungus does not infect other plant species and though it spreads rather slowly, with patience it can bring Dyer’s Woad to a manageable state.
Dyer’s Woad is a prime example of the problems faced by land managers who deal with introduced plant and animal species. All states in the U.S. deal with weed problems and have Weed Boards managed by the States' Departments of Agriculture, with authority and responsibility to control weeds given to each county under the direction of the County Weed Supervisor.
Our field trip will take us to Antelope Island State Park. It is the home of one the largest publicly owned herds of buffalo in the United State that depend on the vegetation of the Island for food. It, too, has its problems with weeds as described by the Weed Management of Antelope Island 2001: "Noxious weeds are a vegetative wildfire raging out of control. However, unlike a wildfire, noxious weeds spread silently through the years and by the time we realize there exists a problem, it is often too late to eradicate the invader. We then are left to manage around these species and spend large sums of money to simply keep them at bay."
Prior to the invasion of Antelope Island in 1847 by Anglo-Saxons, the island was dominated by a blue bunch wheatgrass/sage brush community. This supply of natural vegetation was inviting to the early settlers who almost immediately brought livestock to the island. The island’s vegetation has been overgrazed for nearly one hundred and fifty years leading to its conversion from the blue bunch wheatgrass/sage brush community to an open grassland system that is now dominated by the introduced, invasion species, such as cheatgrass (Bromus tectorum). Cheatgrass is a spring annual that grows rapidly with spring moisture and completes its life cycle before the hot, dry summer months found prevalent in Utah. As a result the cheatgrass is dry by June, hence it is also called June grass, and presents an extreme fire hazard. Frequent fires fueled by cheatgrass have aided in the loss of the native community of plant and the rapid spread of cheatgrass over the island. Farming, construction, and mans visitations are other influences that have brought changes to the islands plant communities.
Today we find eight of Utah’s noxious weeds on the Island: dyer’s woad, whitetop, musk thistle, diffuse knapweed, spotted knapweed, Canada thistle, bindweed, tall whitetop, and dalmatian toadflax. Other invasive weeds found on the island that present some concern include houndstongue, Russian olive, tamarisk, common burdock, moth mullein, and cheatgrass.
Just as the biocontrol fungus has been introduced on Dyer’s Woad, many other measures of biocontrol have been and are being introduced into Utah’s populations of noxious and invasive weeds. Presently a Weber State University student, Jolene Hatch, is working with an insect introduced to help in the control of dalmatian toadflax on Antelope Island.
The website for the Weber County Weed Department contains information, including picture identifications and control measures, about noxious and invasive weeds found in Weber County, Utah. It is an excellent site and one you ought to visit for more information about the weeds of Weber County.
Weed Management on Antelope Island State Park, June 2001
Torell, J.M. 1991. Weeds of the West. Publisher - The Western Society of Weed Science in Cooperation with the Western United States Land Grant Universities Cooperative Extension Service
Field Trip Guide (PDF) Review Questions (PDF)
Return to the Antelope Island Field Trip Home Page
Botany Department Field Trips Page
Botany Department Home Page