March 21, 2012

With new concerns about herbicide-resistant weeds and the spread of invasive noxious plant species, producers, land managers, and landowners are challenged to find the best control solutions for their operations. Following are several questions and answers to consider as you plan integrated weed management measures for your farm. This is the second of two Q&A’s on this topic.

Canadian thistle

Also see Q&A: Factors to Consider in Weed Management Strategies – Part I, CropWatch, 3/16/2012 Getting a Jump on Invasive Plant Management, CropWatch, 7/11/11 North American Invasive Plant Ecology and Management Short Course, scheduled for June 26-28, 2012, in North Platte

Question 1. Invasive plant species that infest riparian areas and rangelands can span large areas and involve terrain with limited access. Assessing the scope of the infestation is important to allocating resources to meet management objectives, including potential eradication. Location of invasive plant population(s) within a range of plant communities is also important and should be considered when prioritizing control efforts and those populations likely to expand quickly. What decision tools exist to help make landscape-level management decisions? How can these tools be implemented? What survey techniques are appropriate when considering the goal of the survey effort?

Answer. A successful management strategy will have clearly defined goals and objectives. These should be the basis for selecting inventory, survey, and monitoring methods for invasive plant population distribution and spread within a region. Without knowing the what, where, and extent of an invasive plant population, it will be difficult to develop an effective integrated weed management strategy. Several questions related to the objectives should be asked and possible constraints such as cost, size, and access should be considered when deciding what information to collect and how it should be collected. The most appropriate and efficient inventory and survey methods should be used, followed by a monitoring plan to determine changes in populations and impacts by invasive plant species on neighboring plant communities.

Question 2. Canada thistle continues to be a problematic weed in wild land settings and can be found in most North American states and Canadian provinces. Even with the use of integrated weed management tools, it possesses significant staying power. The most effective control efforts integrated methods to reduce seed from plants and in the soil (seed bank) and from vegetative structures underground. Why is Canada thistle so resilient in wet lands? What are the added considerations when managing a weed with multiple dispersal mechanisms?

Answer. Canada thistle is thought to have been introduced into North America in 1750. It was declared a noxious weed first in Vermont in 1795 and later in New York. By 1873, it had achieved noxious weed status in Nebraska and probably could have been found at similar infestation levels in many states throughout the country. Why has control been so elusive? First consider how long Canada Thistle has been in North America, its carbohydrate reserves, and its reproductive features, including a far-creeping and deep root system with adventitious buds, it is not surprising that Canada thistle has become such a widely distributed invasive plant species. For weeds with multiple seed dispersal mechanisms, control efforts must related to plant growth and development both above- and below-ground throughout the season.

Steve Young
Weed Ecologist, West Central REC, North Platte