Last updated: June 10. 2014 4:03PM - 111 Views
By Dean J. Houchen Pheasants Forever Wildlife Biologist



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PREBLE COUNTY — In the past month, how many of you have noticed the days getting longer? Well let me ask this question, how many of you out there have noticed that one particular troublesome weed is growing quickly and showing signs of blossoming? If you have, then congratulations! It is that time of year again when the Canada thistles are up and getting ready to flower. How can this be? Two weeks ago they were just small rosettes on the ground.


Well it is simple; Canada thistle grows rapidly in response to 14-16 hour days (Beck 2008). As a result, the plants bud around early June in this part of Ohio.


Why is this news article warranted, you may ask? Well, there are a few little known facts about Canada thistle that attention needs to be brought to, particularly in the next couple of weeks. The first fact is that Canada thistle is a perennial plant, meaning that it will continue to grow year after year. The second fact is that Canada thistle seeds can remain viable in the soil for up to 20 years (Beck 2008). The seed does not necessarily contribute to the local spread around the plant, but to the long distance spread of the species. Seeds have been recorded to spread, by wind, up to a half mile (Wilson 2009).


The third, and probably most important, fact is that localized spread (around the plant) is vegetative. This means that the plant either sends out roots that sprouts grow off of, or the plants roots are cut or disturbed and the pieces of the root sprout into seedlings. According to Robert Wilson, Nebraska Extension Weed Specialist, Canada thistle roots can grow 9-16 feet horizontally and 6-9 feet vertically in one growing season. Thistles grow in circular patches that can be one large interconnected plant. If the patches are tilled, root segments that are one inch in length can produce seedlings.


Now that we know a little more about what makes this plant a bear to control, we have figured out why this article is warranted. Management of an established Canada thistle stand starts with seed control. If you cannot treat thistles in the spring with herbicide, your first line of defense is to limit seed production. This is accomplished by mowing the thistle stalks when they start bearing unopened seed heads. Thistles are getting ready to flower in the next week or soon after, so the time to mow is now. Mowing will limit or eliminate the seed production for the year. This will slow the introduction of seeds into the soil bank. Repeated applications may be needed if the plants get mowed a touch early because they will try to grow another seed head. Treating Canada thistle is not a one and done process. This plant is extremely resilient and the area where it was initially treated will need to be scouted in following years to address re-sprouts (Wilson 2009). Remember the old saying April showers bring May flowers. Well, June daylight brings thistles to fight. For assistance with thistle or noxious weed questions contact me at: Dhouchen@pheasantsforever.org, phone, 740-624-7945


If you would like more information on the spread, growth, and control of Canada thistle please refer to these publications:


Beck, K.G.2008.Canada Thistle: Extension Fact Sheet 3.108. Colorado State University Extension, Fort Collins, CO.


Wilson, R.2011.Noxious weeds of Nebraska: Canada Thistle . University of Nebraska-Lincoln Extension Publication EC171. Lincoln, NE.

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