Here ya go ---
Canada thistle is an aggressive perennial weed that reproduces from vegetative buds in the root system and from seed. Root systems can extend 15 feet deep or more. New plants can develop from root pieces as small as .025 inch long by .0125 inch in diameter. Individual plants can produce up to 1500 seeds per flowering shoot. Seeds can remain viable in the soil up to 20 years. These facts dictate that management efforts must be directed towards long-term planning.
The key for effective long-term control is to implement a management plan that consistently prevents the formation and dispersal of seed and to stress the plant and force it to use stored root nutrients.
Therefore, a one-time treatment for Canada thistle will not be effective. Management and control effects must be planned for several consecutive growing seasons in order to prevent new seed formation/dispersal and at the same time deplete the nutrient reserves that have built up in the root system.
Control measures that have been found to be effective for the management of Canada thistle on small acreage properties are:
Mowing: The most effective mowing technique is to mow the infestation at 25 to 30 days intervals, 4 to 5 times per season, throughout the entire growing season over several (4-5) years. The purpose of the intensive mowing is to stimulate Canada thistle shoot growth thereby depleting the plants root reserve. Mowing alone will not eradicate an infestation but can reduce infestation density by 50%.
Due to Canada thistles extensive root reserves a one-time mowing of the plants during the growing season is not an effective control technique. Similarly, a one-time hand pulling of Canada thistle during the growing season is also not an effective control technique. A one-time mowing or hand pulling will stimulate plant growth and increase infestation size and density.
Herbicide treatment: There are several herbicides available locally that are very effective for controlling Canada thistle within pasture and rangeland grasses. Curtail, Redeem, Milestone, Forefront and WeedMaster are selective, general use herbicides, available over-the-counter, with a short soil residual that controls many broadleaf plants including Canada thistle. Applied at labeled rates they will not damage grasses. Do not apply to trees, shrubs, flowers, or garden areas. The herbicides are concentrates that are mixed with water and then sprayed onto the target plant. Herbicide uptake is through the plant foliage. Read and follow all label directions. Wear the proper protective gear (rubber gloves, long pants, long sleeve shirt, rubber boots, and eye wear) when spraying.
Timing of application is dependent upon the stage of plant growth. The best time to treat Canada thistle is after the plant is fully emerged (meaning lots of foliage available for herbicide uptake) is actively growing, and prior to bud stage.
Best of luck. (It's a nasty, tough bugger.)
AKfish
