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Thistle and wild parsnip control

I would be very pleased to hear some advise/experience with control of Canada Thistle and Wild Parsnip.  This is the third growing season for our 18 acre prairie planting.  There are about ten acres with some thistle, most of it sparse, but a few patches quite thick (10 x 15 foot patches) and a long patch at the crest of our hill 10 ft x 75ft.  I had mowed some patches last year and removed the material (by hand) and those areas are actually fairly good this year.  The 2 acres around our house I actually pulled by hand last year and those areas have some thistle returning (I know I did not get all the small plants last year). 
 
I'm trying to decide when and how to attack the thistle this year.  My energy and time is waning and I need to do this efficiently.  My plan is to mow the thicker patches and remove the material (my back gets sore just thinking about it), and cut the flowers off the more spotty areas so that I don't have to remove large quantities of perfectly good prairie plants.  I'm hoping to enlist some teenagers to help with these jobs. 
 
I need to know what the thistle plants sould look like when I cut them and how much do I take off.  Should I cut at the base if possible, or with the plant still go to seed lying on the ground?  If I cut just the flower off will it produce more flowers later in the season?  Can I just cut the flower off and let it fall?  How long after the flower blooms can I cut it and leave it without it going to seed on the ground?
 
The parsnip is very spotty but already has the yellow flowers on it and is about 2.5-3 feet tall.  I remember last year it got to 4-5 feet easily.  When should this be removed and can I just cut off the flower? 
 
Overall we're quite pleased with the planting.  It looks great even in the second year and we've counted 41 species so far (~110 planted).  I'm hoping the maintaince drops off in the next few years.  I can see I'm going to need to pursuade my neighbor to let me mow his fallow Thistle crop each year!  I tried burning this year and there wasn't enough dead grasses to sustain a burn.  Hopefully next year.
 
Any thoughts would be welcome.
 
Larry Sullivan, Dodge County, WI
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