Mark some with bamboo sticks and spray if at optimum size as directed by product, have never used barrier h. Then spray all of the ones you can find. Mark on clender the date of spraying and keep checking till you see no trace and i mean no trace of the weed not even a little brown leaf, you...
Sorry forgot to say if spraying Ragwort do not let the horses back into the field or area till all signs of the plant have gone not just the grazing withdrawal time on the spray. Split the field up into paddocks and do one or two at a time depending on your grassland management and requirements...
Bit of a rant but trying to put some of you correct on ragwort myths!!!!!!!!
To put the record strait I am not a vet, feed, seed or nutrition company but know how to get the best out of grassland and have a successful business maintaining grassland for the equine industry I have no affiliation...
May just want a scratch or groom look at the following to possibly help.
http://www.delaval.co.uk/Products/CowComfort-and-farm-supply/CowBrushes/default.htm
Hope it helps if not get a new fencing contractor?!