Just replied on your other thread I left it 3 weeks to make sure the ragwort had died and decomposed completely, otherwise the horses will eat the still toxic but dead ragwort.
True- I only used it last year whilst I was waiting for my Headland to arrive- i does work when used in the right concentration but obviously isn't economical and isn't specifically designed for ragwort so can't guarantee anything.
I'd leave it a month, or until the ragwart has died off completely- may take longer if my recent experience with weedkiller on thistles and docks is anything to go by. If its in the process of dying it is more likely to be eaten. Saw your other thread- I'd be really cross about her spraying it. I'd never spray ragwart- much safer to pull out by hand.
Round up is an effective weedkiller for all weeds that are not woody, so young Rugwort plants are killed by round-up especially if they are growing lust.
Woody is the key word!
Round up as with all weedkillers works less effective if the weeds are in a drought condition as the stomata are not open and intake of weedkiller is not occuring.
Also round up needs 24hrs with no rain due for maximem effect.
Finally round up kills grass so you will have spots all over the fields and rugwort seedling sprouting up in these places in mass.
SBK from the garden centre is the best
Take this from a horticulturlist
Rob