Thank you calistoga for your response: I have done it - cut it right back to the ground because even the stems were affected. Now we just have to wait for next Spring and see if the root managed to survive... I have bought another fungicide called Serenade that is the choice of a different garden centre. You know, what with the cost of the fungicides and the spraying equipment, it would have been cheaper just to have dug the d*** thing up and put in another one!!

Appears you're correct. Treatments for powdery mildew must be applied at the first hint of disease. Harvest the pink tomato and let it ripen on the counter. Then open up that area as much as possible to increase air circulation. Water at ground level. Remove the brown portions of the leaves because thy won't ever re-green and, right now, they are limiting air circulation within the plant.

If the foliage is mildewed over the entire plant I'd go ahead and cut them back to just an inch or two above the ground. If they're in a lot of shade they will continue to decrease every year, though--you're right about moving them. It isn't a small job but maybe you can move one at a time?

This is a bad time of the year to try to do anything to it because I'm pretty sure you're going to have to dig it up to see what's going on. You didn't say how long the tp has been in place but if it has developed some roots you might be able to save them both. I'm hoping that is the case, don't think you'd see any tp growth this year at all if the graft had failed with no roots produced. Regardless, what's done is done. I'd say your best bet is to dig it up this fall, being careful to get all of the roots. Wash them off really well so you can see what's going on in the root department! If you see the 2 different kind of roots (tp will typically be less tuberous than the herb.) carefully separate them. Might want to leave the roots in the shade for a few hours before attempting, they're pretty brittle when first out of the ground but get a bit more flexible after a bit. If there is no tp root there examine the graft. If it still looks viable I'd probably prune anything from the herbaceous root that looks to be growing above ground and replant so that the graft is a few inches below ground. Bet this 2nd option isn't even a possibility though--either the graft is good and you're growing tp roots but the herbaceous root hasn't died off because of planting depth or you'll only have herbaceous roots when you get it out of the ground. I'm certainly not a tree peony expert, just started seriously collecting them a few years ago myself. Hopefully someone with far more experience will chime in and give more expert advice. Good luck, hoping for the best!