Add the latter solution to the former, stirring well and use immediately. Apply this at least 24 hours before a forecasted rain. Plants will require at least three applications, one each week to a fortnight or so. The first application should be applied as the new growth emerges. Wet thoroughly the entire plant and all the undersurfaces of the leaves.
Thrips can attack flower buds which then open partially, turn brown and drop off the plant.
Timber Press, Oregon. A study of the genus Paeonia. London, Royal Horticultural Society. The Random House Book of Perennials. Volume I, Early Perennials.