I planted this hedging about 3 weeks ago and the leaves on a good number of the plants are going white. Is this Box Blight? What would you recommend to do?
Young woody plants, especially those as small as this, can get a set-back when planted out into conditions much tougher than those where they were raised.
Young plants of this size need high quality soft soil with good drainage. They need to be watered, even if planted from pots, until they have become established. You will have to replace them, ideally with somewhat bigger, more hardened plants, and do not use the bark so close.