QuestionsHow to growTrees and ShrubsPests and Diseasesbrown patches on rhododendron 0 Vote Up Vote Down Emer Gilmartin asked 14 years ago I have brown patches on the underside of 2 white rhododendrons . will i cut all the affected parts out and will this spread to other plants of same family. 1 Answers 0 Vote Up Vote Down Gerry Daly Staff answered 7 years ago Brown patches of leaves can be due to a variety of causes … shading, dogs, physical damage etc. Wait and see, and if the branches are dead, cut them off where they arise.