several of my hydrangeas have white powdery mildew. since it is so close to the time to drop the leaves is there any harm if i don't treat them? also, any recomendations on a fungacide? thanks in advance - jon
white powdery mildew
No one has responded, so I'll just tell you what I do - I have the same problem, and I've had it before. I just let the leaves drop. I do try to clean up around the plant before I dump tree leaves all around them. I don't really see how we can avoid these problems in our area. It won't damage the plants. Dirr says, "immunity to mildew does not exist within H.macrophylla, and the best hope is for high resistance".
Ray
And I will add that I suggest you try spraying with Messenger next year, as soon as the leaves start emerging, and every 4-5 weeks thereafter. You would be increasing your plant's resistance to mildew and all other infectious organisms. This stuff is terrific. Although you didn't mention whether they got more stress than usual this year, be sure that they don't get stressed next year from lack of water , watering at the bottom, not the top. Excess moisture on the leaves spreads mildew (and leaf fungus and black spot, etc) like wildfire, but watering too little creates a stressed plant that is susceptible to mildew.