Every year, my Crepe Myrtle gets mildew, but I was told not to worry about it, since it's deciduous, and it would lose the infected leaves anyway. But this year, it's the worst I've ever seen. I park my car next to it, and it looks like it's been snowed on! My question is--is it worth treating? and if so, what should I use? It's a good size tree, I guess about 20 ft. high, and about 10 ft in spread.
Powdery mildew can be hard to avoid if you have a cultivar that's susceptible as yours seems to be. The best thing to do is to plant mildew resistant cultivars (any of the ones named after Native American tribes are supposed to be resistant and I'm sure others as well). If you don't want to replace your tree though there are some things you can do to make the problem better. First of all practice good hygiene and clean up all the fallen leaves in the fall vs leaving them sit there. Air circulation is also important, so if the tree is overgrown or crowded by other plants I'd do some pruning to thin things out. You can also spray fungicides. Also lay off the fertilizer if you've been fertilizing it--the new tender growth can be more susceptible. But no matter what you do, if you have a susceptible plant you are likely to have a constant battle on your hands. http://www.ipm.ucdavis.edu/QT/powderymildewcard.html http://gardening.about.com/od/gardenproblems/a/PowderyMildew.htm
Thanks ecrane for the great links, they're very helpful. It's a pretty tree, and usually flowers nicely every year, so I don't want to rip it out. I'll try some of the remedies, and see how it does, and next year I'll work on prevention beforehand. I've never seen it this bad, so I've never tried prevention before, but I guess I better get on it!
If you've been letting the diseased leaves lie around under the tree instead of cleaning them up that may be why it was worse this year. Weather conditions can contribute too so you will probably find some years are worse than others even if you take the same preventative measures every year.
I'm good about cleaning up the old leaves, but in reading more on your links, it seems as though Crepe Myrtles are literally the poster child of powdery mildew. That explains a lot...
The good news is we're having a major heat wave down here, and the temp in Newport is 97! The UC Davis site says that mildew may be killed if it hits 95. I may have lucked out! We'll see when I get home, and over the course of the next few days.