Crape Myrtle Powdery Mildew
My beloved crape myrtle has succoumbed to powdery mildew. We have tried pruning it to thin out the branches to try to increase air flow, but this has not been successful. When it leafs out, it starts beautifully, but by July, the leaves begin to deteriorate, and then the blooms also. It is probably seven years old, so is quite mature. Thinking that it must be replaced with a mildew resistent variety. How would we destroy the diseased one (I am sure that the roots would be quite extensive.) Could a new tree be put in the same place? Appreciate your time and help!!
You've analyzed the problem and, yes, the solution is to simply replace the crape myrtle with one that is resistant to powdery mildew. (Unless the site is too shady for crape myrtle and that is encouraging the powdery mildew. In which case, you may want to replace with a different shrub.)
You can prune it down and then dig up the stump. Medium and small roots can be left in the soil. They will decompose and enrich the soil. Yes, you can replace in the same spot.
You do not need to dispose of the cuttings in any special way. Throw on a bush pile or put out in the trash.
If you can't dig up the stump, you can try treating the freshly cut trunk immediately with a systemic herbicide--with the ingredients either glyphosate or triclopyr--that will go down and help kill the roots.