I have eunoymus shrubs infected with powdery mildew…not responding to fungicide. They are nearly bare of leaves now and the branches are white. Do I uproot and destroy the shrubs? And if so, do I need to treat the soil before replanting? Thanks!
Powdery Mildew is considered to be the most common, and most difficult to control, disease of euonymous. Ontario’s Ministry of Natural Resources recommends the use of a sulphur-based sprays, and the fungicide Serenade Garden is available as a ready-to-use home garden product that is also approved under the Ontario Pesticides regulations. Its active ingredient is a patented strain of Bacillus subtilis that does not harm beneficial insects or wildlife and has been found to suppress powdery mildew.
However, as you have discovered already, fungicide sprays will not cure a moderate-heavy infection; rather, they work best as preventative and should be applied before the shrubs leaf out or at the very first sign of infection.
For this year, then, your best tactic is to remove and destroy (not in your compost!) all plant parts that are infected.
Since the active growth period for your shrubs is slowing down, as unsightly as the shrubs may be, they are unlikely to have been permanently damaged. Pruned back hard to clean wood, they will grow again next year and you can begin preventative treatment in the spring.
Make sure you clean up any fallen leaves at the end of the season. It is also important that the shrubs are not crowded and have good sunlight.