Can I compost plants with powdery mildew in the City of Portland's yard debris pickup? I called Metro's Recycling Hotline. The person that I talked to wasn't familiar with powdery mildew, but suggested that I put the infected plants in the garbage rather than the yard debris.
Should be no problem at all. Powdery mildews only survive on a living host and the composting process will kill the fungus as well as the plants. Not many plant pathogens survive the process. There is some evidence that plants with Verticillium wilt might survive and be a problem when used as mulch. Check out these resources in the PNW Plant Disease Management Handbook: