Thanks, I have no interest in treating or controlling it over and over. I want it gone. They were just fine until I bought some new ones. I don’t overwater them. There were some days when the room was stuffy and humid and it wasn’t time for air conditioning yet. That’s when the problem started. I just want to know when I am ready to start over with new ones, will there still be spores around from the old ones? Thanks

Where do you buy the orchard spray? I have Physan on hand and I was hoping that would do the job but I keep having to spray every few days. For a long time I didn’t buy any Rex begonias because I didn’t want to have to deal with powdery mildew. Then I was able to obtain some from leaf cuttings and they did fine for a year. It was only when I bought these new ones I started having trouble.☹️

Good luck in your future endeavors!

Good air circulation generally helps to keep most molds in check. You mentioned the problem didn't appear until the room was warm and stuffy ....

Yes, but there were days like that last fall and the spring before and the begonias I had at those times were ok. I don’t have a ceiling fan and I’m not going to run the air conditioner when it’s not that hot, so I don’t know what else to do.. 😐

Powdery mildew spores are pretty much everywhere, so unfortunately there's no "safe" waiting period that guarantees they won't come back. I'd focus more on cleaning the area where the plants were, removing any fallen leaves, and improving air circulation before bringing in new begonias.

If your previous Rex begonias did well for a year, I'd guess the conditions eventually became favorable for the mildew rather than the spores coming specifically from the nursery. When you get new ones, giving them a little extra space and avoiding wet foliage can make a big difference.

Powdery mildew spores can stick around for a while, but they usually need a suitable host and the right conditions (high humidity and poor air circulation) to become a problem. I'd give the area a good clean, wipe down the shelves and pots, and wait a few weeks before bringing in new Rex begonias. Also, this article has some helpful tips on preventing powdery mildew on begonias, not just treating it . It might help you avoid the same issue with your next plants.

Wow, this thread has been awakened after five years. Mildew is the bane of a lot of begonias, not just rexes. Thin leaf canes/shrubs such as Sinbad, Don Miller, Maurice Amey, and others are notorious for mildew in fall (and sometimes in summer such as Lynda Dawn). Also a lot of the big polka dot canes are very susceptible to mildew outbreaks. Most attacks for me are in fall when the night temps are getting chilly. Keeping them warm for winter under 12 hour light cycles helps keep most healthy. Monitor your most susceptible plants and spray as needed - and that includes all the plants in the same room. Two to three gallons of Orchard Spray keeps most things looking tip-top. Also do not water heavy in winter unless your plants are actively growing.