Perennial phlox cultivars have improved a lot over the last 20 years. These days it’s much more rare to see a major breakout of powdery mildew that affects the entire plant. Powdery mildew spores spread in warm, dry conditions but wet foliage encourages mildew growth.
![A photo of white phlox flowers in bloom.](https://emsgarden.com/wp-content/uploads/2024/07/20240710_124510629_iOS-Medium.jpg)
I really cram my plants together for mass blooming effect, so I already increase the odds of fungal diseases breaking out because my plants don’t get enough air circulation. I’m willing to take that risk each year.
Wisconsin’s State Climatology Office reported that in May and June of this year our state tallied more precipitation than any other May-June period on record, and my city had already documented almost as much precipitation through mid-July than we usually see for an entire year.
You would think that all that constantly-wet foliage would be a great breeding ground for fungal diseases, but I’m quite pleased with the general lack of powdery mildew on my phlox plants. The glaring exception is ‘Red Riding Hood’:
![A photo of phlox leaves covered with white, powdery mildew.](https://emsgarden.com/wp-content/uploads/2024/07/20240622_215943475_iOS-Medium.jpg)
This outbreak occurred already in mid-June, but the plant held tough and still churned out a lot of flowers:
![A photo of 'Red Riding Hood' phlox flowers blooming atop leaves with powdery mildew.](https://emsgarden.com/wp-content/uploads/2024/07/20240720_135944155_iOS-Medium.jpg)
![A photo of 'Red Riding Hood' phlox flowers blooming atop leaves with powdery mildew.](https://emsgarden.com/wp-content/uploads/2024/07/20240720_135932129_iOS-Medium.jpg)
‘Delilah’ has a small outbreak of powdery mildew:
![A photo of Phlox 'Delilah' flowers blooming.](https://emsgarden.com/wp-content/uploads/2024/07/20240720_140153885_iOS-Medium.jpg)
![A photo of Phlox 'Delilah' leaves affected by powdery mildew.](https://emsgarden.com/wp-content/uploads/2024/07/20240720_140159606_iOS-Medium.jpg)
But ‘Ferris Wheel’ has no spots:
![A photo of 'Ferris Wheel' phlox flowers blooming.](https://emsgarden.com/wp-content/uploads/2024/07/Ferris-1024x768.jpg)
‘Purple Flame’ is also powdery-mildew free:
![A photo of 'Purple Flame' phlox flowers blooming.](https://emsgarden.com/wp-content/uploads/2024/07/20240709_135103279_iOS-Medium.jpg)
And ‘Garden Girl’ shows no sign of disease:
![A photo of 'Garden Girl' phlox flowers blooming.](https://emsgarden.com/wp-content/uploads/2024/07/Garden-Medium.jpg)
‘Bright Eyes’ is older than most of these other phlox cultivars, but it’s trying to stay healthy. I just noticed the first white spots appearing on the leaves.
![A photo of 'Bright Eyes' phlox flowers blooming atop green leaves that have some white spots on them.](https://emsgarden.com/wp-content/uploads/2024/07/20240720_140511142_iOS-Medium.jpg)
Most perennial phlox cultivars claim on their plant tag that they are resistant to powdery mildew. But whether your plant develops the disease in a given year depends a lot more on the weather conditions and/or if it gets good air circulation.