The Demo Garden Blog

Last week, one of our Master Gardeners asked, “Why don’t the zinnias in the Demonstration Garden have powdery mildew? Zinnias always get powdery mildew!”

My brilliant answer to that question was, “Well, for some reason the weather has not been as good for mildew this year. Let’s not complain!”

Of course, no sooner had a I said that, then I saw this out on our zinnias:

Yes, my friends, that is none other than the pesky fungus, Powdery Mildew. This fungus shows up on the leaves first, looking like spots of talcum powder. The disease will eventually spread to the flowers, then kill the plant.

Powdery mildew is particularly fond of cooler, low-humidity weather. That would explain why we are just starting to see it now. If we really wanted to fight the disease in the Demonstration Garden, we could spray with Immunox or some other fungicide. However, we’re near the end of the growing season. It’s probably just as well to let nature take its course at this point.

The mildew is showing up on the ‘Benary’s Giant Mix’ Zinnias, which is an older variety of zinnia with no resistance to the disease. You should be able to find zinnias to plant that are resistant to powdery mildew, but ‘Benary’s’ is THE BEST zinnia for cutting flowers. It will be interesting to see if any of our other zinnia varieties end up with powdery mildew.