Wednesday, June 24, 2009

Powdery Mildew

According to our local paper, we have had “roughly 40 days” of rain since the beginning of April or about 12 inches. The gardens are green and lush.

Penn State Extension’s “Plant Disease Facts”, lists conditions that favor powdery mildew:

- High relative humidity at night
- Low relative humidity during the day
- 70-80 F temperatures

That sounds like our weather forecast.

Aptly named, powdery mildew looks like someone with a diaper emergency tripped and dumped baby powder all over the leaves. I usually don’t see much of it in this area until the steamy nights of August.

The phlox in the pictures is a prime example. Mildew also infects the leaves of cone flowers and zinnias. It usually doesn’t kill the plant but it makes the leaves unattractive. The lower leaves will will eventually curl up and turn brown.

The best control is to buy disease resistant plants. Being disease resistant doesn’t mean the plant will never get mildew but that plants are less susceptible to the fungus. Spacing and pruning plants for maximum air flow can help. Cleanup and discard plant debris in the fall.

A little gardening trick is to plant a shorter plant that doesn’t get mildewed in front of the mildew-prone plant to hide the unsightly leaves.

(More information on powdery mildew and mildew resistant plants from Clemson University Extension.)


Kathy said...

Since my peonies get a horrible case of powdery mildew... would it be okay to cut the begetation off? They are finished blooming for the season...

Marie said...

I have never heard of anyone cutting all the vegetation off after blooming so I don't know. I imagine the leaves (even if they are a bit ugly) still carry on all the processes necessary to keep a plant alive.

There are fungicide sprays marked for peonies but I never have used them.

Perhaps cutting a few of the stems to open the plant for air circulation may help.

I usually ignore the mildew and then cut everything off in the fall and trash it.

Kathy said...

its a rhetorical question for now...since everything has started growing. i won't have time to ponder this again for some time. the rain has been both a blessing and stress for landscapers. thanks.

Morning Glories in Round Rock said...

That is a pretty significant case of powdery mildew, Marie. I was going to ask if you sprayed, but then you answered that question for me. I have that problem with my crepe myrtles, but I never spray either.

Marie said...

You're right. There are so many other gardening tasks to think about now. Your new garden project (added to your "regular" work load) will keep you very busy, I'm sure!

I half-heartedly tried spraying with a baking soda mix several times but it just didn't seem worth the effort.

donna said...

My phlox aren't bothered by mildew but the phlox plant bugs got after them this summer.

Marie said...


Bugs, oh no! But, I think Phlox are such pretty, long-blooming plants that they are worth growing - mildew, bugs and all.