Powdery mildew--how much to cut back?

18 years ago

Hi all. This is the first year all my peonies have bloomed. Unfortunately, two of my herbaceous peonies have pretty bad powdery mildew with the humidity we've had here in Brooklyn.

I started using a fungicide but I understand this won't help existing damage. The mildew is on all the plant stems as well as over half the leaves. Should I just cut these plants back to the ground and keep applying the fungicide? I hate to cut them but I don't want to lose them!

Thanks to all for your help.

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Comments (4)

maifleur01
18 years ago
Chris, do you actually have mildew? I thought I did until I reached down to pluck a leaf and part of the mildew hopped to another leaf. This year I have a whole bunch of some type of leafhopper?? that looks like a dot of white gauze with a sail right under some of the leaves. If I am really fast I can swish some of them before they get away with my hand. If anyone knows what this type of ???is please let me know.
chris123
Original Author
18 years ago
Hi maifleur--

It's definitely powdery mildew--definitely not bugs.

Thanks,
Chris
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jenny_in_se_pa
18 years ago
Chris - this happened to mine last year but I left all the stems intact until frost got them and then cut them back afterwards. They leafed out and bloomed like normal this year. I figured that whatever little green part was left on the leaves was still helping with photosynthesis and for increasing the rhizome.

However I noticed that mine held off as long as they could this year but they are now showing the signs again due to the weather. I sprayed some fungicide but will probably still keep the foliage.

Some have reported no problems with cutting back (or even mowing down) their peonies and getting good bloom the following year so if you want, you could go on and cut them back and discard the trimmings in the trash.
DianeKaryl
18 years ago
Chris, not to minimize the possible damage the mildew has already done, have you tried other formula..other than the fungicides to treat this problem.

The mildew can indeed cause damage in that it obscures sunlight and photosynthesis from the leaf of the plant.
Usually we are told to try to improve the air circulating thru the bed and it is caused from the hot temperatures and the moisture laden air.

Unfortunately the advice is to remove any and all damaged or covered portions of the plant. If this includes the stems, then ...sorry, them too.

There are a number of remedies and one is
two TBSP baking soda.....to 1/2 tsp vegetable oil...to a quart of water. (in Canada...that's a litre)
You can add 1/2 tsp dishsoap to help the oil emulsify when shaken---not stirred.

You might also consider trying to increase the plant's drainage capability by adding an amount of builder's sand to the soil under the plant.