It is powdery mildew and happens most usually during dry weather, not wet as most would think. The way to deal with it is before it happens by spraying with a commercial fungicide or a home made remedy of milk and water as a prentitive(about a 1 to 9 ratio I think) mixed in a sprayer. Now that the mildew is on the monarda, you may be able to keep it from getting mush worse by using the commercial fungicide.

Definitely powdery mildew. Since the plant looks pretty well spent/bloomed out, cut it back and dispose of the cuttings anywhere but in your compost pile - if you compost. And make sure to clean up any fallen leaves and pieces because if left in place, even over the winter, rain splash up can reinfect the plant all over again.

After cutting back, you might treat it as recommended above, since it will continue to put out new growth well into the fall.

You can help avoid powdery mildew by thinning out some stems so there's good air circulation, and by not wetting the leaves when watering. But sometimes, despite all best efforts, PM happens.

I never could get monarda to take hold for me, but I sometimes run into the same thing with phlox.

I used a native red Monarda in the Butterfly Garden that was covered in PM from the get go this spring. Kind of expected it, though. Didn't spray anything because of butterflies but guess I could've used the milk solution mentioned.

Was going to switch to some newer purple Monarda varieties that are advertised as mildew resistant but I see you've got a purple Monarda. If I find out from experienced people on Butterfly Forum that treating with milk solution is alright I may still switch out the red for one of the more resistant varieties. I'll put the red Monarda in an outlying area where it can fight it out with poison ivy, garlic mustard, poke weed and whatever else decides to invade after I think I've pulled all of some other weed.

At the beginning of this gardening venture I thought it would take a year or two to get the beds straight as to what worked and didn't. Then I could just sit back and tend to plants needs and enjoy. Now I realize making gardens isn't something you do once and then tweak a couple times. It never ends...LOL.

That said, I have the feeling I'm going to be pulling red Monarda seedlings from all over the place next spring... LOL. I've cut off to the ground all the moldy old stems and foliage with spent flowers and it's already spreading by runners with new little Monardas popping up.

In any event, I'm going to treat early and often if it doesn't harm the butterflies. Don't think nectaring hummingbirds are as sensitive as butterflies.

I have a very dense, about 6' in diameter, patch of Monarda 'Raspberry Wine'. It is said to be "very mildew resistant". To date, it doing fine...no mildew, which considering the thickness of the growth and recent dry spell surprises me greatly. The same patch last year was much smaller and thinner, but did eventually suffer from a minor bout of mildew near the end of the it's bloom time.

Gazania - did you order your Raspberry Wine through a catalog or garden center? I'd love to dig out some of the Monarda I have and add some that are more mildew resistant.

janice, I ordered them from Bluestone in the spring of '07.
Here is a pic of what 2 plants became in this their second season.

{{gwi:257112}}

Here is a link that might be useful: Bluestone

Thanks for your helpful advice!

I have cut down the Monarda and threw out the foliage.

The worst pest in my organic garden over the years has been powdery mildew. I have learnt a few things the hard way and have fewer problems with this nuisance now.

It is good to remember that some plants never get powdery mildew no matter what and other plants likely will, no matter how they are grown. I really don't like spraying anything and have learnt that it pays to discard those older varieties of easily infected plants and buy ONLY the newer mildew resistant varieties. Far less work in the long run. Those that head the list for susceptibility in my garden have been: Monarda, Summer Phlox, Peas, Grapes, and some Veronicas. I'm sure there are a other trouble makers too.

Here is my list to prevent this problem from developing in the first place:

1. Use only resistant varieties. THE most important thing! (I particularly recommend 'Violet Queen' for a Monarda--also less prolific than the older types.)
2. Good Ventilation-thin out thick plants with decontaminated shears.(Hot soapy running water or a weak bleach solution.) Also keep potential problem plants spaced well...and away from fences.
3. Avoid shade but water well. I find dryness + shade to be a trigger for P.M. Water thoroughly and early in the day, so the plant dries quickly. Avoid evening watering in late summer at all costs. It is a guaranteed recipe for trouble in my area.
4. Dispose of any diseased leaves or branches that you DO find promptly in a closed container, so the mildew can't blow around in the wind and create further problems.
5. I have never seen this anywhere in all my garden reading, but feel that under planting a susceptible plant with a thick resistant ground cover can keep it from getting infected. I'm guessing that the ground cover is blocking interaction between powdery mildew and the soil. This also helps to keep consistant moisture in the ground, as would a mulch...so this might be the reason it works too. I often use Moss Phlox for underplanting. The odd piece of grass manages to grow through but it never, ever gets the dreaded P.M. Moss Phlox, although gorgeous in the spring does need to be trimmed well or divided every year or two, to keep it nice, so you might want to try another, lower maintenance alternative.