Powdery mildew is usually caused by drought stress, though some monarda cultivars seem to get it no matter what.

Have you considered goldenrod? Or mountain mint? That stuff positively hums late summer.

Powdery mildew is very much climate related. It tend to proliferate when climatic conditions are most suited - dry soil, high nighttime humidity and relatively warm soil and air temperatures. Kind of a perfect combination of prime incubation factors. And this is why the disease tends to show up later in the season when these factors are at their peak.

Make sure the soil stays evenly moist and is not allowed to dry out excessively. And it doesn't hurt to run sprinklers that actually hit the foliage of the affected plants, as PM spores are unable to gain a foothold on wet tissue or in water. But make sure you do so early enough in the day so foliage can dry adequately before nightfall. Allow plenty of air circulation around any susceptible plants and avoid excessive shade. And as always, seek out varieties that are known for their resistance to PM.

As noted, PM spores need plant tissue to overwinter on so spraying soil is unnecessary. Clean up and discard all plant material still remaining that might have been affected.

There are many products used to control PM - natural, homemade and chemical. All will work in varying degrees but as none are very long-lasting, the timing of any sprays should coincide to just before the disease is likely to appear.

mad_gallica: Last summer was very draughty, come to think of it. None of the bee balm I've planted in the area in prior years have ever really taken off, though.

Goldenrod has a weedy reputation in the area. Are goldenrod and mountain mint plants that you could chop to the ground to allow the daffodils to bloom in the Spring, and would they smother the yew hedge behind them?

NHBabs: Clearing away the debris is one thing I'm thinking of. Problem is I'm worried I'd damage the young bulb shoots. (Which are already sprouting for some reason) and wondering if the debris make a good winter insulation.

Anything I can spray on the mulch to make sure spores don't overwinter in that? There is a lot of plant debris there as well as the mulch underneath, so I'm not confident I'll get rid of all of it.

gardengal48: It's an incredibly windy spot, but somewhat shady. Full sun to the North, shade to the South.

You might want to take a look at the monarda results in Mt. Cuba's trial garden. http://www.mtcubacenter.org/plant-trials/category/monarda-evaluation-2014-2016/

It sounds to me by your comments (" I should be able to level the bee balm to the ground to display the bulbs, then count on it growing back by summer." ) that you are not cleaning up your beds in the fall and are leaving diseased foliage to overwinter. With few exceptions, all foliage of perennials can, and certainly in your case should, be cut back in the fall and cleaned out of the bed. Much of your problem may be due to this.

You will just need to work carefully, but since plant tissue (not the mulch itself) is where the spores overwinter, it makes sense to remove as much as you can. Perhaps one a shop vac or small handheld vac to vacuum up remaining debris or one of those leaf blower things to remove any remaining debris, and then a light layer of mulch to cover any leftovers. Next year, keep it well watered and cut off all stems in fall while it is still green enough to not be dropping a lot of debris, and if that doesn't work, replace with one that is more disease resisitent. Your bulbs shouldn't need insulation, and leaving diseased plant matter in the garden is always a mistake. Phlox and peonies are two others I always remove since they have a higher than average potential for foliar diseases.

Ultimately the overwhelming consensus seems to be you are right. I left the area uncleared because I wanted some of the plants in the bed to reseed. (liatris, Nodding onion, echinacea). I can't water the area regularly, unfortunately...it's at my Mom's place. One of the problems is probably that I didn't realize that bee balm maybe needs more water then the other things there.

i though monarda was supposed to be cut down .. to an inch or two ... either in fall ... or early spring ...

ken

Yes, apparently you are right, ken. I didn't take a weed whacker to it aleredy because I wanted to leave the nodding onion, liatris and echinacea growing with it up long enough to reseed. Now I'm worried about hurting the prematurely-sprouting bulbs.

monarda is notorious for mildew. i'd recommend moving the monarda to a more open area if you have one and replace with something resistant-many things are. i know people who have given up on monarda because of the problem.

How much can you really do to prevent it? Even if you napalmed your yard…. And then planted the next year…. Powdery mildew spores would just blow in from your surrounding area right and you are back where you started.

Nevermore44, I don't think you are entirely correct, since my understanding is that p. mildew is plant specific, so mildew from a phlox won't infect a monarda. If there isn't a source for the spores nearby (old plant material from the same kind of plant) I think you will find the plant is healthier. I'm not suggesting that you can totally prevent disease on a highly susceptible plant, but good cultural practices such as Dave's suggestion of growing it where there's good circulation or thinning stems to increase circulation will help, whereas if you leave all the spores right on top of the plant they are able to infect, it will get diseased early in the season and look like crap all season. There's a wide range between napalming and doing nothing.

Edlincoln, I don't think I would choose a weed whacker as my choice of tool to remove diseased plant material since they have a tendency to spread pieces of plant material around. I use hand hedge shears which cleanly take off a lot of stems at one whack. The linked ones aren't exactly like mine but give the general idea.

That's interesting about there being plant specific... Nature is fun. I was just going to the extreme to stress the point that I think the important word would be "delay" vs "prevent" with pm. I have one planting of an older variant of phlox and pm always gets it early right as it starts to bloom. I remove the entire plant to the ground fairly early each year.... But it always hits the exact same time the next year. I have no other phlox and I live in a garden desert in my subdivision... I don't think a single home I pass in and out of the neighborhood has anything besides the original landscaped plants.... Non being phlox.

The only other perennial that gets pm for me was an old peony... Which got the axe because of it. And then of course the late season squash get it.

so to the original poster... Given your circumstances ..... And this isn't a plant that you are passionate about enough to put up with tight cultural practices.... And ...You would only being delaying the inevitable maybe a bit later in the season....(as others bring up.)....Looking into a replacement species would probably work better for you.

As far as it being plant specific...the echinacea growing right next to it never gets powdery mildew, despite echinacea supposedly being somewhat susceptible.

I just can't get Bee Balm to take...which is odd. In theory it should be perfect for the spot. It's supposedly a garden thug. I like the scented foliage, native status and the pollinator value.

Ahhh.... I think pm just doesn't take on many plants.. But the pm that gets bee balm is the same type that gets phlox.... (I auto recant taht statement if it's found to be wrong). You could try some of the hyssops.... They have various sizes... Don't need any attention.... And they smell great too. ( I also auto recant that suggestion if they are susceptible to pm..... Though they aren't for me)

Babs is correct. There are 5 large groupings (scientists call them 'tribes') of fungi that develop into powdery mildew and these contain numerous genera and countless species, all of which target specific plant hosts. The powdery mildew that affects ninebarks is not the same as that which attacks apples and pears; lilacs develop another type and different still are the types that affect cucurbits. Generally plants need to be in the same family to be considered "contagious" to each other.

There ARE resistant cultivars of bee balm on the market, as there are cultivars of phlox. If your garden is regularly plagued with PM, I'd suggest seeking these out. I have had excellent results with 'Jacob Cline' - a big, robust plant with intensely red flowers produced over an extended period and loved by hummingbirds. I have never experienced PM with this variety and the PNW is probably the fungal (and particularly PM) capital of the universe, so I consider that a pretty good endorsement.

btw, 'resistant' does not mean 'immune'!