My monarda has powdery mildew. Although I thinned the monarda in the spring and it's not at all crowded, the hot humid weather we're having right now seems to have gotten to it anyhow.
I have a couple questions:
1) What do I do? Do I just cut it all down and hope that contains the infection? I don't have to remove the plants entirely, do I?
2) I have some garden phlox ('David') nearby. (What I was thinking when I put two powdery mildew susceptible plants side by side I'll never know.) Will the powdery mildew spread to the phlox? It looks so pretty right now I'd hate to see that happen. How can I prevent it from spreading?
Any advice is welcome. This is the first year I've ever had powdery mildew.
What to do about powdery mildew
The good news is powdery mildew is unsightly but not normally fatal, although it can spread to other susceptible plants (I think, although I'm not positive, that 'David' is one of the mildew resistant phlox). I have no personal experience on this, but I've seen people post about using milk or baking soda (maybe mixed together?) or else there are various fungicides that would work on it, check the label on things you might already have around, if they kill powdery mildew it'll say so on the label.
One word: Neem Oil. OK that's two words but you get the idea :0). Good all-around pesticide AND fungicide.
You can also try a product called Organicide:
http://www.organiclabs.com/images/logos/100_Organicide.pdf
fungicide 3 in one from walmart. Like the post above it is just neem oil in that product. It works great on monarda. I use it on mine. it is rated an organic product. clears it up fast.
Peter Crisp at the University of Adelaide found milk (10% solution in water) is effective in controlling powdery mildew:
http://www.publish.csiro.au/?paper=AP06052
Reports on his paper have stressed the need for regular application and good coverage. UC Davis says milk is more effective when a surfactant such as canola oil (Biotrol)is added to it:
http://wineserver.ucdavis.edu/pdf/attachment/64%20control%20of%20mildew%20in%20greenhouse.pdf
Lactoferrin is one of the compounds in milk which fights mildew. Interestingly enough, lactoferrin is also found in tears and saliva. Crying over infected plants might help!
lol paul
Well, I see the article said 10% milk to water, but I don't see how much canola oil to add....any ideas?
Probably about 1 tablespoon of canola oil to each gallon of mixture.
Thanks for all the great advice! I'm going to have to give the milk and canola oil a shot. If that doesn't work, I'll look into the other solutions. Or...I could just cut the plants back and keep an eye on the nearby phlox. (Yes, David is supposed to have excellent mildew resistance, but still.) They monarda are pretty much done flowering now. But it's still good to have this information for next time! (And there's always a next time, isn't there?)
My cosmos are getting powdery mildew because of all the rain and humidity we've been having here in Maine. I'm going to try the milk and canola mixture to see if it helps. Big sigh.