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Powdery mildew on Monarda Bee balm

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Zone 8-9 Washington
Posts: 627
Posted: Tue Apr 13, 2010 6:20 pm   Post subject: Powdery mildew on Monarda Bee balm

I don't know why it is the only plant to get it but it doesn't make sense. The plant is in my makeshift greenhouse so the leaves are dry. I do not get them wet when I water it but it has powdery mildew.

I hope that I am right that it is powdery mildew, well wrong if it is nothing but I see way too much of this every year. I have a copper fungucide I can use. The upper leaves have nothing on them and the plant is growing very fast even though it is still cold here. I did see a couple aphids in it and have been collecting lady birds to eat them so they don't get bad.

Is it normal for lower leaves to get it in a greenhouse type setting even though the lower leaves stay dry when I water the plant, or as dry as I can keep them anyway?

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West - Friesland
Posts: 9542
Posted: Wed Apr 14, 2010 12:57 am   

Adjustments to make:
--Remove the leaves infected with the powdery mildew
--Give water from below
--Make the plant's milieu less congested so that the plant has better airflow
--Get rid of those aphids! Insects are one of the methods for spreading this fungal infection

Chemical treatment:
--Potassium bicarbonate, neem oil, sulfur or copper based fungicides

Home made treatment:
1 tablespoon of baking soda
+½ teaspoon of liquid soap
+1 gallon of water

I have read that the young leaves are the most common to be infected, but my personal experience is otherwise...not just with Monards but courgette and cucumber plants for instance.
A greenhouse is generally a place where airflow is minimal and they can tend to be humid intermittently.

If you had access to a microscope and some Calcium Hydroxide you could establish the diagnosis quickly. Without that you will just have to use your eyes and assume that it is powdery mildew. If you try the suggestions above the plants will not be harmed and if it goes away, then the diagnosis will be established with 99% probability.

Good luck with this problem.

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