Friday, May 14, 2010

Who Powdered my Pansies?

We have the most beautiful batch of Violas in 200mm pots.  Three separate colours including white and  Deep Marina.

Oh, yes they are this beautiful.
Except for one thing.... the foliage is full of powdery mildew.  Our sales people have been driven mad with desire.  They can see these beautiful plants but the production team won't let them be touched.

Powdery Mildew is not a fungal disease that we deal with all that regularly.  We often get plenty delivered to us on hanging baskets that we are sending to the flower & Garden show.  The fungus just loves the Autumn weather; cool nights, high humidity and still days.  The other factor that has affected our Violas is they were returned from the Flower & Garden Show display and cut back to re-grow.  Under normal circumstances this wouldn't be an issue but cutting the plants back stressed them enough to allow the Powdery Mildew fungus to attack.

That's a really nasty infestation of Powdery in Zinnia.  From my experience Powdery can really destroy a plant but usually it just hangs around making the plant miserable and it is very contagious if the conditions are right.

What to do?  First and foremost prevent infestation! Remove any infected plants.  Ensure hight light levels, yes that's right if possible get your plants out from under the shade.  There are very few plants that will need or like shade cover between now and December.  The other thing we do in the green houses is turn the fans on.  Quite simple, we have fans that stir the air around to prevent that close humid environment developing that fungi like.  The other thing I have seen (but never used myself) greenhouse growers use is Sulfur Burners, sulphur is very effective in controlling the Powdery fungi. I'm sure these are available for enthusiasts from Sage Horticulture, but they are of no value out of doors.

OK so sometimes we still get infected.  Commercially there are some very specific fungicides for controlling Powdery mildew, BayletonTM  comes to mind but I'm not aware of it being available on consumer packages. A Lime Sulphur  spray should be available from most good garden centres.  I have made the mistake of spraying Powdery with a general fungicide assuming that if it was effective on Botrytis (Grey mould) it would be effective on Powdery... wrong! So don't do that. I have found two interesting organic sprays: baking soda and milk.  The baking soda idea matches one sent to me this week by Marina who suggested this basic recipe to control aphids and sooty mould.  Marina's spray didn't include baking soda and she replaced the water with dish water, I think that might just frighten the Aphids away. Thank's Marina.

Last resort?  Dilute Quarternary Ammonia, some household disinfectants contain ammonia in this (quarternary) form.  It works, but it needs care not to burn the plants and you must use the quarternary form.  If the foliage is especially dense (think our Viola crop) it is very difficult to get the ammonia solution in contact with the fungus so we might have to cut them back again.... Oh I'm getting dizzy.

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