Question
A week ago I transplanted tomato seedlings into 4" peat pots so I can have nice size plants by late April.  I kept them in a large plastic container under florescent lights.  Now I discovered the pots are all covered with powdery mildew.  I gently brushed away the mildew with warm water and vinegar.  Still the mildew is returning.  What can I do for these small tomato plants?
Help!
Daniela

Answer
Hi Daniela,

Powdery mildew can be devastating to tender seedlings. The mildew originated with some spores that were in the soil or peat pots that you used. Then the constant moisture of the soil and the lack of good air circulation helped create a hospitable environment for the development of those spores.

Powdery mildew is a fungus and there are fungicides that can be used to treat powdery mildew, Check the label carefully to see if a particular fungicide is effective against powdery mildew and safe to use on tomatoes.

Otherwise, try to keep the soil a bit drier, provide more heat and sunlight, and increase the air circulation by using a fan.

All of that said, once a fungus infection takes hold on seedlings, the success rate is not good. Good luck with yours.

Please let me know if any of this is unclear or if you have any additional questions.

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Regards,
Will Creed, Interior Landscaper
Horticultural Help, NYC

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