Is this powdery mildew?

I've been battling powdery mildew in my budding plants but haven't seen much of it in my veg area--except for this whitish looking stuff on the base of my plants. Is this PM, another disease, or something totally harmless?

I've got an ebb & flow set up with veg plants under 8 bulb T5 fluorescents. Humidity ranges from 40-60% with temps in 70-85 range. I've got plenty of air exchange and fans running but keeping it in check has been tough.


Stem PM 2.jpg
 
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