Sounds like spider mites if it's little blobs of white stuff and it's on the underside of the leaves or in the nooks and crannies of the plants. Looks like tiny cottony webs. I use regular rubbing alcohol and wipe the leaves down. Rinse the plants off when you are done. Unless it's a major infestation all over the greenhouse that should be sufficient. If it's everywhere you will need to use a miticide or an insecticide.
If it's a powdery substance all over the leaves it could be mildew. You would also see the white stuff on the surface of the potting medium. Unless your plants were kept way too wet with no air movement this is highly unlikely. With mildew you would notice a wet kind of decaying smell in the pot of the affected plant.

Oh, if you use a magnifying glass you can see tiny spider mites. They are usually kind of reddish.

I have not seen any moving things, do dab with alcohol, wiould it hurt to pour the alcohol on the bark, let it stand for a bit and then rinse????

Well, I've never done that so I don't know. Wipe the leaves thoroughly with the alcohol. Use a Q-tip in the crevices of the leaves. Sometimes just dabbing at the white spot is not enough. If you are going to pour something into the pot itself, go ahead and use some insecticide. The reason you use alcohol to wipe leaves is it removes little pests, slight mildew, etc. better than soap and water. It is not an insecticide. Spider mites are so tiny you will not see them move unless you look at the leaves in bright sunlight or with a flashlight and use a magnifying glass.
The reason I'm suggesting insecticide for you is I know you have a greenhouse and lots of plants. If you still have shelves above and below plus hanging plants your plants are more at risk for cross contamination. Your air movement is not ideal due to the crowding even with a fan. You are getting ready to start heating the greenhouse and the air will be damp and stagnant. I think you need to apply both fungicide and insecticide to all your plants before you close them up for the winter.

This advice is specific to MaryAnn only. If you just have a few plants growing in ideal conditions usually chemicals are not necessary.

I have to tell you guys that all of my plants are looking great and I think it's mostly due to the advise that you guys have been able to give. Thanks so much.