High temps, high humidity, over-watering and low light contributes to powdery mildew. Since grouping plants raises humidity, it's best keeping your Jade solo.

Jades prefer cool temps, high light, low-little humidity and well-draining soil.
Placing a fan in the room, 'as long as breeze isn't aimed directly on plant/s,' help, a lot.'

What's the temperature in the room Jade lives? How often do you water? These are questions you have to ask yourself to figure the cause of mildew.

Are you fertilizing? There's no need to fertilze Jades in winter, especially since you're in MI. Avoid chemical fertililzers w/high Nitrogen.
Once you rid mildew, and your Jade sends out new growth, an organic fertilizer is a better choice.
Water in the morning. It'll give your Jade the rest of the day to dry off, discourages disease, and 'prevents powdery mildew.' Most important, soil should dry between waterings before more water is added.

Two most important factors are: Jades/succulents need sun, (the more the better,) and well-draining soil.

It's probable you've over-watered. Do you check soil before giving soil a drink? Does the pot have drainage holes?

I found this recipe online.

1 teas of Baking Soda
1 quart of Water
2-3 drops of dish soap
Garlic...(Sulfur is effective against powdery mildew. Garlic contains high levels of sulfur. So a 'few cloves,' should be addeed to Baking Soda mixture.) Allow mix to sit overnight before spraying, and shake thoroughly before use.

You did the right thing spraying with Baking Soda, especially if it was applied as soon as you noticed mildew. Spray once a week with the Baking Soda solution.

Hopefully, your Jade will resume to health..In the future, be careful when watering, place your Jade in a cooler room with the brightest light. Artificial light strengthens foliage. Any light will do.

Good luck, and keep posting..Toni

I have a large specimen jade that developed a serious case of powdery mildew when I brought it in from outdoors in the fall.

Apart from following all of the good housekeeping practices (not overwatering, removing the dead leaves, ensuring adequate ventilation, and washing my hands after working on the plant), I treated it with a fungicide containing propiconazole, in this case Honor Guard PPZ.

After consulting the application instructions, I determined that the application rate should be 8 oz. per 100 gallons. I went to my local drugstore and the druggist gave me a free eye dropper that was calibrated in ml. I also purchased a cheap plant mister for less than two bucks at my local odd lot store. I mixed 2.3 ml. of the fungicide in one gallon of water and applied it with the plant mister to the tops and bottoms of all leaves and stems until the liquid was dripping off (i.e. everything was wet). You should follow the MSDS instructions and do this somewhere where the runoff will not be problem (e.g. outside or on a large plastic sheet). Also observe the handling and personal protection warnings.

The good news is that the fungicide did not kill the plant. The other good news is that the powdery mildew is completely gone (I pinched off all of the dead or dying leaves a week after treatment), the plant has returned to good health and is setting new leaves, etc., approximately eight weeks after treatment.

The bad news is that a 4 oz. bottle of Honor Guard PPZ (available from Control Solutions Inc.) is around thirty bucks. Mind you, if you have a large plant that you wish to keep, it is well worth it and you should have enough fungicide to carry out literally hundreds of treatments.

Al

Did you follow all of the "must" directions regarding proper, safe, and legal use? I'd like to see pictures of you in the protective gear, lol. And this dangerous chemical is not recommended for indoor, household use.