We had a nice warm autumn day here in Melbourne so I decided to have a look in the super and also remove the queen Excluder. The plan was to leave the super on over winter. The super is about 25% full of honey while the brood box was completely full of brood and honey, when I checked about a month ago.
I removed the roof and then the lid and noticed there is some mould on the underside of the lid. There is also a little bit on the cables running across the top of the flow frames but the rest of the flow frames are mould free.
I have a flow hive classic with the bottom vent completely shut. The entrance is fully opened but I had planned on closing it up a bit for winter. Should I open the vent to help the hive air out or leave the bees to manage it.
I have flipped the lid so the mouldy side is now facing up and am letting the roof sit in the sun. I’ll put it back on later this afternoon when it starts cooling down.
That is of zero concern if your roof is not leaking. I wouldn’t leave the Flow super on over winter (propolis is a PITA to remove the next season), but it is your hive, and your choice.
I agree with @Dawn_SD , I certainly wouldn’t be leaving the flow super on over winter if I was in Melbourne. I would be taking @Semaphore 's advice, based on his experience.
Your roof may be leaking, which will contribute to the mold. Condensation will form in the roof area even if it doesn’t leak. Anything in the hive will get mold on it, if it doesn’t have a good covering of bees on it. Therefore as winter approaches, the population will naturally wane, leaving more areas not covered in bees, thus allowing more mold to form on those areas.
During the peak of the season, I would still reduce that entrance to an area of 15 sq.cm. So, if the entrance is 1cm deep, it only needs to be 15cm long. If it is 1.5cm deep, which the flow classics seem to be, it only needs to be 10cm. long. During winter you can reduce it further.
