Black mold is probably 'artillery fungus' whick comes from trees.
Im on the Chespeake which has similar high humidity problems. To remove mold from my sails
I 'spritz' on a detergent with a "sodium silicate" base, cover with a plastic tarp and let soak. The soaking will 'dissolve' the mold cells and leave them vulnerable to release by gentle scrubbing with a long handled soft brush. You can use chlorine bleach but that only kills the mold and leaves the cellular debris to become the nutrient source for other species of mold, etc. Sodium silicate based detergents wont affect WHITE woven dacron polyester - dont do this to laminated sails
and NEVER clean a mylar sail this way. Thorough rinsing is needed to release the mold and detergent. I do this with the sails on the boat - slowly raise the sail as I 'spritz', cover, slowly raise while scrubbing, cover, slowly raise while I blast away with a water
hose. Once scrubbed, for any remaining 'shadow stains' I apply a diluted mix of oxalic acid and water
(also removes tannin stains) then thoroughly rinse. I do this on a cool, humid, windless day so the mix doesnt dry out ... soak time is important.
Caution: dont do this if you have bare teak
decks or other exposed bare teak
as the caustic detergent will lift
off all the dead UV destoyed surface cells from the teak .... sodium silicate is also know as a moderate 'teak etchant'. Sodium Silicates will also strip all the wax from the gelcoat
... so you will need to re-wax the boat.
For areas inside and outside that routinely form mold, I simply use a modern version of the 'whitewashing' that was successful for our ancestors for thousands of years .... I simply lightly spritz on the sodium silicate and let it dry. Mold wont propagate on a surface that is 'caustic'.
If possible, I never ever cover or furl my sails unless they are completely dry. For roller furled sails I usually apply APSEAL 303 Fabric
Guard (better than Scotchguard) as a water repellent over the 'suncover' portions --- keeps the sail from 'uptaking' water when furled. Dont confuse with APSEAL 303 UV Protectant.
Hope this helps.