Better ventilation. Are these plants in a greenhouse? Usually it is home growers that have problems with air circulation. Anyway, anything you can do to keep the atmosphere 'bouyant' (sp) will help.

H

Thanks Howard, They are in a greenhouse. TOMD63

I have the same plant and the leaf spots. I also have them on the canes. While Howatd is correct, I think the culprit is water/misting. This Den may be particularly sensitive to water/mist. If you do not have good air circulation, water does not evaporate and creates spotting. Since I have been very careful not to get any water on the leaves, the spots have stopped. Nice growing BTW!
Clara
PS the old spots will remain.