Certified GKH Gardening Expert
There could be several reasons for this and it's often difficult to pinpoint the precise cause. Brown, dead spots on leaves are usually scorching, a sign that your plant is getting too much light. If this is not the case, look towards watering. Brown spots can also be due to a lack of watering. Fungus can be a cause as well, but this is more prevalent in overly moist plants. Of course, in your area, humidity can play a factor here, so a fungal problem could be more plausible. If this is the case, a fungicide should take care of the issue.