I would not do painting of the stem..I would water more frequently, at times daily before the sun hits the plants, when temps are expected to soar beyond 100F. They may still lose some leaves in the process, after all they are tropical plants, not desert plants, so it will either drop some leaves to conserve its water or get burnt leaves but it will grow new ones. Humidity is too low or nil anyways during very hot weather days. So even if you water everyday, it will evaporate just as fast. Important thing is it gets to drink water.
