Leaf spots can be caused by fungi, bacteria or growing conditions. Water drops remaining on leaves or high humidity are necessary for infection. Whatever the cause, the affected leaves should be removed and the probable cause corrected. They come into the home on new plants or with plants which are put outside for the summer. Insects may come in on clothing or when the door is open.
Scale insects are among the most difficult to control.
These insects are mobile when young, but then settle and secrete a protective covering that can't be penetrated by insecticides. The best control is a systemic insecticide. Soft-bodied insects like aphids, mealybugs and whiteflies are easily controlled with insecticidal soaps and pesticides like malathion. Insecticidal soaps are relatively effective for mites. These tiny spiders feed on the underside of leaves.