Spots on leaves
Water-soaked spots, sometimes with a yellow halo, usually uniform in size, sometimes with a sticky ooze may be caused by bacteria. Fungi may also cause spots. Fungal leaf spots often have distinctive features such as a red ring around the spot; a concentric ring or target spot pattern; small black dots (fruiting bodies) in the dead tissue; cracks in the affected tissues with orange, black or tan ooze; a powdery, felt-like or fluffy growth on affected parts. If you suspect a bacterium or fungus is causing spots, remove and destroy severely affected plant parts, avoid splashing water on the foliage since this spreads the microorganisms causing the problem, and provide good air circulation.
Many tropical plants develop spots on foliage that is old and ready to be dropped. This is normal.
Pale washed out, white or gray spots, usually irregular in shape and size may be caused by too much light or heat.
Brown corky spots or lumps can be caused by too much water, especially during cool, humid weather. This is especially common on peperomia, geranium and many succulents.
Leaves drop off
Many plants drop leaves when there is a sudden change in temperature, amount of light or humidity. Exposure to natural gas or manufactured gas may also cause leaves to drop. Some seasonal leaf drop is normal for plants, as new leaves are produced. Insect infestations and lack of water can also cause leaf drop.