Question
I have a Rubber Plant that has rust colored  spots all over the older leaves.  I have new ones coming on but the older ones just turn brown and fall off.  What kind of pest or disease am I up against.   I am also dealing with Gnats in my office, but they are not the problem with the leaves.  Thanks!

Answer
Brandy,

It sounds like you have a fungal problem and the gnats are caused by overwatering. The fungal problem may be worse due to the overwatering.

When you water a plant you need to empty the drain tray of all excess water an hour after you water it then you do not water the plant again until the plant is dry. That means until the soil feels dry on the surface and if you insert a bamboo skewer into the soil it comes out dry. Also the plant feels light weight when it is picked up.

Plants roots need alternating periods of moist then dry. During the dry periods they breathe in carbon dioxide through the soil and expel oxygen through the leaves. If the soil is constantly moist they cannot go through this cycle so the roots start to rot and the rotting roots
attract fungus gnats which then lay eggs in the soil. The only way to get rid of them quickly is to pour rubbing alcohol in the soil, it will kill the gnats and eggs and will not hurt the plants roots, but then if you do not let the plants dry out you just continue the root rot and kill the plant that way. You have to let your plants dry out between waterings. You should only need to use the alcohol 1 time. The gnats should not come back if you empty
the drain tray an hour after watering the plant and let the plant dry out between each watering. Letting the plant dry out may help with the fungal infection also but I would also spray the leaves daily for a week with Lysol Spray making sure to get the tops and bottoms of all the leaves. After the first week I would continue spraying it twice a week for 3 more weeks. That should take care of the problem. Good luck.

Darlene