Question
My sister has a prayer plant that has been getting white spongy/stringy sacs. They look like spider sacs to me, so we were wondering what exactly they are and what to do about it. The leaves that the sacs on are dying off, so if you could help us out that would be great! Thanks.  

Answer
Hello Chelsea,

From your description it sounds like you have a mealy big infestation. The cottony substance is a result of the waxy protective covering these pests produce.

First the plant should be moved away from any other house plants to keep the bugs from spreading.

There are two ways to kill off these pests.
The first would be a houseplant insecticide designed to deal with mealy bugs. With this you can simply follow the directions on the bottle. Generally what they say is to spray the plant down then wait a few days and spray again repeating the process until the bugs are gone.

The second solution, if you don't like using toxic chemicals, involves dish soap and rubbing alcohol (you'll need a clean spray bottle). First, make a mixture of dish soap and water and either wash the plant by hand or use a spray bottle to soak it. The soap will break down the waxy covering of the bugs. Then make a spray of 1 part alcohol and 4 parts water. Spray the plant down with this to kill the bugs. Wait a few days and repeat the process making sure the get every part of the plant.
You need to do multiple treatments with both methods because you probably wont get all the bugs on the first try and you definitely wont get all the eggs.

Good luck,
Justin