Jessica,

First, please don't panic and toss a plant. It is always possible to save a plant and I hate the thought of letting the pests "win", which is what happen when you toss a plant instead of tossing the pests and keeping the plant.

Whiteflies outdoors are not that hard to control as many beneficial insects feed upon them, including lady bugs and green lacewings, both of which you can purchase and release. Keeping the ladybugs and lacewings around will be more difficult for you with a balcony garden than it would be for those of us who have in-ground gardens with plenty of plants to lure in the lady bugs. I am not sure if lady bug houses work. I have one that's very cute and decorative, but the lady bugs don't overwinter in it. They live in our mudroom, greenhouse, potting shed and garage instead. To keep ladybugs around, you need to have lots of plants that they like to visit. I do not know how you achieve that with a small balcony garden, but you might be able to attract them to your plants by using wheast. You can make it yourself or order it from either insectary supply stores or garden supply stores.

When you rely upon ladybugs, green lacewings and other beneficial insects to control the pest insects, there is a predictable pattern to how it works. First, the pest insects show up and multiply rapidly because the beneficial insects aren't there yet. This is because the beneficial insects will not show up and multiply until the pest population is large enough to feed their young. So, you always will have to exercise some patience and wait for the beneficials to show up. Once the beneficials like lady bugs show up, the adults will not necessarily feed on the pest insects nearly as much as their larvae will, so to some extent, you have to exercise more patience while the lady bugs lay eggs and the eggs hatch. Then their larvae (which look like little gray and orange alligators) will feed voraciously on many garden pests.

However, even in the absence of beneficial insects, you can easily control whiteflies outdoors by hosing them off the plants with a sharp stream of water (this works well for aphids and spider mites as well) and by following up with a spray of insecticidal soap (the one I have in a spray bottle in my shed is made by Safer's). It is a lot harder to control white flies indoors, so be glad you aren't growing indoors in a greenhouse or something.

Here's a great article from MEN that talks about white fly control:

How To Control Whiteflies

My garden is heavily planted with flowers of many different kinds to attract/keep beneficial insects in the garden. I just am not sure how effectively you can do that with a balcony garden, though having a handful of flowers around would help---even if it is just one pot that contains some sort of flowers that attract lady bugs.

Finally, be sure you are not over-feeding the plants too much nitrogen. Plants that get more nitrogen than they need always seem to be extra-attractive to pest insects. I believe that when they get too much nitrogen, the plants produce extra carbs, and those extra carbs are very attractive to pests.

Good luck,

Dawn