I have had whiteflies on outdoor plants several times. They particularly like my tomatoes and strawberries and nicotiana.

I rarely have a serious problem with them though. I almost never spray my plants with any sort of insecticide, so I usually have a high population of beneficial insects. Any time a pest population gets high, the beneficials will be sure to find it.

Having said that, I do try to keep the numbers down - just because a really bad outdoor infestation isn't that common, doesn't mean I'm going to sit on my rear and do nothing. I will hose off the undersides of the badly infested leaves, and occasionally, I will take a bucket of soapy water and a sponge and wipe off the undersides of the leaves.

If it's a plant that I'm growing strictly as a foliage plant (and it's badly infested), or a plant that comes indoors over the winter, I will spray the undersides of the leaves with neem oil. It has an unpalatable taste to most insects, so they will tend to leave those leaves alone. Be careful when spraying - be sure to check for signs of beneficial insects like lacewings, ladybugs and ladybug larvae (google a picture of a ladybug larva so that you learn to recognize them). If you see them, do not spray! Neem oil will kill beneficials as well as the pests.

Hanging the yellow strips outdoors is kind of a waste - you would need so many that it's hardly worth it.

BP

Thanks BP! I went and got some Neem oil...seems to be working!