How to kill whiteflies on a poinsettia that grows outside?

Hello and good summer to y'all.

I have a poinsettia bush that is about 6 years old and grows outside. (San Diego). It has grown to a good 6 feet tall and provided us with a nice Xmasy feeling looking out the window. Last fall it got attacked by whiteflies and by winter it looked sort of raggedy. I tried whatever I could get at Home Depot but the flies remained. They are still there, not too many (there were much more in December) but enough to make the leaves look sort of stippled, they are small and curled and tend to fall down.

I'm thinking about covering it with a large transparent plastic sheet (painters use them) and setting off a few roach bombs inside then leave it like that for a few days.

Is it too drastic?

Before you do something like that I'd doublecheck that the roach bomb would kill whitefly--not all pesticides kill all bugs. I'm also not sure you need to do something that drastic--first thing I would do is check the label of the pesticide you've used before and make sure it lists whitefly. If it does then you can use it but you probably need to keep after them--many insects either multiply like crazy or already had some eggs/larvae going before you kill them, so you need to be really vigilant for a while and re-treat the plant regularly until you get rid of them. You might also doublecheck to make sure you don't have a 2nd problem going on here--spider mites can also cause leaf symptoms like that, so I'd take a close look at the undersides of the leaves and see if you've maybe got them too (they will look like very tiny brownish/reddish dots, very hard to see unless you're looking closely)

We struggled with whiteflies for a couple of years on our large hibiscus. It grows indoors, but I would treat an outdoor infestation the same. A couple of times it got so bad that we just stripped off ALL of the leaves. I finally hit upon a really good writeup about whiteflies are so difficult. 1) Their generations overlap, so there are always young ones. 2) Almost nothing will kill the eggs and larvae. 3) Forty days was given as the time it takes to get at all generations.


What finally worked is this.

Insecticidal soap every few days for up to 40 days, always under the leaves, as that is where they breed. This gets the live flies immediately, but you have to hit them. They aren't harmed by crawling on or eating the stuff.

Neem every week. This attacks the digestive and reproductive systems of the flies you don't hit with the soap.

After the infestation calms down significantly, hang sticky yellow labels (available at garden centers) and watch the count that get stuck. You can see if you're getting a sudden increase. And when they're all gone, you'll get a warning that they're coming back. Since it's outside, you'll have to be vigilant forever.

LAS

Well, what I want to avoid is having to spray the plant down daily, for several weeks. First of all I am a very part time gardener and sometimes have no time to spend in the garden. Second, most of the pests are on the underside of the leaves, and as I said it is a large plant and it is impossible to spray all leaves from below, all the time. Third, after almost a year of seeing these critters suck the sap of my plant, I am mad.

The curious thing is that nothing else in the garden is affected., I have 2 large hibiscus bushes, although quite far away, I have a euphorbia nicotinifolia (quite close taxonomically), none of them have any whiteflies on.

i would whack it down and start over with fresh leaves. aren't you supposed to cut them anyway? we always do here in the south.

Another thing that worked for me, but would only work to prevent, not cure, a heavy infestation, was that I learned what the eggs looked like and just scraped them off with my fingernail. I'm posting this reply for the folks that come back to it later for whitefly advice, because I can see that this is even more labor intensive than spraying. And it does pretty much have to be done every day.