Hi Pierre,

Where are you located? Do you know if you have other host plants for whitefly? There are a number of different species. Some of them are partial to particular plants. Where I live, in the southeast USA, privets are the most common host plant. I had privet hedges all around my old house, and had a large cottage garden that sounds similar to yours. I didn't grow lupines, and mostly found the whiteflies bothered lilies and echinacea, though they didn't swarm them as badly as you describe.

In reading, it sounds like lupines are very vulnerable to aphids, thrips and whitefly.

I used a combination of yellow sticky traps, insecticidal soap, and simply hosing them off the plants to control them, but it probably would have taken removing the privets all together to really control them. The problem is they breed so quickly. Hosing probably worked as well as anything, but I would have to do it twice a day. I think it's really important to get after them as soon as they appear, and that is why the sticky traps are useful. The insecticidal soap is a contact killer and is effective on adults. However, it may require spraying every 2-3 ays for a couple of weeks and every one or two weeks after that. I'd be concerned about burning the plants with that kind of schedule.

I dug up and brought some of my lilies with me when I moved last year, and in doing so, inadvertently also brought whitefly. However, there are no privets here and it appears I have eliminated them.

I think it unlikely you can eliminate them from your lupine, which is apparently a significant host plant. Probably the most realistic goal is to control them enough that they do not absolutely weaken and marr the plant and blooms. You will probably need to plan on dealing with them at least daily during the peak of the whitefly season.